Weld Material in Exchangers

[robday2000]

Hi guys,

I have a few chemical analysis reports that do not match up on the Niton Gun. The welded areas were inside exchangers. The exchanger was 410ss. The tested areas were welds were in pretty bad shape. Moderate corrosion on the surface of the welds.

Mo 1.25
Ni 59.25
Fe 20.84
Mn 1.24
Cr 15.20

Mo 0.05
Ni 62.20
Fe 15.10
Mn 7.00
Cr 13.30

Mo 0.90
Ni 61.55
Fe 20.29
Mn 2.00
Cr 12.85

Mo 0.32
Ni 67.35
Fe 10.51
Mn 4.87
Cr 14.71

I'd imagine that these welds are all some sort of inconel but I'd like to leave it for the experts to decide. (i am only an apprentice afterall). I was more concerned about the high manganese content in one of the readings. This was taken in an area of corroded weld on a 410SS nozzle.

FYI the last analysis was of a good weld area. I am trying to find out why some of the welds have maintained their integrity while others have been eaten away.

Any experienced heads care to throw me some ideas?

I like learning about these things.

Regards
Rob

 

[Ron]

How do the chemistry results compare to the chemistry of the filler material? Do you have the spec on the filler material? Do you have any mill certs on the 410SS? What is the type of corrosion that has been seen? Is the corrosion going into the heat affected zone or is it limited to the filler material? What type of liquid goes through the nozzle?

 

[EdStainless]

Is this unit coming out of service? Will you be able to do any destructive testing? micros?

These results are too inconsistent for a conclusion. I would like ot say that the first three have greater amounts of weld dilution, but where would #1 get the Mo?
I think that you are going to have to look at micros and check carbon levels to really figure this out.

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Plymouth Tube

 

[robday2000]

The filler used is what we are trying to find out.

The corrosion is along the surface of the weld and it seems to have chewed away at patches rather than the whole weld itself.

In contrast, we have weld areas in the same exchangers where the weld has not been eaten away at all.

The goal is to find out what the good weld is made from and use that in place of the corroded weld. I'm not certain of the product running through these exchangers.

thanks

 

[robday2000]

The exchangers are currently being inspected. I don't think they will be coming out of service.

What can we expect to find using micros and looking at carbon content??

The dilution will be the reason why I'm not getting much help from the PMI Unit.

This is intriguing for me. My scope of work doesn't go as far as working out why equipment is failing etc but I like to ask about these things.

Regards

 

[DVWE]

I'm not certain of the product running through these exchangers.

That is critical information which is needed to help assess the corrosion/reason for corrosion. Can you find out?

 

[EdStainless]

As hard as this may be I suggest that you mill some metal out of a good weld. Then you can get an accurate analysis done in a lab. You need to look for Nb and Ta.
I am guessing that the corroded welds have extensive secondary phases present (carbides, nitrides, sigma and so on) which tie up the Cr and Mo preventing them from doing their job of resisting corrosion.
I am leaning toward this being one of the Ni-Cr fillers (A, B, 182)
What has me stumped is that I would guess that any of these have much better corrosion resistance than the 410.

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Plymouth Tube

 

[stanweld]

Nickel base alloys may exhibit the described corrosion in sulfidic environments within specific temperature ranges. In these environments E309 would have been a better choice to weld ferritic 410 type stainless steels.

 

[metengr]

Rob;
Here is some advice;
(1) I would not rely on the results of a portable alloy analyzer for determining the chemical composition of corroded welds in service. The results will be significantly influenced by existing corrosion products that you will not be able to remove completely.

(2) Seek professional help by contacting a metallurgical lab and have one of their metallurgical/material engineers evaluate your problem. You can work directly with the lab and learn first hand. I can think of several possibilities for what you are observing in this heat exchanger but this would only be speculation and you need to establish the root cause for proper corrective action.