Method for protecting a steel pipe against corrosion

Abstract

The present invention relates to a method for preventing corrosion at the interface between a steel pipe to be protected (1) and a steel support cradle (2a) for this pipe (1). According to the invention, this method comprises the steps of: - calculating the lifting force (F) to be applied at a lifting point (P) of the pipe (1) to lift it between 0.03 m and 0.06 m, relative to the cradle (2a), - calculating the value of the stress σ experienced by said pipe (1) during lifting, - placing a load distribution plate (6) on the ground, fixing a lifting cradle (7) against said pipe (1) and positioning a lifting device (5) between the two, - actuating the lifting device (5) to lift the pipe (1), - inserting at least one zinc plate (8) between said cradle to be protected (2a) and the pipe (1), - lowering the pipe (1) to place it on said plate (8). Figure for the summary: Figure 5

Description

Title of the invention: Method for protecting a steel pipe against corrosion FIELD OF THE INVENTION

[0001] The invention lies in the field of protection against corrosion.

[0002] The present invention relates more specifically to a method of protecting against corrosion a steel pipe, in particular a penstock, resting on a cradle-type steel support.

[0003] The term "forced conduit" refers to a conduit used to bring pressurized water from a reservoir located high up to the turbine of a hydroelectric power station. STATE OF THE ART

[0004] When a steel pipe rests on a steel support, a corrosion effect is often observed if there is moisture present at the interface between the two.

[0005] In the particular case of penstocks, which are pipes used to transport water under pressure from one point to another, and which are arranged outdoors, a corrosion effect of the steel is often observed. This corrosion generates losses in thickness of the pipe and the support, which can be detrimental to the mechanical strength of the structure.

[0006] A first solution known from the state of the art to solve this problem consists of making modifications to the cradle-shaped support and to the pipe to make their contact surface flat and to provide a stainless steel plate in contact with the pipe and high-density HDPE pads in contact with the support, so as to thus have two materials insensitive to corrosion.

[0007] A second solution known from the state of the art to solve this problem consists of covering the pipe and its cradle-shaped support with an anti-corrosion coating, at least at the points of contact between the two (by injecting diluted paint into the contact between the pipe and the support). However, such a coating has only a very low durability, due to the regular relative movements and friction between the penstock and its support and the non-resistance of anti-corrosion coatings to friction. This solution is therefore no longer implemented given the very negative feedback regarding its efficiency.

[0008] The implementation of the first solution (i.e. the only sustainable and efficient solution) proves to be particularly difficult for penstocks, which supply hydroelectric power stations in particular and which, consequently, are often located in mountainous areas, with a steep slope and difficult to access.

[0009] Furthermore, the applicant's hydroelectric park is significant, since the number of these supports is considered to be around ten thousand.

[0010] The aforementioned known, durable and efficient technical solution is therefore extremely expensive, long and tedious to implement, given the number of these supports and the fact that it is necessary to transport equipment, tools and intervention personnel in mountainous areas without road access, which requires helicopter transport. Statement of the invention

[0011] The invention therefore aims to propose a method for protecting a steel pipe and its steel support against corrosion, which is efficient, durable, simple to implement and less expensive than the methods known from the state of the art.

[0012] To this end, the invention relates to a method for preventing corrosion at the contact interface between a steel pipe to be protected, in particular a penstock, and a steel support cradle for this pipe, called the "cradle to be protected", this pipe resting on said cradle to be protected and on at least one other support cradle.

[0013] According to the invention, this method comprises the following steps:

[0014] -a) calculation of the lifting force F to be applied at a lifting point of the pipe to be protected to lift said pipe to be protected by a height f of between 0.03 m and 0.06 m, relative to said cradle to be protected,

[0015] -b) calculation of the value of the stress o undergone by said pipe during lifting at said height f,

[0016] -c) comparison of this stress value o undergone with a maximum value of stress o max beyond which the pipe is damaged, this maximum value of stress o max being equal to min (Re / 1.35; Rm / 1.8), Re being the elastic limit of the material constituting said pipe and Rm being the breaking strength of the material constituting the pipe, and if o is less than or equal to o max, then carrying out the following steps:

