4 replies to this topic

[cjre2]

Sirs,

We had a recent maintenance turnaround in the refinery last June 2011. One of the units which undergone inspection and maintenance is our Atmospheric Pipestill (Crude Distillation Unit), APS-2 (with two drum overhead system). Upon opening and inspection of the overhead exchangers (E-61, E-03 A-D, E-01 A-D), we have found signs of accelerated corrosion (see attached inspection results). We usually maintain the Cl content of the APS-2 Overhead sourwater within 10-30 ppm and the sour water pH within 5.5-6.5. We achieve this by injecting caustic in the crude and injection of Organic neutralizer at the inlet of E-03 A and E-03 C (see attached). On top of this, we are also using corrosion inhibitor to combat corrosion in E-03A-D and E-04 A-D as we expect water to condense in these exchangers (injection in the same region as the organic neutralizer). We are in the process of putting up a continuous water wash to help combat this corrosion but if you have other recommendations, please let us know.

In addition to the aforementioned heat exchangers, we have also seen significant corrosion in E-61 and E-01 B and E-01 D in spite of the fact that we do not expect water to condense in that section of the plant (see attached diagram). We are currently analyzing what could have caused the excessive corrosion in the overhead exchangers. As we do this, we will greatly appreciate if you can help us by sharing your experience and by enlightening us with your knowledge regarding corrosion in this type of system. Given the urgent nature of this troubleshooting, hope you can squeeze some time out of your busy schedule in helping us troubleshoot this problem. Lastly, if you have experience in processing crudes which resulted to high rate of corrosion in the CDU overhead, please let us know as well.

Should you need further details and information please let us know. Hoping for your favorable response. Thank you.

Attached Files

•  Visio-CDU Overhead_General.pdf   29.35KB   124 downloads
•  Inspection Results for E-61, E-03 A-D, E-01 A-D_General.pdf   1004.08KB   102 downloads

Edited by cjre2, 07 July 2011 - 05:12 AM.

[Technical Bard]

Continuous water wash is a good idea. Ammonia or a quaternary amine injection with this water may also be helpful.

In the upstream (dry) exchangers, there is the possibility of ammonium chloride sublimation from gas to solid phase at temperatures above the water dewpoint. This creates crystals on the steel that absorb water from the gas, producing HCl at the pipe wall. This could be part of your problem.

[cjre2]

Continuous water wash is a good idea. Ammonia or a quaternary amine injection with this water may also be helpful.

In the upstream (dry) exchangers, there is the possibility of ammonium chloride sublimation from gas to solid phase at temperatures above the water dewpoint. This creates crystals on the steel that absorb water from the gas, producing HCl at the pipe wall. This could be part of your problem.

Thank you for the reply. We will install a wash water system this year to address the corrosion in E-03 A-D. How can we verify the deposition of NH4Cl in the dry exchangers? How can we address it if we have validated possible deposition in the dry exchangers? Thanks.

[Technical Bard]

I don't have the reference handy - but there have been papers published (the earliest is from the 1940s).
Here is a website that explains it:
http://answers.yahoo...14142619AAHCbVE

You need to use the partial pressures of NH3 and HCl in the gas and determine if the fugacity (or Gibbs energy) of those gas components is in equilibrium with the possible solid phase. The link calcs it from first principles. You may be able to find a quicker empirical method on the net somewhere.

Continuous water wash is a good idea. Ammonia or a quaternary amine injection with this water may also be helpful.

In the upstream (dry) exchangers, there is the possibility of ammonium chloride sublimation from gas to solid phase at temperatures above the water dewpoint. This creates crystals on the steel that absorb water from the gas, producing HCl at the pipe wall. This could be part of your problem.

Thank you for the reply. We will install a wash water system this year to address the corrosion in E-03 A-D. How can we verify the deposition of NH4Cl in the dry exchangers? How can we address it if we have validated possible deposition in the dry exchangers? Thanks.

[cjre2]

Hello there! Thank you for your input. We are now in the process of validating if salt dew point exist in the dry exchangers. In case there is, what can you recommend to address the problem?