×
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

polythionic acids

polythionic acids

polythionic acids

(OP)
What is polythionic acids?

RE: polythionic acids

The most common fluid causing intergranular corrosion in hydrocarbon plants is polythionic acid.  Both austenitic and straight chromium grades of stainless steels can be attacked by polythionic acid.  This phenomenon is usually an internal problem, occurring on the process-exposed side of a piping run, vessel shell, exchanger bundle, heater tube, etc.  The phenomenon usually starts with the stainless steel surface forming a thin iron sulfide film because of exposure to small amounts of sulfur, usually from hydrogen sulfide in the process stream.  During a shutdown, in the presence of air and liquid water, often dew point water, the sulfides convert to polythionic acid.  The polythionic acid then corrodes the chromium-depleted grain boundaries of the sensitized alloy.  Since stainless steels are usually supplied to fabricators in the solution-annealed condition, sensitization is usually confined to weld affected zones.

K. Phan

RE: polythionic acids

To add to K Phan's excellent description of how polythionic acids form and what they do to sensitized stainless steels, they are weak sulfuric acids with the formula H2SxO6, where x is usually 2 to 5.  ASTM G35 describes procedures for testing SS in polythonic acids at room temperature to determine relative susceptibility to intergranular SCC.

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