comparison between relief system and HIPPS system 1

[hassann]

hello every body
my question is about comparison between relief system (psv and its flare system)and HIPPS system
with respect to RAM and SIL study.
Which following is true or false?
1. Maitainability of the psv systems is better than the HIPPS system.
2. Availability of the psv systems is better than the HIPPS system.
3, Reliability of the psv systems is better than the HIPPS system.
4. SIL Level of the HIPPS system is 3 and more than the psv system.
5. In general psv system has more cost of HIPPS.
6, with respect to environmental aspec HIPPS and PSV systems are almost equal.

Best Regars, Hassann

 

[KevinNZ]

There a reason there a lot more PSVs in service than HIPPS systems. If HIIPS was easy and cheap everybody would do it.

 

[The Obturator]

Be aware that to use a HIPPS (High Integrity Pressure Protection System) in lieu of traditional Pressure-relief Devices, you must satisfy certain provisions. For example. If the system is designed to ASME, it must follow the Rules laid down in ASME XIII Part 13 - Rules for Overpressure Protection by System Design. This further breaks down into whether the pressure is self-limiting or not self limiting.


*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[LittleInch]

Very few things are that black and white.

And you need to define "better". Cheaper? Less time?

2 and 3 should be very similar

4. I'm pretty sure a spring relief has at least SIL 3 rating
5 Usually the other way around IME.

6 Impossible to say. Often something like a HIPPS system is used where a relief system isn't feasible or where a release could escape to the environment. To me the question is meaningless without specifics or context.

Is this for a thesis or something?

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

 

[shvet]

1 - depends on PSV construction
2 - site dependent
3 - site dependent
4 - incorrect as SIL is not related to self-controlled devices
5 - incorrect for most cases
6 - site dependent

For info

Failure on demand is the critical factor for PSV and HIPPS both. You can:
- calculate those for HIPPS by a standard applicable in your case
- found and compare those for PSV in

https://www.amazon.com/Guidelines-Process-Equipment-Reliability-Tables/dp/0816904227

https://www.amazon.com/OREDA-Offshore-Reliability-Data-Handbook/dp/B0034GF52U

Note that HIPPS is prone to human factor (at engineering, procurement, construction, commissioning, operation etc.) and therefore is less controllable and more risky. While PSV is more codified and therefore more foolproof. Every case is unique and requires specific treatment.

 

[georgeverghese]

Must say 4 and 5 are surely not true
1, 2 and 3 are true provided you've got 2x100 % (or better) inline PSVs' with isolation block valves upstream and downstream.
And for 6, HIPPS has less environmental impact, since most PSVs' will leak a little.

Unless you are in the TUV / DIN world, in some parts of continental Europe, HIPPS systems are not preferred.

 

[TiCl4]

LittleInch,

In LOPA we take PSVs as two orders of magnitude reduction, which would equate to a SIL 2.

If a HIPPS system is truly a SIL 3, it would technically be more reliable. However, to achieve SYSTEM-WIDE SIL 3 capability would require some detailed PFD analsys of individual components PFDs. Depending on the system, multiple SIL-3 instruments and decision making processors are likely to be required.

In most cases, cost HIPPS >>> PSV

 

[shvet]

In LOPA we take PSVs as two orders of magnitude reduction, which would equate to a SIL 2.

Can you please explain why?

failure on demand SIL2 = 10^-2 - 10^-3

meanwhile e.g. OREDA PSV FoD = 10^-5 - 10^-6

 

[LittleInch]

OK, it's been a while since I got involved in those sorts of discussions. I do recall the intense calculation of the reliability of each component alright. Most of mine were pressure protection at the end of pipelines where it isn't practical to have a relief tank to drain a pipeline which won't stop flowing and is two or three pressure classes above the station pipework.

Is a PSV a lower PFD than an instrumented system?

Maybe I got it wrong but I did think it was difficult to beat a simple spring loaded PSV (or multiple PSVs) with an instrumented system.
But totally agree about the cost.

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

 

[TiCl4]

LI,

A PSV can be lower or higher PFD than an instrumented system, depending on design. System PFD is a statistical collection of individual component PFDs. Usually the instrument/transmitter, connecting line, decision making computer, and final control element/connecting line are considered in the loop analysis.

