Limitation of Allowable stress of SS in high temp. acc, div 2

[modern53]

Dear All,

Regarding high design temperature(~600C)and SS304H as material our client ask us to design a reactor according to ASME VIII Div 2 and performing creep analysis. Acc. to SecII-D max. applicable temp. based on Div 2 for SS304H is 800F(~427C)and there is no allowable stress for 600C. For strength cal. may i follow div 1? and if i follow div 1 do i have to perform creep analysis based on div 2?

Thanks in advance

 

[desertfox]

Hi modern53

My advice would be talk to your client and see if you can use a material that as values of yield stress at 600 deg C
applicable to the code.

desertfox

 

[TGS4]

Div 2 does not allow design into the creep regime. If you have Div 1 allowable stresses, then you may design in accordance with Div 1. Unfortunately for you, your options are design to Div 1 or use a different material.

 

[modern53]

TGS4,

In the client specification, it is mentioned "Pressure vessels which operate in creep range of the materials of construction shall be designed acc. to Div2"! is it referred in Div2 that design into the creep regime is not allowed?

 

[blacksmith37]

Is it possible to suggest a "cold wall" design (internal thermal insulation )? This is often more economical ,even at 900F.

 

[TGS4]

modern53 - go back to your client. Have them review the scope of Division 2. ("The client may not always be right, but they are always the client")

 

[Jmoore1]

Generally:
Division 1 has less engineering and more safety factors
Division 2 has more engineering and less safety factor

If the exact same conditions for a vessel were applied to div 1 , it would be thicker, larger, and more expensive to fabricate than if it were designed to div 2. However engineering costs for the Div2 vessel will be greater.

The reason you can not design a div 2 vessel in the creep range is because the safety factor is not there to allow it....especially with catastrophic failure of creep with a thinner wall.

Your client either misunderstood division 2's applications, or mistyped....IMO they are looking for more safety if the vessel is within the creep range, and therefore they should design the vessel to division 1 for more material, not division 2 for less.

Im not saying that division 2 is "less safe" but there is more engineering done to verify the vessel than in a divison 1 design.