7 replies to this topic

[Yogesh Bhatt]

Hi All

 

We have 5 wells operating in an offshore platform. Each flowline connects the production manifold.

 

We have 2 cases here:

 

CASE1: HIPPS valves installed on each well flowline.

 

CASE2: HIPPS valve installed only on the production header.

 

Now I need to know which case would be ideally preferred and why ? I don't think technically there is any issue having any of the cases. But in my opinion CASE 2 should be preferred for the following reasons:

 

1. Having single HIPPS system on the platform will occupy lesser space compared to having 5 of them.

2. I am not sure about the cost but I think in CASE-2 cost would be less even though the valve size is higher beacuse of lot of instrumentation and electrical requirements in having 5 numbers of small size valves.

3. Having 1 no. HIPPS valve seems more reliable than having 5.

 

Experts! please provide your valuable experience on this and also correct me if my opinion is wrong.

 

Thanks

[shan]

HIPPS is intended to protect the production platform.  The number and location of HIPPS shut down valves depend on the location of piping spec breaks.

[paulhorth]

Yogesh,

 

I agree with you that the second case, with a single HIPPS system on the production header, is to be preferred, provided that the header has the same design pressure as the flowlines, equal to the shut-in pressure of the wells.

Reasons are those you state, in addition there is the requirement for regular testing of a HIPPS system. If you had five of them you would be testing very frequently. And each HIPPS will require a dedicated logic box housed in a safe (fireproof) location with hard wiring etc.

 

Paul

[Yogesh Bhatt]

Thanks Paul.

 

Can we achieve SIL-3 in both the cases ? Also I would like to know how these SIL levels are decided.

My senior told me that in CASE-1 we can not achieve SIL-3. Why is that so ?

 

I would appreciate if you can help me with the clarifications.

 

Thanks

[Sathya R]

SIL Levels are decided during SIL study where in effect (environmental, human life and loss of prouction and maintenence cost)of failure  of the shutdown element is evaluated and SIL Level is verified based on Probability of Failure on Demand(PFD).

[fallah]

Yogesh Bhatt,

 

Since all devices used in HIPPS components; process sensors, logic solver, final element, might contribute to the potential PFD for the HIPPS, the structure of the relevant loop must be defined and specified as a system such that the entire loop meets SIL degree requirement.

Then, each HIPPS in both cases (1,2) can achieve SIL3, but if the sensing location would be downstream of the production header, your senior concern about the case 1 might be logical because it might during a process upset all 5 HIPPS valves not to be closed at the same time due to, let say, differences (even minor) in their response times.

[paulhorth]

Yogesh,

 

I agree with Fallah's post.

I would add that it is more demanding for five separate HIPPS systems to meet SIL3 when combined, than for a single system. There are 5 times as many ways for a fault to occur, so the individual systems would have to be 5 times more reliable to meet the overall requirement for SIL3 (which means a probability of failure on demand of 1 in 1000). This may be what your senior has in mind.

 

The SIL level REQUIREMENT for a protection system is decided as Sathyanarayanan says, by determining the  consequences of a failure, and from that, esimating the acceptable frequency of such an event. The SIL RATING of the protection system (its reliability, its frequency of failure) has to match the requirement, and the rating is something certified by the equipment suppliers based on redundancy of components, frequency of testing, and their own quality procedures.

 

Paul

[Yogesh Bhatt]

Thanks everyone for your valuable explanation. This gives me a better understanding.