Ball Valves: Carbon Steel Trim 1

[JohnLL]

I was wondering if it is possible to use carbon steel ball and seats -without overlaying- in a ball valve with:
-oil service with no H2S no CO2
-low corrosion in pipeline, but as per DNV assumed 3mm (min. value)

The standards (ISO, API) have general expression about suitability of material. There are some specs theoretically accept carbon steel even for sour service applications.
However, any valve datasheet I have seen proposed duplex, CRA or stainless steels for trim OR carbon steel+ overlaying.

my question is:
1- considering corrosions like pitting, is it practical to use carbon steel in such a case?
2- is there any reference allows /prohibits it explicitly?
3- does using duplex/overlayed CS/CRA make delay in valve delivery (if it is the common only option, what delay means??

 

[SNORGY]

(1) If pitting is a concern you probably want a material with a higher PREN than carbon steel.

(2) I would see no reason to not use carbon steel in a ball valve if there was negligible corrosion in the carbon steel pipe on either side of it. Presumably you want the valve to seal when you close it, so as long as there is no wear or damage to the metal or elastomer as a result of exposure to the service, I assume that carbon steel would be fine. However, valve material selections are made relative to the service exposure, and while a piece of pipe can tolerate some corrosion or erosion without leaking, the internals of a valve cannot - at least not to nearly as great an extent. Accordingly, CS is typically not a good choice.

(3) I assume that they have to shape the ball, then send it out and coat it, then inspect the coating or overlay, then machine it, then send it back for assembly into the valve. This takes longer than just machining a ball from one base metal.

Regards,

SNORGY.

 

[JohnLL]

Dear SNORGY
thanks for your complete reply.
My understanding from your response is that although in THEORY it is possible to use CS, PRACTICALLY no body take the risk.

It agrees with my experience, while I have not seen any valve with just CS ball/seat without overlay.

But it remains under question, if there is no option for just "shape" the ball of CS and use it, what delay we are talking about? What I am saying is that you should at least have two options to compare and mark one as "delayed".

 

[gerhardl]

Hello both above!

To SNORGY / JohnLL: ditto (1 No, 2 Maybe, 3 Yes)

To JohnLL: A delay is always a commercial and practical question depending on freight time, available machinery, materials and operators and might in some cases be shortened by higher price.

Only way to get a relatively dependable answer is to ask for a bid or preliminary bid for the job.

If you are offering an alternative with delay: do not bind yourself to a firm date and/or offer with ample leeway. Try to get your sub-supplier to agere to penalty if late delivery.

 

[valvesarefun]

I do not think that any manufactuer will offer a valve with a carbon steel ball that is not plated with some sort of CRA. At least I know I wouldnt.

Positive shut-off requires that both seat and ball have relatively smooth surfaces, particularly in a metal seated valve. Carbon steel will not stay smooth for very long under most pipeline conditions due to the formation of surface rust, so a manufacturer couldnt guarantee with any degree of certainty that the sealing integrity will last over the life of the valve, or even beoynd the warranty period for that matter.

Nickel plated carbon steel is very commonly used for valve trim these days. Given that it is a cost effective alternative to stainless steel trim and it is readily available, I'm not sure why anyone would elect not to have the plating.