HP steam control valve: CS vs SS

[rusty_sim]

Hello

What are your thoughts on globe control valve body material choice for high pressure steam? The supply pressure is 41.5 barg 254C design and typically 37 barg saturated operating, which is dropped down to 10 barg for distribution to heat exchangers, process vessels etc. The control valve is controlled by a downstream pressure transmitter through a PID loop. Upstream of the valve is an automated parallel slide gate valve for auto-isolation.

I will commission my letdown station soon (end of the month), where I selected CL600 A 351 CF8M stellite trim control valves from Samson
On another project my colleague followed me but selected CL300 A 216 WCB stellite trim instead however he won't be commissioning for months

I'm working on design for a new project and am not sure which is the better material. I selected stainless previously because my manager told me we've had problems with CS valves (different manufacturer - won't name for professional reason) on HP steam before and wanted to give stainless a go.

Some background info: steam supply is typically customers scope and saturated (no superheat or accumulator) therefore quite wet. Separators are not typically installed, however me and my colleague being young are trying to convince senior engineers about the benefits of them.

Valve: Samson 3251

https://www.samson.de/pdf_in/t80520ca.pdf

Any insight would be much appreciated
Kind regards

 

[mk3223]

May clarify what's the issue of the CS valve used previously in the steam service.
Either CS or SS material are suitable for steam service if the cost is not an issue.

 

[pennpiper]

rusty_sim,
What is the material the rest of the steam system piping components including pipe, fittings, flanges, block valves, check valves, etc?

Sometimes its possible to do all the right things and still get bad results

 

[rusty_sim]

Hi gents

Cost is not much of an issue and the valve sizes are typically < 100 NB so not huge. We use bypasses to handle the large turndowns required in dairy plants. The connecting pipework is carbon steel including the flanges, valves etc. Line traps are typically thermodynamic stainless steel sometimes with downstream wafer stainless check valves. On HP line traps we tend to socket weld the check valve.

It was "bad experience," which I believe could mean the typical:
- wiredrawing (oversized valves),
- poor trapping (condensate carryover),
- trim erosion etc.

I imagine the CS would be a more wear resistant material but then SS is softer and corrosion resitant

Kind regards

 

[gerhardl]

Hello rusty sim,

This is a typical 'on the one side / on the other side' question. The problem with all steam installations is not what the piping and layout are designed for, but the very often occurring misuse over time: wet steam, improper draining and filtering, improper later additions, failing maintenance, blocked filters, operators without schooling and experience etc., etc.

With proper use of a good constructed and operated total steam system, a steel constructed valve from a renowned producer (with long-life products) should be a good solution with life length usually (almost) as long as the total installation.

In such an installation a stainless steel valve should not be necessary, and would not ad much.

If there is a fear of 'unforeseen' misuse or occurrences, or increased safety for corrosion is wished for, stainless steel valves are better.

And of course: a complete stainless steel piping and component installation is the technically best solution, cost not considered.

 

[hacksaw]

Steam purity can be important in wet steam applications, what are you seeing?

Are you dealing with continuous operation with proper deaeration, and BFW handling?

 

[mk3223]

As identified the bad actors, it seems the CS material is not the issue for the failure of the control valve. Ensure steam traps working properly, and use satellite trim for the control valve as required in the steam service.
A process improvement is to use a proper size of the control valve, which may eliminate the valve trim erosion problem, and provide an adequate operation turndown for the valve. So, the bypass valve can be used as designed to be.