Threaded connection

Abstract

Threaded connection for exploration and production of a hydrocarbon well. The threaded connections comprises a first pipe with a first thread having a first perfect thread portion and a thread runout portion adjoining an unthreaded surface of the first pipe; and a second pipe with a second thread configured for rotational make-up with the first thread, wherein when made up the second thread axially overlaps the unthreaded surface. At the first perfect thread portion there is contact with radial interference between the first thread and the second thread; at the thread runout portion there is contact with less radial interference than at the first perfect thread portion; and at the unthreaded surface there is a clearance or contact without radial interference between the second thread and the unthreaded surface.

Description

[0001] Threaded connection

[0002] The present invention relates to a threaded connection for exploration and production of a hydrocarbon well, as well as a pipe for use in the threaded connection.

[0003] A threaded connection for the exploration and production of a hydrocarbon well generally comprises a first and second pipe, wherein one of the pipes is at a terminal end thereof provided with a thread on its outer circumferential surface, and the other pipe is at a terminal end thereof provided with a corresponding thread on its inner circumferential surface.

[0004] To form (or make-up) the threaded connection, the terminal end of the pipe having the thread on its outer surface is inserted (or stabbed) into the terminal end of the pipe having the thread on its inner surface, after which the pipes are rotated with respect to each other to make-up the connection wherein the threads engage.

[0005] When a string of pipes comprising a multitude of made up threaded connections is located in a hydrocarbon well, the string of pipes with the threaded connections are often subjected to harsh circumstances, including, for instance, high internal and / or external pressures, and large compression and / or tension loads. The string of pipes including the threaded connections are designed to maintain their structural integrity while being exposed to these harsh circumstances.

[0006] The structural integrity of the string and its threaded connections relies on numerous variables, among which the thread configuration of the threaded connections, and the structural properties of the pipes.

[0007] The threads of the threaded connection are designed to perform various functions. In particular, each thread comprises a load flank, a stab flank, a crest, and a root. The load flanks provide support against axial tension loads applied to the pipes, while the stab flank can be used to provide support against axial compression loads. In addition, in some cases the root of the thread on the outer surface of one pipe has a slightly greater outer diameter than the crest of the thread on the inner surface of the other pipe. This causes the root and crest to radially interfere with each other, which results in elastic deformations at the threads during and after make-up of the connection. By doing so, the threads can be used as a seal for hydrocarbon fluids. Further, the threads can extend along a certain taper angle with respect to the longitudinal axis of the pipe. This allows a part of the thread of the first pipe to pass in axial direction a part of the thread of the second pipe during stabbing, which can help speed up the above mentioned make-up process.

[0008] As mentioned above, performance of the threaded connections further relies on the structural properties of the pipes on which the threads are provided.

[0009] A common way of manufacturing threaded connections for the exploration and production of a hydrocarbon well is by hot rolling a steel cylinder, wherein a piercer is pushed through the cylinder from one longitudinal side to the other, into a seamless steel tubular member. After forming the seamless steel tubular member, a thread is applied to a longitudinal end of the tubular member by cutting away excess material with a thread cutting tool. The portion of the tubular member that is not provided with a thread is normally left untreated. As a result, the unthreaded portion generally has an irregular surface with a roughness that is greater than the roughness of the machined surfaces of the threads.

[0010] In cases where a tapered thread is required, the thread cutting tool is arranged to progress along a certain taper angle starting from (or approaching) the untreated surface of the tubular member. In such cutting process, the resulting thread may have a runout portion adjacent the untreated surface of the tubular member, as near the untreated surface there is not enough material to form a full formed thread portion. In this thread runout portion the thread may not provide the same support against axial tension and / or compression as the rest of the pipe thread. On the other hand, a corresponding pipe that has been manufactured by the same method does not necessarily have a thread runout portion at a corresponding location. On the contrary, the corresponding pipe generally has a thread that, when made-up with the former pipe, has a thread having full formed thread turns opposing the thread runout portion. Moreover, when the connection has been made up, the full formed thread often axially overlaps the untreated surface of the former pipe.

[0011] When analysing these type of threaded connections, the inventors found that while a certain amount of radial thread interference is beneficial for sealability, the radial thread interference tends to deform the terminal end of the pipes. This behaviour is especially relevant for threaded connections that comprise a first pipe with a thread having a thread runout portion and an adjoining unthreaded portion wherein, when made up, both the thread runout portion and the unthreaded portion are in axial overlap with the thread of a second pipe, because in such case there is a possibility that during use the unthreaded surface of the first pipe is contacted by the thread of the second pipe. This contact can lead to galling at the surface of the unthreaded portion of the first pipe, wherein material is removed from the unthreaded surface of the first pipe. During cyclic loading of the threaded connection one or more cracks may propagate from the surface area at which the material was removed, due to which cracks the connection may break, in particular when the connection is subjected to tensional loads. Accordingly, the inventors found that contact between the thread of the second pipe with the unthreaded surface of the first pipe can damage the unthreaded surface of the first pipe, which in turn can be detrimental to the structural integrity of the pipe.

[0012] Attempts have been made to reduce the risk of damaging the threads at the thread runout portion. However, none of the proposed solutions actually provides a cost effective way of manufacturing a threaded connection wherein the risk of damage to the threads at the thread runout portion as well as at the unthreaded surface of the pipe adjacent the unthreaded portion is reduced, while making optimal use of the thread, in particular of the thread runout portion.

[0013] It is an object of the present invention to provide an improved, or at least alternative, threaded connection that is less susceptible to damage, in particular, as a result of the threads of one pipe contacting the unthreaded surface of the other pipe, while maintaining beneficial functionality of the threads.

[0014] The object is achieved in a first aspect in accordance with the present invention with a threaded connection for exploration and production of a hydrocarbon well, comprising: a first pipe with a first thread having a first perfect thread portion and a thread runout portion adjoining an unthreaded surface of the first pipe; a second pipe with a second thread configured for rotational make-up with the first thread wherein when made up the second thread axially overlaps the unthreaded surface; wherein:

[0015] - at the first perfect thread portion there is contact with radial interference between the first thread and the second thread;

[0016] - at the thread runout portion there is contact with less radial interference than at the first perfect thread portion; and

[0017] - at the unthreaded surface there is a clearance or contact without radial interference between the second thread and the unthreaded surface.

[0018] By providing a threaded connection, wherein there is radial interference between the first thread and the second thread at the first perfect thread portion, the first thread and the second thread contact each other with less radial interference at the thread runout portion, and the second thread of the second pipe is clear from, or contacts without radial interference, the unthreaded surface of the first pipe, thread contact is maintained in the first perfect thread portion as well as in the thread runout portion. As such, cooperation between the thread of the first pipe and the thread of the second pipe is ensured, even in the thread runout portion.

[0019] At the same time, and while there is no radial interference between the thread of the second pipe and unthreaded portion of the first pipe, the reduced radial interference at the thread runout portion tends to reduce radial deformation of the pipes towards each other at the unthreaded portion of the first pipe. As such, the chance that the second thread of the second pipe contacts the unthreaded surface of the first pipe, is reduced, therewith reducing the risk of galling at the surface of the unthreaded portion of the first pipe, wherein material from the unthreaded portion could be removed. As such, the risk of damage at the unthreaded portion of the first pipe is reduced.

[0020] Accordingly, with the configuration of the present invention the threads can be utilized up to and including the thread runout portion, while at the same time structural integrity of the threaded connection can be maintained.

[0021] The pipes, that are made of steel, are generally cylindrical. Each pipe extends along a longitudinal axis. When made up the longitudinal axes of the pipes are coaxial. Normally, the longitudinal axis of each pipe starts in a first longitudinal direction and ends in the first longitudinal direction.

[0022] The pipes have two longitudinal (or terminal) pipe ends, namely: a first longitudinal pipe end and a second longitudinal pipe end located opposite to the first longitudinal pipe end. Normally, the pipes comprise at the first longitudinal pipe end a thread, and at the second longitudinal pipe end a further thread. The threads can be provided either at the inner or outer circumferential surface of the longitudinal end of the pipe. A longitudinal (or terminal) pipe end having the thread provided on its outer circumferential surface is referred to as a “pin”. A longitudinal (or terminal) pipe end having the thread provided on its inner circumferential surface is referred to as a “box”.

[0023] A pipe can have at the first longitudinal pipe end a pin, and at the second longitudinal pipe end a pin, or a box. Alternatively, the pipe can have a box at the first longitudinal pipe end, and a box at its second longitudinal pipe end. A pipe having two boxes is generally referred to as a “coupling”. The pin, and the box, extend along the longitudinal axis of its pipe. The pin comprises a pin terminal (or distal) end, and a pin body (or proximal) end opposite the pin terminal end. The box comprises a box terminal (or distal) end, and a box body end opposite the box terminal end.

[0024] The unthreaded surface of the first pipe may be of a pipe body portion. The pipe body portion is, in longitudinal direction along the longitudinal axis of the first pipe, located further from the longitudinal pipe end than the first thread.

[0025] The first pipe comprises a first thread, and the second pipe comprises a second thread. The threads extend helically along the circumferential surface of the pipe.

[0026] The (first and second) thread comprises a root, a crest, a stab flank, and a load flank. The stab flank faces towards the terminal end of its pin or box, and the load flank faces away from the terminal end of its pin or box.

[0027] Preferably, the threads are tapered so as to change in diameter towards the longitudinal end of the pipe. In particular, in case the first thread is a tapered box thread provided at the inner circumferential surface of the pipe, the (box) thread is tapered so as to increase in inner diameter towards the terminal end of the pipe. In case the first thread is a tapered (pin) thread provided at the outer circumferential surface of the pipe, the (pin) thread is tapered so as to reduce in outer diameter towards the terminal end of the pipe.

[0028] The threads comprise a multitude of thread turns. As is convention in the art, a thread turn may refer to a turn of a thread extending 360 degrees along the circumference of the pipe.

[0029] The first thread has a first perfect thread portion and a thread runout portion. In particular, the thread runout is, in longitudinal direction along the longitudinal axis, located between the first perfect thread portion and the unthreaded surface of the first pipe.

[0030] The first perfect thread portion has full formed thread turns with a maximum thread height. The thread runout portion is a portion of the first thread having thread turns that reduce in thread height in longitudinal direction towards the unthreaded surface. The thread runout portion can adjoin the first perfect thread portion. The thread height may be measured, in radial direction with respect to the longitudinal axis, in particular per thread turn, between the stab flank and the load flank. It should be appreciated that a thread runout portion can extend over part of a turn or over multiple thread turns.

[0031] The second thread of the second pipe may engage the first perfect thread portion and the thread runout portion of the first pipe. When the connection has been formed (or made-up), the second thread overlaps, in longitudinal direction along the longitudinal axis of the first (and second) pipe, the unthreaded surface of the first pipe.

[0032] In particular, when the threaded connection has been formed (or made-up), there is at the first perfect thread portion of the first thread contact with (a first) radial interference between the first thread and the second thread. In particular, the crest of the second thread may radially interfere with the root of the first perfect thread portion. Preferably, the root of the second thread also radially interferes with the crest of the first perfect thread portion. Further, when the threaded connection has been formed (or made-up), there is at the thread runout portion of the first thread contact, in particular between the first thread and the second thread, with less radial interference than at the first perfect thread portion. Hence, there may be at the thread runout portion contact with a second radial interference between the first thread and the second thread, wherein the second radial interference is less than the first radial interference. In particular, the crest of the second thread may radially interfere with the root of the thread runout portion. There may be a clearance between the root of the second thread and the crest of the thread runout portion.

[0033] In addition, at the unthreaded surface there is a (radial) clearance or contact without radial interference between the second thread, in particular the crest of the second thread, and the unthreaded surface.

[0034] The threads of a first and second pipe may radially interfere when a first thread having a certain outer diameter is made up with a second thread having an inner diameter that is smaller than the outer diameter of the first thread. In particular, the (pin) thread provided at the outer circumferential surface of the first pipe may extend along a greater diameter than the (box) thread provided at the inner circumferential surface of the second pipe. For example, the crest of the pin thread may have a diameter that is larger than the root of the box thread and / or the root of the pin thread may have a diameter that is larger than the crest of the box thread. As will be appreciated by the skilled person, preferably the difference in diameters is selected such that deformation of the threads is within the elastic limit of the material of the pipe. Embodiments in accordance with the first, and second, aspect of the present invention are described in the following.

[0035] In an embodiment in accordance with the first aspect of the present invention, the first thread has a positive first stab flank, and a positive first load flank, and the second thread has a positive second stab flank, and a positive second load flank. A positive flank is a flank that tends to reduce the axial width of the crest of a thread turn, whereas a negative flank is a flank that tends to increase the axial width of the crest of a thread turn. In particular, the positive first and second stab flanks extend at a stab flank angle of 3 - 15 degrees, and the positive first and second load flanks extends at a load flank angle of 3 - 10 degrees. The stab and load flank angles are measured between the flank and a plane perpendicular to the longitudinal axis of the pipe.

[0036] In an embodiment in accordance with the first aspect of the present invention, the thread runout portion is located, in longitudinal direction along the longitudinal axis of the first pipe, further from the longitudinal end of the pipe than the first perfect thread portion. In particular, the thread runout portion is located between the unthreaded portion and the first perfect thread portion.

[0037] In an embodiment in accordance with the first aspect of the present invention, the first pipe comprises from the longitudinal end thereof towards the pipe body portion, consecutively:

[0038] - the first perfect thread portion;

[0039] - the thread runout portion; and

[0040] - the unthreaded surface.

[0041] In an embodiment in accordance with the first aspect of the present invention, the first thread is provided at the outer circumferential surface of the first pipe, and the second thread is provided at the inner circumferential surface of the second pipe. In particular, the first thread is a tapered thread, wherein the unthreaded surface is located at a greater diameter than the thread runout portion, and the thread runout portion is located at a greater diameter than the first perfect thread portion. In such case, the second thread is also a tapered thread.

[0042] In an embodiment in accordance with the first aspect of the present invention, there is at the root of the thread turn of the thread runout portion, which thread turn adjoins the unthreaded surface, contact with less radial interference than at the first perfect thread portion. In particular, the radial interference at the thread runout portion is at the root of the thread turn that adjoins the unthreaded surface. More in particular, the radial interference at the thread runout portion is at the thread turn root that adjoins the unthreaded surface of the first pipe. Even more in particular, the radial interference at the thread runout portion is at a part of the root that ends on the unthreaded surface of the first pipe. The radial thread interference at the thread runout portion can be present throughout the thread runout portion. In such case, the radial thread interference is present from the first perfect thread portion up to and including the root of the thread turn of the thread runout portion which root adjoins the unthreaded surface. The radial thread interference at the thread runout portion may decrease, in longitudinal direction, from the first perfect thread portion up to the root of the thread turn of the runout portion which thread turn root adjoins the unthreaded surface of the first pipe.