[0017] -d) choice of a lifting device, such as a jack, capable of applying the force of lifting F calculated in step a),

[0018] -e) laying at least one force distribution plate on the ground, at the point of lifting the pipe, fixing a lifting cradle against said pipe at said lifting point and positioning the lifting device chosen in step d) between said force distribution plate and the lifting cradle,

[0019] f) actuation of the lifting device to lift the pipe to the height f above the cradle to be protected,

[0020] g) introduction of at least one zinc sheet between said cradle to be protected and the pipe to be protected, this zinc sheet covering the entire contact surface between the pipe to be protected and the cradle to be protected,

[0021] h) lowering the pipe to be protected to place it on said at least one zinc sheet.

[0022] Thanks to these features of the invention, the steel pipe can be lifted without being damaged and said at least one zinc sheet inserted between the steel support cradle and the steel pipe serves as a corrosion pile, corrodes and thus prevents corrosion of the steel parts.

[0023] Furthermore, the tools used (lifting tool, force distribution plate and lifting cradle) can easily be transported to the intervention site.

[0024] Finally, this process is simple to implement and inexpensive.

[0025] Preferably, said at least one zinc sheet is fixed to the cradle to be protected by folding and hammering its edges against said cradle to be protected and / or by fixing using fixing elements, such as screws and dowels.

[0026] Preferably, the lifting point is located at a distance from said cradle to be protected of less than 2 meters, preferably less than 1 meter.

[0027] Advantageously, the lifting cradle is chosen so as to have a contact surface with the pipe to be protected equal to or greater than the contact surface between the cradle to be protected and the pipe to be protected.

[0028] According to a first embodiment variant, said steel pipe to be protected is fixedly retained in an upstream anchoring block and in a downstream anchoring block, said cradle to be protected and said at least one other support cradle are arranged between said upstream anchoring block and said downstream anchoring block, the lifting point is located at a distance from the upstream or downstream anchoring block to which it is closest which is less than or equal to 20 meters.

[0029] According to this first variant, the lifting force F, expressed in Newtons, is equal to:

[0030] 2.5 x L xmxgx cos(a) + 3 x E x I xf / Lm3

[0031] According to this first variant, the stress o, expressed in Pa, undergone by said pipe during lifting to said height f expressed in meters, is equal to:

[0032] M x D / (2 x I) + La x ma xgx sin(aa) / S + 3xExfxD / (2x Lm2),

[0033] with M equal to the bending moment linked to the weight of the pipe to be protected (1), expressed in Nm andM = L / 4xgxmx cos(a).

[0034] According to a second embodiment variant, said steel pipe to be protected is fixedly retained in an upstream anchoring block and in a downstream anchoring block, said steel pipe to be protected is supported by at least four support cradles including said cradle to be protected, arranged between said upstream anchoring block and said downstream anchoring block, in that the lifting point is located at a distance from the upstream or downstream anchoring massif to which it is closest which is greater than 20 meters.

[0035] According to this second variant, the lifting force F, expressed in Newtons, is equal to:

[0036] 3 x L1 x ml xgx cos(ab)

[0037] According to this second variant, the stress o, expressed in Pa, undergone by said pipe during lifting to said height f, expressed in meters, is equal to:

[0038] M x D / (2 x I) + La x ma xgx sin(aa) / S,

[0039] with M equal to the bending moment linked to the weight of the pipe to be protected (1), expressed in Nm andM = Ll / 3xgx ml x cos(ab). DESCRIPTION OF FIGURES

[0040] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0041] [Fig.l] is a diagram of a pipe, such as a penstock, supported on several support cradles and fixedly retained in an upstream anchor block and in a downstream anchor block.

[0042] [Fig.2] is a diagram similar to that of [Fig.l], but in which the pipe is lifted, the lifting point being located at a distance from the downstream anchor block less than or equal to 20 meters.

[0043] [Fig.3] is a diagram similar to [Fig.l], but in which the proposed lifting point is located at a distance from the upstream anchoring mass greater than 20 meters.

[0044] [Fig.4] is a diagram similar to [Fig.3], but in which the pipe is raised.

