A fatigue testing method and testing fixture for fiberglass pipe fittings

Abstract

A fatigue testing fixture for fiberglass pipe fittings includes a vertical fixing base with a left fixing base and a right fixing base on its two sides. Both the left and right fixing bases are fixed to a horizontal base. A first groove and a second groove are respectively provided on the side of the left and right fixing bases opposite to the vertical fixing base. A first fiberglass pipe is positioned between the vertical fixing base and the left fixing base, and a second fiberglass pipe is positioned between the vertical fixing base and the right fixing base. A fatigue testing method for fiberglass pipe fittings is also provided, comprising fatigue test A and fatigue test B. The fiberglass pipe fatigue testing fixture of this invention horizontally clamps two sections of fiberglass pipe, effectively simulating the state of the fiberglass pipe fitting as a supporting component. Applying cyclic fatigue loads to the testing fixture effectively simulates the shear force and axial pressure received by the fiberglass pipe, enabling testing of the durability of the fiberglass pipe as a supporting component and exploring the ultimate failure mechanism of the fiberglass pipe.

Description

Technical Field

[0001] This invention belongs to the field of fiberglass pipe testing, and specifically relates to a fatigue testing method and testing fixture for fiberglass pipe fittings. Background Technology

[0002] Currently, most cryogenic LNG storage tanks in my country are double-walled tanks, with insulation material filling the space between the inner and outer tanks to keep the inner tank warm. Fiberglass pipes are commonly used as support members between the inner and outer tanks of cryogenic LNG storage tanks. During transportation, these fiberglass pipes primarily bear axial and radial fatigue loads. Fiberglass is a complex non-metallic material, and the design of fiberglass pipes as support structures typically only considers the theoretical strength of fiberglass, neglecting the durability and ultimate failure mechanism of the fiberglass pipes as support components.

[0003] CN206515169U discloses a circumferential bending fatigue testing device for fiberglass pipes, which can specifically perform multiple, high-frequency fatigue tests on the axial path of fiberglass pipes to avoid fatigue cracks in fiberglass pipes, prevent leakage and increase maintenance costs. It mainly considers the circumferential fatigue test of fiberglass pipes; it does not involve the durability and ultimate failure mechanism test methods and test fixtures of fiberglass pipes as supporting components. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a fatigue test method and test fixture for fiberglass pipe fittings, so as to test the durability of fiberglass pipes as supporting components and explore the ultimate failure mechanism of fiberglass pipes.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A fatigue testing fixture for fiberglass pipe fittings includes a horizontal base, a vertical fixed base, a left fixed base, and a right fixed base; the horizontal base is provided with the left fixed base and the right fixed base respectively, and the vertical fixed base is provided at its upper end; the vertical fixed base is provided with a third groove and a fourth groove on both sides respectively; the left fixed base and the right fixed base are provided with a first groove and a second groove respectively; the vertical fixed base and the right fixed base are respectively connected to a fatigue load application mechanism.

[0007] Furthermore, the center points of the first groove, the second groove, the third groove, and the fourth groove are on the same axis.

[0008] Furthermore, the vertical fixing base is T-shaped, including a top plate and a vertical plate; both sides of the connection between the top plate and the vertical plate are provided with first reinforcing ribs; and a first through hole is opened on the top plate.

[0009] Furthermore, both the left and right fixed seats are L-shaped, comprising a vertical plate and a horizontal plate; a second reinforcing rib is provided at the connection between the vertical and horizontal plates; and a second through hole is provided on the vertical plate.

[0010] Furthermore, the top plate of the vertical fixing seat is connected to the fatigue load application mechanism; the vertical plate of the right fixing seat is connected to the fatigue load application mechanism.

[0011] Furthermore, the fatigue load application mechanism is a hydraulic device; the hydraulic device includes a longitudinal force transmitter and a transverse force transmitter; the longitudinal force transmitter and the transverse force transmitter have the function of adjusting the magnitude of the fatigue load and the number of fatigue loads.

[0012] The present invention also provides a fatigue testing method for fiberglass pipe fittings. This testing method utilizes the aforementioned fatigue testing fixture for fiberglass pipe fittings and includes the following steps:

[0013] S1: Calculate the fatigue load. Based on the rated service life, rated loading capacity, and mileage within the rated service life of the LNG storage tank, calculate the axial load N1 and radial load N2 of the FRP pipe within the rated service life.

