Segmental Retainers in Pressure Seal Bonnet Valves

[Piper_at_work]

We are purchasing a pressure seal bonnet gate valve in CF8C body with Trim 17. The vendor is providing segmental retainer in A182 Gr F6, they are insisting that since the retainer has to bear heavy thrust, F6 is the best material to go with. The gasket support ring (below segmental retainer) is in SS347. I have apprehensions about the corrosion of segmental retainer fitted in SS347 body.

I would like to know if F6 is an acceptable material.

 

[Danlap]

Hello,

It is a general courtesy in this forum to greet. Despite the fact that we all have problems which requires (free) advise asap.
Your explanation is not clear enough, a general drawing from your side would be helpful.
I can only assume this is Class 900# or above. Size 2"? (since bigger sizes commonly come with membrane design of which you did not mention).

below is my two cents. Assuming this is the (similar) ring position you've mentioned. We used AISI 410 and in some we use Aluminum.
the sealing capability is much more important than corrosion resistance in my view.

Heavy thrust= yes. But it also required to elastically deformed to seal. this is practically like an RTJ for flange.

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

 

[Piper_at_work]

Thanks for the valuable information MR!

Yes the valve is 2" and class 1500. I have attached a similar drawing to clarify my question above (can't post actual vendor GAD).

So from what you said, is it safe to assume that a segmental retainer of AISI 410 in a valve with SS347 body and trim won't have bad consequences? Is there any general practice to use the same material for segmental retainer as the valve trim? Because as far as I know, there is no governing standard for the same.

Regards,
Piper

 

[TugboatEng]

The segmental ring is not exposed to the process fluid therefore doesn't need to be resistant to the process fluid. If your valve were installed inside of a tank or in a marine environment where corrosive conditions are atmosphere side of the valve then the 410 segment ring would be a problem.

 

[Danlap]

Hi Piper,

I agree with TugboatEng, segmental ring indeed is not supposed to be in direct contact with process fluid, so no need to make it from similar trim material.
Just saw your drawing, we also had some of this installed (not the 30 years old Ring-O valve of my earlier snip). Mainly used in my refinery for steam and/or hydrogen services.
Please do not simplify my below comments, as I don't know your product, how many cycles and lifetime expectancy
AISI 410 in a valve with SS347 body and trim won't have bad consequences? Risk is ALARP
Is there any general practice to use the same material for segmental retainer as the valve trim? Not that I'm aware of. Again segmental ring is not supposed to be in contact with product.

Further disclaimer:
- it does in contact with your outside environment e.g. rain, corrosive sea environment, etc. So this is a factor to be considered.
- As mentioned earlier, bigger sizes with membrane, smaller sizes (<2") with this ring. However failure modes are mainly the same: corrosion and fatigue lifetime. Why fatigue? it follows ups and downs of pressure fluctuation inside the valve. Which one will goes first? In my refinery fatigue hits first after 20,000 cycles (approximately 10-15 years). Imagine this as our respiratory membrane. Corrosion take effect several years after that (we do have some valves exposed to corrosive environment).
This is not a maintenance-free valve, we need to inspect the ring/membrane every other 2-3 shutdown or TurnAround.

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

 

[HitokiriAoshi]

As previously mentioned, the valve meets the standard requirement. As segment ring is not in contact with fluid.

Now, let's break down what the segment ring is supposed to do. Its primary job is to provide a packing against the upward load of the gasket, and it does not perform sealing function, which is achieved by the bottom edge of the pressure sealed gasket. As such, even if we assume this material is slightly corroded, there would be no difference in function.

One need to think why 347 was selected in the first place, typically it's selected for thermal reason. If the 410ss satisfy the thermal and strength requirement, i would approve said valve for usage, unless the valve is is currently at the valve manufacture AND there are no delivery difficulties, otherwise, there are much bigger fish to fry.

Regards,

Luke | Valve Hax |

https://valvehax.com/

 

[mohan55]

Hi, Considering segmental ring as pressure containing part and trim 17, F6 is not acceptable.

Duplex grade to be used.

In order to withstand high thrust, segmental rings to be sized accordingly.

Thanks and Regards,

G Mohan

 

[HitokiriAoshi]

^-- incorrect information, just fyi.


Luke | Valve Hax |

https://valvehax.com/