Relationship between Part 4 and Part 5 in 2007 Div 2 1

[SRFCav]

I'm confused about the requirements of Div 2, Part 4 with regards to welds, and how they fold into a design qualified by the procedures of Part 5.

Specifically: Part 4 requires a Type 1 or Type 2 butt weld at a Category B joint. Is it then true that a Part 5 design must adhere to this requirement also?

Though that seems very reasonable, I cannot find any specific statement to that effect. I would appreciate any guidance that might be offered.

 

[TGS4]

The simple answer is that it depends. Are you using Part 4 or Part 5 to design your component/vessel? Is there any statement in Part 5 that restricts you to design features/details in Part 4?

 

[SRFCav]

The intent is to design the device by the rules of Part 5.

I can not find within Part 5 any requirement to use any specific requirements of Part 4. There is mention that certain stress quantities need not be checked if Part 4 details are used, so some mixing of the procedures seems expected.

But the only evidence I have that any Part 4 requirement may be ignored is from 4.1.5.1, where it says that "the design thickness (of a vessel part) may be established using the design-by-analysis procedures in Part 5, even if this thickness is less than that established using Part 4 design-by-rule methods."

If the Division is willing to surrender even basic shell thickness to analysis, then the welds might also be free of the Part 4 requirements of type per Category. But I don't want to make that assumption unless there is support for it from people more experienced than I.

 

[TGS4]

The only other place that Part 4 is mentioned is in paragraph 5.3.1.1.

From a design-by-analysis perspective, if you can prove a design through analysis, there is essentially no design restriction. Fabrication and inspection are additional requirements, but you would have to meet those requirements for a Part 4 design as well...

You should also read paragraph 4.2.1.

 

[SRFCav]

Thank you for your guidance; I was too narrow in my interpretation of 4.2.1, it being difficult to imagine that Section VIII would abandon the requirement of butt welds at Category A and B joints. But, taken at its word, and assuming there is no controlling text I've missed, that is what it appears to do.

Thanks again for your thoughtful response.