[0014] S2: Determine the number of fatigue load cycles. Based on the design service life of the LNG storage tank, the annual usage time, and the transportation mileage, estimate the number of fatigue load cycles X that the equipment will withstand within its design service life.

[0015] S3: Debug and conduct fatigue test A. Install the FRP pipe fittings onto the FRP pipe fitting fatigue test fixture created in this invention; debug the FRP pipe fitting fatigue test fixture, set the fatigue load magnitude and number of cycles, and conduct fatigue test A; check whether the integrity of the FRP pipe fittings has been damaged.

[0016] Furthermore, in step S3 above:

[0017] The fiberglass pipe fitting includes a first fiberglass pipe and a second fiberglass pipe; one end of the first fiberglass pipe is embedded in the first groove of the left fixed seat, and the other end is embedded in the third groove of the vertical fixed seat; one end of the second fiberglass pipe is embedded in the second groove of the right fixed seat, and the other end is embedded in the fourth groove of the vertical fixed seat; the top plate is fixedly connected to the longitudinal force transmitter; the vertical plate is fixedly connected to the transverse force transmitter; the applied load size N1 and the number of applied loads X are input on the transverse force transmitter control device; the applied load size N2 and the number of applied loads X are input on the longitudinal force transmitter control device;

[0018] Start the hydraulic equipment and conduct fatigue test A. After the number of cyclic loads applied to the transverse and longitudinal force transmitters on the hydraulic equipment reaches the set number of loading times X, the hydraulic equipment stops applying fatigue loads to the top plate and vertical plate; check whether the first and second fiberglass pipes are damaged.

[0019] Furthermore, methods for detecting whether FRP pipe fittings have been damaged include using radiographic testing equipment, observing the appearance, and measuring dimensions. Observe and measure the location and type of damage to the FRP pipe; record the total number of fatigue load cycles, the magnitude of the fatigue load, and the location and type of damage to the pipe fitting.

[0020] S4: Conduct fatigue test B. If the FRP pipe fitting is undamaged, continue to increase the number of cycles for the undamaged FRP pipe fitting and conduct fatigue test B until the FRP pipe is damaged. Then stop applying cyclic fatigue load and record the relevant data.

[0021] Furthermore, in step S4 above:

[0022] If both the first and second fiberglass pipes are damaged, the test should be stopped.

[0023] If neither the first nor the second FRP pipe is damaged, continue increasing the number of fatigue load cycles on the undamaged first and / or second FRP pipes via the longitudinal and transverse force transmitters to conduct fatigue test B until the first and / or second FRP pipes break. Then, stop the test, i.e., stop applying the cyclic fatigue load. Observe and measure the location and form of the breakage of the FRP pipes. Record the total number of fatigue load cycles, the magnitude of the fatigue load, and the location and form of the breakage of the pipe fittings.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The present invention provides a left fixed seat and a right fixed seat on both sides of the vertical fixed seat. Two fiberglass pipes are symmetrically arranged between the vertical fixed seat and the left and right fixed seats. The ends of the fiberglass pipes are embedded in the grooves and abut against the vertical fixed seat, the left fixed seat, and the right fixed seat. Such a clamping fixture effectively simulates the state of the fiberglass pipe as a support structure.

[0026] 2. The present invention fixes a longitudinal force transmitter to the top plate of the vertical fixed base to simulate the radial shear force on the fiberglass pipe; fixes a transverse force transmitter to the vertical plate of the right fixed base to simulate the axial force on the fiberglass pipe; by adjusting the magnitude and number of cyclic loads applied by the longitudinal and transverse force transmitters, the cyclic load on the fiberglass pipe can be simulated, which has high fidelity and is easy to operate.

[0027] 3. Based on the rated service life, rated loading capacity, and mileage within the rated service life of the LNG storage tank, this invention calculates the magnitude and number of axial cyclic loads and radial cyclic loads that the FRP pipe will experience within its rated service life. Fatigue test A is then conducted to determine whether the FRP pipe will break under the rated cyclic load. Fatigue test A can reflect the durability index of the FRP pipe.

