DYNAMIC SEAL OF BALL VALVES 1

[BFZHA]

Dear All,

I am specifying a ball valve 3/4" for a corrosive service and I am not sure if a provision of corrosion allowance of 3mm is enough to avoid any leakage problem during service or I have to specify also weld overlay for dynamic seal area?

Thanks.

 

[bcd]

A 3/4" ball valve is relatively small in size and nearly the smallest ball valve that can be made. Ordering the valve with an extra 3 mm wall thickness for a corrosion allowance is not going to be possible with standard products. It will be a special and expensive order. Same is true with asking for weld overlay for the dynamic seal. Not phsically possible to put a good weld on the sealing surface and remachining considering the size of the valve.

Unless this is a totally new service where there is no industry experience, I suggest you look at what has been used before in this service and has proven to work well. Then specify and order that product.

 

[gerhardl]

Please specify more details! A sensible answer
might exsist but are depending on the purpose of the description.

1. Description for procurement; describe details of function, fluid, pressure and flow instead of describing in detail a valve, and require valve suitable for fluid and flow conditions. Let bidders open for or suggestions of quality improvement by additional technical features. Alternatively: specify valve constructions that have proved by long standtime suitable for (exact?) similar service. Certifications : as necessary.

2. Description for sale: information as given in point 1 should be available for you through the enduser.

3. Additional remark: Sour service is often an unprecise summary of actual certificates required with complete material requirements described or necessary.

For your case: If an overlay is necessary and accepted should be answered through underlaying description of fluid and certifications described for the application.

 

[BFZHA]

Thanks for your answers,
The valves will be used for a drain of crude oil line near pig trap. After discussion with client, he ask us to consider only 3 mm of corrosion allowance according to his experience.
Even if this provision is sufficient for a pipeline, however we are not sure that it can avoid leakage.
I think a use of stainless steel can be a reliable solution regardless of cost.

 

[gerhardl]

If a high-grade SS is well compatible with the fluid I would have gone for that, both for corrosive resistance and for strength.

(For some corrosive fluid types and temperatures and additives other materials of higher (or even lower) degree could prove better)

 

[PeterIgg]

I would agree with gerhardl. The other option may be, assuming that the valve is screwed 800#, go with a 1500# rated or 4000 psi. Similarly it is almost never feasible to look at overlay on such a small valve.
However my real reason for bothering to type is: 3mm corrosion allowance on a 3/4" line?? And, as I have commented before, with that level of corrosion in a valve it will have long since ceased operating as a valve, it will just be an expensive orifice. I appreciate that many valves are installed and left open, but really, good practice would dictate that all valves should be tested for operability on a regular basis and once you have significant corrosion I suggest that you will find this during such a test.
Rant over.