[Ptitcoad]

Hello,

I am working on an LNG installation in China shipyard. Yard is currently connection LNG stainless steel (316L) pipe system to equipments / LNG tanks.
It is done by mean of stainless steel flanges.
Pipes are fit up according WPS requirements for gap. Once fit up is checked, welding is done. However after welding, it can be observed several misalignment between flange on pipe, and equipment flange / LNG tank connection piece flange (already welded in workshop).

When doing welding, flanges which will be later on bolted together are not guided, for example with a guiding pin (ref pictures). Yard explains that it would create stress in the welding seam.
Instead they suggest to complete welding, then add again welding material to heat the welding seam and "correct" the pipe+ flange misalignment. Not the good way to solve the problem I guess.

Has anybody some advices on what is correct practice for this case or similar one?

Thanks
Antoine

[Poland308]

Common practice is to two hole the flanges and make sure they get welded on level. If it's code work it may require adding a fitting like a 45 and then cut it down to the appropriate angle to make the flanges match up.

[LtBadd]

Hello Antoine and welcome to the forum
As Josh stated you need to be sure the flanges are "two holed" level when tacking. Also check that the vertical face is level to the pipe. With stainless you can expect some movement, and adjusting the flange by doing a light fusion pass to move the flange is typical practice.

two hole flange setup.gif (24.05 KiB) Viewed 570 times

[Rick_H]

Hello Antoine and welcome to the forum
As Josh stated you need to be sure the flanges are "two holed" level when tacking. Also check that the vertical face is level to the pipe. With stainless you can expect some movement, and adjusting the flange by doing a light fusion pass to move the flange is typical practice.

two hole flange setup.gif

Perfect...same method I use as well. I will say I do not get as much movement as I see in the photos shown above however. I also suggest a sturdier support, that may help with some of the movement as well if you can fit it in. Those WPS are similar to what I use as far as settings.

[Ptitcoad]

Thanks for clarifications!

When you mean to "two holed" the flange(s) : you mean that they should be properly supported/guided during welding?

Thank you,
Antoine

[Poland308]

If you look at the picture Richard put up you will see on the right side where they use two of the bolt holes in the flange and level them. If you do this to all the pieces you build then the flanges will always line up.

[Ptitcoad]

Thanks Poland

Antoine