SA-182F316L low stress material

[Steve.sw90]

While designing a kettle type heat exchanger, I am having a confusion if I should use low stress material for body body flange and tube sheet.
Also which are the scenario where low stress material should be used, I have read note G5, still having a curiosity to know in actual industry where low stress material is preferred and where high stress material can be used.

 

[SnTMan]

Steve.sw90, generally lower allowables are used at gasketed joints. Body flanges, flat covers, tubesheets if gasketed, etc. Otherwise higher allowables are used.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Steve.sw90]

SnTMan, what if I go with higher allowable stress, is it a mandatory requirement for gasketed joint of a U-stamp vessel.

 

[Steve.sw90]

Also in that case I believe shell to which flange is welded should also be made low stress material for e.g. Sa-240 316L.
For me deformation in shell during operation could cause more damage to flange connection.

 

[SnTMan]

Steve.sw90, use of lower allowables is not mandated by Sec VIII, Div. 1, as far as I know. It is fairly common for client specs to required it and I have seen a few that require use of lower allowables for all materials that have it, normally austenitic stainless.

Aside from client specs it is your choice what to use where, but use of lower allowables for flanges, etc. and higher allowables for everything else is very common.

I will add that if a gasketed joint leaks due to distortion of the members of the joint, you are done. Not repairable.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Steve.sw90]

In such case will it be ok to check for material with low stress at operating pressure and temperature, and high strength material used for design pressure and temperature.

 

[pressvessel]

The thread title had me thinking that the OP is interpreting the "L" in "316L" as "low stress". I always thought the "L" refers to "lower carbon content" (which may result in lower mechanical strength). We used to specify the "L" grades only when needed for improved corrosion resistance?

Regarding the two lines with stress values per st/st grade (ASME II Part D tables): We used the lower values only where it is critical to minimize deflection (e.g. flanged/gasketed joints) or when specified by clients.

I find the last question by the OP an interesting one as I have not seen this approach before. It could result in a slight reduction in flange thickness? Whether or not it would be worth the risk of possible sealing issues during testing is debatable.

 

[Steve.sw90]

No confusion regarding L, it stands for low carbon content improving weld quality of SS.
anything above operating condition should be incidental, causing material exposed to higher tension for short period of time at certain operating temperature.

or else we can multiply operating condition with certain factor for eg. 1.25 or 1.15 and check design based on amplified values.

 

[SnTMan]

Steve.sw90, aside from client specs, you are not mandated to use lower allowables. If you are feeling lucky, go for it.

As an alternate approach, why not used dual certified material, and then use the lower allowables of straight grade (non-L) material?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Steve.sw90]

Really Good Idea Mike, thank you.

 

[Steve.sw90]

Dear mike,

On further discussion regarding this with our AI, conclusion is as below,

These different stress values have been RECOMMENDED for SS materials where bending stresses are predominant.
I feel the manufacturer should have good knowledge and strong justification for use of higher allowable stress where bending stresses are governing. He may demonstrate this by performing alternate calculations.

Regards,
Stephen