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Welding Steel Pipe Residual Buckling Problem Knowledge

Author: Suli Lee
by Suli Lee
Posted: Aug 15, 2018

Different from the seamless steel pipe, the residual stress caused by the part of the buckling moment (referred to as the residual buckling moment or the residual bending moment) of the welded steel pipe has a significant influence on the service performance of the welded steel pipe. The industry's understanding and research on the residual buckling of welded steel pipes has become more and more important. At present, when ordering steel pipes, in order to ensure the safety and reliability of pipelines (especially some important oil and gas pipelines), the residual rebound control of the welded pipes is usually clearly quantified and attached to the more demanding steel pipe orders. Supplementary technical conditions. This practice has become a common practice.

In the manufacturing process of the welded steel pipe, the strip is fed into the roll-up former at a certain angle and direction, and is subjected to bending deformation of the three-roll bending machine, sizing of the outer holding roller or the inner supporting roller, and internal and external welding devices. After the welding process, a part of the elastic bending moment remains in the inside of the finished tube blank. This part of the buckling moment is balanced with the moment required to keep the tube blank in a circular shape, and the tube blank itself is in a state of tending to elastic recovery. If the tube blank is cut along its axial direction and its circumferential direction constraint is removed, the remaining buckling moments of this part are freely released, resulting in a rebound of the tube blank. This is the so-called residual resurrection of welded steel pipes.

After the welding of the welded steel pipe, there is no cold expansion process, so that the residual enthalpy of the welded pipe after welding is complicated and diverse, such as uneven distribution and high peak value, and the residual stress difference of the longitudinally submerged arc welding pipe produced by each manufacturer is better. Big. The existence of large residual tensile stress inside the welded steel pipe is one of the main reasons for limiting the use of welded steel pipes.

On the one hand, the residual tensile stress is superimposed on the transport pressure to become the driving force for the crack instability expansion; on the other hand, due to the non-uniformity of the residual stress distribution, there is a high residual tensile stress in the welded steel pipe. After the high stress and working pressure are superimposed, in the presence of corrosive medium, stress corrosion damage or corrosion fatigue damage is easily generated, resulting in early failure of the pipeline: this is also the reason why the reliability of the welded steel pipe is lower than that of the UOE welded pipe.

Moreover, with the increase of the conveying pressure and the improvement of the steel grade of the welded pipe, this problem is more prominent. However, for the external sizing former, the bending curvature 1/R2 formed by bending deformation of the strip in the three-roll bending machine of the former is greater than the bending curvature 1/R of the finished blank. At the time, by the constraint and control provided by a damping device (special design required) added to the spiral direction of the output of the tube blank, the tube blank of?2(Ro) in the small diameter state can still be welded. Previously, it was possible to expand outward to the specified pipe diameter RO and achieve the purpose of sizing the pipe blank by the outer holding roller. As shown in Fig. 633, the produced tube blank has a circumferential negative elastic property.

That is to say, the external sizing former is used as an auxiliary control means by means of a constraint provided by a specially designed damping device. It is also possible to produce a tube blank having a circumferential negative elastic property. Although this kind of damping device has not been applied yet, the rationality and feasibility of this kind of technical guarantee can not be denied. The above is the elastic characteristics of welded steel pipe.

About the Author

A worker from a steel pipe company, which is located in China.

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Author: Suli Lee

Suli Lee

Member since: May 29, 2017
Published articles: 154

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