[0028] 4. After fatigue test A is completed, check whether the FRP pipe fittings are damaged. FRP pipe fittings that are damaged are unqualified products. FRP pipe fittings that are not damaged after fatigue test A are subjected to fatigue test B, and the number of applied fatigue load cycles is increased until the FRP pipe fittings are damaged. Record the number of fatigue load cycles, the magnitude of fatigue load, the location of damage, and the mode of damage. Statistically analyze the failure mechanism in the table to provide a theoretical basis for the subsequent optimized design of FRP pipe fittings. Attached Figure Description

[0029] Figure 1 Overall structural diagram of the invention;

[0030] Figure 2 Schematic diagram of the clamping fixture installation structure of the present invention;

[0031] Figure 3 Schematic diagram of the cross-sectional structure of the left fixing seat of the present invention;

[0032] Figure 4 Schematic diagram of the cross-sectional structure of the right fixing seat of the present invention;

[0033] Figure 5 Schematic diagram of the cross-sectional structure of the vertical fixing seat of the present invention;

[0034] Figure 6 Flowchart of the experimental method of this invention.

[0035] Wherein: 1-Horizontal base; 2-Vertical fixed base; 20-Top plate; 21-Vertical plate; 3-Left fixed base; 4-Right fixed base; 40-Vertical plate; 41-Horizontal plate; 5-Longitudinal force transmitter; 6-Transverse force transmitter. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] As attached Figure 1-2As shown, a fatigue testing fixture for fiberglass pipe fittings includes a horizontal base 1, a vertical fixing seat 2, a left fixing seat 3, and a right fixing seat 4. The horizontal base 1 is provided with the left fixing seat 3 and the right fixing seat 4, and the vertical fixing seat 2 is located at its upper end. The vertical fixing seat 2 has a third groove and a fourth groove on its two sides. The left fixing seat 3 and the right fixing seat 4 have a first groove and a second groove, respectively. The vertical fixing seat 2 and the right fixing seat 4 are respectively connected to a fatigue load application mechanism. (See attached diagram.) Figure 2-5 As shown, when using this test fixture, the first fiberglass pipe and the second fiberglass pipe are symmetrically clamped on both sides of the vertical fixing seat 2; the ends of the first fiberglass pipe are respectively embedded in the first groove and the third groove; the ends of the second fiberglass pipe are respectively embedded in the second groove and the fourth groove; the center points of the first groove, the second groove, the third groove, and the fourth groove are on the same axis to ensure that the fiberglass pipe fittings are on the same straight line during the clamping process; this installation and clamping method can effectively simulate the state of the fiberglass pipe as a support structure between the inner and outer tanks of the LNG storage tank, with a high degree of simulation.

[0038] As attached Figure 1 and appendix Figure 3-5 As shown, both the left fixed seat 3 and the right fixed seat 4 are "L"-shaped, including a horizontal plate 41 and a vertical plate 40, with a second reinforcing rib at the connection between the horizontal plate 41 and the vertical plate 40; the vertical fixed seat 2 is "T"-shaped, including a top plate 20 and a vertical plate 21, with a second reinforcing rib at the connection between the top plate 20 and the vertical plate 21; this design enhances the structure of the experimental fixture; the top plate 20 has a first through hole, and the vertical plate 40 has a second through hole; the top plate 20 is fixedly connected to the longitudinal force transmitter 5 by bolts, and the vertical plate 40 is fixedly connected to the transverse force transmitter 6 by bolts; the longitudinal force transmitter 5 and the transverse force transmitter 6 can provide cyclic fatigue loads, and the magnitude and number of fatigue loads can be adjusted; the fatigue load applied by the longitudinal force transmitter 5 is used to simulate the radial shear force on the fiberglass pipe, and the fatigue load applied by the transverse force transmitter 6 is used to simulate the axial pressure on the fiberglass pipe, making operation convenient.

[0039] This invention also provides a fatigue testing method for fiberglass pipe fittings, comprising the following steps:

[0040] S1: Calculate the fatigue load. Based on the rated service life, rated loading capacity, and mileage within the rated service life of the LNG storage tank, calculate the axial load N1 and radial load N2 of the FRP pipe within the rated service life.

