API Valve Trim Type & NACE reqs (Gates, Globes, Checks)

[Krausen]

Forum - I know there have been past threads on this, but my question relates to a specific question on the company standard I'm working with on API valve trim types & NACE requirements:

Question 1) - Under the company standard I'm working with, if the process service is "Sour Water" or hydrocarbons with "Wet H2S", then all carbon steel & low alloy valve trims shall be upgraded from typical API Trim #8 to API Trim #5 & NACE certified (aka "Trim #5 NACE"). Does the requirement stand to reason? (Note our local valve suppliers do not stock or typically order any "Trim #5 NACE" valves & they claim we are the only company requiring this that they work with. When we do order "Trim #5 NACE" valves from our local suppliers, our costs & lead times are roughly double that of Trim #8 valves. If it's a rush order, the cost deltas are even higher).

Question 2) - Right or wrong, I can understand requirement for NACE certs for valves in "Sour Water" or "Wet H2S" service, but what is the logic for having Trim #5 valves in this type of service? These services are not high temperature, nor are they erosive. How does providing dual-hardfaced seating surfaces (under Trim #5) improve anything in this service type? My understanding is having a differential hardness between seating surfaces (aka Trim #8) is always ideal for long-term sealing reliability for gates, globes, checks.

 

[Danlap]

Hello,

Your questions are quite complex since it covers multiple aspects.
Lets use some baselines:
a. Non-NACE trim (spindle, obturator and seats) might subject for hydrogen embrittlement shall exposed to extended period of time with wet H2S
for example: if spindle of gate valve broken at close position, it might cause complete shut down of certain Plant. Personally been in this situation due to hydrogen embrittlement, PASCC or Stress Corrosion Cracking 3x for the last 10 years. Emergency shutdown to (re) startup can be 4-8 days ore more with losses from 500k to 1million Eur/day and reputational damage (for unable to deliver product as promised to customer).
b. Petroleum and refining industry, like it or not, is starting to become less favorite for share holders.
It used to be a Star (*Boston matrix market diagram) high market share-high growth, but now is just Cash cow (high market share - low growth) and due to no more expansion is allowed then most of the end user (read: operator not share holder) try to prevent their sites becoming Dog (low market share - low growth) or even Problem Child.
In summary: Operator will try their best to prevent emergency shutdown even if this means that they have to overdesign their valve trim requirements
c. Hardfacing especially Stellite in particular is 'hard'. Thus machining and precision lapping will be more expensive. To add that Trim 5 meaning Seat(s) and Wedge will be (full) Stellited as well.
d. Thousands of valve suppliers all over the world, which is quite saturated. End User's Procurement department may not have full overview of the competition, and only expect that there are 'cheaper' manufacturer due to this situation.

With regards to your questions:
Q1: see point a and b above. About the price, there are not so many sub-machining companies which are expert in hard facing, machining and lapping. Thus trim 5 indeed will be challenging more costly.

Q2: the logic is to prevent e.g. spindle break and left wedge in close position lead to shutdown. see point a. Indeed for example hydrogen embrittlement may be limited due to not NACE vs sour in combination with high temperature or high pressure. But to cherry picking which one should be trim 5 and which one is not (out of ten or hundred thousands valve) is also costly, thus conservative overdesign approach is used.
Stellite 6 vs Stellite 6 is less prone for galling. thus there would be no issue to use both (same grade) Stellite on wedge and seat. Also gate and globe is rate B (some bubbles per minute) as per ISO 5208 and check valve is Rate E, hence tightness is less of the concern on this matter.

PS: I am not metallurgist.

Just my two cents.

Regards,
D