Liquid Hydrocarbon Permeation and HDPE Pipe
Liquid Hydrocarbon Permeation and HDPE Pipe
(OP)
Hi guys
We're having some issues with the inability to fuse HDPE pipe which has been attributed to the natural gas quality, specifically hydrocarbon liquids. These is indication of bubbling of the plastic after preheat making it difficult to get a high quality fusion. I've done some research and can see that it is indeed the hydrocarbon that is causing this issue (http://www.easternct.edu/sustainenergy/EnergySemin...)
I have a few question.
1) Is the permeability of the hydrocarbon dependent on the specific components of the NGL? For example does it matter if it's C3, C4, C5, C6, etc?
2) Other than using mechanical connection methods to join the piping, is there any other way to make the connection? Other than also reducing the HC inside the piping. Maybe some higher grade HDPE?
Any help is appreciated.
We're having some issues with the inability to fuse HDPE pipe which has been attributed to the natural gas quality, specifically hydrocarbon liquids. These is indication of bubbling of the plastic after preheat making it difficult to get a high quality fusion. I've done some research and can see that it is indeed the hydrocarbon that is causing this issue (http://www.easternct.edu/sustainenergy/EnergySemin...)
I have a few question.
1) Is the permeability of the hydrocarbon dependent on the specific components of the NGL? For example does it matter if it's C3, C4, C5, C6, etc?
2) Other than using mechanical connection methods to join the piping, is there any other way to make the connection? Other than also reducing the HC inside the piping. Maybe some higher grade HDPE?
Any help is appreciated.





RE: Liquid Hydrocarbon Permeation and HDPE Pipe
you must get smarter than the software you're using.
RE: Liquid Hydrocarbon Permeation and HDPE Pipe
RE: Liquid Hydrocarbon Permeation and HDPE Pipe
Drying the pipe is a long and slow process involving heating the pipe to below melting for an extended time. The process would also need to be validated. The only source of this information that I can imagine is the pipe manufacturer.
RE: Liquid Hydrocarbon Permeation and HDPE Pipe
"1.4.10 Additional reliability and safety concerns for LDCs and end users due to natural gas liquids include the impact to polyethylene (PE) plastic piping, plastic piping components and current handling / pipe joining methodologies. According to APGA, approximately fifty percent of the typical LDCs distribution system is now comprised of plastic pipe and approximately ninety percent of new pipe installed is now plastic (2003 OPS Annual Report). Hydrocarbon gas constituents that are normally present within historical acceptable levels will have a minimal effect on the long-term strength of the plastic. However, it has been shown that aliphatic gaseous fuels of higher molecular weights (“heavy hydrocarbons”) tend to be absorbed to a small extent by PE. This absorption somewhat reduces the long-term strength of PE pipe materials. Further, if the (NGLs) are routinely present, these liquids can cause a greater reduction in long-term strength up to 40% 7. In addition, it has been reported that during the heat fusion joining of PE piping that has been in service conveying fuel gases that consist of, or include heavier hydrocarbons, the PE surfaces being heated in preparation for fusion on occasion will exhibit a “bubbly” appearance. The bubbling is a result of the rapid expansion (by heat) and passage of absorbed heavier hydrocarbon gases through the molten material, which could compromise the fusion joint if not properly recognized 8 9 10."
I know that at least many years ago it was common practice in natural gas systems to try to remove as many of these liquids as possible, e.g. by way of "drips" or drip pots, though this report indicates this practice has apparently been discouraged in many areas since the 1990's.
It should also be understood other authorities have explained for many years that "hydrocarbons" can potentially be near everywhere else in the external e.g. soil and construction environments( and be absorbed into pipes from these sources as well), as e.g. I think explained quite well at http://www.google.com/url?sa=t&rct=j&q=&am... , with incumbent effects on plastic piping and liabilities etc.
All this considered and given this body of knowledge, you might want to get the promoters/purveyors of the plastic piping on record with regard to aspects of these issues, including the following:
1. How can I recognize when the pipe has absorbed an unsuitable level of undesirable or prohibited contamination from whatever source, BEFORE I produce any defective fusion joints (or lateral connections, etc.?
2. If I do not see alarming external "bubbling" on the weld bead, how do I know/be assured that there are no unseen or unknown defects within the weld or fused area caused by same that I cannot see?
3. In the event that the extent of the contamination of the pipe is undetermined or the pipe cannot be replaced before being put back in service (e.g. in emergency circumstances etc.), what EXACTLY does the pipe manufacturer mean by alternative "suitable mechanical connection methods" (particularly given the sort of unGodly complexity of accomplishing correct fusions in all manner of field and weather circumstances, even without any contamination, represented by all the caveats etc. in the 30-some page document you linked to in the OP!)