We want to design a blank for 6inch

[Muhammad Ijaz]

We want to design a blank for 6inch carbon steel (API 5L B) piping. Design pressure is 25kg/cm2g and design temp are 74 deg C and minus 10 deg C.
Flange is 6"-300# A105 WN RF and gasket id is 168.3mm.
Available material is A285C 15 mm thk plate. For given design conditions, min thickness of blank comes out as approx 10.2mm. But for imapct test, per Para 323.2.2 of ASME B31.3, lowest exemption temperature is minus 9.4 deg C for nominal thickness (15/4=3.75mm) of blank.
How stress ratio for blank can be calculated to use temperature reduction value from fig 323.2.2B for imapct test exemption?

Regards,
Ijaz

 

[akpipelineengr]

Calculate the the design pressure that the nominal 15mm blank is good for, then use the ratio of that design pressure to your actual design pressure as the stress ratio. Refer to 323.2.2(b)(2).