Internal welding on roof after hydrotest (API 650 tank)
Internal welding on roof after hydrotest (API 650 tank)
(OP)
Continued from thread404-448069: Welding on API 650 Tank after Hydrotest !...
I am working on a project which consists of fixed cone roof newly built API 650 tanks, passed the hydro test requires some welding to be performed.
In the current condition, As per Fig.5.3a roof-plate joint, lap joints of roof are externally fillet welded. Our design considered the same and test has been completed. As per its service requirement, the tank needs to be internally coated inclusive of its roof and accordingly the support structure was built as external.
In order to pass the holiday testing after internal coating on the roof, the interior side open lap joints shall be sealed. Hence, My contractor is planning to do one pass welding on the roof joints to close the gap and also to avoid any crevice corrosion in the open area of the roof joint.
Since the tank has been already hydro tested, In accordance with 7.3.6.1 of 12th Edition of API 650, only non structural small attachments may be allowed to weld please see the extract below. I need expert advice to achieve the same. Please help.
7.3.6.1 This hydrostatic test of the tank shall be conducted before permanent external piping is connected to the
tank. Attachments to the shell defined in 5.8.1.1, located at least 1 m 3 ft above the water level, and roof
appurtenances may be welded during the filling of the tank. [u]After completion of the hydro-test, only non-structural
small attachments may be welded to the tank in accordance with 7.2.1.12.
I am working on a project which consists of fixed cone roof newly built API 650 tanks, passed the hydro test requires some welding to be performed.
In the current condition, As per Fig.5.3a roof-plate joint, lap joints of roof are externally fillet welded. Our design considered the same and test has been completed. As per its service requirement, the tank needs to be internally coated inclusive of its roof and accordingly the support structure was built as external.
In order to pass the holiday testing after internal coating on the roof, the interior side open lap joints shall be sealed. Hence, My contractor is planning to do one pass welding on the roof joints to close the gap and also to avoid any crevice corrosion in the open area of the roof joint.
Since the tank has been already hydro tested, In accordance with 7.3.6.1 of 12th Edition of API 650, only non structural small attachments may be allowed to weld please see the extract below. I need expert advice to achieve the same. Please help.
7.3.6.1 This hydrostatic test of the tank shall be conducted before permanent external piping is connected to the
tank. Attachments to the shell defined in 5.8.1.1, located at least 1 m 3 ft above the water level, and roof
appurtenances may be welded during the filling of the tank. [u]After completion of the hydro-test, only non-structural
small attachments may be welded to the tank in accordance with 7.2.1.12.
RE: Internal welding on roof after hydrotest (API 650 tank)
At first I thought you would be OK since only the roof structure is required to be complete and the hydrotest is testing the shell and foundation only and not the roof plates. But then I looked at your drawing and from the wedge being cut out this looks like it may be a self-supported cone roof. If so, the roof plates are structural and you are going to have a harder time.
RE: Internal welding on roof after hydrotest (API 650 tank)
Yes the roof is self supporting type. The roof joints are already welded from outer side (External platform, structural are erected. Hydro test completed but only for the shell).
As you see from the typical lap joint of the roof of the attached sketch, the interior weld is marked by me. This is the planned activity.
But, it is not a full fillet weld (only a single pass to close the opening of lap).
Even though the activity is minor, carefully performed with no issues, the acceptability of the code to perform this task is my concern.
Thank you so much again.
RE: Internal welding on roof after hydrotest (API 650 tank)
RE: Internal welding on roof after hydrotest (API 650 tank)
My purpose of welding is to seal the gap of the interior side of the roof lap joint which is useful to make the holiday test (after internal lining) pass.
May be sealant can serve the purpose; but, it will last soon and can't be permanent to avoid any crevices between the open joint.
PLEASE SEE THE ATTACHED SKETCH.
RE: Internal welding on roof after hydrotest (API 650 tank)
RE: Internal welding on roof after hydrotest (API 650 tank)