Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

Hipps System At Gas Wells For Gre Flowline Protection


This topic has been archived. This means that you cannot reply to this topic.
5 replies to this topic
Share this topic:
| More

#1 rizwangoheer

rizwangoheer

    Veteran Member

  • Members
  • 30 posts

Posted 02 December 2013 - 08:46 AM

Hello Guys,

 

This is first time, I am going to post a topic for your value able comment. Actually I am working on as Process Engineer on Green Field Project, which have both oil  & gas production wells and then onward oil & gas processing facility. Basically this is a sour oil & gas treatment facility.

In  said project I am working on Gas Wellhead, Onplot Manifold, then further gas processing including separators, Compression, TEG Dehydration. Here I have a challange in Design Review regarding GRE Flowline protection with Wellhead HIPPS. Below are  the complete details for the system and I have also attached a sketch for better understanding.

 

Multiphase fluid is produced from Gas wellhead at about 250 bar FTHP and 40~60 C FTHT depending on the production flowrate. The pressure is reduced to <110 bar at the wellhead through an automated choke. The gas well fluid stream flows to Gas Inlet Separator  operating at 100~103 bar.

 

If the choke valve fails in open condition or Gas Inlet Separator  inlet valve closes on ESD activation, then 900# flowlines and piping downstream of the choke valve will be exposed to high pressure well fluid. For each well head, over pressure protection system is provided to safeguard the underrated GRE flowline from overpressurisation.                                                                                                                                                                                                                       According to initial proposed design, four gas wells connected through GRE flowline from wellheads to On Plot Manifold at station. The gas well flow lines have GRE segments of approx 5 kilometers length with design pressure of 120 barg.                  As per Shell Guideline on SIL Assessment & Implementation , Partial relief Valve with HIPPS is provided on production header to protect flowlines for over pressurization from wellhead side for ‘blocked in’ condition.  HIPPS failure for one well (for 5 number of wells) is considered for the sizing of this relief valve as per EP Guideline on Process Safeguarding.                       During project Design Review workshop, there was an action requesting to confirm that GRE flowline would not be over pressurized (from wellhead side) with relief valve provided on common production header set at 113 barg.  I worked out on TGNET that RV on common manifold will overpressurize the GRE line when it will reach its releving condition 124 barg. So Now I am trying to close this action with the following basis." As the HIPPS System is SIL 3 rated as per PFD calculations, so this HIPPS only is adequate to protect the GRE flowline from overpressurization from wellhead. Partial relief valve is only provided to protect the On Plot Manifold incase of failure of one well HIPPS out of 4 wells." Any one can advise me either this is correct approcah to close this action or I need to make some other changes. 

Attached Files



#2 Bobby Strain

Bobby Strain

    Gold Member

  • Members
  • 3,528 posts

Posted 02 December 2013 - 07:26 PM

You must review your findings with Shell. What we consider adequate may not satisfy Shell. And make certain that Shell assumes full responsibility and liability for any design according to their guides and specifications.

 

Bobby



#3 paulhorth

paulhorth

    Gold Member

  • ChE Plus Subscriber
  • 396 posts

Posted 05 December 2013 - 06:46 AM

Rizwangoheer,

It seems to me that, in the event that one wellhead HIPPs system fails and the PSV on the manifold is relieving, then the flowlines will indeed be overpressured. The pressure during relieving will be about 124 barg at the manifold end, but will be higher than this at the wellhead end because of the pressure drop from the flowing wellhead through 5 km of flowline. You can calculate this DP using the relieving flowrate.

 

This situation will only occur if there has been, first, an ESD valve closure at the manifold, second, a HIPPS failure at one wellhead. The frequency of the overpressure should thus be low, below 10 exp -3 per year. The duration will be the time taken to manually actuate the SCSSV from the hydraulic panel (assuming the original fault is not in the panel) which should be quite short if it can be done remotely.

 

I don't know the provisions of your piping code for GRE flowlines, but the code for steel piping can allow an excursion above design pressure if the the exposure is limited to a certain number of hours per year. I suggest you get this checked by a piping material specialist.

I think you could be OK due to the low probability but you need to get this reviewed and agreed by the relevant specialists. Otherwise you would have to reduce the set pressure of the manifold PSV and you are already not much above the normal operating pressure.

 

Paul



#4 rizwangoheer

rizwangoheer

    Veteran Member

  • Members
  • 30 posts

Posted 06 December 2013 - 12:32 AM

Mr. Bobby,

 

Many thanks for your response. But I share this topic here on this forum b/c I think I can have another solution for this issue.

 

Hope that some one can definitely give me a better solution.

 

thanks

goheer



#5 Malek

Malek

    Junior Member

  • Members
  • 14 posts

Posted 13 December 2013 - 01:25 AM

API 521 section E.4.2 states that " In accordance with ISA S84.01, a necessary step in safety-instrumented system design is to set a safety
integrity level (SIL) or availability value target for system design. The system is assigned as a SIL-1, SIL-2 or
SIL-3 system, with SIL-3 being the most robust and most reliable and SIL-1 being the least. Associated with
each SIL is a minimum performance requirement, i.e., a minimum of 90 % availability for SIL-1, a minimum of
99 % availability for SIL-2, and a minimum of 99,9 % availability for a SIL-3 system."
 
personally, I think it's double jeopardy, you could give no credit for such scenario.
 
 
Malek


#6 qadi

qadi

    Junior Member

  • Members
  • 22 posts

Posted 06 December 2014 - 09:26 AM

Dear Gents

 

GRE only stand for low pressure, what's max pressure GRE withstand

 

Rregards






Similar Topics