[0043] An advantage of the above embodiment is, that the entire thread runout portion can be utilized.

[0044] In an embodiment in accordance with the first aspect of the present invention, the second thread comprises a second perfect thread portion for engaging the first perfect thread portion, wherein: the crest of the first perfect thread portion contacts, in particular interferes with, the root of the second perfect thread portion; and the root of the first perfect thread portion contacts, in particular interferes with, the crest of the second perfect thread portion.

[0045] In particular, the first perfect thread portion extends along a first perfect thread portion taper angle, and the second perfect thread portion extends along a second perfect thread portion taper angle, wherein the first perfect thread portion taper angle is equal to the second perfect thread portion taper angle.

[0046] In such embodiment, the first and second perfect thread portion may together form a seal for sealing hydrocarbon fluids.

[0047] In an embodiment in accordance with the first aspect of the present invention, the thread runout portion extends along a thread runout portion taper angle, and the first perfect thread portion extends along a first perfect thread portion taper angle, wherein the thread runout portion taper angle is equal to the first perfect thread portion taper angle.

[0048] An advantage of the above embodiment is, that it is possible to easily manufacture the first Pipe. Within the context of the present document, thread taper angles may be measured in a longitudinal section extending through the longitudinal axis of a pipe between the longitudinal axis of the pipe and a plane passing through the pitch diameter of the respective thread.

[0049] In an embodiment in accordance with the first aspect of the present invention, there is a clearance between the crest of the thread runout portion and the root of the second thread.

[0050] In an embodiment in accordance with the first aspect of the present invention, the second thread comprises a second distal thread portion for engaging the thread runout portion. In particular, the second distal thread portion extends along a second distal thread portion taper angle, and the thread runout portion extends along a thread runout portion taper angle, wherein the second distal thread portion taper angle is greater than the thread runout portion taper angle. More in particular, a difference between the second distal thread portion taper angle and the thread runout portion taper angle is at least 0,29 degrees. Even more in particular, a difference between the second distal thread portion taper angle and the thread runout portion taper angle is at most 0,74 degrees. It will be clear that a difference between the second distal thread portion taper angle and the thread runout portion taper angle can be between 0,29 degrees and 0,74 degrees.

[0051] In an embodiment in accordance with the first aspect of the present invention, the second thread comprises a second distal thread portion for engaging the thread runout portion, and a second perfect thread portion for engaging the first perfect thread portion. The second distal thread portion can be located closer to the longitudinal end of the second pipe than the second perfect thread portion. In particular: the second perfect thread portion extends along a second perfect thread portion taper angle, and the second distal thread portion extends along a second distal thread portion taper angle, wherein the second distal thread portion taper angle is greater than the second perfect thread portion taper angle.

[0052] Preferably, the crest and root of the second perfect thread portion extend along the same second perfect thread portion taper angle, and the crest and root of the second distal thread portion extend along the same second distal thread portion taper angle. As such, the height of the thread turns remains the same throughout the second perfect thread portion, and throughout the second distal thread portion. The second perfect thread portion may adjoin the second distal thread portion. An advantage of the above embodiment is, that less interference at the thread runout portion may be achieved in a cost effective manner. In particular, the second distal thread portion with steeper second distal thread portion taper angle can be obtained by adjusting, during manufacturing, the trajectory of the thread cutting tool. As such, reduced interference at the thread runout portion can be obtained without requiring additional cutting tools.

[0053] In an embodiment in accordance with the first aspect of the present invention, a difference between the second distal thread portion taper angle and the second perfect thread portion taper angle is at least 0,29 degrees.

[0054] In an embodiment in accordance with the first aspect of the present invention, a difference between the second distal thread portion taper angle and the second perfect thread portion taper angle is at most 0,74 degrees.

[0055] In an embodiment in accordance with the first aspect of the present invention, a difference between the second distal thread portion taper angle and the second perfect thread portion taper angle is between 0,29 degrees and 0,74 degrees.

[0056] In an embodiment in accordance with the first aspect of the present invention, the thread height of the second perfect thread portion and the second distal thread portion is the same. In particular, the height of the second thread remains the same throughout the second thread.

[0057] In an embodiment in accordance with the first aspect of the present invention, the second perfect thread portion comprises at least 6 thread turns, in particular 6 to 12 thread turns. In such embodiment, the first perfect thread portion can comprise at least 6, in particular 6 to 12, thread turns. In embodiments comprising a second pipe with a second thread having a second distal thread portion, the second distal thread portion may comprise at least 6 thread turns, in particular 6 to 12 thread turns. The thread runout portion may comprise at least 6 thread turns, in particular 6 to 12 thread turns.

[0058] In an embodiment in accordance with the first aspect of the present invention, when made up, the second distal thread portion is configured to engage the entire thread runout portion, and the second perfect thread portion is configured to engage the entire first perfect thread portion. In an embodiment in accordance with the first aspect of the present invention: the first perfect thread portion adjoins the thread runout portion; and the second perfect thread portion adjoins the second distal thread portion.

[0059] In an embodiment in accordance with the first aspect of the present invention, the first perfect thread portion extends along 20% - 70% of the first thread, In particular, the first perfect thread portion extends along 30% - 60% of the first thread. More in particular, the first perfect thread portion extends along 40% - 50% of the first thread. Additionally, or alternatively, the second perfect thread portion extends along 20% - 70% of the second thread, In particular, the second perfect thread portion extends along 30% - 60% of the second thread. More in particular, the second perfect thread portion extends along 40% - 50% of the second thread.

[0060] In an embodiment in accordance with the first aspect of the present invention, the radial interference at the thread runout portion, in particular at the root of the thread turn of the thread runout portion which thread turn (root) adjoins the unthreaded surface, is at most 77% of the radial interference at the first perfect thread portion. In particular, the radial interference at the thread runout portion, in particular at the root of the thread turn of the thread runout portion which thread turn (root) adjoins the unthreaded surface, is at most 63% of the radial interference at the first perfect thread portion. More in particular, the radial interference at the thread runout portion, in particular at the root of the thread turn of the thread runout portion which thread turn (root) adjoins the unthreaded surface, is at least 40,6% of the radial interference at the first perfect thread portion.

[0061] As explained above, a certain amount of interference is required for effectively utilizing the threads. The inventors found that interference at the thread runout portion, in particular, at the root of the thread turn adjoining the unthreaded portion, of at most 77% allows to make efficient use (in particular of the flanks) of the thread runout portion, while the risk that the second thread contacts the unthreaded surface of the first pipe is reduced. Further, the inventors found, that a radial interference of at most 63% reduces the chance of yield at the thread runout portion. The inventors found that with radial interference at the thread runout portion of at least 40,6% of the radial interference at the first perfect thread portion, the thread turn adjoining the unthreaded surface can be utilized despite the occurrence of elastic deformations at other thread turns of the thread runout portion as a result of radial interference at these other thread turns during and after make-up of the threaded connection. In an embodiment in accordance with the first aspect of the present invention, the radial interference at the thread runout portion, in particular at the root of the thread turn of the thread runout portion which thread turn (root) adjoins the unthreaded surface, is 50% of the radial interference at the first perfect thread portion.

[0062] This way, contact pressures can be equally distributed over the thread turns of the thread runout portion.

