I'm not aware of any code requirement that specifies flushing before hydrotest of a gas pipeline, but it's good practice in any case.
Certainty of cleaning is achieved by flushing anyway, whether or not a code specifies or just recommends it be done. If you are the client, then you should be specifying your requirements in this regard to ensure that it happens.
Never heard of a return flush line for a long pipeline. Depending what you have used for your flushing fluid, or what chemicals have been added, you might have to arrange for intermediate storage, treatment and disposal via tanks and tankers. Plain water is not usually a problem to dispose of, but that's not always true.
Hydrotest water is explicitly prohibited from surface discharge in the U.S. I would bet that flush water is worse. I've never flushed a line before a hydrotest, and often run a pig (or several) with air after the test to get the bulk of the nasty out. The test water always comes out red and awful.
As i've heard, one of the objective of flushing of piping is to remove internal scales which are formed after first pass of pipe weldment. This will be achieved by high speed circulation of fluid (in case of gas piping, i think water). In case of pipeline, how we can remove these scales (and also possible remained things, say used electrodes)without high speed circulation?
thanks for your response, in advance.
"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit
You're not usually going to flush a long pipeline. Test it and move the test water from test section to test section as you move along the line.
Yes. Buy a bunch of the shorter pigs and run one after the other until they come out clean. Ask the mfgr about the capabilities of the specific model you want, or find out which one he recommends, before buying.
"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit
caet,
A lot of people disagree with me on a lot of things. If I think their arguments are sound, I change my ways. If not I don't. I've found junk in hydrotest water. I once found a skid (railroad tie sized timber) in a pipe that either a vandal or a disgruntled worker stuck in there--flushing would not have shifted that, we only found it when the drying pig never came home.
A pipeline takes ID^2 (in inches) bbls of water per 1,000 ft (do the math, the actual volume is slightly less than this, but 80 bbl water trucks never hold 80 bbl so I'd rather calculate long when ordering water). So 10 miles of 20-inch pipe would take something like 21,0000 bbls of water. That is not a small number to haul, load, or dispose of. I'm only doing that once. Sometimes (if I'm loading from a low point and receiving at a high point so I can get the pig out without losing a lot of water) I'll put a foam pig in front of the water to try to collect junk, but I don't always do that. When dewatering, I'll always chase the last of the water with a pig pushed by air. Generally baggies of grass (don't you drug test BigInch?) or unmatched gloves will have already left in the water trucks (and will be found in the strainer at the SWD site), but sometimes they show up in front of a pig. We found a trace chain that way once.
On the other hand, if there is any way that the stress numbers work out, I will always prefer to do a pneumatic test and never flush the pipe at all. For pneumatic tests, I like to depressurize through the biggest hole available (generally just open the end of a launcher or receiver, and then open the Barrel Isolation Valve to blow it down), that tends to shift anything that is mobile and scour the pipe walls some. I follow that with a pig, but a dry pig is not terribly effective at removing mill scale.
I've never flushed a pipeline either. Just hydros.
Drug testing in south Texas 6 miles from Mexico in the 80's??? Right. Drug testing back then only meant a buyer was checking it's purity. Actually we were lucky we didn't find any bodies. I imagine its much busier now.
Our lease roads and pipeline RoWs doubled as highways for both immigration and drugs. Once they got across highway 83 you could go for 100 miles through the patch without seeing anything but well heads, prickly pear, mesquite, rattle snakes, javalina and armadillos; cross one highway and go another 100 all the way to San Antonio. Highway 16 always had Border Patrol agents every 10 miles, so nobody ran that. I just got back from Colombia, so it was better than guerillias shooting at you and blowing up the pipeline once a week.
"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO BP
"Being GREEN isn't easy." Kermit
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