Weld Overlay of Sealing Areas

[nickypaliwal]

One of our client asks for weld overlay on sealing areas only if Lip-Seal is used for Ball Valves.

If a valves with Lipseal type sealing is recommended to have seal areas with weld overlayed, is it due to corrosion of seal areas or due to corrosion of spring used in lipseal ? If a valves with Lipseal type sealing is recommended to have seal areas with weld overlay, is it due to corrosion of seal areas or due to corrosion of spring used in lipseal ?

 

[valvit]

Lip seals need a very smooth surface finish to provide an effective seal. Any corrosion in the seal area will allow the lip seal to leak, thus the need for the corrosion protection. The lip seal itself, should use a spring made from a corrosion resistant material.

Valvit

 

[nickypaliwal]

Does corrosion of sealing areas due to galvanic corrosion from spring is considered ? I reviewed the Lip Seals design of parker and found that U -Lipseals which is generally used for our client does not have spring in direct contact with the sealing area. PTFE is in contact so galvanic corrosion should not be a concern.

 

[valvit]

I would agree. Since the spring is jacketed by the PTFE, you should not experience galvanic corrosion.

Valvit

 

[nickypaliwal]

Why should then we ask for weld overlay on seal areas for Carbon Steel Valves?

 

[ApC2Kp]

The common carbon steel gate/globe/check valves with metal to metal seats use different materials for trim & provide longer life for shut off. Small amount of corrosion or erosion of body does not result in leak failure, but small amount of corrosion in seat area results in leak-thru that could quickly exceed allowable amount. See API Std 600 for trim numbers 1 to 18.
Ball valves with soft seat PTFE would have little problem of corrosion for the PTFE.
PTFE lip seals have been observed to cause 'fretting' on stainless steel pump shafts. Some add a ceramic coating to pump shaft in area of PTFE lip seals. Surface oxides might get embedded in the PTFE to result in abrasive edge on PTFE lip seal? Ball valve cycling open-closed would not be comparable to pump shaft rotation velocities.

 

[PeterIgg]

My experience is that the reality of the situation is that if you do not use a CRA overlay for your lip seals you will live to regret it! Lip seals are not as forgiving as O rings. Any moisture that gets into the seal area on carbon steel surfaces will cause corrosion which will compromise the seal. Even if your line service is clean, dry gas, the valve will probably be hydro-statically tested, as well as the line into which it is fitted. Try as you may, the reality is that getting all water out of a ball valve after hydro testing is next to impossible without fully disassembling. Secondly, unless stored in a dehumidified environment it is likely that condensation will form inside the valve at some time during storage.

Irrespective of your intended service, using a CRA overlay in the lip seal area is a cheap form of insurance compared to reworking valves after installation.