[0063] In an embodiment in accordance with the first aspect of the present invention, the radial interference at the thread runout portion, in particular at the root of the thread turn of the thread runout portion, which thread turn (root) adjoins the unthreaded surface, is at least 75%, of the radial interference at the first perfect thread portion.

[0064] In an embodiment in accordance with the first aspect of the present invention, the first pipe has a first pipe wall thickness at the thread runout portion, in particular at the root of the thread runout portion, which root adjoins the unthreaded portion, and the second pipe has a second pipe wall thickness at the second thread adapted to engage the thread runout portion, in particular at the crest of the second thread adapted to engage the root of the thread turn of the thread runout portion which thread turn (root) adjoins the unthreaded surface, wherein the first pipe wall thickness is greater than the second pipe wall thickness. In particular, the wall thickness of the second pipe at the second thread contacting the thread runout portion, in particular the thread turn root of the thread runout portion that adjoins the unthreaded portion, is at most 95% of the wall thickness of the first pipe at that location. The wall thickness may be measured in radial direction in a longitudinal section taken at the longitudinal axis of the pipe.

[0065] An advantage of the above embodiment is, that the effect of deformation as a result of radial thread interference can be better controlled. As the first pipe has at the thread root adjoining the unthreaded portion a greater diameter than the second pipe, the second pipe is more likely to deform as opposed to the first pipe.

[0066] In an embodiment in accordance with the first aspect of the present invention, the second pipe comprises an annular relief groove adjacent the second thread for receiving a part of the first perfect thread portion. Preferably, the annular relief groove is adjoining the second thread. More preferably, the annular relief groove is in longitudinal direction located further from the terminal end of the second pipe than the second thread. In particular, the annular relief groove is configured to receive at least two thread turns of the first perfect thread portion. More in particular, the annular relief groove is configured to receive at least two thread turns of the first perfect thread portion, wherein there is a clearance or contact without radial interference between a circumferential surface of the annular relief groove and the crest of the first perfect thread portion. Preferably, the circumferential surface of the annular relief groove is cylindrical or has a cylindrical envelope.

[0067] An advantage of the above embodiment is, that the radial interference at the terminal end of the first pipe can be reduced. This way, the terminal end of the first pipe is less likely to be pushed radially inward.

[0068] In an embodiment in accordance with the first aspect of the present invention, the second thread comprises more thread turns than the first thread.

[0069] In an embodiment in accordance with the first aspect of the present invention, the threaded connection further comprises: a third pipe with a third thread having a third perfect thread portion and a (third) thread runout portion adjoining an unthreaded surface of the third pipe; wherein the second pipe includes a fourth thread configured for rotational make-up with the third thread wherein when made up the fourth thread axially overlaps the unthreaded surface of the third pipe; wherein:

[0070] - at the third perfect thread portion there is contact with radial interference between the third thread and the fourth thread;

[0071] - at the thread runout portion of the third thread there is contact with less radial interference between the third thread and the fourth thread than at the third perfect thread portion; and

[0072] - at the unthreaded surface of the third pipe there is a clearance or contact without radial interference between the fourth thread and the unthreaded surface of the third pipe. In the above embodiment, the second pipe may comprise a box at a longitudinal end of the second pipe, and a further box at a further longitudinal end opposite the longitudinal end of the second pipe, wherein the second thread is provided in the box, and the fourth thread is provided in the further box. In such case, the first pipe comprises a pin at a longitudinal end thereof, and the third pipe comprises a pin at a longitudinal end thereof.

[0073] In an embodiment in accordance with the first aspect of the present invention, the radial interference at the first perfect thread portion is the same as the radial interference at the third perfect thread portion. In particular, the radial interference at the (first) thread runout portion of the first thread is the same as the radial interference at the (third) thread runout portion of the third thread.

[0074] In an embodiment in accordance with the first aspect of the present invention, the first pipe, in particular a first nose portion of the first pipe, comprises a first abutment face, and the third pipe, in particular a third nose portion of the third pipe, comprises third abutment face, wherein the first abutment face and the third abutment face axially interfere with each other upon make-up.

[0075] In an embodiment in accordance with the first aspect of the present invention, the first abutment face has a first outer circumferential edge and a first inner circumferential edge, wherein, in particular over at least 50% of the annulus of the first nose portion, the first outer circumferential edge is in longitudinal direction further from the first thread than the first inner circumferential edge. The third abutment face has a third outer circumferential edge and a third inner circumferential edge, wherein, in particular over at least 50% of the annulus of the third nose portion, the third outer circumferential edge is in longitudinal direction further from the third thread than the third inner circumferential edge.

[0076] In particular, the first abutment face extends, in particular over at least 50% of the annulus of the first nose portion, along a first abutment face angle from the first outer circumferential edge to the first inner circumferential edge with a first abutment face angle, wherein the first abutment face angle, which is formed between a plane perpendicular to the longitudinal axis and the first abutment face, of 0 - 10 degrees. More in particular, the third abutment face extends, in particular over at least 50% of the annulus of the third nose portion, along a third abutment face angle from the third outer circumferential edge to the third inner circumferential edge with a third abutment face angle, wherein the third abutment face angle, which is formed between a plane perpendicular to the longitudinal axis and the third abutment face, of 0 - 10 degrees. Even more in particular, the first abutment face angle and the third abutment face angle are the same.

[0077] In an embodiment in accordance with the first aspect of the present invention, the second pipe comprises an annular relief groove located between the second thread and the fourth thread. Preferably, the annular relief groove adjoins the second thread and the fourth thread. In particular, the annular relief groove is configured to receive at least two thread turns of the first perfect thread portion, and at least two thread turns of the third perfect thread portion. More in particular, the annular relief groove is configured to receive at least two thread turns of the first perfect thread portion and at least two thread turns of the third perfect thread portion, wherein there is a clearance or contact without radial interference between a circumferential surface of the annular relief groove and the crest of the first perfect thread portion, and there is a clearance or contact without radial interference between the circumferential surface of the annular relieve groove and the crest of the third perfect thread portion. Preferably, the circumferential surface of the annular relief groove is cylindrical or has a cylindrical envelope.

[0078] An advantage of the above embodiments with a first and third abutment face is, that radial interference at the first and third perfect thread portions may be increased, therewith increasing thread sealability in these portions. The increased thread sealability may be achieved without introducing substantial deformation of the longitudinal box ends, in particular, because the increased radial thread interference is obtained at a distance from the longitudinal box ends.

[0079] In a second aspect of the present invention, there is provided a pipe, in particular a second pipe, more in particular a second pipe with a box, as provided in any of the embodiments in accordance with the first aspect of the present invention.

[0080] In an embodiment in accordance with the second aspect of the present invention, the pipe comprises a (second) thread. The thread has a positive (second) stab flank, and a positive (second) load flank. In particular, the positive (second) stab flank extend at a stab flank angle of 3 - 15 degrees, and the positive (second) load flank extends at a load flank angle of 3 - 10 degrees. The stab and load flank angles are measured between the flank and a plane perpendicular to the longitudinal axis of the pipe.

