Welded Hastelloy C-276, C-22, C-2000, Inconel 686 -- Freely Interchangeable? 1

[Guest102023]

This is a material sourcing concern as you might have already guessed.
I need to know of any possible complications or incompatibilities between any two of these alloys when fabricated.
I am thinking of using 686 filler metal regardless of selection.
For example, do any require annealing after welding/forming?
.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[metengr]

Solution anneal is not required after welding, but after forming, yes for all of the alloys above for maximum corrosion resistance. By the way, I don't like interchangeable for these alloys because each is a different animal and responds differently to corrosive environments.

 

[Guest102023]

I too don't like interchangeable if I can help it.
The service is crude overhead piping where C-276 is the recommended alloy.
It is exceeded in corrosion resistance by the others I listed in many applications; is that also true for this application?

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[metengr]

BTW, I would strongly suggest you make time to visit the Haynes web site and Special Metals web site for all of the necessary technical information related to welding (DMW welding) and fabrication for the above alloys.

 

[metengr]

brimstoner;
You need more information to perform a proper material comparison. What is the operating temperature of the line, flow, corrosive species, acid or reducing environment, pH....? This is not something anyone on this forum can easily answer off the top of the head, nor would I risk such a off the cuff recommendation.

Do as I said, and visit the web sites and evaluate corrosion performance based on your stated service conditions.

 

[metengr]

Review this so I don't leave you hanging

http://www.nickelinstitute.org/~/me...sIndustrySelectionGuidelinesUpdate_10073.ashx

 

[EdStainless]

One issue is that because C276 has been made as a generic for so long there is both good quality material and some very poor quality material out there.

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Plymouth Tube

 

[moltenmetal]

Depends: do you need the full corrosion resistance of a particular C grade, or is it just a service where 316 isn't good enough and C is the next tool that was handy? That's frequently the case, especially for instruments- middle resistance grades like super-duplexes or high Mo austenitics aren't offered. In that case, you don't get a choice. The vendor selects a grade and makes their units from that, and they give you only two options generally- 316 and whatever C grade or grades they choose to use. For coriolis meters for instance, that's ALWAYS C-22, not C-276, whether you like it or not. So in reality, unless your line consists ONLY of pipe and fittings, you're likely going to have a mixture of C grades.

Who says that C-276 is the recommended alloy, and on what basis do they say that? I've had clients who insisted on a particular grade but when we dug into it, we found out that they had been using devices for years made from other grades and hadn't even realized it. Corrosion and superstition often go hand in hand.

These grades do have different resistances to different corrodents, which again differ depending on product form and post fabrication treatments. But that is only meaningful for particular corrodents and when a particular alloy is specified. And as EdStainless says, there are some generic versions missing some important alloying constituents out there.

 

[weldstan]

Up alloying of the weld filler metal is generally recommended. Whether the use of 686 is correct for all of your services and alloys stated is another story.

 

[Guest102023]

mm,
I appreciate your comments, and I have not said what the service is - it is for a crude overhead line, where erosion-corrosion and the other usual suspects are issues. Droplet impingement corrosion is a specific problem. We are very aware the current MoC is very insufficient.

316 is definitely not an option; C-276 was recommended by an experienced corrosion consultant who has been active in NACE for many years.

I would definitely like to know what to watch out for when buying C-276 or other C alloy. Is it down to composition, processing, and/or country of origin?

p.s., knowing nothing about coriolis meters I had to google it. See if you can spot the error on page 3 of this brochure -

https://www.honeywellprocess.com/library/support/Public/Documents/34-VF-25-11.pdf

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[moltenmetal]

Hmm, looks like a confusion of 8s and 6s...

 

[EdStainless]

And many people forget that the 6% Mo superaustenitics are a lot better than 316 and 2205, and not nearly as expensive as a Ni based alloy.

In my book the big factor in favor of the newer generation C alloys is that they have better microstructural stability, that is they are less likely to form detrimental secondary phases (such as in weld HAZ).

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Plymouth Tube