[0041] S2: Determine the number of fatigue load cycles. Based on the rated service life, rated loading capacity, and mileage within the rated service life of the LNG storage tank, estimate the number of fatigue load cycles X that the equipment will withstand within its design service life.

[0042] S3: Debug and conduct fatigue test A. Install the FRP pipe fittings onto the FRP pipe fitting fatigue test fixture created in this invention; debug the FRP pipe fitting fatigue test fixture, set the fatigue load magnitude and number of cycles, and conduct fatigue test A; check whether the integrity of the FRP pipe fittings has been damaged.

[0043] In step S3 above, the fiberglass pipe fitting includes two fiberglass pipes, namely the first fiberglass pipe and the second fiberglass pipe; one end of the first fiberglass pipe is embedded in the first groove of the left fixed seat 3, and the other end is embedded in the third groove of the vertical fixed seat 2; one end of the second fiberglass pipe is embedded in the second groove of the right fixed seat 4, and the other end is embedded in the fourth groove of the vertical fixed seat 2; the top plate 20 is fixedly connected to the longitudinal force transmitter 5 by bolts; the vertical plate 40 is fixedly connected to the transverse force transmitter 6 by bolts; the applied load size N1 and the number of applied loads X are input on the control device of the transverse force transmitter 6; the applied load size N2 and the number of applied loads X are input on the control device of the longitudinal force transmitter 5; the hydraulic equipment is started to perform fatigue test A. After the number of cyclic loads applied by the transverse force transmitter 6 and the longitudinal force transmitter 5 on the hydraulic equipment reaches the set number of loading times X, the hydraulic equipment stops applying fatigue loads to the top plate 20 and the vertical plate 40; the first fiberglass pipe and the second fiberglass pipe are checked for damage.

[0044] To detect whether fiberglass pipe fittings have been damaged, methods such as X-ray inspection, visual inspection, and dimensional measurement can be used.

[0045] Observe and measure the damaged parts and damage forms of the FRP pipes; record the total number of fatigue load cycles, the magnitude of the fatigue load, and the damaged parts and damage forms of the pipe fittings.

[0046] S4: Conduct fatigue test B. If the FRP pipe fitting is undamaged, continue to increase the number of cycles for the undamaged FRP pipe fitting and conduct fatigue test B until the FRP pipe is damaged. Then stop applying cyclic fatigue load and record the relevant data.

[0047] As attached Figure 6 As shown, if both the first and second fiberglass pipes break during this step, the test should be stopped. Record relevant data in the test record table, such as the location of the breakage, the form of the breakage, the shape and structure of the breakage, the load magnitude, and the number of load cycles, to provide a theoretical basis for subsequent pipe fitting design and improvement.

[0048] If all FRP pipe fittings are undamaged, or only one fitting is damaged, the fatigue load cycle number will be increased for the undamaged FRP pipes (the count will not be reset to zero); for the FRP pipe fittings that have already been damaged, the relevant test data will be recorded, and no further tests will be conducted.

[0049] For undamaged FRP pipe fittings, fatigue test B is conducted, with the number of fatigue load cycles increased until the FRP pipe breaks. At this point, the test is stopped and the cyclic fatigue load is no longer applied. The location, mode, shape, and load of the breakage are observed, measured, and recorded. The total number of fatigue load cycles and the magnitude of the fatigue load are also recorded. The test data are then entered into a table.

[0050] Test A Test Data Recording Table

[0051]

[0052] Test B Test Data Recording Table

[0053]

[0054] The scope of protection of this invention is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its scope and spirit. If these modifications and variations fall within the scope of the claims of this invention and their equivalents, then the intent of this invention also includes these modifications and variations.