[0045] [Fig.5] is a perspective view of a portion of a pipeline ready to be lifted above its support cradle.

[0046] [Fig.6] is a perspective view of a portion of a pipe resting on its support cradle, after implementation of the method according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0047] Referring to the figures, it can be seen that the steel pipe 1 to be protected generally rests on at least two steel support cradles 2, generally more, spaced from each other, preferably by a constant distance. This steel pipe 1 is for example a penstock.

[0048] Among the steel support cradle(s) 2, a support cradle to be protected, referenced 2a, which is the one that is desired to be protected from corrosion, can be seen in the diagrams.

[0049] The support cradles 2 and the cradle to be protected 2a have a curved portion 20 matching part of the circumference of the cylindrical pipe 1, as can be seen see it for example in figures 3 and 4. This portion 20 constitutes the contact interface between the pipe 1 and the cradle 2, 2a.

[0050] The pipe 1 can move slightly (i.e. slide) relative to the support cradles 2, 2a.

[0051] Preferably, the steel pipe 1 is also fixedly retained (without the possibility of sliding) in at least two anchor blocks and generally more than two, arranged along the entire length of a pipe 1.

[0052] The method according to the invention consists of preventing corrosion at the contact interface 20 between the pipe 1 and the support cradle to be protected 2a:

[0053] - by lifting at a lifting point P, said pipe to be protected 1, so as to move it away from said support cradle to be protected 2a, by a height f of between 0.03 m and 0.06 m (between 30 mm and 60 mm),

[0054] - by introducing at least one zinc sheet 8 between said cradle to be protected 2a and the pipe to be protected 1, this zinc sheet 8 covering the entire contact surface 20 between the pipe to be protected 1 and the cradle to be protected 2a,

[0055] -by lowering the pipe to be protected 1 to place it on said at least one zinc sheet 8.

[0056] Due to the humidity present at the contact surface 20, a corrosion cell is thus created, with a circulation of electrons which stops the corrosion of the steel parts by corroding the zinc sheet 8, the latter thus being sacrificed.

[0057] Preferably, the lifting point P is located at a distance from said cradle to be protected 2a of less than 2 meters, preferably less than 1 meter. This makes it possible not to lift the pipe 1 too much to lift it to the aforementioned height f.

[0058] In order to implement the above-mentioned corrosion prevention method, the following steps are first carried out:

[0059] -a) calculation of the lifting force F to be applied at a lifting point P of the pipe to be protected 1, for lifting said pipe to be protected 1 by a height f of between 0.03 m and 0.06 m, relative to said cradle to be protected 2a,

[0060] -b) calculation of the value of the stress o undergone by said pipe 1 during lifting at said height f, and

[0061] -c) comparison of this stress value o undergone with a maximum value of max stress o beyond which pipe 1 is damaged.

[0062] This maximum stress value o max is equal to min (Re / 1.35; Rm / 1.8), Re being the elastic limit of the material constituting said pipe 1 and Rm being the breaking strength of the material constituting pipe 1.

[0063] The height f is chosen to be able to slide the sheet 8 and not have to lift the pipe 1 too much.

[0064] At the end of the comparison, if we find that o is greater than o max, then we considers that the said pipe 1 cannot be lifted to the desired height f without risk of damage and the process is stopped.

[0065] Conversely, if at the end of the comparison, we find that o is less than or equal to o max, then we carry out the following steps:

[0066] -d) choice of a lifting device 5, such as a jack, capable of applying the force of lifting F calculated in step a),

[0067] -e) laying a force distribution plate 6 on the ground, at the point of support lifting P of the pipe 1, fixing a lifting cradle 7 against said pipe 1 at said lifting point P and positioning the lifting device 5 chosen in step d) between said force distribution plate 6 and the lifting cradle 7,

[0068] f) actuation of the lifting device 5 to lift the pipe 1 by the height f above the cradle to be protected 2a,

[0069] g) introduction of at least one zinc sheet 8 between said cradle to be protected 2a and the pipe to be protected 1,

[0070] h) lowering the pipe to be protected 1 to place it on said at least one zinc sheet 8.

