Substitution for Low-Temperature tubing

[a7992]

Hi All,

I have been asked to see if we could substitute A334 gr.3 for a different material because of the cost and availability of this material. The equipment is designed for -100 F and 620 PSI. I haven't had much luck looking through other ASTM specs to find an appropriate substitute and see only this spec and A333 for tubing for low temperature service.

Does anyone know of a stainless steel specification for tubing for low temperature service? Does anyone know if we could buy a general service tubing (such as A269) and request a charpy impact test to prove that it has the toughness at low temps? If so, where are those values found? Any other ideas to find a substitute material?

 

[metengr]

The equipment is designed for -100 F and 620 PSI.

Before you go any further and down the wrong path, what equipment? Construction code of equipment?

 

[a7992]

This is a heat exchanger and I am wondering about the tubing inside of the exchanger.

 

[btrueblood]

What fluids is the HX exposed to?

 

[a7992]

methanol

 

[metengr]

Is this heat exchanger built to ASME B&PV Code, Section VIII, Div 1? If so, this changes your approach.

 

[EdStainless]

all of the austenitic stainless grades are suitable for low temp service. For a HX you would want A/SA249.

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Plymouth Tube

 

[a7992]

Metengr...yes this vessel should be built according to that code. Is there somewhere in that code that requires certain materials? Is there something in the code that would not allow us to change to a stainless steel?

 

[btrueblood]

Agree with Ed, there is a lot of info. to back up the lack of a dramatic ductile-brittle transition temperature for austenitic stainless steel. I don't know why BPV section VIII would preclude its use either...but metengr is a smart guy, and I'd like to see his comments.

http://www.bssa.org.uk/faq.php?id=26

 

[metengr]

a7992;
Material selection will be limited to only those materials listed in ASME B&PV Code, Section II, Part D. Do you have any understanding of this Code because you will need to determine tube schedule (wall thickness) and method of attachment to the tubesheets among other essential variables for this heat exchanger. Get some professional help if you are unfamiliar with this Code.

Changing material requires a detailed engineering evaluation regarding ease of material fabrication, availability and cost, in addition to heat exchanger performance. Yes, you can use austenitic grades of stainless that are permitted in Section II and even other low temperature carbon steel tube materials based on your minimum design metal temperature.

 

[a7992]

metengr-

Thanks for the help! I am not familiar with the code but hope to be (graduated college a year ago). I would be recommending a material to the Mechanical Engineer and he would be evaluating the overall suitability based on the other variables you mentioned. I'm just making a recommendation based solely on material compatibility with the service. I'll let hom worry about cost, availability and any design changes necessary to accomodate a new material.

Thanks again for the help! You definitely pointed me in the right direction.

 

[a7992]

I actually did have one last question...can materials that are not specifically stated in the ASTM spec to be used in low temperature service still be used at low temperatures if we know the properties are fine at low temps? Does 316 and 304 stainless steel not need to be impact charpy tested because of the DBTT?

 

[metengr]

a7992;
Yes, that is correct. The austenitic grades of stainless steel do not exhibit a characteristic ductile to brittle transition temperature so the Code committee recognizes this fact and does not require impact testing until extremely cold service temperatures (below -320 deg F) are used in design.

I need to correct one small reference, for ASME Boiler and Pressure Vessel Code design work, ASTM specifications are not referenced directly. The specifications referenced by ASME B&PV Code are specifications listed as SA and have been reviewed and endorsed by Section II. In most cases Section II will adopt the ASTM specification as is. However, this is not always the case and you need to review the SA specification in Section II.

 

[EdStainless]

for example ASTM material specs that allow mechanical testing as an option are usually modified to require it by ASME. Specs that don't require mechanical testing at all are usually not adopted by ASME at all.

This is why earlier I pointed out that you will need to use A/SA249 as a tubing specification and not A269.

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Plymouth Tube