H2SO4 tank nozzle failure 4

[AllenCasteel]

We have a 10,000 gal carbon steel tank with desiccant dryer for 98% sulfuric acid. The tank is approx. 10 years old and shows no sign of significant corrosion or erosion. However, the outlet nozzles to our pumps have a very high failure rate.

2 months ago one of the nozzles failed. It had a very deep groove on the top of the nozzle. The other nozzle had the same problem. We replaced both. I am told that they had been replaced less than 2 years earlier.

One of the new nozzles failed over the weekend -- less than 2 months in service! It shows the same problem; deep groove in the top of the pipe. I am baffled.

I know a little about hydrogen grooving and this is what I would expect to see -- but in 2 months? Any ideas? Nozzle design/orientation? There is talk of replacing with a 316L SS nozzle, but I have reservations about dissimilar metals.

Any help would be appreciated.

 

[NickelMet]

Any chance to get a picture of that nozzle posted?

~NiM

 

[AllenCasteel]

I can e-mail a pic of the failed nozzle. Don't know how to post one.

 

[metengr]

AllenCasteel;
We use 80 - 93% concentrated sulfuric acid for our feedwater treatment systems and we had ran across this situation several times with our carbon steel holding tanks. The reason for the hydrogen grooving is concentrated acid flow thru the carbon steel nozzle. The flow of concentrated sulfuric acid erodes the protective iron sulfate layer on the carbon steel, similar to an erosion/corrosion mechanism. The corrosion results in hydrogen evolution causing the grooving.

To alleviate this problem we had to install AISI Type 316 SS nozzles for acid flow rates less than 8 fps. If the acid flow rate exceeds this value, you might need to upgrade to an Alloy 20 nozzle. The dissimilar metal weld will not be a problem in this application because your anode (steel tank) to cathode (SS)area ratio is large. As a side note, keep a close watch on the concentration level of the sulfuric acid in the storage tank. Any moisture will reduce acid concentration ( below 70%) and result in local corrosion attack to the carbon steel vessel.

 

[JoeTank]

The max flow rate thru carbon steel piping is normally limited to 2 to 3 fps. Sometimes large CS shell nozzles are used, then reduce down to SS pipe at a faster flow rate. I think about 6 fps is typical for SS pipe.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[NickelMet]

Allen:

Follow this link -

http://www.meic.com/Newsletters/2003/Winter03.htm

There is a picture of some hydrogen damage in a sulfuric service line. Read the article and see if you can apply their thinking.

As for getting a pic, I don't think we can post on the BB site. If my profile is working, it should list an email to contact me. (Profiles weren't working at last check...)

~NiM

 

[AllenCasteel]

Thanks for all the replies. The information about the acceptable flow velocities for different materials of construction is very useful.

I think we solved our problem. It looks like a downstream check valve was allowing water to weep into the acid piping while the pump was shut off. The piping is Teflon-lined all the way back to the tank nozzles, so only the nozzles showed the corrosion. There was an automatic double block and bleed on this water line that had been abandoned -- probably because it needed maintenance.

This is why I had reservations about changing materials of construction without finding the true cause of the failure. Down the road something else would have failed.

Thanks for the help.

 

[metengr]

Allencast;
Interesting find. If the water made it to the nozzle it could have gone further back into the tank as well, adjacent to the nozzle. When the opportunity presents itself, check the thickness of the carbon steel wall for several inches above the entire nozzle. You might have locally corroded the tank wall above the nozzle during this time.

 

[MJCronin]

AllenCasteel,

SteveB and metengr are correct about the use of SS for nozzles with high H2SO4 velocities.

For a more authoritative source to support your decision, I suggest that you purchase a "Recommended Practice" published by NACE.

NACE RP-0294 discusses the design of sulfuric acid storage tanks and "sleeved nozzles" for H2SO4 storage.

Also, see these links:

http://www.nace.org/nace/content/technical/ctw2k4Agendas/stg34/TG300draftOR.pdf

http://www.hghouston.com/dcforum/DCForumID1/131.html

By the way, are you causing erosion in the inlet piping to the tank when you refill it ?....Do you have an internal "dip tube " inside of the tank and does the tube strike against an impact plate welded inside of the tank ?

Come back with more specifics about your tank....

My opinion only.......

MJC

 

[AllenCasteel]

M J Cronin,
Where can I purchase a copy of NACE RP-0294? I searched their web site and can't find it anywhere. Do I have to be a member to buy?

We do not have an internal dip tube on the fill pipe. The tank is filled from the bottom which serves the same intent. I do not like bottom-filling, but it's not my design. We have not seen corrosion anywhere except the outlet and recirc nozzles where the water was discovered.

Allen

 

[NickelMet]

Allen:

That document has been withdrawn (currently inactive). I don't know if anything replaced it. However, you can order it from IHS I believe. (

http://www.ihserc.com)

There are other sources for sulfuric acid items. Try the Nickel Institute (

http://www.nickelinstitute.org)

for one. Documents they have:

#1318 - THE CORROSION RESISTANCE OF NICKEL-CONTAINING ALLOYS IN SULPHURIC ACID AND RELATED COMPOUNDS (1983)

#10057 - SELECTION AND PERFORMANCE OF STAINLESS STEELS AND OTHER NICKEL-BEARING ALLOYS IN SULPHURIC ACID (1990)

I may have other documents in my library and I'll look. If there is anything I can point you to on the web, I will.

~NiM

 

[MJCronin]

Also see this link on H2SO4 systems design..

http://www.genchemcorp.com/pdf/tsr5078.pdf

MJC

 

[aybee]

the nozzle wasn't a seamed grade was it? sounds like preferential attack on a weld line?..Aybee