[0071] In practice, excavation can be carried out before placing the force distribution plate. Preferably, the lifting cradle 7 is fixed, for example strapped onto the pipe 1.

[0072] Preferably, one or more sheets 8 may be arranged, for example one to five sheets, with a thickness preferably around 1 mm. The number of sheets depends on the chosen protection duration, which increases with the number of sheets.

[0073] Preferably, the or each zinc sheet 8 is fixed to the cradle to be protected 2a by folding and hammering its edges against said cradle to be protected 2a and / or by fixing using fixing elements 81, such as screws and dowels, (see [Fig.4]).

[0074] As mentioned previously, the pipe 1 is retained in at least two anchor blocks and even generally more than two.

[0075] In the remainder of the description and the claims, it is however considered that a portion of the pipe 1 is retained in an upstream anchoring block 3 and in a downstream anchoring block 4 and that the point P of lifting of the pipe is located between these two blocks 3 and 4. First situation:

[0076] [Fig.l] illustrates a first situation in which the pipe 1 to be protected is fixedly retained in an upstream anchoring block 3 and in a downstream anchoring block 4, and the cradle to be protected 2a and said at least one other support cradle 2 are arranged between said upstream anchoring block 3 and said downstream anchoring block 4.

[0077] Furthermore, in [Fig.l], the lifting point P is located at a distance from the upstream anchor block 3 or the downstream anchor block 4 to which it is closest, which is less than or equal to 20 meters. In the example shown, point P is 20 meters or less from the downstream anchor block 4.

[0078] In this first situation, the lifting force F to be applied to lift the pipe 1 and the stress o undergone by this pipe during this lifting are calculated as follows.

[0079] Calculation of the lifting force F to be applied to lift the pipe 1 by a height f of between 0.03 meters and 0.06 meters, relative to said cradle to be protected 2a:

[0080] The lifting force F, expressed in Newton, is equal to:

[0081] 2.5 x L xmxgx cos(a) + 3 x E x I xf / Lm3

[0082] with:

[0083] Lm (see [Fig. 1]) is equal to the distance between the lifting point P of the pipe to be protected 1 and the downstream 4 or upstream 3 anchor block closest to this lifting point P. Lm is expressed in meters and Lm is less than or equal to 20 meters.

[0084] L is equal to the maximum distance between two successive support cradles 2 over a distance equal to 3 x Lm, this distance of 3 x Lm being measured from the upstream anchoring block 3 or downstream anchoring block 4 whose lifting point P is closest. For example, if the lifting point is at a distance less than or equal to 20 m upstream of the downstream block 4, the distance 3 x Lm is to be considered upstream of the downstream block starting from the latter block. If the lifting point is at a distance less than or equal to 20 m downstream of the upstream block 3, the distance 3 x Lm is to be considered downstream of the upstream block starting from the latter block. In other words, if the distances between two successive cradles 2 are different over the distance 3 x Lm, then we retain the maximum value L of these different distances and if these distances are constant, then the maximum distance corresponds to L.

[0085] L is expressed in meters.

[0086] As can be seen in [Fig.2], it is considered that the length of the pipe 1 whose mass is taken up (lifted) by the lifting device 5 when the latter is applied to the lifting point P, is equal to 2.5 x L.

[0087] Consequently, m is equal to the maximum value of the mass per unit length of the pipe 1, over the length of the pipe 1 equal to 2.5 x L, the mass of which is taken up by the lifting device 5. In other words, whether this mass per unit length is constant or not over the length of 2.5 x L, the maximum value is taken.

[0088] m is expressed in kg / m.

[0089] g (acceleration of gravity at the surface of the earth) is equal to 9.81 m / s2.

[0090] E is equal to the Young's modulus of the material of pipe 1. E is expressed in Pa.

[0091] I is equal to the moment of inertia of pipe 1 at the lifting point P. I is expressed in m4.

[0092] f is equal to the desired lifting height (see [Fig.2]), f is expressed in meters and is between 0.03 meters and 0.06 meters.

