Above Ground Storage Tanks
Above Ground Storage Tanks
(OP)
Dear Engineers,
What does it mean when the label of a crude fixed doom roof tank indicates a partial stress relief?
Is it related to the welding of the clean out door? and how does it usually applied?
Thanks
What does it mean when the label of a crude fixed doom roof tank indicates a partial stress relief?
Is it related to the welding of the clean out door? and how does it usually applied?
Thanks
RE: Above Ground Storage Tanks
For an older tank, refer to the standard under which it was built.
But yes, this would usually be a flush manway, or flush shell nozzles, or shell nozzles/manways inserted and stress-relieved per 5.7.4.2 or 5.7.4.3, all of which are specified to be stress-relieved into a shell plate which is then welded into the tank.
For small tanks, it is sometimes feasible or desired to stress-relieve the whole tank, but this is uncommon.
RE: Above Ground Storage Tanks
However, out of my curiosity, how is it possible to stress relief the bottom reinforcement plate of the clean out door when only replacing it?
Thank you very much.
RE: Above Ground Storage Tanks
The assembly includes the bottom reinforcing plate as well as a portion of shell plate.
See API 650 5.7.4.1:
5.7.4.1 All flush-type cleanout fittings and flush-type shell connections shall be thermally stress-relieved as an
assembly prior to installation in the tank shell or, alternatively, after installation into the tank shell if the entire tank is
stress-relieved. The stress relief shall be carried out within a temperature range of 600 °C to 650 °C (1100 °F to
1200 °F) (see 5.7.4.5 for quenched and tempered materials) for 1 hour per 25 mm (1 in.) of shell thickness. The
assembly shall include the bottom reinforcing plate (or annular plate) and the flange-to-neck weld.
RE: Above Ground Storage Tanks
Does we have to stress-relief the whole clean-out door assembly afterwards? or just PWHT of the new welding of the new annular plates to the new door reinforcement plate?
Or, in this case, is not required.
Thanks.
RE: Above Ground Storage Tanks
RE: Above Ground Storage Tanks
Thank you for your swift reply.
Actually, the thickened plate has a metal loss of about 34%, while the butt welded annular plates with it has around 64% reduction on both sides.
All corrosion attacked these plates in the 40 cm area near the bottom lap-welded plates.
As long as we are replacing all the Tank floor, we guess that it is better to replace the door clean out reinforced bottom plate, as well.
Do you agree about that?
Best wishes,