Chemical resistance of plastic pipe

Plastic pipe is manufactured from many different compounds with the most common being pvc (sometimes referred to as pvcu or upvc, where the “u” stands for unplasticised, meaning it is rigid), cpvc (or corzan) abs and polyethylene. The choice as to which plastic to use is often dependant on the chemical formula of the substance that is passing through the pipe and fittings.

Pvc pipe is a pipework system with a very good level of chemical resistance to both acids and alkalis, and it is also very good with salts. Although pvc pipe is suitable for highly concentrated acids, bases and hypochlorites, when used in such applications it is recommended that a special chemical resistant solvent cement is also used. Where pvc is not suitable, is in the use of chlorinated and aromatic hydrocarbons. 

CPVC (or as it is sometimes referred to pvc-c pipe) is suitable for most mineral acids, salts, paraffinic hydrocarbons, alcohols and salts. CPVC pipe is a modified pvc polymer that is used to form a plastic pipe with a much higher chemical and temperature resistance than standard pvc pipe. The higher temperature rating also makes if the plastic pipe of choice over normal pvc when using warm or hot chemical solutions. This is because the chemical resistivity of all plastics reduces with increasing temperature. 

Abs pipe is manufactured from a styrene and so is a completely different type of compound and has a very different chemical resistance profile.  The styrene nature of abs pipe makes it very impact resistant down to temperatures as low as -40, because of this ABS is often chosen over pvc for glycol circuits. Abs is only resistant to weak acids but can handle weak to medium alkalis. This property also renders it suitable for chilled food areas, soft drinks and high purity water. ABS is also more abrasion resistant than most other thermoplastics and so if often the choice for abrasive slurries.

Polyethylene pipe (sometimes denoted PE, LDPE, MDPE or HDPE, where the LD, MD and HD stand for Low Density, Medium Density and High Density respectively) has a very good all round chemical resistance. PE pipe will withstand almost all acids and other caustic compounds and, at 20 degrees centigrade, it also resists all organic and inorganic solvents.  Where PE pipe is not suitable, is in applications involving  strong oxidising acids such as ozone gas, or liquids laden with very high concentrations of ozone.  Like ABS Pipe, PE pipe is also suitable down to low temperatures and can be used for glycol circuits etc. ABS usually takes precedence because of the ease of installation as it uses a simple solvent cement process rather than a heat weld system. It should be pointed out that smaller diameter PE pipe can be connected by compression fittings, but these use polypropylene and other rubberized compounds for the sealing rings which may have an adverse effect on the chemical resistance of the pipe system.