During the past 15 years nylon 11 (or PA11) has been extensively tested as a piping material for natural gas at pressures up to 200 psig. Polyethylene (PE) has been used for many decades in the USA and around the world in the same application, but is limited in the USA to 125 psig operating pressure. Above that pressure only steel was approved by the USDOT until January 2009 when the federal pipeline safety code Title 49 CFR Part 192 was revised to permit the use of PA11 at pressures up to 200 psig. The system is available commercially from Georg Fischer Central Plastics (Shawnee, Oklahoma)
During the past 6 years several manufacturers of PA12 evaluated that material for the same application, and there are several trial installations operating around the country. Based on the results of the trials and laboratory work, the proponents of PA12 hope to have Title 49 CFR Part 192 amended with PA12-specific language. I have been frequently asked to explain the difference between PA11 and PA12. I will briefly do that in this post.
PA11 and PA12 are engineering plastics with similar properties. The various manufacturers have similar product ranges with many grades covering a wide range of flexibility, from highly plasticized to glass or carbon fiber filled. They are often specified for the same types of applications, sometimes interchangeably. PA11 and PA12 are made from monomers that come from different sources. PA11’s monomer is derived from the oil of the castor plant, which is grown in large quantities in India, Brazil and other countries. PA12 is entirely petroleum based, with the monomer synthesized starting with the commodity chemical butadiene.
PA11 was commercialized first around 1955 by what is now Arkema (France). The process for the monomer was patented, and the polymer was available only from Arkema which is still the sole producer of PA11, probably due to the highly complex monomer synthesis process. Seeing the technical advantages and commercial value of this new long-chain nylon polymer, several chemical companies began working on a competitive product, but since there was a strong patent file on PA11 they focused on other polyamides with similar monomer chain lengths. PA12 was commercialized in 1966 by what are now Evonik Industries (Germany) and EMS Grivory (Switzerland). Arkema introduced their own PA12 product in 1971, and Ube Industries (Japan) introduced their PA12 in 1979.
The materials have similar performance in most applications. For natural gas distribution pipe both materials have earned a hydrostatic design basis of 3150 psi at room temperature and 1600 psi at 80° C. Although similar, they are different enough that they should never be mixed together for processing. There are rumors that pipes of the two different materials can be joined by electrofusion and butt fusion, but there have been no published results of such studies.
If you want to know more about PA11 and PA12, contact me for a discussion.
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1 comment:
This is great stuff, thanks for posting! I was wondering if you knew anything about the commerical applications for PA 11 and PA 12-- such as products used on the retail end of the spectrum, as opposed to just piping.
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