To my recollection, achieving a SIL 3 system rating requires something like, at minimum, two independent SIL 3 instruments, two independent SIL 3 (maybe SIL 2?) decision making computers, and two independent final control elements that each can fully implement the necessary controls action. The necessary SIL rating on the individual components as well as number of independent loops can be adjusted to meet necessary PFD. Additionally, the inspection frequency for function testing of the interlock loop also alters the PFD calculations.

SVET,

That is industry standard LOPA failure rate from the Center for Chemical Process Safety. The page you posted has failure to open on demand high-end failures at a mean of 8 failures to open in 10^5 hours of operation. I do not see how that correlates to a PFD of 10^-5 to 10^-6. Nobody in their right mind would expect that kind of PFD; a SIL 4 for a single device is preposterous.

 

[georgeverghese]

Field operators have on more than one occasion complained to me be about scheduled preventive maintenance impracticalities with a SIL 3 HIPPS system and with related production downtime issues.

 

[hassann]

Thanks a lot for your helpful comments.

Is this for a thesis or something?

This is one part of my Master's degree in Engineering .
following are more details.
API rp 14C says:
"The application of HIPPS requires the application of rigorous analysis, planning, and QA/QC procedures during the definition and design phases to ensure a safe HIPPS design."
and again API rp 14C emphasis:
"The use of HIPPS should be applied only when a traditional method for relief system design, in accordance with API 521, is not practical. Justifications for the HIPPS shall be documented and approved by the owner/operator."

I should study to understand what is the philosophy of behind this API approach? Actually my question is why does API 14c prefer PSV to HIPPS and finally I have to prepare a report about this difficult subject.

 

[hassann]

In most cases, cost HIPPS >>> PSV

It is obvious that individual hipps cost (2 ESD valve, 3 transmiter, logic solver ...) is more than individual psv but I mean from PSV is PSV system including piping, headers, k.o. drum, flare stack and tip and ...

 

[LittleInch]

The piping headers etc are often (though not always) required for other vents, blowdowns, other relief scenarios and hence their cost is not attributable wholly to the situation where a HIPPS can be used.

IN those locations where this PSV system vs HIPPS is the only reason then yes, that gets included in the practicality of the design, not to mention space for all that equipment.

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

 

[TiCl4]

If you need a flare stack, header, etc, then the burden cost of that PRV SYSTEM is shared amongst ALL the PRVs that feed the system. As always, the costs can go either way depending on required design. You have to do the engineering to figure it out.

You asked

"In general psv system has more cost of HIPPS."

So, in general, adding on a PRV to an existing plant will cost less than adding an additional HIPPS. There are obvious excpetions (addition of the PRV requiring an upsizing of the vent header / flare, permitting changes, etc..), but again, you asked for a "general" answer.

 

[LittleInch]

"Actually my question is why does API 14c prefer PSV to HIPPS and finally I have to prepare a report about this difficult subject."

My guess is that PSV systems are seen as simple, very reliable and have been used for decades and have been proven to be reliable and work effectively for relatively low cost. The engineering design is straightforward and well understood / codified in API 521.

HIPPS on the other hand are seen as complex, require significant engineering thought and design and to make them sufficiently reliable, require multiple sensors, a dedicated expensive logic solver and fast acting valves to close on demand.

It's only difficult for you I think because you've not gone through the process before or had to apply a HIPPS system and understand what is required and why. I hope our answers give you a bit of insight into that.

We don't normally answer student thesis type questions though so count yourself lucky....

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

 

[hassann]

We don't normally answer student thesis type questions

I have been working in the offshore oil and gas company for 12 years and I am studying at the same time. Anyway, I am very lucky to have an experienced supporting colleague like you for sharing own knowledge with me.

 

[LittleInch]

Well good for you - you have my appreciation as its far from easy working and studying.

Hope you understand a bit better now?

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

 

[hassann]

So, in general, adding on a PRV to an existing plant will cost less than adding an additional HIPPS.

You are right. But improvement of existing plant is not my concern. my question is about new plant design and construction.