Gate and Globe Valves

[PipelineDeptTME]

Hi
Can someone please guide me how to specify integral/ renewable seat rings in Gate and Globe valves. When should we specify integral and when renewable? Is there any code that specifies this requirement.

Also, please advise whether all gate/ globe valves will have a back seat. if yes, is there integral/ renewable concept for that as well.

 

[gerhardl]

Hello PipelineDeptTME,

You are asking a specific question on a general basis. The answer will vary with all operation variables (fluid, flow, size, pressure, temperature, operational variables among a lot more).

The general answer is that the valve should be as simple as possible to give the cheapest cost/lifetime, considered cost of stops and main maintenance, inclusive cost and changing costs of spares.

There is no direct general technical answer to your question.

 

[PipelineDeptTME]

Thanks gerhardl, I understand that point.
Is there a specific reply on the question on back seat ?

 

[gerhardl]

Please explain what you mean in this case with 'back seat'.

 

[Danlap]

Hi PipelineDeptTME,

Align with Gerhardl, that the answer is rely on customer (risk, experience, cost over lifetime, is this engineered valves or standard item, etc.) in conjunction with manufacturer motives whether they are comfortable to supply integrated parts (that meet client leakage specification) and are they into selling spare parts/maintenance strategy?
Plus whether the effort to install new parts and its supporting activities is more expensive in comparison with buying and installing new valves

For example:
Case: Pure hydrogen high pressure system, to be blocked by single isolation wedge gate valve size 24”. To be conservative no leakage allowed through downstream (ISO 5208 Class B)
For standard carbon steel body with Stainless steel trim
As an end user, one might think that Hydrogen might passed the gap between the non-integrated Seat and body from downstream – cavity and upstream. Hence, end user will prefer integrated Seat
As a manufacturer with relatively minimum experiences, they would think whether the Seat against Body welding process can be done in one go and whether the end pressure test result will be for sure ok. If not, they must open the welding again and re-do the whole thing

But if this is for very expensive Hastelloy or Duplex body with duplex trim, then the story might be different.
Maybe End user will avoid to buy the whole valve in the future and only stock the interchangeable Seat and or back seat, spindle and gate. And make it flange instead of butt welded

I would say similar assessment for back seat. Is the function only for back-seat or also as anti-extrusion packing? Does the precision machining or tolerance can be met if it is integrated or not? Etc.

Kind 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