Conc Sulf Acid Damage to Alloy 20?? 3

[SETXINSP]

Just wondering if anyone else has or is experiencing corrosion of Alloy 20 gaskets with 93% sulfuric acid? Had a valve flange and gasket get corroded away in a deadleg right off of the acid tank far away from any water getting to it. All material is Alloy 20 and the deadleg is from the middle of a 3" tee that's welded to a RF flange and that's where the valve was bolted in. Operates at about 85 degrees F. This isn't the first gasket leak but the furthest from water in the system we have had. Is it possible that condensation is somehow forming inside at these flange locations causing the problem? That's the only thing I can think of as to how this would keep happening like this. Thanks for any ideas, experiences, comments, etc!

 

[shvet]

I have extensive experience with H2SO4 and here is my 5¢:
- inadvertent dilution (you do not know about)
- gasket metal off-spec (unless you have an excellent Positive Material Indentification programm implemented)
- occasional local overheating (you do not know about)
Note that items 1 and 3 could have happened long ago.

Being you I would not be so confident in points like "Operates at about 85 degrees F", "far away from any water getting to it", "All material is Alloy 20". I have come across the most incredible cases.

 

[SETXINSP]

Thank you for the response and yes I don't put a lot of faith in those things that I put as far as operating temp and material. That's what everything is supposed to be anyway that's why I put that in there. About the water, I was just meaning for this specific location, it's not right up against the water stream even though we have failures there too but I believe I know the cause of that already.

I believe we are having some type of inadvertent dilution but I can't figure out how it would have happened in this one spot in particular. The leak point was on a 2 part 3" ball valve that is bolted to the process side obviously on one side and then the other side of the valve just had a blind flange installed. The failure happened on the process side flange and also where the valve body is bolted together, the bolts were also corroded internally at that point. That's why I think there is some type of temperature issue possibly causing condensation inside of the components that is causing this failure because if it's not that then I have absolutely no other ideas at this point. But like you said if it started long ago like when the unit was first brought online then I'm never going to really know for sure what happened. Just wanting to get a head of these failures so we quit having them.

 

[shvet]

What material valve and piping is made of?

 

[SETXINSP]

It's all Alloy 20 material. Valve bodies, valve trim, gaskets, pipe, everything that I have information on anyway. I haven't been able to get really into the valve itself and see if some other material is used in that particular valve that would be weak link yet. Gaskets are alloy 20 IR with graphite filler.

 

[TugboatEng]

Graphite is VERY noble. It's possible your corrosion is galvanic. Also, because everything is the same material slight differences in metallurgy may cause the gasket to be anodic to the system. Do consider using C276 for gasketing.

 

[SETXINSP]

Thank you for the response! That is definitely something I will also look into!

 

[EdStainless]

Could it have started on the OD?
Condensation forming weak acid in the gasket crevice?
Or is it possible that the flanges or gaskets could have been contaminated at installation?
Dead legs can be a real pain sometimes.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[SETXINSP]

@edStainless that is what I am assuming is that it started as a crevice corrosion because it's the only thing that makes sense to me as of right now. It's absolutely possible they were contaminated at installation but I won't know for sure. Now I went this morning and examined the flange surface of the valve and there is corrosion on the outside of the gasket sealing surface but the bolts that hold the 2 part 3" ball valve together is looking more like the prime suspect now that I've gotten to examine it. It looks like some type of gasket material was coming out of that interface and the bolts at the bottom were corroded severely and one of them was completely in half. So it may be a weak link inside of that valve.

 

[mk3223]

Are there two different corrosion locations on the piping, or the possibly extended from one to the other?
Be caution and take necessary PPE to get close to the leaking pipe.

 

[MJCronin]

What are you not posting pictures ... Its a very easy process and may help you get better answers

.... and why are you NOT TELLING US WHO manufactured the gaskets ?

In all of the PIPING SPECIFICATIONS that I have written and sealed as a pipinng engineer, I was certain that the gaskets could endure the P&T and corrosive conditions of the media ..... Why can't yours ?

Have you called the gasket vendor ?... what did they say when you called ?

This topic has been discussed before ....

https://www.eng-tips.com/viewthread.cfm?qid=367030

MJCronin
Sr. Process Engineer

 

[shvet]

I recommend asbestos in PTFE envelop

 

[SETXINSP]

@mk3223 yes there are two different leak locations. The one this post is about was an area that didn't make sense to me at the time but I think I'm narrowing it down. The second is right at check valves which I believe the BFW is working at a higher pressure and mixing with the acid and corroding the check valve pin and making the flapper fall off and then pushing further back in the system causing those flange leaks. This post is about a valve that leaked at the flange is what I was told, however after further investigation, I found out that it was more likely started at the location where the two valve pieces meet and there is a grafoil/TFE gasket inside there. So the acid had to eat through the seat of the ball valve then infiltrate this area to destroy that gasket and start leaking and then corroded the bolts. At least that's what I come up with anyway. Also, what I didn't know when I posted this is that this leak location is in a small trench that has a steam condensate dump that runs all the way down the trench to this valve. This valve is at the end of a part of the trench area and this steam condensate just sits there with that valve flange slightly submerged or very close to the water. I took an IR camera out there and scanned that entire area and that SC comes out at 150 F and is still about 120-130 F where it sits under that valve. Actually just talked to ops while typing this out and that trench would actually fill up submerging the valve in this hot SC so now it seems like a no brainer as to why this happened!

 

[SETXINSP]

@MJCronin as far as your questions, at the time of the original post, I didn't have pictures of any of this just yet. I do now however. As to why I didn't say who manufactured the gaskets, well that's simple. I don't know who the manufacturer is because I haven't seen the gasket. This work was done on a weekend and maintenance changed the gasket out and trashed it unfortunately. The piping specs for this line is all Alloy 20 so obviously it should be able to handle the service which it looks like it can but it was just at the time I was unaware of some conditions as stated in my previous post as to why this could possibly happen but now it makes more sense as to what happened and why. Thanks for the questions and the link to the other discussion about this!

 

[mk3223]

Great. It looks that you have got the better picture of where’s the incident and what’s happened. It could be a trouble as the Alloy20 material is used up to 150F for the sulfuric acid process.

 

[MJCronin]

Finally .... after 47 reasonable questions and aHUGE waste of time .... we have the total picture !!!

Replace your scummy gaskets with slightly more expensive gaskets rated for H2SO4 service and you are done ...

=============================================================================================================

Oh, ... and the next quection that you post .... Make sure that you leave out the most salient (look it up) details !

.... on behalf of everyone here at eng-tips ..... GOOD LUCK !!

MJCronin
Sr. Process Engineer

 

[SETXINSP]

@MJCronin nobody begged for you to come post anything so next time I have a "quection" (USE SPELL CHECK NEXT TIME FOR ILLITERACY PROBLEMS) make sure you avoid it and don't bother with your remarks that are absolutely not helpful and a waste of everyone's time. Now get back to work being a waste of space in the world.