[0081] In an embodiment in accordance with the second aspect of the present invention, the (second) pipe comprises a (second) thread having a (second) perfect thread portion extending along a (second) perfect thread portion taper angle, and a (second) distal thread portion extending along a (second) distal thread portion taper angle, wherein the (second) distal thread portion taper angle is greater than the (second) perfect thread portion taper angle. In particular, (second) pipe terminates in a longitudinal pipe end, wherein the (second) distal thread portion is located closer to the terminal end of the pipe than the (second) perfect thread portion. More in particular, a difference between the (second) distal thread portion taper angle and the (second) perfect thread portion taper angle is at least 0,29 degrees. Even more in particular, a difference between the (second) distal thread portion taper angle and the (second) perfect thread portion taper angle is at most 0,74 degrees. Even further, a difference between the (second) distal thread portion taper angle and the (second) perfect thread portion taper angle can be between 0,29 degrees and 0,74 degrees.

[0082] It will be clear to the skilled person that the second aspect of the present invention may include features relating to the first aspect of any combination of the above described embodiments of the first aspect.

[0083] Advantages of the present invention in respect to the first aspect may also be applicable to the second aspect of the present invention.

[0084] For a better understanding of the present invention, and to show how the same may be put into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

[0085] Figure 1 shows part of a longitudinal section of a threaded connection of the prior art;

[0086] Figure 1 A shows a detailed section IA of the threaded connection as shown in

[0087] Figure 1;

[0088] Figure 2 shows a part of a longitudinal section of an embodiment of a threaded connection in accordance with the present invention;

[0089] Figure 2A shows a detailed section 11 A of the threaded connection as shown in

[0090] Figure 2;

[0091] Figure 2B shows an alternative detailed section 11 A of a threaded connection as shown in Figure 2;

[0092] Figure 3A and 3B provide part of a longitudinal section of first and second pipes of an embodiment in accordance with the present invention;

[0093] Figure 4 provides a schematic representation of a part of a longitudinal section of a threaded connection of the prior art of Figure 1 ;

[0094] Figure 5 provides a schematic representation of a part of a longitudinal section of an embodiment of a threaded connection in accordance with the present invention;

[0095] Figure 6 shows a part of a longitudinal section of an embodiment of a threaded and coupled connection in accordance with the present invention;

[0096] Figure 6A and 6B show a detailed section VIA of the threaded and coupled connection as shown in Figure 6; and

[0097] Figure 7A - 7D show graphs indicating contact pressures measured in various embodiments of threaded connections. Figure 1 shows part of a longitudinal section of a threaded connection 1000 of the prior art. The threaded connection 1000 comprises a first pipe 100 and a second pipe 200, each pipe extending along a longitudinal axis 109, 209.

[0098] The pipes 100, 200 comprise a pipe body 101, 201 with an outer circumferential surface 106, 206 and an inner circumferential surface 110, 210. Each of the pipes 100, 200 ends in a longitudinal (or terminal) pipe end 102, 202, and a further longitudinal (or terminal) pipe end (not shown). The longitudinal pipe ends 102, 202 terminate in an end face 108, 208, respectively. The longitudinal pipe end 102 is a pin 107, and the longitudinal pipe end 202 is a box 207.

[0099] The first pipe 100 comprises on its outer circumferential surface 106 a helically extending first thread 103. The first thread 103 extends in a longitudinal direction 120 along the longitudinal axis 109 from the pipe body 101 towards the end face 108 of the first pipe 100. The first thread 103 is located between the end face 108 and the pipe body 101 of the first pipe 100.

[0100] The first thread 103 comprises a first perfect thread portion 104, and a thread runout portion 105. The thread runout portion 105, in particular the root 114 thereof, starts at the outer circumferential surface 106 of the first pipe.

[0101] The second pipe 200 comprises on its inner circumferential surface 210 a helically extending second thread 203. The second thread 203 extends in a longitudinal direction 220 along the longitudinal axis 209 from the pipe body 201 towards the end face 208 of the second pipe 200. The second thread 203 is located between the end face 208 and the pipe body 201 of the second pipe 100. The second thread 203 consists of a second perfect thread portion 204, which extends from the second pipe body 201 towards the end face 208 of the second pipe 200.

[0102] In the shown embodiment, the second perfect thread portion 204 of the second pipe 200 engages the first perfect thread portion 104 of the first pipe 100 as well as the thread runout portion 105 of the first pipe 100.

[0103] Both the first thread 103 and the second thread 203 comprise a stab flank 111, 211 , a load flank 112, 212 a crest 113, 213 and a root 114, 214. The stab flank 111 of the first thread 103 faces away from the first pipe body 101. The stab flank 211 of the second thread 203 faces away from the second pipe body 201. The load flank 112 of the first thread 103 faces towards the first pipe body 101. The load flank 212 of the second thread 203 faces towards the second pipe body 201. Further, the crest 113 and the root 114 of the first thread 103 face radially outward, in particular in a radial direction 121 , away from the longitudinal axis 109. The root 114 of the first thread 103 is located closer to the longitudinal axis 109 of the first pipe 100 than the crest 113 of the first thread 103. The crest 213 and the root 214 of the second thread 203 face radially inward, towards the longitudinal axis 209. The root 214 of the second thread 203 is located further from the longitudinal axis 209 of the second pipe 200 than the crest 213 of the second thread 203.

[0104] With reference to Figure 4, the first thread 103 of the first pipe 100 and the second thread 203 of the second pipe 200 extend along a (single) first thread taper angle 130 and a (single) second thread taper angle 230. The angles 130, 230 are measured between the longitudinal axis 109, 209 and pitch diameter 132, 232 of the threads 103, 203.

[0105] As can be seen in Figure 1A, the second thread 203 engages the thread runout portion 105 of the first thread 103, wherein the crest 213 of the second thread 203 contacts the root 114 of the thread runout portion 105 of the first thread 103 wherein there is radial interference 402. The radial interference 402 is shown in Figure 1A by the overlap in radial direction 121 between the crest 213 and the root 114. Further, in Figure 1A it can be seen that the crest 213 of the second thread 203 contacts the unthreaded outer circumferential surface 106 of the first pipe 100 wherein there is radial interference 400. The radial interference 400 is shown in Figure 1A by the overlap in radial direction 121 between the crest 213 and the unthreaded outer circumferential surface 106 of the first pipe 100. The latter radial interference 400 can damage the outer surface 106 of the first pipe 100 during use of the threaded connection 1000.

[0106] Figure 2 shows a part of a longitudinal section of an embodiment of a threaded connection 1000 in accordance with the present invention. It will be clear that the threaded connection 1000 in accordance with the present invention comprises similar features as the threaded connection 1000 shown in Figure 1, wherein similar reference signs denote similar features.

[0107] However, the threaded connection 1000 of Figure 2 is different from the connection 1000 of Figure 1. In particular, the second thread 203 of the embodiment of Figure 2 comprises a second perfect thread portion 204 and a second distal thread portion 205. The second perfect thread portion 204 adjoins the second distal thread portion 205. The second perfect thread portion 204 is located, along the longitudinal axis 209, closer to the second pipe body 201 than the second distal thread portion 205. The second distal thread portion 205 is closer to the end face 208 than the second perfect thread portion 204.

[0108] The first thread 103 comprises a first perfect thread portion 104 that adjoins the thread runout portion 105. The second perfect thread portion 204 is adapted for rotational engagement with the first perfect thread portion 104, wherein there is radial interference 401. The second distal thread portion 205 is adapted for rotational engagement with the thread runout portion 105. The second perfect thread portion 204 extends along a second perfect thread portion taper angle 230. The second distal thread portion 205 extends along a second distal thread portion taper angle 231. The second distal thread portion taper angle 231 is greater than the second perfect thread portion taper angle 230. The second distal thread portion 205 extends along a pitch diameter 233 (see Figure 5).

