Welding and repair welding after hydrostatic testing of pressure vessels

It can be welded or repaired by welding, but if the repair exceeds half of the wall thickness, a new hydrostatic test is required; see GB150-2011, clause 11.4.6 for details

If there are issues after the pressure test, welding repairs are definitely necessary.

The pressure test of pressure vessels should be the final step; gaskets, support fittings, etc. should be welded first. After the pressure test, the leak can be repaired by welding; a new pressure test should be conducted after the repair. At the same time, attention should be paid to the requirements regarding welding repairs for pressure vessels that have heat treatment specifications. For repairs carried out after a pressure test, if the repair depth exceeds half of the wall thickness in containers, a new pressure test must be conducted.

Why is repair welding required after a pressure vessel’s hydrostatic test? 1 There is a leak in the weld or the base material; such a leak must be penetrative. If it is believed that the problem can be resolved by removing the defects and then performing welding repairs, then a hydrostatic test is naturally required after those repairs, as the previous hydrostatic test was not successful. 2 Because dents have formed due to impacts, in such cases, if the container’s repair depth is no more than half of its wall thickness and no post-weld heat treatment is required, it is not necessary to conduct another pressure test. 3 After the hydrostatic test was successful, it was found that some fittings had been missed during welding. If no post-weld heat treatment is required, these fittings can be welded without the need to conduct another pressure test. The situation becomes more complicated when heat treatment is required after welding.

Thank you all for your answers. I’m facing a situation now: the client requires that the equipment be manufactured under the factory’s water pressure, but they do not allow the prefabricated welding components (gussets) for the ladder platform to be welded there; instead, those gussets need to be welded on-site. Generally, gasket welding is completed before the hydrostatic test. However, due to my limited knowledge, I have not been able to find any theoretical basis stating that welding is not allowed after the hydrostatic test. I would like to ask everyone: which standard specifies such a requirement?

Hello, defects were detected after the hydrostatic test, so the welds were repaired. When the repair depth exceeds half of the wall thickness, a new hydrostatic test must be conducted. But what if, after the hydrostatic test, a gusset plate for the ladder platform needs to be welded onto the cylinder wall? Is this situation allowed?

If the equipment requires heat treatment, the gasket welding must be completed before the hydrostatic test. If heat treatment is not required, then this requirement doesn’t apply.

Hello! But even after applying water pressure, welding should not be allowed casually, right? Otherwise, things will get chaotic, won’t they?

This post was last edited by Pinocchio on 2017-10-20 at 11:22. Why doesn’t the client allow the pre-welded components of the ladder platform to be welded before the hydrostatic test? It is usually allowed. Shell material grade? Welding dimensions of the shimming plate? If it is Q345R, for fillet welds of smaller size, no post-weld heat treatment is required, nor is a re-hydraulic test necessary.

For containers with jackets, the inner cylinder must pass a hydrostatic test before the jacket can be welded on – does that sound confusing to you?