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 ?
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Corrosion Allowance
- Thread starter Chill5
- Start date
gr2vessels
Mechanical
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
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
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!
gr2vessels
Mechanical
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
cheers,
gr2vessels
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.
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.
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.
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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.
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