[0109] The first perfect thread portion 104 extends along a first perfect thread portion taper angle

[0110] 130, and the thread runout portion 105 extends along a thread runout portion taper angle

[0111] 131. The first perfect thread portion taper angle 130 and the thread runout portion taper angle 131 are equal to each other. The second perfect thread portion taper angle 230 is equal to the first perfect thread portion taper angle 130. However, the second distal thread portion taper angle 231 is greater than the thread runout portion taper angle 131.

[0112] An important difference between the threaded connection 1000 of Figure 1 and the threaded connection 1000 of Figure 2 is, that in the threaded connection 1000 of Figure 2 there is radial interference 402 at the thread runout portion 105, in particular less radial interference than the radial interference 401 at the first perfect thread portion 104, and there is a (radial) clearance 500 (as shown in Figure 2B) between the crest 213 of the second thread 203 and the outer circumferential surface 106 of the first pipe 100 or there is contact without radial interference (see Figure 2A) between the crest 213 of the second thread 203 and the outer circumferential surface 106 of the first pipe 100.

[0113] In addition, as can be seen in Figure 2A and 2B, the second thread 203 engages the entire thread runout portion 105 of the first pipe 100, wherein there is radial interference 402 at the thread runout portion 105 up to and including at the root 114 of the thread turn 1 of the thread runout portion 105 which thread turn 1 adjoins ends on the circumferential outer surface 106 of the first pipe 100. As such, the entire thread runout portion 105 is utilized when the connection 1000 is in the made up position. In other words; there is no part of the thread runout portion 105 left unused when the connection 1000 has been made up. The radial interference 402 at the root 114 of the thread turn 1 of the thread runout portion 105 of the first thread 103 which root 114 adjoins the unthreaded surface 106 of the first pipe 100 is at most 77%, in particular at most 63%, of the radial interference 401 at the first perfect thread portion 104. In particular, the radial interference 402 at the root 114 of the thread turn 1 of the thread runout portion 105 of the first thread 103 which root 114 adjoins the unthreaded surface 106 is at least 40,6% of the radial interference at the first perfect thread portion 104.

[0114] In particular, the entire load flank 112 of the thread runout portion 105 of the first thread

[0115] 103 is in contact, preferably wherein there is axial interference (not shown), with the load flank 212 of the second thread 203. Further, there is radial interference 402 between the root 114 of the thread runout portion 105 and the crest 213 of the second thread 203. At the thread runout portion 105 there is a radial clearance between the crest 113 of the thread runout portion 105 and the root 214 of the second thread 203.

[0116] When the connection 1000 has been made up (or assembled), the second perfect thread portion 204 engages the first perfect thread portion 104, wherein the crest 113 of the first perfect thread portion 104 is in contact with the root 214 of the second perfect thread portion 204 wherein there is radial interference 401. In addition, the root 114 of the first perfect thread portion 104 contacts the crest 213 of the second perfect thread portion 204 wherein there is radial interference 401. The crest 213 and root 214 of the second perfect thread portion 204 interfere more with the crest 113 and root 114 first perfect thread portion

[0117] 104 than that the crest 213 of the second distal thread portion 205 interferes with the root 114 of the thread runout portion 105.

[0118] The first perfect thread portion 104 extends along at least 20% - 70%, in particular 30% - 60%, more in particular 40% - 50%, of the first thread 103. The first perfect thread portion 104 comprises 8 perfect thread turns that are engaged with 8 perfect thread turns of the second perfect thread portion 204. In Figure 2 the first and second perfect thread portions 104, 204 are separated visually from the second distal thread portion 205 and the thread runout portion 105 by line 600. At this line 600, the thread taper angle of the second thread 203 changes from the second perfect thread portion taper angle 230 to the second distal thread portion taper angle 231, which change introduces a change from the first radial interference 401 at the first perfect thread portion 104 to the second radial interference 402 at the thread runout portion 105. The wall thickness 215 of the second pipe 200 at the second thread 103 contacting the thread runout portion 105, in particular the wall thickness 215 taken at the crest 213 contacting the root 114 of the thread runout portion 105 adjoining the unthreaded surface 106, is at most 95% of the wall thickness 115 of the first pipe 100 at that location.

[0119] The second pipe 200 has an annular relief groove 216 in the inner circumferential surface 210. At final make up, one or more thread turns of the first thread 103 are located in the annular relief groove 216, wherein there is a radial space between the one or more thread turns and an inner surface 217 of the annular relief groove 216.

[0120] Figure 6 shows a further embodiment of a threaded connection 1000 in accordance with the present invention. The threaded connection 1000 comprises a first pipe 100, a second pipe 200, and a third pipe 300. In this embodiment, the first and third pipes 100, 300, are the same as the first pipe in the embodiment shown in Figure 2.

[0121] The main difference between the embodiment of Figure 2 and the embodiment of Figure 6 is, that the second pipe 200 of the embodiment of Figure 6 is a coupling 200. The coupling 200 comprises at a terminal pipe end 240 thereof a box 241 for rotational engagement with the first pipe 100, and at a further terminal pipe end 242, located opposite to the terminal pipe end 240, a further box 243 for rotational engagement with the third pipe 300. Each box 241, 243 is the same as the one shown in Figure 2.

[0122] The third pipe 300 has a third thread 303 having a third perfect thread portion 304 and a thread runout portion 305. The thread runout portion 305 adjoins an unthreaded surface 306 of the third pipe 300. The second pipe 200 includes a fourth thread 253 configured for rotational make-up with the third thread 303 wherein when made up the fourth thread 253 axially overlaps the unthreaded surface 306 of the third pipe 300.

[0123] At the third perfect thread portion 304 there is contact with radial interference 401 between the third thread 303 and the fourth thread 253. At the thread runout portion 305 of the third thread 303 there is contact with less radial interference 402 than at the third perfect thread portion 304. At the unthreaded surface 306 of the third pipe 300 there is a clearance or contact without radial interference between the fourth thread 253 and the unthreaded surface 306 of the third pipe 300.

[0124] Between the two boxes 241 , 243 there is provided an annular relief groove 216 with an inner circumferential surface 217. In particular, the annular relief groove 216 is located between the second thread 203 and the fourth thread 253. The inner circumferential surface 217 is parallel to the longitudinal axis 209.

[0125] When the connection 1000 has been made up, the end face 108 of the first pipe 100 contacts the end face 308 of the third pipe 300, wherein the end faces 108, 308 are in axial direction along the longitudinal axes 109, 209, 309 located within the annular relief groove 216. There is a radial clearance between the inner circumferential surface 217 of the annular relief groove 216 and the first thread 103 and the third thread 303.

[0126] In the embodiment of Figure 6, the first pipe 100 comprises a first abutment face 108, and the third pipe 300 comprises a third abutment face 308. The first abutment face 108 and the third abutment face 308 axially interfere with each other upon make-up of the threaded connection 1000.

[0127] As can be seen in the longitudinal section view of Figure 6A and 6B, the first pipe end 102 (or pin 107) has a first annular nose portion 119 (or first pin nose 118) which first annular nose portion 119 comprises an annular abutment face 108 with a first outer circumferential edge 116 and a first inner circumferential edge 117. The first outer circumferential edge 116 is in longitudinal direction further from the first thread 103 than the first inner circumferential edge 117. Similarly, the third pipe end 202 (or pin 307) has a third annular nose portion 319 (or third pin nose 318) which third annular nose portion 319 comprises an annular abutment face 308 with a third outer circumferential edge 316 and a third inner circumferential edge 317. The third outer circumferential edge 316 is in longitudinal direction further from the third thread 303 than the third inner circumferential edge 317.

