Skirt material for column

[MikeG7]

Is it permissible to use structural grade material for skirts for ASME VIII Div.1 equipment?
Quoting UG-4(b) Material for nonpressure parts, such as skirts, supports,
baffles, lugs, clips, and extended heat transfer surfaces,
need not conform to the specifications for the
material to which they are attached or to a material specification
permitted in this Division, but if attached to the
vessel by welding shall be of weldable quality [see
UW-5(b)]. The allowable stress values for material not
identified in accordance with UG-93 shall not exceed 80%
of the maximum allowable stress value permitted for similar
material in Subsection C.

The above suggest that non-ASME II material is permitted.
I am unsure exactly how one arrives at a "similar" material?

Our inspector is questioning the fact that structural grade materials which are not in ASME II do not have any published strength data beyond room temperature and hence are not acceptable materials.

Michael

 

[TGS4]

Your inspector makes a valid point. How hot above ambient are you going?

 

[MikeG7]

Hi Trevor
The vessel is 145 degress Centigrade and is insulated. Below that is about 0.5 m of compatible material SA-240 316L material (not insulated) and then the carbon steel skirt is attached
I would say that the skirt would not exceed 40 degrees Centigrade

 

[MikeG7]

This link suggests that provided a welding procedure is in place, it is permitted

https://www.eng-tips.com/viewthread.cfm?qid=361739

I believe carbon steel strength for use in design purposes does not diminish at 10-15 degrees above ambient - would you agree?

 

[TGS4]

I think that your assessment of the temperature seems fair, and your arrangement of compatible material below the vessel for a certain length is fairly standard. Essentially, the Vessel Code doesn't really have jurisdiction of that structural material below the 316L...

 

[MikeG7]

Trevor
Thanks for the reply. Further please if possible could you give opinion about how to go about ensuring or meeting the following criteria:
1) "weldable quality" as specified in UG-4(b)
2) establishing "similar" material and determining an allowable compressive stress against which to compare actual strength to ? (the word "similar" is referred to in UG-4(b) )

 

[MikeG7]

I should have qualified my previous statement by saying that my approach to assessing the use of S355JR material (with room temperature only properties) is to have selected my "similar" material as P265GH carbon steel (with a 265 MPa Yield strength at room temp) and from that, our software (Compress) determines an allowable strength according to the temperature.

 

[SnTMan]

Sounds like an unneeded headache to me. Is the difference in cost or availability over a listed material enough to make it worth the trouble?

Regards,

Mike

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

 

[MikeG7]

Both S355JR and SA-516 Gr 70 are readily available - higher cost with the graded material but probably more leaning towards the higher yield capacity of the structural steel.

 

[SnTMan]

OK, I see, not familiar with those specs...

Maybe look at SA-537 Cl2?

Regards,

Mike

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

 

[MikeG7]

We already have the material Mike so I was trying to determine if the material is appropriate, and if it is out of the jurisdiction of the Code. TGS4 has said it is out of the code scope, so now I need to establish a basis that it is weldable and what it's strength is if it is not at room temperature but 15 degrees above RT

 

[SnTMan]

Well, best of luck

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

 

[MikeG7]

Thanks, I hope luck has nothing to do with it!
I still have this query what is meant by "of weldable quality" by ASME UG-4 (b) if anyone can offer advice on that and on what is meant by "similar" material in terms of determining the compressive stress.

 

[SnTMan]

See UW-5(b) to start. Know what you mean about luck

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

 

[r6155]

1)If wind or seismic is part of the design then tensile stress may be in the skirt.
2)The owner must be informed.

Regards

 

[MikeG7]

Yes most definitely wind is part of the design and there would be stress in the skirt from wind. What must the user be informed of exactly? That there is tensile stress?
What I'm trying to establish is the allowable stress (in tension or compression) against which to base the design on for a material that is not listed in ASME II (as permitted by UG-4(b).

 

[r6155]

Owner need to know the material not listed in ASME, and he can reject it. He pay.
All design drawings and calculations need to be approved by the ownwer. He pay.
What says the contract?.

Regards

 

[MikeG7]

Kind of a double thing here - spec sheet says design to ASME and ASME says skirt material not required to be ASME II listed material. Other comments above seem to concur this.
Sure, the user can reject it if it's in the contract that all material used must be ASME II material, regardless of the Code UG-4 (b) requrements.
Am I missing something here? Let me point out that chosen material strength +/- 30% higher in yield that other avaialbe graded material, so there is certainly a good reason behind it.

 

This is a case where 'less is more'.
Smart designers will spec ASME materials just so this kind of question never arises.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[MikeG7]

That's got me laughing.
But seriously, if there is something "wrong" with using structural material I would appreciate a heads up. I've seen the use of structural steel as supports or skirts specified in other specifications from reputable and established international organizations where the skirt or support is not directly welded to the vessel.