Claims

1. A fatigue testing method for fiberglass pipe fittings, comprising using a fatigue testing fixture for fiberglass pipe fittings, characterized in that, Includes the following steps: S1: Calculate the fatigue load. Based on the rated service life, rated loading capacity, and mileage within the rated service life of the LNG storage tank, calculate the axial load N1 and radial load N2 of the FRP pipe within the rated service life. S2: Determine the number of fatigue load cycles. Based on the design service life of the LNG storage tank, the annual usage time, and the transportation mileage, estimate the number of fatigue load cycles X that the FRP pipe will withstand within its design service life. S3: Debugging and fatigue test A, the FRP pipe fittings include the first FRP pipe and the second FRP pipe; Install the fiberglass pipe fittings onto the fiberglass pipe fatigue test fixture, wherein one end of the first fiberglass pipe is embedded in the first groove of the left fixed seat and the other end is embedded in the third groove of the vertical fixed seat; one end of the second fiberglass pipe is embedded in the second groove of the right fixed seat and the other end is embedded in the fourth groove of the vertical fixed seat; fix the top plate to the longitudinal force transmitter; fix the vertical plate to the transverse force transmitter. Debug the fatigue test fixture for this FRP pipe fitting, set the fatigue load size and number of cycles, and input the applied load size N1 and the number of applied load cycles X on the transverse force transmitter control device; input the applied load size N2 and the number of applied load cycles X on the longitudinal force transmitter control device; Start the hydraulic equipment and conduct fatigue test A. After the number of cyclic loads applied to the transverse and longitudinal force transmitters on the hydraulic equipment reaches the set number of loading times X, the hydraulic equipment stops applying fatigue loads to the top plate and vertical plate; check whether the first and second fiberglass pipes are damaged. S4: Conduct fatigue test B. If the FRP pipe fitting is undamaged, continue to increase the number of cycles for the undamaged FRP pipe fitting and conduct fatigue test B until the FRP pipe is damaged. Then stop applying cyclic fatigue load and record the relevant data.

2. The method for fatigue testing of steel pipe fittings according to claim 1, characterized in that: Methods for detecting whether FRP pipe fittings have been damaged include using radiographic testing equipment, observing the appearance, measuring dimensions, observing and measuring the damaged parts and damage types of the FRP pipes; recording the total number of fatigue load cycles, the magnitude of the fatigue load, and the damaged parts and damage types of the pipe fittings.

3. The method for fatigue testing of steel pipe fittings according to claim 2, characterized in that: In step S4: If both the first and second fiberglass pipes are damaged, the test should be stopped. If there is no damage to the first or second fiberglass pipe, continue to increase the number of fatigue load cycles of the longitudinal and transverse force transmitters on the undamaged first and / or second fiberglass pipes, and conduct fatigue test B until the first and / or second fiberglass pipes break. Then stop the test, that is, stop applying cyclic fatigue loads. Observe and measure the damaged parts and types of damage to the fiberglass pipe; Record the total number of fatigue load cycles, the magnitude of the fatigue load, the location of pipe failure, and the form of failure.

4. The fatigue testing fixture for fiberglass pipe fittings according to claim 1, characterized in that: Includes a horizontal base, a vertical fixing base, a left fixing base, and a right fixing base; The horizontal base is provided with a left fixed seat and a right fixed seat, and a vertical fixed seat is provided at its upper end; The vertical fixing base is provided with a third groove and a fourth groove on both sides respectively; The left and right fixing seats are respectively provided with a first groove and a second groove; The vertical fixed seat and the right fixed seat are respectively connected to the fatigue load application mechanism; The center points of the first groove, the second groove, the third groove, and the fourth groove are on the same axis.

5. The fatigue testing fixture for fiberglass pipe fittings according to claim 4, characterized in that: The vertical fixing base is T-shaped and includes a top plate and a vertical plate; Both sides of the connection between the top plate and the vertical plate are provided with first reinforcing ribs; The top plate has a first through hole.

6. The fatigue testing fixture for fiberglass pipe fittings according to claim 5, characterized in that: Both the left and right fixed seats are "L" shaped and include a vertical plate and a horizontal plate. The vertical and horizontal plates are both provided with a second reinforcing rib. The vertical plate is provided with a second through hole.

7. The fatigue testing fixture for fiberglass pipe fittings according to claim 6, characterized in that: The top plate of the vertical fixing seat is connected to the fatigue load application mechanism; The vertical plate of the right fixed seat is connected to the fatigue load application mechanism.

8. The fatigue testing fixture for fiberglass pipe fittings according to claim 7, characterized in that: The fatigue load application mechanism is a hydraulic device; The hydraulic equipment includes a longitudinal force transmitter and a transverse force transmitter. The longitudinal force transmitter and the transverse force transmitter have the function of adjusting the magnitude of fatigue load and the number of fatigue load cycles.

Images