[0093] a is equal to the slope of the pipe 1 over the length of the pipe 1 equal to 2.5 x L whose mass is taken up by the lifting device 5, if this slope is constant over this length of 2.5 x L or is equal to the lowest of the slopes of the pipe 1 over the length of the pipe 1 equal to 2.5 x L whose mass is taken up by the lifting device 5, if this slope is not constant over this length of 2.5 x L.

[0094] a is expressed in degrees.

[0095] Calculation of the stress g undergone by said pipe 1 during lifting to said height f:

[0096] This stress o undergone by said pipe 1 during the lifting of pipe 1 to said height f, is equal to:

[0097] M x D / (2 x I) + La x ma xgx sin(aa) / S + 3xExfxD / (2x Lm2)

[0098] with M equal to the bending moment linked to the weight of the pipe to be protected 1, expressed in Nm andM = L / 4xgxmx cos(a).

[0099] The constraint o is expressed in Pa and the height f in meters.

[0100] In these two formulas, Lm, L, m, g, E, I, f and the angle a have the same meanings as those mentioned above for the calculation of the lifting force F.

[0101] Furthermore:

[0102] ma is equal to the maximum value of the mass per unit length of the pipe 1 over the length of the pipe 1 between the upstream anchor block 3 and the lifting point P.

[0103] ma is expressed in kg / m.

[0104] D is equal to the diameter of pipe 1. D is expressed in meters.

[0105] La is equal to the length of the pipe 1 between the upstream anchor block 3 and the lifting point P. La is expressed in meters. La is less than or equal to 20 meters.

[0106] S is equal to the section of pipe 1 at the point of lifting P. S is expressed in m2.

[0107] aa is equal to the slope of the pipe 1 over the length of the pipe 1 between the upstream anchoring block 3 and the lifting point P, if this slope is constant or is equal to the highest of the slopes of the pipe 1 between the upstream anchoring block 3 and the lifting point P, if this slope is not constant.

[0108] aa is expressed in degrees. Second situation.

[0109] [Fig.3] illustrates a second situation in which the pipe 1 to be protected is fixedly retained in an upstream anchoring block 3 and in a downstream anchoring block 4, and the cradle to be protected 2a and said at least one other support cradle 2 are arranged between the blocks 3 and 4, as previously, but in which the lifting point P is located at a distance from the upstream anchoring block 3 or from the downstream anchoring block 4 to which it is closest, which is greater than 20 meters.

[0110] In the example shown, point P is more than 20 meters from the upstream anchor block 3 to which it is closest.

[0111] In this second situation, the lifting force F to be applied to lift the pipe 1 and the stress o undergone by this pipe during this lifting are calculated as follows.

[0112] Calculation of the lifting force F to be applied to lift the pipe 1 by a height f of between 0.03 meters and 0.06 meters, relative to said cradle to be protected 2a:

[0113] The lifting force F, expressed in Newton, is equal to:

[0114] 3 x L1 x ml xgx cos(ab)

[0115] with:

[0116] L1 equal to the maximum distance between two successive support cradles 2, over a distance between the second support cradle 2 upstream of the lifting point P and the second support cradle 2 downstream of the lifting point P.

[0117] L1 is expressed in meters.

[0118] In this second situation where the lifting point P is further from the anchoring block to which it is closest, and as can be seen in [Fig.4], it is considered that the length of the pipe 1 whose mass is taken up (lifted) by the lifting device 5 when the latter is applied to the lifting point P, is equal to 3 x Ll.

[0119] ml is equal to the maximum value of the mass per unit length of the pipe 1, over the length of the pipe 1 equal to 3 x Ll, the mass of which is taken up by the lifting device 5.

[0120] ml is expressed in kg / m.

[0121] g (acceleration of gravity at the surface of the earth) is equal to 9.81 m / s2.

[0122] ab in degrees is equal to the slope of pipe 1 over the length of pipe 1 equal to 3 x Ll whose mass is taken up by the lifting device 5, if this slope is constant over this length of 3 x Ll or is equal to the lowest of the slopes of the pipe 1 over the length of the pipe 1 equal to 3 x Ll whose mass is taken up by the lifting device 5, if this slope is not constant over this length of 3 x LL

[0123] ab is expressed in degrees.

