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THE TRUE COST OF AN INEXPENSIVE PLASTIC LINED PIPING SYSTEM Many companies today are being misled by price when choosing a plastic lined piping system. PTFE is the least expensive fluoropolymer resin used to plastic line pipe. It is three to four times less expensive than other fully fluorinated fluoropolymers. Because of the extremely low pricing, PTFE is being used in service conditions that should use other fluoropolymer linings for better longevity. PTFE is not the best liner for all services. Yes, it is chemically resistant to most chemicals and will handle temperatures up to 500° F (260° C), but it has some properties that lead to shortened system life. PTFE is mechanically weak and wants to cold flow when squeezed between two metal flanges. Thickening the PTFE only makes this problem worse, as does high temperature. PTFE resin is only one-half as strong as other fluoropolymer resins. As the temperature goes up and down, PTFE becomes weak enough to cause flange joints to loosen and product to leak. Tensile strength is also measured in pounds per square inch (psi) and in order to attain the same tensile strength as other fluoropolymers, you have to double the thickness (sq. in.), which contributes to more cold flow and joint creep.
Resin |
P V D F |
EC TF E |
E T F E |
P T F E |
Tensi le (psi) |
45 00 -6 50 0 |
60 00- 70 00 |
6 7 0 0 |
30 00 |
PTFE lined systems have relatively loose liners when compared to other fluoropolymer lined systems because PTFE stress relieves itself over time, that means all the liner movement is concentrated at the flange face which can result in premature liner failure. PTFE is the most permeable fluoropolymer used to line pipe. The ASTM specification for plastic lined pipe, F-1545, says it must be vented. These vents allow any product that permeates the liner to be released into the atmosphere. In some cases this permeant combines with moisture in the atmosphere and forms an acid, which attacks the metal pipe. Over time this results in enlarging of the vent holes causing eventual structural failure of the steel pipe. All of these problems, cold flow, loose liner, lack of tensile strength, and permeation can lead to premature failure of a plastic lined piping system. When the plastic lined system fails, consider the cost of replacement, labor cost to change, and the cost of downtime when the system could be otherwise producing. This does not include any damage caused by leaking product, which, depending on the severity of the leak, could include EPA fines caused by product spills or OSHA investigations and fines if employee safety is compromised. The total cost of the failed PTFE lined system becomes much higher when these events are added in. That inexpensive PTFE lined system just became very expensive, which is why considering the tougher maintenance-free plastics for extended system longevity and a clean environment is an absolute must. |
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