×
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

alternative to MOS2 coating on inconel 718 to avoid SCC?

alternative to MOS2 coating on inconel 718 to avoid SCC?

alternative to MOS2 coating on inconel 718 to avoid SCC?

(OP)
We are installing flanges on a ahigh temperature steam line, and the flange seal ring normally is supplied with a baked-on MOS2 molybdenmum disulfide coating. The service is steam service to 500-540 C ( 932-1004 F).

We have been advised that MOS2 forms H2S when exposed to steam, and will cause SCC on high strenght alloys such as inconel 718.

Can anyone confirm this is an issue with a baked on MOS2 coating, or can advise an equivalent graphite style coating to be used in lieu of MOS2?

"Nobody expects the Spanish Inquisition! "

RE: alternative to MOS2 coating on inconel 718 to avoid SCC?

What is the decomp temp for MoS2?
You could look at HBN (hex boron nitride) or WS2 (tungsten disulfide)

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: alternative to MOS2 coating on inconel 718 to avoid SCC?

Trying to understand the why - the INCO 718 flange has the MoS2 coating to prevent galling or diffusion bonding of the flanges when made up? Would nitriding the flanges help? Boron nitride spray may work too, but like graphite spray coatings it's not very permanent - you would apply it just before making up the flange joints.

RE: alternative to MOS2 coating on inconel 718 to avoid SCC?

To avoid galling of the seal ring during assembly, I would use graphite versus the MoS2 baked coating.

RE: alternative to MOS2 coating on inconel 718 to avoid SCC?

Sounds like a Grayloc seal ring, and if so the coating is necessary for more than just the initial mate-up. Being a pressure energized seal, you would expect some movement with pressure fluctuations. Can't suggest a coating alternative for you that will be durable under those conditions.

RE: alternative to MOS2 coating on inconel 718 to avoid SCC?

WS2

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: alternative to MOS2 coating on inconel 718 to avoid SCC?

(OP)
It looks like we may use MolyKote P-37- works well at HP steam turbine inlet casing and valve flange bolts.Graphite would work as well, but the seal ring supplier has not accepted that solution.

"Nobody expects the Spanish Inquisition! "

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