What is the most rare damage mechanism?

[Stallionbreed]

In API 571 there is about 70 different types of damage mechanisms list. Of course, each different mechanisms has a variety of variants.

From your experience, which mechanism is the most rare? Personally, I have never seen dealloying myself.

 

[TugboatEng]

Dezincification is common in my industry. Does that count?

 

[mrfailure]

Looking at failure mechanisms that way is sure to lead to misdiagnosis of the issues you are working on.

What I do is gain as much understanding of the failure and system it occurred in as I can. Then, I can narrow down the possibilities of what is in the realm of possibility to what could have happened, including possible failure mechanism(s). You may well need to do further testing to confirm/eliminate the possibilities. I only look at probability of candidate mechanisms if I cannot confirm data through analysis, assuming two or more potential mechanisms are still present.

At the end, you have to determine what makes the most sense for the system you are looking at.

 

[mrfailure]

Your example of dealloying is a good one for why you should not put faith in how rare a mechanism is.. In your world, you never see dealloying but both TugboatEng and myself see this mechanism in the systems we look at.

 

[EdStainless]

While dealloying is rare in Fe and Ni alloys it is common in Cu and Al alloys.
I was shocked once when I found a list of environments that would cause SCC in every know alloy system (even Au and Pt).
What is rare for one engineer may be day to day for another.

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P.E. Metallurgy, consulting work welcomed

 

[Stallionbreed]

Thank you all for the responses. I do understand one is rare to one engineer may not be rare to another. My apologies for not making that clear.

I was just curious to see what others have experienced.
I try to read API 571 often to become more aware of 70+ mechanisms.

 

[Guest102023]

Detransmogrification?
Spontaneous combustion?
Just kidding.

Seriously, I am on a team examining a single unique failure in a pipe about two decades back, which stymied highly qualified investigators at the time, and we have not been able to add anything to their work. Any further information is confidential. There are probably more cases like ours.

Fair to say the rarest mechanism hasn’t been discovered yet. A finding of ‘indeterminate’ however usually means insufficient information.

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

 

[mrfailure]

One thing I would warn about is creating a new mechanism that is not documented in the literature. What you think is new can in fact be usually be explained from knowledge we already have; you just have to examine from various angles to ferret this out. If you think you have a new mechanism, examine thoroughly - it indeed does happen on exceedingly rare occasions.

 

[blacksmith37]

That is going to depend on the industry; The materials used and he environments. For example stress corrosion cracking of modest strength carbon steel occurs in gas pipelines and almost nowhere else. And you are not going to see titanium hydriding unless you have titanium equipment.

 

[springrise]

I've come across an idea of thermogalvanic corrosion cell (i.e. same material but different temperatures causing corrosion) which I consider to be rare - at least as a main cause of damage. Anyhow, this is not even mentioned in the API 571.

 

[weldstan]

The rarest failure that I have seen was knife edge corrosion at the interface of braze alloy and copper pipe in low pressure gas distribution. It was only observed in lines that contained natural gas with a very small amount of oxygen that was sourced from a singular gas formation source.

 

[WKTaylor]

Oxygen depletion corrosion on the fay surfaces for SStl alloys fastened together... typically in an aggressive [heat] environment.

Regards, Wil Taylor
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o We believe to be true what we prefer to be true. [Unknown]
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[Guest102023]

knife edge corrosion at the interface of braze alloy and copper pipe in low pressure gas distribution.

I'd love to see the report that came out of that.

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

 

[EdStainless]

I am partial to 6% Mo alloys exposed to high temp.
Mo oxide forms and it has a melting point below the alloy.
The liquid Mo oxide begins running down the part cutting grooves in it.

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P.E. Metallurgy, consulting work welcomed

 

[Guest102023]

Speaking of superaustenitics, the long time standard filler metal 625 is no longer recommended. The Moly segregates strongly in the weld deposit, which in some more aggressive chloride environments can lead to localized corrosion. Not a new mechanism but a new example of a well understood mechanism.

One of the higher Mo fillers like C-286 or C-22 is now recommended.

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

 

[weldstan]

brimstoner: The report was made by the Stanford Research Institute over 60 years ago and is held by the involved gas utility company and possibly SRI. I did review the report and was involved in investigating same type of corrosion incidents. Essentially, the failures occured predictively every ten years usually involving a catastrophic event. At the time of my leaving that company, I wrote a report to remove and replace the involved piping for a distance of a mile downstream from the previous event repairs at 8 to 9 year intervals - eventually removing all piping subject to failure.

 

[isoca]

Anything you find in the literature or detailed information about it means it's not rare. If someone has spent money and effort to carry out tests and publish them, it is because their consequences have already been observed more than once. Very rare things are not in the books yet

 

[Stallionbreed]

isoca,

can you think of a damage mechanism that isn't discussed in literature?