7 replies to this topic

[Ibnu84]

Dear All,

 

Refer to API 14C, overpressure protection should have 2 protection layers, i.e Safety Intrumented Fuction (primary) and Mechanical Protection or PSV (Secondary).

 

API 14C section of A.9.2.c.5 states that, a PSV may not be installed if :

Input source is a well(s) having a pressure greater than the maximum allowable operating pressure of the pipeline and is equipped with two SDVs (one of which may be the SSV) controlled by independent PSHs connected to separate relays and sensing points. Other input sources having a pressure greater than the maximum allowable operating pressure of the pipeline are protected by PSVs.

 

Now, my case is:

There is an Oil Well utilizing gas lift system in a wellhead platform.  The gas lift pressure is 600 psig, wellhead pressure (upstream choke valve) is 150 psig, and pipeline pressure is 80 psig.  Existing pipeline was rated for 600# means fully rated.  There is a pipeline replacement plan, and my client wanted to change the pipeline rating to 150#.

 

It is clear that, the pipeline shall be protected from overpressure.  And I was thinking a blocked discharge PSV is required to protect the pipeline.  However, installing PSV will have a lot of modifications in the existing wellhead platform (install KO Drum, etc, which may not be possible). 

The existing platform is utilizing pneumatic system.  See the attached sketch for more detail.

 

My questions:

Is installing additional PSHH and SDV acceptable to replace the PSV requirement?  Can anybody share their knowledge and understanding of the API 14C section A.9.2.c.5 above?  Is it explaining about HIPPS?  Is there any issue about reliability of pneumatic system  (PSHH, etc..).

 

 Pipeline Replacement.pdf   24.65KB   155 downloads

 

Thanks and Regards

Ibnu84

[fallah]

Ibnu84,

 

In the first part of the A.9.2.c.5 as an item of Safety Analysis Checklist for Pipelines, it almost states a HIPPS by which (with a high SIL level) as per API 521 we can eliminate the need to a particular relief device for protection of downstream pipeline with lower design pressure...

 

It includes field instruments, logic solvers, final control elements,..(1oo2 or 2oo3 with two closing device) and can be reliable enough to forget about installation the PSV in your case...

Edited by fallah, 25 June 2013 - 04:20 AM.

[SUPRIYAPRA]

I believe it is talking about HIPPS as we have similar situation. Installing additional PSHH and SDV acceptable to replace the PSV requirement is correct.

[Sharma Varun]

Yes HIPPS is what you are looking for & as indicated by fallah, to answer " Is there any issue about reliability of pneumatic system (PSHH, etc..).", high SIL level is required for reliability.

[batavle]

Dear All,

 

Please be informed that SHELL DEP states consideration of PSV downstream of HIPPS valve to account for HIPPS valve leakage.

 

Thank you.

 

Regards,

[mohammad reza]

Dear All 

 

Also as per Exxon mobile practice considering PSV at downstream of HIPPS valve for HIPPS valve leakage scenario is mandatory. 

 

Best regards

[Yogesh Bhatt]

I believe HIPPS would be more reliable than using a PSHH and a SDV. Moreover, since HIPPS is equally reliable as a PSV, you can definetely replace the requirement of PSV here.

 

Regards

Yogesh

[Fakhri]

I think API 14.c only requires an independent loop for the secondary protection layer. API says only separate sensing points and separate relays. The required reliability of the loop should be determined by a SIL classification study.

 

The next questions can the second loop be connected to the same SIS? I think if SIS is already SIL rated to the highest required SIL during SIL classification it is okay.

 

Best regards,

 

 

Fakhri