Low carbon steel and caustic service

[nashchahal]

I have a steam jacketed pressure vessel made up of SA 516 GR 70 low carbon steel. It is rated at MAWP 72 psi, 350 F.and built to ASME,Section viii, Division 1. Year of manufacture was 1995. The manufacturer is now out of business.

I am thinking of changing its use and derating it to operate at 212 F, ambient pressure with 10 % NaOH by weight solution in city water and animal tissue.

I would appreciate knowing:
1.If the welds and bends were stress relieved when the vessel was manufactured.
2. Will the mild steel be compatible with caustic soda service at the conditions mentioned.
3. What type of corrosion can be expected? Is SCC an issue here?

 

[rupalredkar]

First question: To know if pressure vessel was stress relived you have to check drawings, if thickness is bigger than 1 1/2 in, then it was stress realived since it is a code requirement.

Second question: To know if it has to be stress relived for sodha caustic services, the rule is it is going to be working a temperature above 60ºC (128ºF), which it si not the case, stress realive it is not necessary.

Third question: Yes, the risk with this product it is caustic embritlement.

 

[MJCronin]

nash,

Consider asking the caustic soda suppliers (PPG, DOW and others) about the requirements for caustic soda piping and storage tanks.

Information can be found at:

http://www.dow.com/causticsoda/handl.htm

http://www.solvayminerals.com/pdf/brochures/caustic_soda.pdf

http://www.ppg.com/chm_chloralk/Bulletins/LiquidCaustic.pdf?title=Liquid.Caustic.Soda

I believe you will find that carbon steel becomes a bad material choice for caustic duty above abou 150F

Also see:

http://www.hghouston.com/index/hghouston_S.htm

Good luck....

Let us know what your final selection is and please complete this thread with that information

MJC

 

[Rich2001]

RE: 1.If the welds and bends were stress relieved when the vessel was manufactured?

Look at the Data Plate on the vessel, and the data rport it will state if it received any postweld heta treatment.

If you do not have the data report contact the Nation Board of Boiler & Pressure Vessel Inspectors

http://www.nationalboard.org/

to get a copy of it (if it is registered)