Spring Material for Relief Valves 2

[nickypaliwal]

Our vendor has supplied SS Spring for Relief Valve in place of Inconel X750. Can we accept it for portable water service ??

Also which standard should I refer for Valve internals as General Piping Specifications by Shell only says about Inconel 718 and 750 for spring material.

 

[OGMetEngr]

If the customer spec requires 718 or X750 for the spring material, then that's what should be supplied. As for the suitability of SS springs in potable water, well that depends on which SS grade, temperature, water composition and impurities, flow rate, etc.

 

[metengr]

Pressure relieving devices (PRD's) on pressure retaining components constructed to ASME Boiler and Pressure Vessel Code and ASME Piping Codes are designed and built by a manufacturer that has certified their PRD design in accordance with the National Board Safety Relief Valve Certification program. I am sure there are international standards which provide guidance for PRD's for use on non-ASME components.

Typically, PRD selection is determined by the qualified vendor with input from the owner/user or design firm. Materials for valve internals are based on the PRD manufacturer. So, the bottom line is there is no standard which provides this specific guidance. The owner/user or design firm must work directly with the vendor for a PRD valve.

As long as the vendor is in agreement with your stated service conditions, I see no reason to not accept the valve for service.

 

[metengr]

Also, you should investigate why the limitations for Inconel 718 and X750 and are they limited to PRD's in specific service conditions versus potable water service.

 

[nickypaliwal]

Is there any document , code and standard for reference.... how should i check the applicability and where?

 

[nickypaliwal]

As per API 526, We can use CS and Alloy Steel for spring of relief valves for Air and Water Service. Please suggest any specific reason for use of X750 over SS in portable water service @ Temp 52 Deg C.

Also where can I check suitability of SS or CS for Spring..

 

[EdStainless]

Given the range of Cl and chlorine content (with risk of chloramines) in potable water I would not use a heavily cold worked SS spring.
CS with an appropriate coating would work, but a Ni alloy would be easier and safer in the long run.

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Plymouth Tube

 

[metengr]

The reason you can use carbon steel and alloy steel is because the spring is not submerged or exposed to potable water. This is a relief valve. The spring is external to the valve body.

 

[nickypaliwal]

Thanks for clarification. I used to believe there are both types of relief valve, spring as wetted and non-wetted part. Can we use SS Spring in a CS valve for portable water@ 52 Deg C ??

 

[metengr]

For wetted service, no, I would stay away from an austenitic stainless steel spring. For non-wetted service, no issues.

 

[nickypaliwal]

What could be the reason for not accepting ASS in wetted service ?? Also can spring be wetted part in relief valve ?
Is it corrosion ?

 

[EdStainless]

Corrosion (either pitting or stress corrosion cracking) would be why you would not want to use a SS spring in wetted service.
There are pressure regulating valves where the springs are wetted.
In most true relief valves (not supposed to actuate)

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Plymouth Tube

 

[OGMetEngr]

A customer may specify a Ni-base alloy spring for situations where the cost of failure/replacement outweighs the added cost of the Ni alloy. They could also specify in situations where the process conditions may change in the future (even if current process conditions are acceptable). These are a couple of examples of less obvious reasons for specifying Ni-base alloy springs. The comment by EdStainless sums up the primary reasons why SS springs are not ideal for this service.

 

[tbuelna]

718 Inconel is a heat treatable alloy, unlike austenitic stainless steels. If the spring is subject to high cyclic fatigue loading conditions, 718 Inconel would give better performance than austenitic cres alloys.