Welding on API 650 Tank after Hydrotest !

[MaruthiKK]

Hi Friends,

Iam 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 open lap joints shall not be open. 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. After completion of the hydro-test, only non-structural
small attachments may be welded to the tank in accordance with 7.2.1.12."

 

[JStephen]

Are you needing to do all of the welding on the underside of the roof now that hydrotest has been completed? I don't see where you really say what welding you'll perform.
I'd have to look through the wording of API-650 more. The paragraph you quote is speaking about welding to the shell specifically.
In terms of meeting the letter of the code- you may need to redo the hydrotest.
In terms of there being a problem with the shell or bottom due to welding the underside of the roof- I'd say it's unlikely, perhaps the biggest danger being damage from scaffolding or something. You will get some added distortion in the roof, perhaps some extra column loading from that.
Consider caulking those seams for now and seal-welding at some point in the future if the hydrotesting is a major issue.

 

[MaruthiKK]

Stephen thanks for your quick response.

Let me write more specifically:

Tank configuration is 8m dia X 14m height with 3nos longitudinal lap joints on the roof (Please see the snap attached). Service is waste water storage.

Please see the wording of API-650, It states "After completion of hydro test, only non-structural small attachments may be welded to the tank as per 7.2.1.12 (i.e. Insulation cleats, clips, studs...etc.)". Contractor interprets that roof is not the part of the hydro test and so welding is permissible there. Welding is not at the shell; this is specifically for roof plate internal side lap joint seal weld (Just to close the open lap joint; not for strength purpose full thickness fillet weld).

Currently planned welding is to seal the inward side lap joint of tank roof), not a complete thickness fillet weld. So the chances of distortion is not foreseen. I can't imagine extra loading to the roof from the external attachments (if any).

Contractor had built the scaffolding already for the purpose of internal painting for the tank. Rework may not be difficult now to perform.


Your below statement is unclear:
"Consider caulking those seams for now and seal-welding at some point in the future if the hydro testing is a major issue"

Thank you.

 

[SnTMan]

MaruthiKK has continued this conversation in a more appropriate Storage Tank Engineering forum:

thread1452-448110


Regards,

Mike


The problem with sloppy work is that the supply FAR EXCEEDS the demand