Re: [PipingDesign] Pig

From: <Geoff>
Date: Wed Sep 10 2003 - 17:53:00 EDT

Steve,

A risk analysis of this operation will drive you to find out more about the condition of the pipe before rushing in and pigging the line.

The problems with a steel line could be scaling, high levels of corrosion or local blockage. Running an intelligent pig htrough a small section (uphill) and reversing it out(compressed air downhill) may give some idea as to the problem. Also you may be able to get a CCTV into places such as air valve or scour valve locations.

If you have scaling then you are looking at an acid clean short term and antiscalant dosing in the future.

If the line is heavily corroded you may be looking at sliplining this one to keep it going and running a parallel line to meet the flow required.

If pigging is required I would pig from the bottom but make sure that I had to hand compressed air to drive the pig in reverse. Also some good metering so That I knew how much water had gone into the line before the pig got stuck. Then a field crew could dig it up and make a repair.

Geoff
--- Steve McKenzie <Mechproj@xtra.co.nz> wrote:



Gents

I am looking at having a portion of water supply line pigged out because its friction loss is around 4 times what it was. The line is 10" steel, 3/8" wall and is a rising main taking water from a pond to the top of a hill about 330m higher up. The pipe length is 3900m, reasonably constant incline (but a few level portions at road crossings) and currently flows at about 70 l/s. Line pressure at the bottom end is 44 bar and there is an atmospheric vent as the top end.

I have no experience in pigging and am unsure what the outcome will be and the best way to do it.
My nightmare is blocking the line; I can take it out of service for a few days, but longer than this would cost millions as it would shut down a processing plant.
The pig supplier suggested going from the top to the bottom using compressed air to force the pig down the line (there is no water supply at the top of the hill).
The pigging contractor thinks going from the bottom to the top using water to drive the pig up the line is the best way to go. I can see pros and cons with both options, but am tending to favour the water (uphill) option because of the flushing action of the water.

But what do I know?

Any experience or suggestions would be appreciated.

Cheers

Steve McKenzie

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