Local hydrotest on closing girth seams
Local hydrotest on closing girth seams
(OP)
Have anyone heard of or using so called 'local hydrotest" by welding a half pipe either inside or outside of the vessel to cover a closing girth seam, then pressurize the half pipe to hydrotest pressure.
We have many vertical large vessels, shop hydrotested in one piece for U-stamp, then cut into many sections for shipping and weld the closing girth seams at field. Many of the closing seams can be more than 200' above ground. Re-hydrotest is impossible due to internals. MT and 100% radiography will be performed and R-stamp is obtained. Just wonder if it is necessary to do so called "local hydrotest" as described above that seems to find pin holes. There is no such test in NBIC. But I have seen people did that long time ago.
In addition to the above question, will only MT and RT be sufficient for the closing seams ? though we have done just that so many times. It is CS with design temp 650F, thk under 1.5".
We have many vertical large vessels, shop hydrotested in one piece for U-stamp, then cut into many sections for shipping and weld the closing girth seams at field. Many of the closing seams can be more than 200' above ground. Re-hydrotest is impossible due to internals. MT and 100% radiography will be performed and R-stamp is obtained. Just wonder if it is necessary to do so called "local hydrotest" as described above that seems to find pin holes. There is no such test in NBIC. But I have seen people did that long time ago.
In addition to the above question, will only MT and RT be sufficient for the closing seams ? though we have done just that so many times. It is CS with design temp 650F, thk under 1.5".





RE: Local hydrotest on closing girth seams
In my opinion, local hydrotests are OK for leak detection, but provide none of the residual stress redistribution that a full hydrotest provides. Whatever you choose to do, make sure that it is well documented, so that 10 years from now, when I do a FFS evaluation on it, I know whether or not to take credit for the hydrotest.
RE: Local hydrotest on closing girth seams
I would prefer volumetric examination of closure welds, in lieu of this test.