H2S Corrosion at Heat Exchanger 3

[Reformator]

Hi,

One of the heat exchangers at Hydrogenation of Benzene unit have high corrosion problems and every year we change tubes. Tubes are carbon steel. Temp at shell - max:90 min:15. Temp at tubes - max:70 min: 15. Fluid at shell - Benzene + H2s, in tube: treated water.

Please, can you suggest me good and cost effective replacement of tubes, in order to resolve corrosion problem?

P.S. possible choices: grade 904L ,Grade 254 SMO, 2205 Alloy. But i dont know which one will suit better in my condition and why

Thank you in advance

 

[Chumpes]

hello
what type(s) of corrosion problem did you encounter ? (generalized corrosion, SCC, ...)
what is the fluid on tubeside ? shellside ? temperatures, vaporizing water or condensing water ?
ppH2S = ?, [H2S] in water = ?, [Cl-] in water = ?
understanding the mechanism is necessary in order to suggest another metallurgy.
regards

 

[MJCronin]

How about some pictures and the HX datasheet ?

Please also post the design drawings of the HX ??

MJCronin
Sr. Process Engineer

 

[Dhurjati Sen]

Dear Reformator,

The corrosion occurs in the shell side or tube side of the cooler?

If you have a yearly shutdown of this unit or you can take out this cooler offline every year, then maybe you are already utilizing the most cost effective approach.

Regards.

DHURJATI SEN
Kolkata, India

 

[blacksmith37]

Admiralty ( inhibited)( 70 Cu, 29 Zn, 1 Sn , + As) was the standard refinery exchanger tube material. Is there a reason not to use it ?

 

[EdStainless]

You wouldn't use a Cu alloy in H2S service, the depassivation leads to rapid dealloying.
After we have answers to the above questions we can offer some guidance.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[MJCronin]

Try this ...

http://www.stainless-steel-world.net/pdf/10073.pdf

The effects of entrained Chlorides and Co2 must also be considered as well as H2S content ...

MJCronin
Sr. Process Engineer

 

[Reformator]

Dear all

Thank you for your answers and sorry for late reply!

Fluid at tubeside is: Treated water
{ 1.Cl = 114mg/l
2.pH = 7.90
3.SO = 25.43 mg/l
4.Sulfur = 347 mg/l
5.CaCO3 = 396 mg/l
6.temp (at tube bundle):max 70 C, min: 15 C. Pressure: 0,75 MPa

Fluid at shell: Hydrocarbon + H2S
{1. temp = max: 90 C min:15
2. Pressure = 0,75 MPa

Problems are mainly at tube bundle, they are all black and corroded, I believe it is due to FeS.

Please, help me to choose right alloy

Thank you!