HDPE (high-density polyethylene) pressure pipe sections can be joined onsite by butt-welding them. However, several precautions must be kept in mind during this field welding exercise in order to maintain the integrity of the pipe sections. This article discusses some of the things that you should never do when you are butt-welding HDPE pressure pipes outside a factory setting.
Welding Different Diameter Pipes
It is unwise for you to weld two pressure pipe sections whose internal and external diameters aren't the same. Poor fusion is likely to occur because the pipes will react differently to the welding parameters. For example, the pipe with the smaller diameter will reach its fusion temperature faster than the pipe with the larger diameter. Consequently, the two pipe sections will not fuse fully due to the difference in their temperature at the point where you join them.
Touching the Pipe Ends
You should also avoid touching the trimmed ends of the pressure pipes that you wish to weld. This is because you may introduce contaminants, such as oil from your skin, which may compromise the integrity of the pressure pipes. Those pipes may later leak and burst as they are used to convey fluids at high pressure. Premature Weld Removal Welds should never be removed from the butt-welding machine before ample time has been allowed for effective cooling to take place. Premature removal may weaken the weld at the time when it is still setting or curing. The result of such points of weakness is that the pressure pipe may fail prematurely due to the inability of the weld seam to cope with the severe service conditions to which it is subjected.
Welding Dissimilar Materials
It is unwise to attempt onsite butt-welding of dissimilar materials, such as HDPE and PTFE (polytetrafluoroethylene) pressure pipe sections. This is because the two materials may have different properties, such as thermal conductivity and melting points. Those differing properties make it difficult for you to select welding parameters that can result in a weld seam of high integrity. Such welding projects should be referred to a factory where precision equipment is available.
Butt-welding isn't the only technique that can be used to join plastic pressure pipe sections. Other methods, such as electro-fusion and flanging, also exist. It is therefore advisable for you to consult experts about the most appropriate joining method for your application. Only then will you avoid making a costly mistake that may threaten the safety of your equipment and personnel.