Valve Trim Design / Material Selection 2

[GainControl]

Can someone suggest a good source to guide in the design of a gas control valve trim (plug and seat) set? I must comply with NACE MR0175.

Some of my questions are...

> What are my material options?
> What should I specify for hardness requirements (plug versus seat)?

Thank you in advance for your reply.

 

[israelkk]

Usually this is a company know how and trade secrets. If you are trying to do it yourself then you should be willing to invest time, money and a lot of frustration until you succeed.

 

[dtn6770]

In a previous life I used a piping "NACE" specification that called for plug valves to have A216 WCB bodies, 316 SS trim, and teflon sleeve material. Sorry, no information on hardness criteria. I haven't broused MR0175 in some time but I'd expect it to address that to some degree. Good luck.

 

[Ashereng]

I would think contacting NACE would be a start.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[abscott]

GainControl,
Assuming you are a user of valves I recommend you talk to the valve supplier and get their recommendation. Some of the preliminary questions I have are 1) what is the gas?,2)what type of valve is this?, and 3) how big is the valve?

Typical valve trim materials are:
316 SS - ASTM A351,CF8M (cast)--- Notes 1,2
316 SS - ASTM A479,GR316,A (bar)--- Notes 1,2,3
416 SS - ASTM A487,CA6NM,CLB (cast)--- Notes 1,4
416 SS - ASTM A582,Type 416,A (bar)--- Notes 1,4
Note 1 - Any weld must be done to NACE welding procedures. Avoid this at all costs.
Note 2 - Material hardness HRC 22 Maximum, no cold working allowed.
Note 3 - Must be in the solution annealed condition per supplimentary requirement S5.
Note 4 - Material hardness HRC 23 Maximum, no cold working allowed.
Hope this helps.
Regards,
ABScott

 

[GainControl]

The gas is natural gas. The valve is a right angled control valve, 2 NPS.

316 SS is a strong candidate. I don't think 416 SS is allowed per NACE because it is a free-machining martensitic SS. The other material under consideration is 410 SS.

My other dilema is the hardness. I believe I need some delta hardness between the plug and seat. If I specify my plug hardness at the max allowed per NACE (22 HRC) what should my seat hardness be?

Thanks

 

[abscott]

GainControl,
The choice of valve trim material is largely based on service conditions (Temperature & Differential Pressure.) You can use 316 SS up to 300 psid and about 600F. Beyond these boundaries the hardened materials are generally used (17-4PH, 410SS, 416SS) but to reduce the corrosion potential NACE requires these materials to be in the "passivated" condition. For reference (Part 3):
17-4PH - double age hardened HRC33 max (table A.27)
410SS - austenitized/double tempered HRC22 max (table A.18)
416SS - austenitized/double tempered HRC23 max (table A.18)

Beyond this, would be the base material to which a coating such as hardfacing is added.

Generally valve plugs and seat rings are made of similar materials with similar hardnesses. For general service valves the HRC 33-38 is very poplular, therefore I would suggest using 17-4PH in a NACE valve.

The concept of "differential" hardness relates to valve trim components that slide on each other. Galling is an ever present danger especially in the 300SS and softer materials. A general rule of thumb is any sliding parts should have 6-10 points HRC differential.
Hope this helps.
ABScott

 

[JimCasey]

Abscott gave you all the good poop about material hardness. Please, Please don't specify the valve from a molecular level. It is so easy to specify something nobody makes that way, so you will either get no bids or finance an R&D project if you do that. Specify the valve you need, then specify that the materials must be in conformance with NACE MR0175. Then evaluate what the vendors offer and pick what you think will work best.

Delta hardness between plug and seat in a globe valve is not usually required, but it is required between the stem and guiding surfaces. The plug should not rub against the seat, just be compressed avainst it. Galling only happens with sliding contact.

 

[Scotsinst]

Be very careful. Up till NACE MR0175-2002 the guidelines were very simple. NACE MR0175-2003 is very different. For example 17-4PH sst is not allowed in any condition in the most recent NACE for pressure containing parts (stem is considered pressure containing). For refinery applications then check NACE MR0103 which is similar to the older NACE MR0175.
Metso have a good guideline which may be available from their website T101-4-4/04 which explains material selection for their Jamesbury ball valve line.
In the old days, 316sst trim (w stellite if required) and heat treated and stress relieved carbon steel body were the only requirements (max rockwell C of 22). It's much more involved now. I agree with the other posts that you should go to several vendors and see what they offer.
You need to know which NACE MR0175 version you are using because the price difference may be great.

 

[GainControl]

abscott-

I hope this message finds you...

Can you tell me the source of your statement: "You can use 316 SS up to 300 psid and about 600F."? I would like a reference that shows my rationale for ruling it out.

Thank you!

 

[abscott]

GainControl,
Sorry for the late post but I have been out of the office several days. The 300 Series Stainless Steels are excellent trim materials for valve trim because they have high corrosion resistance to a wide variety of chemicals. They are however fairly soft and in applications where the velocities are high or there is a substantial energy drop across the trim damage may occur. Even at low pressure drops but with elevated temperature damage may occur.

The maximum pressure drop of 300 psig and maximum temperature of 600F is not in any standard but is a valve industry "rule-of-thumb". If you have any valve manufacturers catalogs (e.g.Fisher) you may find "Trim Charts" that are temperature vs pressure charts that describe the areas where various trim materials may be used. The 300 Series Stainless Steels are blocked-off in the area below 300 psig and 600F. This restriction is for 300 Series trim without hard facing.

Above this region the 300 Series must be hard faced to protect the base material from damage.
Hopes this helps.
Regards,
ABScott

 

[MARKFLOW]

Contact

http://www.mogas.com.

Mogas purchased a patented gas control valve trim for ball valves last winter, called Flexstream. It has some very unique features. MARKFLOW