Valve trims and overlay.

[Jamal12345]

We are procuring ball valv manufacturer is applying 625 over lay on seats and trims. For sour and corrosive service why normally we go for trim and seats overlay. Why we do not consider overlay on other wet areas other than trims like body bonnet internal walls.

 

[The Obturator]

The ball and seats are what keeps the (Ball) Valve tight in a closed position, therefore, depending on application, it is desirably to have them free from corrosion The overlay is done as it is far cheaper than having these whole components in a special material. Other component material are dependant on level of corrosion and/or budget constraints.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Jamal12345]

Thanks Obtrurator for giving clarity on the subject.
I was reviewing choke valve drawing for the same project. I noticed that manufacturer is providing full weld overlay of body bonnet including trims. My question is that why he is doing full weldoverlay for body and bonnet why not only trims and seats.

 

[Danlap]

Good day,

Wall thickness thinning less than 10 years which may lead to external leakage is a rare occasion. But it does happen by some sort of corrosion mechanism, especially when some medium in contact with specific material. Such as pressure boundaries aka body and bonnet.
Hence, in downstream/chemical refinery, for example we normally specifies:
- sulphuric acid --> PFA/PTFE lined body
- Alkylation --> Monel body
- Hot HCI and/or higher alky percentage --> - Hastelloy C2000, Hastelloy C-22, Hastelloy C-276, Inconel 625
Not a metallurgist myself, but once I read a book which mention corrosion rate can be up to 3 mm/year shall using SS316 for sulphuric acid application.

So maybe, some of your process description might trigger the manufacturer to offer such extra over lay. No manufacturer want to see a hole on their valve body after 3-5 years in service.

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[The Obturator]

Choke Valves are seeing more fluid in contact with their body and bonnet. Im particular they most often see erosive particles in the flow, which is probably why your manufacturer has provided this option. You need to ask the manufacturer for specific reasons.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Jamal12345]

Thanks Danlap and Obturator