API STD 650 Section 5.7.4 1

[hamidun]

Dear All,

Based on API STD 650 Section 5.7.4.1, thermal stress relief only applies to flush-type cleanout fittings and flush-type shell connections which are attached to 25 mm thick shell, right? If the shell thickness is 24 mm, we do not need to do thermal stress relief to flush-type cleanout fittings and flush-type shell connections, am I right?

And for Section 5.7.4.2, thermal stress relief only applies to all opening connections NPS 12 or larger which are attached to 25 mm thick shell, right? If the shell thickness is 24 mm, we also do not need to do thermal stress relief to opening connections NPS 12 or larger, am I right?

My final question is, if there is a tank with shell course #1 is more than 25 mm thick, do we need to do thermal stress relief to the shell?

I am currently confused about the requirement of thermal stress relief of API STD 650 whether it applies only to the connections/fittings of the tank shell or it applies to the shell of the tank as well.

Please help, thanks!

 

[JStephen]

Under the standard design, all flush manways and flush shell connections, including the base plates, are pre-assembled and stress-relieved.
Nozzles exceeding certain size and thickness limits are also required to be pre-fabricated and stress-relieved.
There are (or were) some exemptions for smaller tanks in Annex A.
Regular round seams or verts in shell plate over 1" are not required to be stress-relieved.

 

[IFRs]

The 25 mm / over 12 NPS threshold is only for certain grades of steel. Others have a 13 mm threshold and no minimum size for PWHT.

 

[hamidun]

Thanks JStephen,

So, tank with shell thick more than 25 mm is not required to be stress-relieved. The thermal stress relief is required for nozzles, flush-type cleanout fittings and flush-type shell connections.

IFRs,

And that is for nozzles, flush-type cleanout fittings and flush-type shell connections, right? Not for the shell?

 

[IFRs]

Thermal stress relief does not apply to shell plates regardless to the shell thickness unless they are part of an assembly that requires stress relief. Stress relief only applies to shell penetrations when (the material is Group III or less, the plate is over 1" [25mm] thick and the penetration is over 12" NPS) or (the material is Group IV or higher, the plate is over 1/2" [13mm] thick and the penetration requires reinforcing) or (the penetration is a flush cleanout or flush nozzle).

I think I got this correctly, JStephen confirm?

 

[hamidun]

IFRs,

Based on what you said, "unless they are part of an assembly that requires stress relief". This means only for shell plate where nozzle attached (or etc.) requires thermal stress relief, right?

For example a tank consists of 20 plates with 30 mm thick for 1st course, 1 of the shell plates is attached with flush type cleanout fitting, thermal stress relief to be applied is only for that 1 shell plate where flush type cleanout fitting is attached, right? Not a whole 1st shell course.

 

[IFRs]

"Based on what you said, "unless they are part of an assembly that requires stress relief". This means only for shell plate where nozzle attached (or etc.) requires thermal stress relief, right?

Exactly


"For example a tank consists of 20 plates with 30 mm thick for 1st course, 1 of the shell plates is attached with flush type cleanout fitting, thermal stress relief to be applied is only for that 1 shell plate where flush type cleanout fitting is attached, right? Not a whole 1st shell course."

Correct

 

[hamidun]

Thank you so much IFRs!