Stainless Duplex to carbon steel 1

[rmillercwi]

Trying to evaluate the possibility of joining these two materials in a pressure boiler. Looking for some pre-liminary feedback.

Are either of these combinations practical? If so, what are their limitations?


*SA-178A tube (or return bend) to SA-789-2205 tube.
*SA-789-2205 tube to SA-106B header.

Thank you in advance

 

[metengr]

Why would you even consider duplex in this application? Duplex stainless steels are prohibited from use in elevated temperature service. Review ASME Section II for service temp limits of materials of construction. Also, duplex ss are not permitted for use in Section I construction.

 

[rmillercwi]

Thats what I thought too but apparently the new code section II part D allows it up to 600f. The header thickness is kicking this out welding tube to header as it is over 1" thk. Thinking theres no way not to stress it.

To get around the stress relieving, we are thinking of putting stubs on the header, stress the assembly and weld the 2205 to the stub. 178a ~ 2205.

 

[EdStainless]

So this part can never see service over 600F in your system under any conditions?
Just because a material is listed in SecII doesn't mean that its use is allowed in SecI.

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Plymouth Tube

 

[HotStab]

For welding Duplex and Super-Duplex to low alloy steels, as far as I know, a buttering of nickel CRA (alloy 625) is always required and the same alloy is used as weld metal. But this procedure is for butt welds between pipe and flanges, I can’t figure out the same in a tube to heater welding.

 

[stanweld]

Duplex alloy 2205 has been and is currently being used in the preheating section of Heat Recovery Steam generators (temp < 300F) prior to deaeration. The headers have also been duplex. Carbon steel or low alloy steels are used thereafter.

 

[rmillercwi]

^ I am aware they have been used in HRSG's for several years but in my experience the base materials have always matched. IE duplex to duplex. My experience with this material has always been used in section 8 unfired boilers and have advised my colleages as such.

My department is insisting this combination duplex to cs is acceptable in section 1 fabrication up to 600f. Looking for opionions of code enterpretation and practicality of the application. I agree, simply because it is acknowledged in section 11 does not mean it is automaticly accepted in section 1. Would like to raise the flag but want to be right before raising a stink.

 

[stanweld]

Based on the expense of duplex over carbon steel, why would you want to? The galvanic mismatch will also pose a problem. Just because one can do something per Code does not make it sound engineering.

 

[metengr]

This material is not permitted for Section I construction. Please review PG-9. Also, the only code case I have seen where a component is designed and built to Section VIII for Section I use is for CS drums.To even consider your scenario would require a code case.

 

[rmillercwi]

If I read this section correctly, PG-9.7 does allow this material in economizers (which this is btw, my fault for not clarifying and perhaps the root of the confusion) I got into the habit of calling everything a boiler. SA-789 (S31803 only)

 

[metengr]

rmillercwi;
Just to clarify and thanks for the additional information, PG-9.7 is for unfired components that could fall under the Jurisdiction of Section I. If this economizer can be isolated, this material cannot be used under Section I.

Now, something to think about, should there be any operational event that results in this tube/header material reaching 600 deg F or higher (lack of flow or inadequate flow of feedwater), you can have a most serious problem with loss of toughness in this material. This is the designer's responsibility to consider.

 

[rmillercwi]

Thank you all for your responses.