Gas Piping is a very critical and important criteria in a cogen power plant. Not only it is extremely hazardous in the event of a leakage, it will cause severe impact if exposed to even a small ignition of a spark.
Hence, extra precaution has to be taken during selection and also during installation of gas piping.
Normally, all gas piping are using at least a Seamless Pipe as well as Seamless Fittings for this application. In this case, the pipes that is being used here is Seamless 4″ A53 GrB Pipes fully certified by the pipe manufacturer.
Seamless Pipes For Gas Piping
Seamless Fittings for Gas Pipes
As Gas pipes demands a good quality and safety issues, X-Ray 100% of Penetration Test is required.
To ensure better quality, spooling of the gas pipes are usually welded offline, ie outside the premises of the installation site. By doing so, the area can be enclosed to prevent air flow effecting the argon gas welding of the pipe joints. (Note that the pictures below does not depicts a Gas Argon welding, just for illustration purposes only.)
Welding of Gas Pipes
After spooling of the pipes, it is then installed at site and welded together. By doing so, the chances of reject during Xray test will reduces.
Gas Pipes
Gas Piping Installation
Upon completion of the gas piping, the schematic diagram is drawn upon and all the joints are marked accordingly into the drawing. This will gives an idea to the X Ray suppliers on the joint indication and a summary of report will be make based on the results of the shoot. THis results and the joints will eventually be compiled into an Inspection Test Plan Report and finally compiled into Manufacturers Data Report to be submitted to the client.
X Ray Joint Diagrams
Once this is all ready, the X Ray contractors are called upon and arrangement is then made with the client to clear off the working area as X Ray radiation is hazardous and no person is allowed inside the premises during XRay shooting. For this purposes, X Ray are usually done from midnight until morning inside a factory.
Once the X Ray results are out, joints which are rejected are identified and marked on the pipes. To ensure that we do the repair right, we do a Dye Penetrant Test, a long and tedious procedure but ensuring the process is correct.
DPT test is a procedure by applying a layer of red oxidant on the area of rejected joint. Using a grinding wheel, the rejected parts is grinded off and then applying another white layer to wipe off the first layer, once the defect point is detected, a small red dot will appear, as shown below.
Dye Penetrant Test on Gas Pipe
Once the red dot is detected, it means that this is the area where the X Ray has detected a defect. The grinding wheel then grinds off the spot and retest to ensure there is no more defect part before welding is done again on that section.
Dye Penetrant Test and X Ray Test
After that, the defected part is Re Xray again until the joints are passed. After all joints are passed, the gas pipes are flushed using Nitrogen Gas and is pressurised for a few hours depending on the specification and requirement. Upon completion, the final procedure is final painting on the gas pipes, usually Yellow color according to the local authorities requirement.
Final Gas Pipe