[0128] The first and third annular nose portions 119, 319 comprise abutment faces 108, 308 wherein over at least 50% of the annulus of the nose portions 119, 319 the first inner circumferential edge 117, 317 is located in longitudinal direction closer to the first thread 103 than a first outer circumferential edge 116, 316. In particular, the first abutment face 108 extends from the first outer circumferential edge 116 to the first inner circumferential edge 117 along a first abutment face angle a, wherein the first abutment face angle a, which is formed between a plane 800 perpendicular to the longitudinal axis 109 and the first abutment face 108, is 0 - 10 degrees. The third abutment face 308 extends from the third outer circumferential edge 316 to the first inner circumferential edge 317 along a third abutment face angle p, wherein the third abutment face angle p, which is formed between a plane perpendicular to the longitudinal axis 309 and the third abutment face 108, is 0 - 10 degrees. In particular, the first abutment face angle a and the third abutment face angle p are equal to each other.

[0129] During the make-up process, the first abutment face 108 and the third abutment face 308 contact each other, wherein, due to their configuration, the first pin nose 119 and the third pin nose 319 are pushed radially outwards the inner circumferential surface 217 of the annular relief groove 216. When the connection 1000 has been made up, wherein the first abutment face 108 axially interferes with the third abutment face 308, there is a radial clearance between first thread 103 and the inner circumferential surface 217 and a radial clearance between the third thread 303 and the inner circumferential surface 217. Providing the annular relief groove 216 with part of the first thread 303 and part of the third thread 303 located therein allows to increase radial interference 401 at the first perfect thread 104 and the third perfect thread 304. This can help to improve sealability at the first perfect thread 104 and the third perfect thread 304.

[0130] Figure 7A - 7D show graphs indicating the results of FEA analyses performed on embodiments of a threaded connection 1000. The graphs provide an indication of the contact pressure present per thread turn of the threaded connection 1000.

[0131] Figures 7B - 7D show that one can design a threaded connection 1000, wherein radial thread interference at the thread runout portion 105 is maintained and interfering contact at the unthreaded surface 106 of the first pipe 100 is prevented.

[0132] In Figure 7A - 7D, thread turns of the first pipe 100 are numbered 1 - 18, wherein the first perfect thread portion 104, the thread runout portion 105, and the unthreaded surface 106, of the first pipe 100 are indicated. Thread turn 0 indicates the position where there is no thread root 114 on the first pipe 100.

[0133] In the embodiments of Figures 7A - 7D, the first perfect thread portion taper angle 130 is 1 ,79 degrees. The thread runout portion taper angle 131 is also 1 ,79 degrees. Further, the second perfect thread portion taper angle 230 is 1 ,79 degrees.

[0134] Figures 7A - 7D show the results of FEA analyses performed on threaded connections 1000 comprising first and second pipes 100, 200 being made of steel having a yield strength of 110 ksi, wherein the outer diameter of the first pipes 100 is 5,5 inch (139,7 mm), the inner diameter of the first pipes 100 is 4, 78 inch (121 ,4 mm), and wherein the first thread 103 and second thread 203 has five threads per inch. While performing various FEA analyses, the inventors found that the FEA results, in particular in view of deformation wherein the crest 213 of the second thread 203 could come into contact with the unthreaded surface 106 of the first pipe 100, are largely similar for various threaded connections 1000 regardless of variables such as the wall thickness of the pipes, the longitudinal length of the pipes, the outer diameter of the pipes, the inner diameter of the pipes, the steel grade, and the number of threads per inch.

[0135] Figure 7A shows a graph indicating contact pressures per thread turn in a threaded connection 1000 of the prior art. The first thread 103 has a first thread taper angle that is equal to a second thread taper angle of the second thread 203. As can be seen, there is a relatively high contact pressure measured at the unthreaded surface 106 of the first pipe 100. Such contact can, in particular when the threaded connection 1000 is subjected to tensional and compression, lead to galling at the unthreaded surface 106 of the first pipe 100.

[0136] Figure 7B shows a graph indicating contact pressures per thread turn in a threaded connection 1000 in accordance with the present invention. The threaded connection 1000 has a first thread 103 extending along a single first thread taper angle 130, and a second thread extending along a single second thread taper angle 230, wherein the first and second thread taper angles are equal to each other. The radial thread interference has been reduced with respect to the radial thread interference throughout the entire first and second thread. As a result, there is no radial interference between the crest 213 of the second thread 203 and the unthreaded surface 106 of the first pipe 100. However, it was observed that although in this embodiment there is a reduced risk of galling at the unthreaded surface 106, there is also less thread sealability than in the embodiment of Figure 7A.

[0137] Figure 7C and 7D show a graph indicating contact pressures per thread turn in a threaded connection 1000 in accordance with the present invention. Figure 7C and 7D show that radial interference along the first thread 103 can be influenced by introducing a change in the thread taper angle of the second thread 203. To maintain adequate thread sealability at the first perfect thread portion 104, the taper change is introduced at the start of the thread runout portion 105. In these embodiments, the first perfect thread portion 104 comprises 9 thread turns 10 - 18 that are engaged with 9 thread turns of the second thread 203. The thread runout portion 105 adjoins the first perfect thread portion 104. The position at which the taper angle of the second thread 203 changes is indicated with reference numeral 600. The first perfect thread portion taper angle 130 of the first perfect thread portion 104 is equal to the second perfect thread portion taper angle 230 of the second perfect thread portion 204.

[0138] The second thread 203 of the second pipe 200 of the embodiment shown in Figure 7C and 7D has a second perfect thread portion 204 and a second distal thread portion 205. The second perfect thread portion 204 has a second perfect thread portion taper angle 230 that is smaller than the second distal thread portion taper angle 231 of the second distal thread portion 205. In Figure 7C, the second distal thread portion taper angle 231 is 2,08 degrees. The difference between the second perfect thread portion taper angle 230 and the second distal thread portion taper angle 231, as well as the difference between the thread runout portion taper angle 131 and the second distal thread portion taper angle 231 , is 0,29 degrees. In this embodiment, there is radial interference at the thread turn 1 adjoining the unthreaded surface 106 of the first pipe 106, and no radial interference between the crest 213 of the second thread 203 and the unthreaded surface 106 of the first pipe 100. The radial interference 402 at the root of the thread turn 1 adjoining the unthreaded surface 106 is 77,15% of the radial interference 401 at the first perfect thread portion 104.

[0139] As can be seen in Figure 7D, it is possible to further increase the difference between the second distal thread portion taper angle 231 and the second perfect thread taper angle 230 in order to further reduce contact pressures, in particular contact pressures that would exceed a yield threshold as indicated by line 700. In this regard, reference is made to the contact pressure at thread turn 1 of Figure 7C. A person skilled in the art would appreciate that different designs can have different yield thresholds, in particular depending on the type of steel used for the threaded connection 1000.