[0124] Calculation of the stress a undergone by said pipe 1 during lifting to said height f:

[0125] The stress o undergone by said pipe during lifting to said height f is equal to:

[0126] M x D / (2 x I) + La x ma xgx sin(aa) / S

[0127] with M is equal to the bending moment linked to the weight of the pipe to be protected 1, expressed in Nm andM = Ll / 3xgxmlx cos(ab)

[0128] The constraint o is expressed in Pa and the height f in meters.

[0129] In these two formulas, Ll, ml, g and ab have the same meanings as those mentioned above in the second situation for the calculation of the lifting force F.

[0130] Furthermore:

[0131] ma is equal to the maximum value of the mass per unit length of the pipe 1 over the length of the pipe 1 between the upstream anchor block 3 and the lifting point P.

[0132] In other words, whether this mass per unit length is constant or not, we always take the maximum value of this mass per unit length. P. For example, if the mass per unit length is equal to 1,000 kg / m over a distance equal to L and 1,200 kg / m over a distance equal to 1.5 x L, we take for the calculation a mass per unit length equal to 1,200 kg / m.

[0133] ma is expressed in kg / m.

[0134] D is equal to the diameter of pipe 1. D is expressed in meters.

[0135] I is equal to the moment of inertia of pipe 1 at the lifting point P. I is expressed in m4.

[0136] La is equal to the length of the pipe 1 between the upstream anchor block 3 and the lifting point P. La is expressed in meters. La is greater than 20 meters.

[0137] S is equal to the section of pipe 1 at the point of lifting P. S is expressed in m2.

[0138] f is equal to the desired lifting height (see [Fig.4]), f is expressed in meters and is between 0.03 meters and 0.06 meters.

[0139] aa is equal to the slope of the pipe 1 over the length of the pipe 1 between the upstream anchoring block 3 and the lifting point P, if this slope is constant or is equal to the highest of the slopes of the pipe 1 between the upstream anchoring block 3 and the lifting point P, if this slope is not constant.

[0140] aa is expressed in degrees.

Claims

Claims

1. Method for preventing corrosion at the contact interface between a steel pipe to be protected (1), in particular a penstock, and a steel support cradle (2, 2a) of this pipe (1), called the “cradle to be protected” (2a), this pipe (1) resting on said cradle to be protected (2a) and on at least one other support cradle (2), this method being characterized in that it comprises the following steps: -a) calculation of the lifting force (F) to be applied at a lifting point (P) of the pipe to be protected (1) to lift said pipe to be protected (1) by a height f of between 0.03 m and 0.06 m, relative to said cradle to be protected (2a), -b) calculation of the value of the stress o undergone by said pipe (1) during lifting to said height f, -c) comparison of this stress value o undergone with a maximum stress value o max beyond which the pipe (1) is damaged, this maximum stress value o max being equal to min (Re / 1.35; Rm / 1.8), Re being the elastic limit of the material constituting said pipe (1) and Rm being the breaking strength of the material constituting the pipe (1), and if o is less than or equal to o max, then carrying out the following steps: -d) selection of a lifting device (5), such as a jack, capable of applying the lifting force (F) calculated in step a), -e) placing at least one force distribution plate (6) on the ground, at the lifting point (P) of the pipe (1), fixing a lifting cradle (7) against said pipe (1) at said lifting point (P) and positioning the lifting device (5) chosen in step d) between said force distribution plate (6) and the lifting cradle (7), f) actuation of the lifting device (5) to lift the pipe (1) to the height f above the cradle to be protected (2a), g) introduction of at least one zinc sheet (8) between said cradle to be protected (2a) and the pipe to be protected (1), this zinc sheet (8) covering the entire contact surface (20) between the pipe to be protected (1) and the cradle to be protected (2a), h) lowering the pipe to be protected (1) to place it on said at least one zinc sheet (8).

2. Method according to claim 1, characterized in that said at least a zinc sheet (8) is fixed to the cradle to be protected (2a) by folding and hammering its edges against said cradle to be protected (2a) and / or by fixing using fixing elements (81), such as screws and dowels.

3. Method according to claim 1 or 2, characterized in that the lifting point (P) is located at a distance from said cradle to be protected (2a) of less than 2 meters, preferably less than 1 meter.

