How to prevent deformation of stainless steel ventilation pipe after welding?

To prevent the deformation of stainless steel ventilation pipes after welding, measures can be taken from design, processing, welding and post-welding treatment, as follows:

Design aspect

Reasonable selection of welding form: On the premise of meeting the use requirements of ventilation pipes, try to choose a welding form with short weld length and small welding amount, such as using butt weld instead of fillet weld to reduce unnecessary weld.

Optimize the weld layout: make the weld symmetrically distributed on both sides of the neutral axis of the pipeline, avoid the weld concentrating on one side, make the welding stress evenly distributed and reduce the possibility of deformation. For example, for larger diameter pipes, double-sided symmetrical welding can be used.

Processing aspect

Ensure the flatness of the material: before welding, check and correct the flatness of the stainless steel plate to ensure that there is no obvious deformation and warping before welding, so as to avoid aggravating the deformation during welding due to the unevenness of the plate itself.

Reserved anti-deformation: according to the experience and practical data of similar projects in the past, predict the deformation direction and deformation amount of the pipeline after welding, and set a certain anti-deformation amount in advance during assembly. For example, it is expected that the pipeline will arch upward after welding, and the pipeline can be bent downward at a certain angle in advance during assembly to offset the deformation after welding.

Welding aspect

Select the appropriate welding process.

Adopt low current, multi-layer and multi-pass welding: low current welding can reduce welding heat input and reduce the scope of heat affected zone, and multi-layer and multi-pass welding can disperse heat, and the thickness of each layer of weld should not be too thick, generally controlled at 3-5mm, thus reducing welding deformation.

Gas shielded welding, such as argon arc welding, is preferred. Gas shielded welding has the advantages of concentrated heat, stable arc and good protection effect, which can effectively reduce heat loss and oxidation during welding and reduce the possibility of deformation.

Control welding sequence

Step-by-step welding withdrawal method: the weld is divided into several sections, and the welding is carried out in the order opposite to the welding direction, so that the shrinkage of each section of the weld cancels out part of each other and reduces the overall deformation.

Symmetrical welding method: For longer welds, symmetrical welding is adopted from the middle to both ends, so that the welding stress is evenly distributed on both sides of the pipeline, which offsets part of each other, thus reducing deformation.

Use appropriate fixture: During welding, use special welding fixture to fix the pipeline and limit the free deformation of the pipeline during welding. The clamping force of the fixture should be moderate, which can effectively fix the pipeline without causing damage to the pipeline.

Post-welding treatment

Stress relieving treatment: After welding is completed, stress relieving treatment shall be carried out on the pipeline in time, such as vibration aging and heat treatment, so as to reduce the welding residual stress and thus reduce the deformation caused by stress release.

Slow cooling: after welding, let the pipeline cool slowly in the natural environment, avoid forced cooling, and prevent uneven shrinkage caused by too fast cooling speed from causing deformation.