Corrosion of A249 TP316L HT exchager tubes
Corrosion of A249 TP316L HT exchager tubes
(OP)
I am seeing significant corrosion rates (.020"/yr.) on A249 TP316L HT tubes (.750",.060" AW) in rich amine service (CO removal). These shell and tube heat exchangers were replaced 3 years ago(in-kind). The previous exchangers were in service a little over 10 years. I have pulled samples and in the process of completing metallurgical examinations. I have also sampled tubes with eddy-current but was only able to inspect a small portion of the entire length of the tube due to a hard, tight black corrosion product that could not be removed(10,000 psi hydroblasting could not remove this scale completly). The areas that could be tested revealed 50%-60% wall loss from nominal "t".
Has anyone seen these type corrosion rates in this service with this type SS?
Has anyone seen these type corrosion rates in this service with this type SS?





RE: Corrosion of A249 TP316L HT exchager tubes
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RE: Corrosion of A249 TP316L HT exchager tubes
The sampling of the corrosion deposits was just completed on the SEM. The deposits consisted of 47% iron, 34% oxegen, and 17% carbon.
The high oxegen presence in the amine system was recently attributed to an upstream operational problem. Do you know the effects of O2 relative to corrosion rates in these type environments?
RE: Corrosion of A249 TP316L HT exchager tubes
You have pulled tubes? When will you have lab work?
You cannot trust ET to tell you the type of corrosion. You need to see tubes.
There are not a lot of environments that will cause general corrosion of 316. Has this unit ever been acid cleaned? What is the operating pH?
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RE: Corrosion of A249 TP316L HT exchager tubes
The operating PH noted in the last solvent analysis was 10.69. Also, All Anions (Acetate,Formate,Chloride,etc.) and Heat Stable Salts (HSAS,IHSS) were all well within the Upper limit ranges.
My only thought is during original fabrication (after solution annealing), the bundles were not cleaned,leaving scale formed by the HT process, which would not allow the protective "passive" film to form. What are your thoughts?
RE: Corrosion of A249 TP316L HT exchager tubes
pH 10.7 should be fine.
I hate to ask, but where were the tubes manufactured? Did you have people witness tubing testing? bundle fab? Was there a base-line ET run on the unit?
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RE: Corrosion of A249 TP316L HT exchager tubes
As we did not own this facility at the time of installation I do not know the extent of QA/QC that was performed during fabrication and the equipment file as usual, doesn't have much info.
RE: Corrosion of A249 TP316L HT exchager tubes
You should also do some analysis on the scale to determine its structure, not just composition.
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RE: Corrosion of A249 TP316L HT exchager tubes
RE: Corrosion of A249 TP316L HT exchager tubes
Our guiding info warns against acid gas breakout though, which can occur if the DEA is overloaded... which have nothing to do with your situation, but suggests that you may also need to look at the control and quality of the process side in your investigations... covers all your bases.
Come back and let us know what you've found. :)
Thanks.
Rob
RE: Corrosion of A249 TP316L HT exchager tubes
I have been unable to find out the specific carbon we used.
I keep thinking it was a Pittsburgh material.
Auto Clean
http://www.cuno.com/industrial/petroleum.shtml
Our biggest problem was still fouling and corrosion of the exchangers and reboilers.
The carbon towers and filters helped but didn’t completely resolve this problem. We were constantly rebuilding these tube bundles in our shop due complete plugging caused by the close tube spacing and the triangular pitch which precluded any type of blast cleaning.
The layout man in Fab shop and myself solved this problem by sneaking, (midnight plant test) in a tube bundle, reboiler, with 25% less tubes and on a square pitch. The square pitch was for cleaning if necessary. I have looked at some notes where it was deemed that preventing the hold up of the rich MEA went a long way in preventing formation additional deposits and corrosion.
When both plants were decommissioned 3 years later all exchangers were of this design. None of the square pitch bundles were ever pulled for cleaning. The onstream time for the carbon towers and filters also increased.
Hydroblasting
There are hydroblasters and there are real hydroblasters. I can't say how many times that I've caught hydroblasters changing the tips on a lance to take some of pressure off the operator when manually blasting tubes. We had one incident where blaster took out over 100 tubes in 1200 tube bundle. It got to the point that we required mechanical lancing for all tubes. Even then the selection of the tip is still very critical to keep from eroding tubes.
The operating parameters of tube blasting have to determined and watched during the each operation on a specific bundle. I developed a specific list of the operating parameters needed to clean a specific bundle especially the more difficult ones.
RE: Corrosion of A249 TP316L HT exchager tubes
We are looking at other process variables to assure flashing is not occuring. Are records are inconclusive regarding treatment of the tubes after solution annealing during the original fabrication. At this time that is what I am leaning towards but will let everyone know the final results. Thanks for all the input on this matter.
RE: Corrosion of A249 TP316L HT exchager tubes
The fouling and underdeposit corrosion are the issues to deal with.
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RE: Corrosion of A249 TP316L HT exchager tubes