4. Method according to any one of the preceding claims, characterized in that the lifting cradle (7) is chosen so as to have a contact surface with the pipe to be protected (1) equal to or greater than the contact surface between the cradle to be protected (2a) and the pipe to be protected (1).

5. Method according to any one of the preceding claims, characterized in that said steel pipe to be protected (1) is fixedly retained in an upstream anchor block (3) and in a downstream anchor block (4), in that said cradle to be protected (2a) and said at least one other support cradle (2) are arranged between said upstream anchor block (3) and said downstream anchor block (4), in that the lifting point (P) is located at a distance from the upstream (3) or downstream (4) anchor block to which it is closest which is less than or equal to 20 meters and in that the lifting force F, expressed in Newton, is equal to: 2.5 x L xmxgx cos(a) + 3 x E x I xf / Lm3, with: - Lm equal to the distance between the lifting point (P) of the pipe to be protected (1) and the downstream (4) or upstream (3) anchor block closest to it close to this lifting point (P), expressed in meters, and Lm less than or equal to 20 meters,- L equal to the maximum distance between two successive support cradles (2), expressed in meters, over a distance equal to 3 x Lm, this distance of 3 x Lm being measured from the upstream 3 or downstream 4 anchor block whose lifting point P is closest, - m, expressed in kg / m, is equal to the maximum value of the mass per unit length of the pipe (1), over the length of the pipe (1) equal to 2.5 x L whose mass is taken up by the lifting device (5), - g equal to 9.81 m / s2, - E, expressed in Pa, equal to the Young's modulus of the material of the pipe (1), -1 equal to the moment of inertia of the pipe (1) at the lifting point (P), expressed in m4,

6. - f being equal to the desired lifting height, expressed in meters and between 0.03 m and 0.06 m, - a, expressed in degrees, is equal to the slope of the pipe (1) over the length of the pipe (1) equal to 2.5 x L whose mass is taken up by the lifting device (5), if this slope is constant over this length of 2.5 x L or is equal to the lowest of the slopes of the pipe (1) over the length of the pipe (1) equal to 2.5 x L whose mass is taken up by the lifting device (5), if this slope is not constant over this length of 2.5 x L. Method according to claim 5, characterized in that the stress o, expressed in Pa, undergone by said pipe (1) during lifting to said height f expressed in meters, is equal to: M x D / (2 x I) + La x ma xgx sin(aa) / S + 3xExfxD / (2x Lm2), with - M equal to the bending moment linked to the weight of the pipe to be protected (1), expressed in Nm and M = L / 4xgxmx cos(a), with - Lm equal to the distance between the lifting point (P) of the pipe to be protected (1) and the downstream (4) or upstream (3) anchor block closest to this lifting point (P), expressed in meters, and Lm less than or equal to 20 meters, - L equal to the maximum distance between two successive support cradles (2), expressed in meters, over a distance equal to 3 x Lm, this distance of 3 x Lm being measured from the upstream anchor block 3 or downstream 4 whose lifting point P is closest, - m, expressed in kg / m, is equal to the maximum value of the mass per unit length of the pipe (1), over the length of the pipe (1) equal to 2.5 x L whose mass is taken up by the lifting device (5), - ma, expressed in kg / m, is equal to the maximum value of the mass per unit length of the pipe (1) over the length of the pipe (1) between the upstream anchor block (3) and the lifting point (P - g equal to 9.81 m / s2, - E, expressed in Pa, equal to the Young's modulus of the pipe material (D, -1 equal to the moment of inertia of the pipe (1) at the lifting point (P), expressed in m4, - D equal to the diameter of the pipe (1), expressed in meters, - Equal to the length of the pipe (1) between the massif upstream anchor point (3) and said lifting point (P), expressed in meters, - S equal to the section of the pipe (1) at the point of lifting (P), expressed in m2, - f being equal to the desired lifting height, expressed in meters and between 0.03 m and 0.06 m, - a, expressed in degrees, is equal to the slope of the pipe (1) over the length of the pipe (1) equal to 2.5 x L whose mass is taken up by the lifting device (5), if this slope is constant over this length of 2.5 x L or is equal to the lowest of the slopes of the pipe (1) over the length of the pipe (1) equal to 2.5 x L whose mass is taken up by the lifting device (5), if this slope is not constant over this length of 2.5 x L, - aa, expressed in degrees, is equal to the slope of the pipe (1) over the length of the pipe (1) between the upstream anchor block (3) and the lifting point (P), if this slope is constant or is equal to the highest of the slopes of the pipe (1) between the upstream anchor block (3) and the lifting point (P), if this slope is not constant.

7. Method according to any one of claims 1 to 4, characterized in that said steel pipe to be protected (1) is fixedly retained in an upstream anchor block (3) and in a downstream anchor block (4), in that said steel pipe to be protected (1) is supported by at least four support cradles (2, 2a) including said cradle to be protected (2a), arranged between said upstream anchor block (3) and said downstream anchor block (4), in that the lifting point (P) is located at a distance from the upstream anchor block (3) or downstream anchor block (4) to which it is closest which is greater than 20 meters and in that the lifting force F, expressed in Newton, is equal to: 3 x L1 x ml xgx cos(ab) with: - L1 equal to the maximum distance between two successive support cradles (2), expressed in meters, over a distance between the second support cradle (2) upstream of the lifting point (P) and the second support cradle (2) downstream of the lifting point (P), - ml, expressed in kg / m, is equal to the maximum value of the mass per unit length of the pipe (1), over the length of the pipe (1) equal to 3 x L1 whose mass is taken up by the lifting device (5),

8. - g equal to 9.81 m / s2, - ab, expressed in degrees, is equal to the slope of the pipe (1) over the length of the pipe (1) equal to 3 x L1 whose mass is taken up by the lifting device (5), if this slope is constant over this length of 3 x L1 or is equal to the lowest of the slopes of the pipe (1) over the length of the pipe (1) equal to 3 x L1 whose mass is taken up by the lifting device (5), if this slope is not constant over this length of 3 x Ll. Method according to claim 7, characterized in that the stress o, expressed in Pa, undergone by said pipe (1) during lifting to said height f expressed in meters, is equal to: M x D / (2 x I) + La x ma xgx sin(aa) / S with M equal to the bending moment related to the weight of the pipe to be protected (1), expressed in Nm and M = Ll / 3xgx ml x cos(ab), with - Ll equal to the maximum distance between two successive support cradles (2), expressed in meters, over a distance between the second support cradle (2) upstream of the lifting point (P) and the second support cradle (2) downstream of the lifting point (P), - ml, expressed in kg / m, is equal to the maximum value of the mass per unit length of the pipe (1), over the length of the pipe (1) equal to 3 x Ll, the mass of which is taken up by the lifting device (5), - ma, expressed in kg / m, is equal to the maximum value of the mass per unit length of the pipe (1) over the length of the pipe (1) between the upstream anchor block (3) and the lifting point (P), - D equal to the diameter of the pipe, expressed in meters, - g equal to 9.81 m / s2, -1 equal to the moment of inertia of the pipe (1) at the lifting point (P), expressed in m4, - La equal to the length of the pipe (1) between the upstream anchor block (3) and the lifting point (P), expressed in meters, and La greater than 20 meters, - S equal to the section of the pipe (1) at the point of lifting (P), expressed in m2, f being equal to the desired lifting height, expressed in meters and between 0.03 m and 0.06 m, - ab, expressed in degrees, is equal to the slope of the pipe (1) on the length of the pipe (1) equal to 3 x L1, the mass of which is taken up by the lifting device (5), if this slope is constant over this length of 3 x L1 or is equal to the lowest of the slopes of the pipe (1) over the length of the pipe (1) equal to 3 x L1, the mass of which is taken up by the lifting device (5), if this slope is not constant over this length of 3 x Ll, - aa, expressed in degrees, is equal to the slope of the pipe (1) over the length of the pipe (1) between the upstream anchor block (3) and the lifting point (P), if this slope is constant or is equal to the highest of the slopes of the pipe (1) between the upstream anchor block (3) and the lifting point (P), if this slope is not constant.

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