Instrument Pipe Spool on API 650 tank

[MechEngMSU]

On a recent project we added a sch 40 pipe spool with 150# flanges to accomodate a new pressure transmitter and oxygen analyzer to a spare 8 in nozzle on the top roof of a 150' diameter internal floating roof tank. The vessel has a design pressure of 3 in H2O. Does this pipe need to be designed to a certain coded and/or hydrotested before installation? Would the hydrotest pressure be 4.5 in H2O?

 

[JStephen]

That pressure is negligible and it falls outside the scope of the tank standards. I wouldn't worry about it.

 

[TD2K]

If you are going to fabricate and hydrotest a spool with class 150 flanges, I'd just specify 450 psig as the hydrotest pressure. I want to make sure those welds are good even if the pressures are way below that.

In this case, I'm with JStephen, I'd specify likely just a visual inspection. Operations can tape and leak change the flanges during the commissioning. At these pressures, the chances of a weld failing is about zero.

 

[LittleInch]

See what all the other pipe spools are designed to that are attached to the tank including the delivery or suction line. On the roof you won't have liquid head issues but if you make it the same as one at the bottom of the tank you're safe in case someone relocates your spool piece one day....

25psi design pressure wouldn't take much to test.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way