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Control system integrity same as stafey valve
3

Control system integrity same as stafey valve

Control system integrity same as stafey valve

(OP)
Does anyone know of a packaged valve and control loop that could be used in place of a safety valve for venting steam. This type of system needs to have system integrity that would allow it to replace a safety valve.

RE: Control system integrity same as stafey valve

Look up HIPPS - High Integrity Pressure Protection System, although I'm not sure if it can accomodate steam plant.
HIPPS typically eliminates the use of a Pressure Relieving Device, although you need to be aware if local regulations require such.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

RE: Control system integrity same as stafey valve

you need to talk to your instrumentation and control engineers and mention SIL levels and assessments and see if they know what you're talking about.

You probably need SIL 3 to replace a spring relief.

Biggest issue is that these things normally fail open.

That's why spring reliefs are so useful. Very high reliability, but don't fail open.

Most HIPPS systems are designed to prevent high pressure in a downstream system, but could be engineered to prevent high pressure in a fixed system.

Usually 2 out of three voting (pressure transmnitters) going into a SIL rated control box and then dual solenoids say on a spring return held closed valve. All hard wired.

Total system reliability is then calculated to achieve different SIL levels.

But why??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Control system integrity same as stafey valve

Note that your plants PHA team may have a different way of crediting a controls/interlock system vs a safety relief valve. We've installed relief valves on interlocked systems because the PHA team didn't assign enough credits to the interlock to lower the risk category of the item.

RE: Control system integrity same as stafey valve

(OP)
Thanks for your replies.

The clients as asked us to investigate such a system instead of adding a lot of large (R orifice) safety valves.

RE: Control system integrity same as stafey valve

The highest SIL rating you can get on HIPPS is SIL 3, as far as I know. While an RV is considered to be SIL4. With SIL3 HIPPS, you still need to add a supplementary RV downstream of the HIPPS to account for minor SDV leaks. In many cases, the maintenance and monitoring requirements for SIL 3 HIPPS to maintain its integrity during plant operation are too ardous. Besides you need Corporate Engineering and Operations level approval for your justification.

RE: Control system integrity same as stafey valve

Well your client will likely be rather surprised at the cost.

If this is a cost saving measure, could you use bursting discs instead for a large volume flow, rare event?

Also results in complete blowdown of your steam system if it goes off.

But indeed investigate and then let us know what happens or what the order of magnitude cost difference is.

Sounds to me a bit like a blue sky thinking exercise here.

There are sound reasons why you will struggle to find anyone else doing it this way.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Control system integrity same as stafey valve

3
All,

For compliance with RAGAGEP and industry standards, HIPS (aka HIPPS) do not have to have the same PFD as a relief device. Of course, any individual company can choose to make that an internal standard, but it's not an industry requirement. Refer to API 521 Appendix E. The HIPS SIL requirement can be selected based on the case-specific hazard for the specific application.

When implementing a HIPS, the most critical consideration in my opinion is the company's integrity management system for auditing, inspection, testing, etc. If the company doesn't have a high integrity safety culture and strong internal requirement/controls, then I would avoid using HIPS. When they are used in such companies, I'd recommend designing for SIL 3. But in other companies where there's a strong integrity management system for SIS instrumentation, then I'm perfectly comfortable with utilizing HIPS. In such cases, a particular HIPS could be SIL-1 if that's what is needed to close the risk gap for that specific case.

It's not uncommon to find cases/applications in which relief devices are inadequate or unreliable. In such cases an instrumented HIPS design can often provide the safety protection that's needed. For example, one shouldn't always be satisfied with relief devices in systems that are like to cause plugging, or with relief devices that create a high risk secondary hazard if they do open. We're much better off today having HIPS in our toolkit of options. The one thing we can says that's categorically true for every case is that the engineer must always use their brain to assess what is really needed for each application.

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