Recommended safety devices wellhead flowlines 1

[elquesifilma]

We currently have production wells with ESP (Electrical Submersible Pumps).

What are the typical safety devices to protect the flowline from rupturing form overpressure?

Our flowlines are polyethylene SDR 7 which are rated at 133 psi for Crude service.

The flowlines are tied into 3 phase separator operating at 40 psi. We currently have a check valves and chokes at the casing and tubing.We have a pressure safety high sensor, that if it senses higher pressure on the line exceeding 133 psi, it shuts down the ESP.

Could someone please advise, wether shutting down the ESP is enough protection for my flowline?, or do i require a shut down valve?

Thanks in advance!!

 

[ione]

You need a pressure relief valve capable to divert fluid in event a preset pressure threshold is reached. You cannot rely just on a safety pressure switch.

 

[JLSeagull]

Consider both the PSV and shutdown valve. If an electronic control system is applied, consider a transmitter for the pressure instead of a pressure switch. You can see when a transmitter fails more easily than when a pressure switch fails.

 

[rneill]

In Canada you would need to review CSA Z662 and in particular the section on Overpressure Protection and Pressure Control systems. In my experience, it is quite unusual to provide PSV type protection on flowlines from wellheads. Canadian requirements (Z662) would only require redundant application of pressure control and overpressure protection (consisting of something like automatic chokes and ESD valves).

Take a look at this document, published by the local regulatory authority in Alberta which attempts to distill down the local requirement...

http://www.ercb.ca/docs/documents/d...ol_ForInterpretingPipelinePressureControl.pdf

 

[BigInch]

I as I recall all that's required is an overpressure switch connected to a block valve between the wellhead and the flowline inlet. See API RP-14E. Its for offshore platform piping, but the flowline piping is similar in both situations.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[zdas04]

Engineering practice requires a spec break when the MAWP changes. Typically you have API 3000 flanges on the welhead along with heavy weight wellbore tubulars. Probably rated to several thousand psi. Then you change to pipe from Toys R Us at the wellhead. A spec break with a backpressure valve seems to be the minimum you could do.

The situation that rneil mentions is pretty common, PSV's are really rare on gathering systems. Most people rely on PSV's on production equipment for over-pressure protection in the event that spec break equipment fails to adequately protect the downstream piping and equipment.

I read an incident report just this week where a company was doing a coiled-tubing conveyed re-perf of a lower zone and a valve either failed or got left open and 10,000 psi natural gas was applied to a spoolable composite flow line (MAWP 750 psig) and it failed, caught fire, and burned the coiled tubing rig down (no injuries, significant property damage). It could have been prevented with a viable spec break.

Your ESP can probably build up enought pressure to bust the plastic pipe, but having an overpressure kill is only adequate if the reservoir pressure is too low to fail the pipe.

David

 

[BigInch]

Yes, if the well pressure could go over the pipe design pressure, you would obviously first need some pressure control (although not necessarily a spec break). The ESD would then go between the pressure control and the flowline inlet.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[BigInch]

Oh, yes zdas I see your spec break point. A spec break in terms of design pressure change. I was only thinking of ANSI classes at that moment.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[SNORGY]

rneill:

*STAR* for your post linking to that EUB document. This very morning, not more than 5 minutes ago, I was looking for a long-winded email that I remember writing a couple of years ago explaining "pressure limiting" versus "pressure relieving" systems and their applications in upstream O&G facilities designed to CSA Z662-07. I don't know why I logged into EngTips this morning, other than as a distraction while colleagues were looking through their archives for that email. In any event, that EUB document is *exactly* what I needed; I didn't even know it existed (how scary is that???).

Regards,

SNORGY.

 

[rneill]

There is one minor glitch with the ERCB document in that it shows sensing lines coming from the upstream system. In the event of a pressure control valve or automatic choke attempting to drop the pressure into the lower pressure system, the sensing signal would have to be downstream of the valve and not upstream.

Glad the link was helpful.

 

[BigInch]

I wasn't aware that Canadians had the same flare for understatement as the English.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/