×
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

Corrosion Allowance

Corrosion Allowance

Corrosion Allowance

(OP)
We have customers requiring a min. of 6MM of corrosion allowance on valves. These are 1" A105 Material gate valves.  Can anyone explain what spec. that corrosion allowance can be calculated from.  We are unsure what this really means and how to answer our customer. Is this on the Body, Seat or Disc ?

RE: Corrosion Allowance

Chill5,
The corrosion allowance must be added to every wetted carbon steel surfaces. Hoever, I have doubts that 6 mm corrosion allowance can be applied to 1" valve of any kind. Perhaps change the valve material to a corrosion resistant grade of stainless steel.
cheers,
gr2vessels

RE: Corrosion Allowance

I am always slightly bemused by the requirement for a corrosion allowance in a valve of any kind. Surely by the time there is even 0.5mm of corrosion, let alone 3mm or 6mm, on a seal face it won't be much of a valve, just an expensive resriction? Maybe someone can enlighten me!

RE: Corrosion Allowance

If I'm not wrong, any valve in corrosive application has the trim, valve seat, etc..in a corrosive resistant material, therefore the corrosion allowance would apply only to the housing and non-essential components or replaceable components. That's my understanding of chilly's post.
cheers,
gr2vessels

RE: Corrosion Allowance

Peterigg,

Your statement is correct. Any coorsion in sealing areas will definetly compromise valve tightness. Also, wherever corrosion allowance is required, we should consider it for all parts except areas where sealing function is required.
When required, we design the valve wall thickness as per applicable code on which we add the required corrosion allowance thickness (not included in wall thickness) calculation. If static sealing design is such that corrosion will not affect the sealing, will leave it as standard. In all other cases and specially for dynalic sealings (stroke or rotation) we apply a corrosion resistance coating in the specific area. Can be Nickel plating, Stainless stell overlay or greater depending on service conditions.
Easy solution is to supply a corrosion resistant valve but for large valves, it is more economical to call for carbon steel valve body with corrosion allowance.

RE: Corrosion Allowance

Hi,

For this size of a valve I think 6mm CA is a lot. I doubt if the client really mean this type of a requirement as generic for the complete scope of valves.

If really required it is indeed better to consider a SS body if allowed for the pressure rating. I agree with gr2vessels.
What is the pressure/temp rating by the way?

In other specifications I noted to use weld overlay of the seat pockets if a CA is above 3mm.

Success

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