Duplex stainless weldment failures 4

[geesamand]

My company provides equipment in a variety of corrosion-resistant alloys.

We have done duplex in the past and had a few more mechanical failures (cracking) particularly around HAZs. Even with greatly reduced stress limits we couldn't stay out of trouble.

I have a few areas of focus to get back on track:
1) Design of the weldments for duplex welding heat control. Do certain weld joints lend to worse HAZ phase imbalance.
2) We generally use ASME BPVC allowable stress limits for design. Is this standard practice, and if so, are there cases where we shouldn't?
3) We subcontract welding. Many weld shops "have a procedure for that". What are key questions / criteria to get past the "we can do that" promise to actual success?

I realize these are loaded questions, so I'll take what I can get.

Thanks,

 

[EdStainless]

In duplex there are critical issues other than just heat input.
Are the welds tested for austenite:ferrite ratio?
Are they tested for detrimental intermetallics? (such as A923)
What about pitting corrosion resistance?
While these things are somewhat related they are each important.

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

3) How do you physically vet the subcontractors for their capabilities to successfully weld DSS/SDSS?

http://www.iso3834.org/welding-fabricator-certification-scheme/

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[DVWE]

We subcontract welding. Many weld shops "have a procedure for that". What are key questions / criteria to get past the "we can do that" promise to actual success?

API RP 582 was completely revamped in 2016 to include some pretty tight welding requirements, restrictions, and procedure qualification requirements for DSS. Familiarize yourself with that document, and ask your vendors to do the same.

 

[geesamand]

In duplex there are critical issues other than just heat input.
Are the welds tested for austenite:ferrite ratio?
Are they tested for detrimental intermetallics? (such as A923)
What about pitting corrosion resistance?
While these things are somewhat related they are each important.

Austenite:ferrite is not required per piece.
A923 is called out in some cases. Not all.
Pitting corrosion resistance is not required unless our customer requires it. I don't recall seeing this before.

3) How do you physically vet the subcontractors for their capabilities to successfully weld DSS/SDSS?

We don't really. We avoid working with dirt floor operations but that's obviously not enough and what I'm trying to develop. ISO 3834 is worth a look - does it contain information specific to duplex?

API RP 582 was completely revamped in 2016 to include some pretty tight welding requirements, restrictions, and procedure qualification requirements for DSS. Familiarize yourself with that document, and ask your vendors to do the same.

Good tip, thanks. My copy is 2009 edition, so I will update.

 

[SJones]

3) No. ISO 3834 deals with the quality requirements for welding as opposed to specific technical requirements for materials. It provides a framework for assessing the procedures and processes in place to consistently meet technical specification requirements. The actual technical specification is a different matter. API RP 582 is one guide from which a technical specification can be developed. AWS D10.18 is another, and there are others like the NiDI guide:

https://www.nickelinstitute.org/en/TechnicalLibrary/Other Series/DuplexGuide_16000_.aspx

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

If you are welding duplex then every time there needs to a fixed procedure, documented welder qualification, including both A923 and ferrite measurements.
IMOA publishes a duplex fabrication handbook.

https://www.imoa.info/molybdenum-media-centre/downloads/practical-guidelines/fabrication-series.php

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

You need to determine the metallurgical cause(s) of the failures. It could be based on base material properties or on welding. Fully agree with Ed regarding welding procedure, welder qualification issues.

 

[CWEng]

Duplex HAZs are relatively resistant to cracking during the fabrication process. Were your HAZ cracks during fabrictation or during service? The causes would be quite different depending on the time of occurance.

 

[geesamand]

Duplex HAZs are relatively resistant to cracking during the fabrication process. Were your HAZ cracks during fabrictation or during service? The causes would be quite different depending on the time of occurance.

Cracking during service.

I also got clarification that we did get Ferrite count and intermetallics tested with our work.

Has anyone found the need to reduce stress limits below ASME allowables?

 

[geesamand]

I do appreciate the info provided so far.

Are there weld geometries that you would do in a 300 series that you would avoid in a duplex? If so, why?

 

[CWEng]

So if the cracks are in service, there is a good chance you either have a susceptible microstructure, an environment too aggressive for the Duplex, or a combination of stress/environment that exeeds the duplex capabilties. What do you know about the environemnts for your equipment?

 

[EdStainless]

And what duplex rages are we talking about, S32205?
S31803 is too wide of a chemistry, that is why it has been superseded.

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P.E. Metallurgy, Plymouth Tube