Spring Material for PSVs

[ChemE08]

Hello everyone,
This is my first post but I have made use of this site a few times. A lot of great information contained within this forum.

My question is a simple one (I hope) and revolves around the spring itself used in PSVs. I recently moved to a position where I am inspecting the PSVs more than sizing/evaluation/scenario. Where I would maybe rely on vendor catalogs for spring information is there somewhere else I can look to in order to understand the options and limitations of the various spring materials. For example – let say a spring was switched from CC to SS during an overhaul. Any help is greatly appreciated.

 

[Krimskiy]

Usually, the spring materials are changed due to corrosion issues, so it's best to check with your materials engineer. You can also check API 526 tables, which provide some guidance on normal set of spring materials for various valves.

 

[The Obturator]

falmazan, One of my first replies also.

If you are looking for actual spring ranges of individual springs, then generally, this is manufacturer held information only. However, some end users, approved repair houses, do have tables issued to them (and controlled).

API-526 will only advise on the maximum that the valve is capable of. As an example manufacturer A may have 35 different springs or so to fit the same 1 x D x 2 150 x 150 spring conventional safety relief valve, covering pressures 15 to 285 PSIG, and then in one material. Manufacturer B may have more or less springs for the same.

The valve temperature limitations are governed by the minimum temperature of all the components. Hence a conventional spring carbon steel valve to NACE with Inconel spring will be limited to the maximum temperature of the carbon steel body (WCB 800 F) whilst the inconel spring is capable of much much higher.

Also, a while ago manufacturers (and API-526) changed from carbon steel springs to Chrome steel, offering a higher temperature use to some 650 F. A large number of installed SRV's still have carbon steel springs and get regularly replaced with chrome steel.
Changing set pressure and possibly spring, also requires recalculation of valve size for ongoing suitability.






Regardless, per ISO, only the term Safety Valve is used for all overpressure eventualities.

 

[EmmanuelTop]

Check Chapter 9 at

http://www.leser.com/en/tools/engineering.html

it provides reference codes as well


Dejan IVANOVIC
Process Engineer, MSChE