Hydrotest or Pneumatic test of pipelines
Hydrotest or Pneumatic test of pipelines
(OP)
My dear Engineers:
I just joined this group. I am working on a 56" Gas pipeline (450 km long) in the desert of Saudi Arabia. Water availability for future hydrotest is scarce. Is nitrogen pneumatic test a good alternative and what are the pros and cons.
thanks for your help.
I just joined this group. I am working on a 56" Gas pipeline (450 km long) in the desert of Saudi Arabia. Water availability for future hydrotest is scarce. Is nitrogen pneumatic test a good alternative and what are the pros and cons.
thanks for your help.





RE: Hydrotest or Pneumatic test of pipelines
One written by zdas04 on this is here http://www.engineering.com/DesignerEdge/DesignerEd...
Other posts include http://www.eng-tips.com/viewthread.cfm?qid=345053,
http://www.eng-tips.com/viewthread.cfm?qid=358563
In my opinion, which has changed over time, is that for your instance, yes it's probably a good idea, just be careful at the exposed above ground ends. Using Nitrogen will be very expensive so maybe you will need to do different sections one after another and re-use the gas or just use filtered, dried air.
Biggest issue is usually getting approval from either client or government department.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Hydrotest or Pneumatic test of pipelines
RE: Hydrotest or Pneumatic test of pipelines
You seem to be on the right track with regard not wanting to do a hydrostatic test (that test would be 4.6 million barrels [74 thousand m3], a lot to acquire or dispose of, not to mention the difficulty of drying it and the certainty of leaving enough water behind to create a very large MIC corrosion risk).
On the other hand nitrogen is pretty expensive and REALLY high risk. The problem is that it arrives on bulk trucks as liquid which is kind of cold. The vaporization equipment on the truck uses heat to change it back into a gas. When I write a nitrogen procedure, I make a big deal in the procedure that the nitrogen has to be heated to above 70F [21C], and a recording thermometer is required on the outlet pipe for any post-accident investigation. There have been a number of occasions where the nitrogen temperature was not monitored (or specified in the procedure) and the truck operator tried to hurry the process by injecting nitrogen that was below the ductile-to-brittle-transition temperature and the brittle failure of the pipe was spectacular (one happened near me that resulted in one fatality and permanent injury to two workers, the injection temperature was not monitored but the settings on the truck resulted in gas at -25F [-32C] in the post-accident investigation). Too expensive and too risky.
A fine alternative that I've used many times is to get an air pack that is used for wellbore cleanouts. These machines are pretty readily available, capable of very high pressures, and no risk of ductile-to-brittle transition. The argument that putting air into a hydrocarbon pipe is nonsense since you are testing new pipe that is already full of air.
In addition to the ENGINEERING.com article that LittleInch kindly mentioned, I have recently added a Static Test Document to my web page that might help you understand the issues.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Hydrotest or Pneumatic test of pipelines
of the SMYS. If you have a flaw in the weld that could lead to fracture initiation, you will need to assure that a minimum toughness is assured to prevent ductile shear fracture or brittle fracture. The pneumatic test can be done safely because personnel can be removed from the hazard area during maximum pressurization. In 2 of 3 pipeline hydrotests that I witnessed, failure occurred at long seam welds and it was easy to detect the water spout from afar. It will be easier to see the explosion during a pneumatic test. You must assure, as best as possible, that the weld is sound and the material will leak rather than burst at a leak causing discontinuity.
It is doubtful that you would test 450 km of pipe at one time. You could test sections thereof as is done in the western USA where water is also often in short supply.
RE: Hydrotest or Pneumatic test of pipelines
RE: Hydrotest or Pneumatic test of pipelines