Important Things

IMPORTANT THINGS TO LOOK FOR WHEN PURCHASING PLASTIC LINED PIPE
1. PTFE VS. PFAPTFE lined piping systems are not the solution to all your problems with plastic lined pipe, as some manufacturers would have you believe. There are several problems caused by using PTFE in your piping system. The first is that PTFE is not a melt processable resin. It mustÂ be properly pressured and sintered in order to produce a qualityÂ finished part. This process allows for more porosity in the plastic than melt processable parts. More porosity means more permeation in a product that is already the most permeable used in plastic lined pipe. The second problem is physical strength. Plastics are measured by their tensile strength. PTFE starts out with less tensile strength than other resins and gets weaker as the temperature goes up. It must be made twice as thick just to get the same psi tensile strength as other plastics. This strength is what helps hold the joints tight in a plastic lined piping system. The weaker the plastic, the more susceptible it is to cold flow and joint creep. This means you will have to constantly tighten your joints because they become loose over a period of time and leak. Other plastics with the same chemical resistance as PTFE such as PFA and MFA do not have this problem. The third problem is that some manufacturers recommend PTFE to handle any and every service. There are other resins that do not have the inherent problems of PTFE that can permanently handle these services. ECTFE and ETFE will both handle aggressive chemicals up to 300° F without the cold flow and permeation of PTFE. Most manufacturers only have PVDF or PPL in addition to PTFE to handleÂ lower temperature services and must jump directly to PTFE when theÂ service gets too aggressive for PVDF to handle. PFA and MFA will do anything PTFE can do, without the joint creep and permeation problems. They are also better at handling high purity or aggressive chemicals. You should be able to design the plastic lined piping system to fit the needs of your process and PTFE should be your last choice.
2.COMPLETE SYSTEMSWhen you choose a plastic lined pipe supplier you should make sure they are able to supply all of your plastic lined piping requirements. Many manufacturers fall short when it comes to supplying reducing fittings or pipe sizes 1 ¼", 2 ½", or 5". There also seems to be a scarcity of eccentric reducers, laterals, and reducing 90Â° ells in the market place at the present time. Not having key reducing fittings would make it more difficult to put a pump in line, properly install a drain line, or make a necessary reduction. Not having all the reductions available could cause you to use reducing flanges or two or more fittings together to get the reduction you require. Let's say for example that you require a 12" x 3" concentric reducer but your plastic lined pipe supplier only offers a 12" x 8". You then have the choice of using an 8" x 3" reducing flange or an 8" x 3" concentric reducer to make your reduction. Neither of these options are good ideas. It is important to verify that your plastic lined piping supplier has access to all the sizes and reducing fittings your system will require.
3.PRESSURE DROPWhen you are comparing plastic lined piping systems, make sure you look at the manufacturer's pressure drop charts if pressure drop is a concern to your process. The lowest pressure drop numbers occur in plastic lined fittings with rounded internal corners and uniform wall thickness. Manufacturers who injection or transfer mold their fittings must use a mandrel, which is removed after lining. In order to remove it the mandrel must have a draft. This makes removal much easier but it also leaves the finished ID considerably smaller on one end than the other. If these fittings are put in service you have created a stair step effect that raises both pressure drop and turbulence in your system. Mandrel shift can also occur in fittings manufactured this way. This is where the mandrel is not correctly centered in the fitting allowing the plastic wall thickness to be greater on one side than the other. Another place where pressure drop may occur is when butterfly valves are placed in the line. Injection or transfer-molded fittings have square corners where the plastic face meets the liner. In order for the butterfly valve to open properly, tapered spacers must be used. Rounded corners in some manufacturers fittings and pipe will allow the valves to open properly and allow a smooth flow from the pipe or fitting to the valve.