[0140] In Figure 7D, contact pressures exceeding the yield threshold are prevented. However, in order to make use of thread turn number 1 during operation, it is preferred that a certain contact pressure is still present at thread turn number 1. In Figure 7D, the second distal thread portion taper angle 231 is 2,53 degrees. The difference between the second perfect thread portion taper angle 230 and the second distal thread portion taper angle 231, as well as the difference between the thread runout portion taper angle 131 and the second distal thread portion taper angle 231, is 0,74 degrees. In this embodiment, there is radial interference at the thread turn 1 adjoining the unthreaded surface 106 of the first pipe 106, and no radial interference between the crest 213 of the second thread 203 and the unthreaded surface 106 of the first pipe 100. The radial interference at the root of the thread turn 1 adjoining the unthreaded surface 106 is 40,6% of the radial interference at the first perfect thread portion 104. It should be appreciated that a difference between radial interference at the first perfect thread portion and radial interference at the thread runout portion is not necessarily obtained by a difference in thread taper angle of (a portion of) the thread of the first pipe with respect to the thread taper angle of (a portion of) the thread of the second pipe. It is possible to influence radial interference along the threads of the threaded connection, in particular while designing, a threaded connection, for example, by selecting a particular diameter for one or more thread turns of the first thread of the first pipe and selecting a further diameter for one or more (corresponding) thread turns of the second thread of the second pipe, wherein, when the first and second pipe have been made up, there is a certain radial overlap in diameter at these thread turns. In particular, one can take into account the above described deformation (e.g. bending) of the second pipe with respect to the first pipe, which deformation is influenced by radial interference 401 at the first perfect thread portion 104, for determining a suitable amount of radial interference 402 at the thread runout portion 105.

[0141] Although the accompanying Figures show embodiments comprising a first pipe 100 having a pin, and a second pipe 200 having a box, it is clear that first pipe 100 can have a box, and the second pipe 200 can have a pin. In case the first pipe 100 has a box, and the second pipe 200 has a pin, the thread runout portion 105 is located closer to the pipe body 101 than the first perfect thread portion 104.

[0142] As required, detailed embodiments of the present invention have been disclosed in the figures. However, it is to be understood that the disclosed embodiments are merely exemplary, wherein invention can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

[0143] The terms "a" or "an", as used herein, are defined as one or more than one. The terms multitude or plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and / or having, as used herein, are defined as comprising (i.e. , open language, not excluding other elements or steps). Any reference signs in the claims should not be construed as limiting the scope of the claims or the invention.

[0144] It will be apparent to those skilled in the art that various modifications can be made to the shown threaded connection according to the invention without departing from the scope as defined in the claims.

Claims

CLAIMS1. Threaded connection for exploration and production of a hydrocarbon well, comprising: a first pipe with a first thread having a first perfect thread portion and a thread runout portion adjoining an unthreaded surface of the first pipe; a second pipe with a second thread configured for rotational make-up with the first thread wherein when made up the second thread axially overlaps the unthreaded surface; wherein:- at the first perfect thread portion there is contact with radial interference between the first thread and the second thread;- at the thread runout portion there is contact with less radial interference than at the first perfect thread portion; and- at the unthreaded surface there is a clearance or contact without radial interference between the second thread and the unthreaded surface.

2. Threaded connection of claim 1 , wherein at the root of the thread turn of the thread runout portion, which thread turn adjoins the unthreaded surface, there is contact with less radial interference than at the first perfect thread portion.

3. Threaded connection of claim 1 or 2, wherein the second thread comprises a second perfect thread portion for engaging the first perfect thread portion and a second distal thread portion for engaging the thread runout portion, wherein: the second perfect thread portion extends along a second perfect thread portion taper angle, and the second distal thread portion extends along a second distal thread portion taper angle, wherein the second distal thread portion taper angle is greater than the second perfect thread portion taper angle.

4. Threaded connection of claim 3, wherein a difference between the second distal thread portion taper angle and the second perfect thread portion taper angle is at least 0,29 degrees.

5. Threaded connection of claim 3 or 4, wherein a difference between the second distal thread portion taper angle and the second perfect thread portion taper angle is at most 0,74 degrees.

6. Threaded connection of any of claims 3 to 5, wherein the first perfect thread portion extends along a first perfect thread portion taper angle, wherein the first perfect thread portion taper angle is equal to the second perfect thread portion taper angle.

7. Threaded connection of claim 6, wherein the thread runout portion extends along a thread runout portion taper angle that is equal to the first perfect thread portion taper angle.

8. Threaded connection of any of claims 3 to 7, wherein: the first perfect thread portion adjoins the thread runout portion; and the second perfect thread portion adjoins the second distal thread portion.

9. Threaded connection of any preceding claim, wherein the first perfect thread portion extends along at least 20% - 70%, in particular 30% - 60%, more in particular 40% - 50%, of the first thread.

10. Threaded connection of any preceding claim, wherein the radial interference at the thread runout portion, in particular at the root of the thread turn of the thread runout portion, which thread turn adjoins the unthreaded surface, is at most 77%, in particular at most 63%, more in particular at least 40,6%, of the radial interference at the first perfect thread portion.

11. Threaded connection of any preceding claim, wherein the radial interference at the thread runout portion, in particular at the root of the thread turn of the thread runout portion, which thread turn adjoins the unthreaded surface, is 50% of the radial interference at the first perfect thread portion.

12. Threaded connection of any preceding claim, wherein the wall thickness of the second pipe at the second thread contacting the thread runout portion, in particular at the crest of the second thread contacting the root of the thread runout portion, which root adjoins the unthreaded surface, is at most 95% of the wall thickness of the first pipe at that location.

13. Threaded connection of any preceding claim, wherein the second pipe comprises an annular relief groove adjacent the second thread for receiving a part of the first perfect thread portion.

14. Threaded connection of any of the preceding claims, further comprising:a third pipe with a third thread having a third perfect thread portion and a thread runout portion adjoining an unthreaded surface of the third pipe; wherein the second pipe includes a fourth thread configured for rotational make-up with the third thread wherein when made up the fourth thread axially overlaps the unthreaded surface of the third pipe; wherein:- at the third perfect thread portion there is contact with radial interference between the third thread and the fourth thread;- at the thread runout portion of the third thread there is contact with less radial interference than at the third perfect thread portion; and- at the unthreaded surface of the third pipe there is a clearance or contact without radial interference between the fourth thread and the unthreaded surface of the third pipe.

15. Threaded connection of claim 14, wherein the first pipe comprises a first annular nose portion with a first abutment face, and the third pipe comprises a third annular nose portion with a third abutment face, wherein the first abutment face and the third abutment face axially interfere with each other upon make-up.

16. Threaded connection of claim 15, wherein the first abutment face has a first outer circumferential edge and a first inner circumferential edge, wherein over at least 50% of the annulus of the first nose portion the first outer circumferential edge is in longitudinal direction further from the first thread than the first inner circumferential edge, and the third abutment face has a third outer circumferential edge and a third inner circumferential edge, wherein over at least 50% of the annulus of the third nose portion the third outer circumferential edge is in longitudinal direction further from the third thread than the third inner circumferential edge.

17. Threaded connection of any of claims 14 to 16, and claim 13, wherein the annular relief groove is located between the second thread and the fourth thread.

18. Pipe as provided in any of the preceding claims.

19. Pipe for a threaded connection for exploration and production of a hydrocarbon well, comprising a perfect thread portion extending along a perfect thread portion taper angle, and a distal thread portion extending along a distal thread portion taper angle, wherein the distal thread portion taper angle is greater than the perfect thread portion taperangle, wherein a difference between the distal thread portion taper angle and the perfect thread portion taper angle is at least 0,29 degrees, and / or at most 0,74 degrees.

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