severe corrosion attack 316SS pump in liquid sulphur pit at 140C 1

[Salghetet]

Ladies and Gentlmen
submersed pump for pumping liquid sulfur was failed due to corrosion, failure was in steam jacketing tube which designed to heat sulfur inside the pump, corrosion is external, material of tube is 316SS, temperature between 130 and 150C
liquid sulfur pit is air vetilated, and level of sulfur inside the pit go up and down, vapour is expected above level of liquid sulfur
please advice me with the reason of corrosion and what is the best material to replace the tube

 

[ash9144]

Corrosion in sulfur pits is common. There will be weak acid formation from sulfur and moisture due to steam leaks. In order to answer question of what is better material you need to define how long you expect this tube to last. How long did the 316 tube last?

 

[EdStainless]

The corrosion is much worse in areas that see fluctuating conditions.
If you expect long life you will need to go to a much higher alloy austenitic stainless (alloy 20, AL-6XN or another 6% Mo grade, or even a Ni based alloy).


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Salghetet]

316 SS Tube is in serveice for around two years and expected to be in service for long time as it is in LNG company

 

[EdStainless]

In the old days when sulfur was mined using the Frasch process deterioration of the downhole equipment was a major issue.
It was more common to use standard alloys and only expect 1-2 yr life from them.
If you want long term then you need much more robust alloys.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[ash9144]

Two years is about all you will see from 316 in sulfur pit. You will need A20 or hastelloy if you want longer. I would probably just replace with 304 and plan to do it again in 18 months.

 

[Salghetet]

It is valuable information gents, I preciate
However, There are more than one pump with the same spec but only this pump which failed, the failure not repeated in other pumps
I do not have much information about operation history, so I am looking for the parameters have contributed in failure which may not present in other pits, such as moisture, Chloride and etc...
if someone help with those things which cause the failure

 

[mrfailure]

Just because the other pump steam jacketing tubes have not failed yet does not mean they are not in the process of corroding to failure. After all, something has to be the first to fail. I would not be too focused on why this was the first to go as I would be on determining damage level (if any) in the other tubes.

Aaron Tanzer

http://www.lehightesting.com

 

[EdStainless]

Because of conditions this one went first, trust me the other ones are on their way to failure.
What size tube are we talking about?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Salghetet]

tube size is one inch and failuer is in tube and also in body but not all body and tube, i think it is in area where exposure more to vapor

 

[Salghetet]

in piping class service killed C-Stl is out side the pit
LIQUID SULFUR (STEAM FULL JACKETED/OUTER PIPING)

 

[EdStainless]

The interface with sulfur vapor and damp air will be the very most aggressive.
Perhaps just splicing in a single length of high alloy tube in this zone will work for you.
We make 1"od tube in AL-6XN regularly, I can tell you has it in stock.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Salghetet]

what about coating, do not you think can work to protect external surface of pump

 

[EdStainless]

If you are looking for more than a couple of years I wouldn't go with a coating in this environment.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube