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Thermal Stress Relief on flush-type shell connection vs non-flush-type shell connection

Thermal Stress Relief on flush-type shell connection vs non-flush-type shell connection

Thermal Stress Relief on flush-type shell connection vs non-flush-type shell connection

(OP)
In API 650, under section 5.7.4.1 it is mentioned that " 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."

I would like to understand the difference between a flush-type shell connection and a non-flush-type shell connection. Is the below photo a good example of it?

RE: Thermal Stress Relief on flush-type shell connection vs non-flush-type shell connection

No, there is a separate section for flush-type shell connections, which have the bottom of the nozzle flush with the bottom of the tank, with base plate similar to flush manways.

RE: Thermal Stress Relief on flush-type shell connection vs non-flush-type shell connection

See API 650 Section 5.7.8 and Figure 5.14 for a flush-type shell connection.

RE: Thermal Stress Relief on flush-type shell connection vs non-flush-type shell connection

No. The one on the left is simply a single flanged shell nozzle that has no internal projection and is trimmed even with the tank shell. It does not need PWHT unless (the shell is over 1" thick and the nozzle is 12" NPS or larger) OR (the shell plate is over 1/2" thick and API Group IV or higher). A flush-type shell connection is a completely different beast altogether, characterized (in part) by the inside bottom of the neck (the invert) being in the same plane as the tank bottom plate.

RE: Thermal Stress Relief on flush-type shell connection vs non-flush-type shell connection

(OP)
Thank you everyone for your replies.

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