×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Failure of SS 316 Piping in Spent Caustic Application

Failure of SS 316 Piping in Spent Caustic Application

Failure of SS 316 Piping in Spent Caustic Application

(OP)
We are using SS316 piping for spent caustic lines. Facing frequent failure of piping. I understand SS316 is a good material for this serivce.

However, due to frequent failure, i have proposed to replace piping with PVC. Any comment on thic change or any other suggestion for a better material for this application ?

Thanks
 

RE: Failure of SS 316 Piping in Spent Caustic Application

My first thought was:  Do you understand why your SS piping is failing?

If you don't understand why the pipe is failing, then replacing a material (that's good for the service) with another material may not solve the problem.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

Want to post an image? Look at the FAQ's in forum559: SolidWorks 3D CAD products

RE: Failure of SS 316 Piping in Spent Caustic Application

You describe the service as "spent caustic". Why is the caustic spent? what is it absorbing, disolving i.e. what impurities is it picking up. What temperature is it running at? To assist we need more information. Also to reinforce Patricia's point you need to understand why it is failing so the right solution can be implimented. The questions posed above shoule assist you/us to propose a solution.

Mark Hutton


RE: Failure of SS 316 Piping in Spent Caustic Application

300 Series SS offer little advantage in resistance to cracking over CS in caustic services.

Nickel base alloys are more resistant to cracking and may be required at higher temperatures and/orcaustic concentrations.

“Stainless steels such as austenitic types 304 (S30400) and 316 (S31600) seem even less reliable than carbon steel for caustic service. The application limits for the austenitic SS are 50% caustic and 70°C to 90°C. The 300 series of SS also suffer caustic cracking at temperatures above 100°C.The cracking susceptibility of either 304 or 316 SS is the same and sensitization does not seem to play a role. Problems rarely occur when the NaOH concentration is limited to 10-20%.

The best metallic material overall to handle caustic solutions at all concentration and temperatures is Ni-200 (N02200). Ni-200 can be used even in molten anhydrous NaOH at temperatures as high as 538°C (1000°F).”

If I were you I wouldl use a carbon steel tank for spent caustic services with the requirements bellow.

Cracking can be effectively prevented by means of a stress-relieving heat treatment (e.g. PWHT). A heat treatment at 1150°F (621°C) is considered an effective stress relieving heat treatment for carbon steel. The same requirement applies to repair welds and to internal and external attachment welds.


luismarques

RE: Failure of SS 316 Piping in Spent Caustic Application

spent caustic covers a lot of compositions and cannot be equated to NaOH solutions in water as a basis for material selection.

Are you really planning to use PVC ? What size line and what temperatures?

RE: Failure of SS 316 Piping in Spent Caustic Application

ak.....

OSHA, NFPA and ASME contain cautions about the use of FRP/plastic pipe and plant accidents.

For some fun beachside reading, visit www.csb.gov and read the report about the methanol tank explosion and the death that occured because of plastic piping components.

http://www.csb.gov/index.cfm?folder=completed_investigations&page=info&;INV_ID=57

Plastic/FRP pipe is useful only to very modest operating temperatures. Hope that yours are not too high....

My opinion only

-MJC

  

RE: Failure of SS 316 Piping in Spent Caustic Application

Spent caustic solution from scrubbing HCl or HF fumes could account for attack of 316 SS.

Without composition info, pH & temperature of the 'spent caustic,' it's impossible to give a definite answer.

RE: Failure of SS 316 Piping in Spent Caustic Application

ak1965,
where are you?

Mark Hutton


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources