B31.3 Wall Thickness

[JohnWeal]

Good Morning,
If the #300 pipeline system has to be derated (temperature is 150F) from 740 psi to 680 psi in accordance with ASME B16.5 Table 2-1.1 for group 1.1 Materials, does this mean that the pipeline wall thickness should use the derated pressure in the B31.3 wall thickness calculation?

ie, we can use a thinner wall? The client has specified code B31.1 for 4 pipelines which are between 600m to 4000m long.

The fluid is produced water and sour.

At present we are in FEED, but I feel the EPC Contractor would have to challenge the code specified by the client.

Regards

 

[LittleInch]

If your design temperature is 150F then your de-rated max pressure is 710psi not 680. You are allowed to extrapolate between the limits given, not just take the next one down.

As far as I can see then yes, this becomes your design pressure at that temperature and if 31.3 doesn't de-rate at 150 F (it doesn't for many common pipe materials), so would impact the wall thickness calculations. For 30 psi difference though I can't see it making much difference.

Of more importance is whether you actually NEED to have a design pressure equal to the MAXIMUM flange rating. Many times you don't and that's where you can save money.

Also a far bigger saving could be made by using a PIPELINE design code such as 31.4 or 31.8 instead of a piping code (31.3 or 31.1) which is much more appropriate for anything calling itself a pipeline (your words not mine).

31.1. is for pipework typically found in power stations - this sounds more like a petrochem plant to me and should be covered appropriately.


My motto: Learn something new every day

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

 

[SNORGY]

Do the American pipeline codes call for flange de-rating at 150 F? And, as LittleInch refers to, is it pipeLINE or pipING? Up here (Canada), pipeLINE flanges do not call for derating until 120 C (248 F), provided they are marked as complying with the pipeline-related material codes.