H2S Contamination of a propylene sphere 1

[0707]

We have a propylene sphere, which is feed from a FCC gas concentration unit and has been highly contaminated with lets say 2000 PPM of H2S, because of incapacity of mercaptans removal in downstream Amine treating unit. We think that there is a great possibility to have induced Hydrogen. First- what kind of NDT would you recommend to see if we have HIC? Ultrasonic Backscatter? Acoustic emission? Metallography replicas? What kind of on stream inspection could be done? Second-If by NDT we will find HIC, before repairing, how do we get ride of induced hydrogen. Forum empathy on this subject would be highly appreciated.

Thank you very much in advance Best Regards

Luis Marques

 

[unclesyd]

Comeback with a little more information on the spheres such as material, pressure, temperature, water, exposure time, and so on.

We contaminated two butane spheres with H2S not once but twice. The spheres were AE tested and nothing was found. After the second excursion AE testing again showed no problems. The oldest sphere was isolated and the lower half was tested using an exhaustive MT test, no cracking. There have been two additional AE test, at 3 years and 7 years with not problems.
Both spheres were cleaned due to crap on the walls for the butane.

Back when AE testing first came on the secene we tested two anhydrous NH3 spheres and the results scared the hell out of us. AE will find cracking.

 

[0707]

Unclesyd

Thank you very much for the empathy.
Our sphere has suffered H2S contamination during about three weeks.
Sphere plate material is P335NL1 NF-EN 10028.3 with the following composition: C-0.138, SI-0.48, Mn-1.55, P-0.011, S-0.0004, Al-0.041, Cr-0.032, Cu-0.016, Mo-0.009, N-0.0058, Nb-0.027, Ni-0.039, Ti-0.002, and Fe-Bal.
It is a low S plate.
The sphere was PWHT.
Operation temperature is 40ºC.
Working pressure is 15.5 bar g.
Your AE was done with the sphere on stream? Is it AE really accurate? Let me know in more detail about this subject.
Receive my Best Regards
Luis Marques

 

[unclesyd]

I am not familiar with you MOC but the analysis and thermal history look pretty good from the material side.

I’m trying to get the exact conditions used in testing of the butane spheres. They are tested online at planned intervals. The only problem comes with the coordination of the testing with production demands.

I don’t think the accuracy is a concern at this stage of the game. Early on there was there were concerns but these were quickly dismissed when we checked the first NH3 sphere. The sensitivity even of the earliest equipment was demonstrated by the breaking of a 2H pencil lead between 4 transducers. The resulting signal drove the oscilloscopes to full scale.

I have included some information on sites that have additional information. The Dunegan site is one of the pioneers in the business. The PA site is supposedly the cream of the AE testing services. The information on MonPac concerns the analytical system used to analyze the results. The data is relatively easy to get but analyzing it is the hard part. There is an article on the ASTM Standard.

We helped pay for the development of MonPac system as being the first real user and Dr Fowler, the developer, was a employee at the time. The AE equipment was Dunegan-Endevco. There are two of the original systems in storage at our lab. One thing is that they use far less transducers that when I was directly involved.

http://www.deci.com/index.html

http://www.pacndt.com/

MonPac

http://www.pacndt.com/index.aspx?go=training&focus=MONPAC-PLUS.htm

http://www.pacuk.co.uk/FieldTestServices/Oil&Gas/monPac.htm

http://www.matrixie.com/nh3.htm

ASTM Standard

http://www.astm.org/SNEWS/OCTOBER_2003/carlos_oct03.html

 

[0707]

For the forum information on this topic, at last we have the opportunity to make an intrusive inspection to the propylene sphere, which was highly contaminated with, lets say 2000 PPM of H2S, in April/May this year. The inspection is still in course and at the moment we found through MP (Magnetic particles) lots of relevant crack indications in HAZ. We will keep going on with MP inspection because the half top part welds of the sphere haven’t yet been inspected.

Regards

Luis Marques

 

[0707]

For the forum information on this topic.

On sphere top dome, we found on weld edges, about 100 cracks 2 mm deep, by MPI inspection.

On top circular weld, we found through TOFD about 90 indications of defects between 11mm and 22mm deep up to 600mm length. TOFD operator says that defects indications are similar to lack of fusion weld indications.

By the codes all the above defects should be repaired.

Mean wile to evaluate HIC we are going to do replicas and also micro hardness at the HAZ, at the parent metal, and also in un-affected portions without crack

Plate thickness is 40mm

Luis Marques