Basic Joining Techniques

Disclaimer: The data furnished herein is based on years of experience, testing and our vendors engineering information. All reasonable care has been taken to ensure the accuracy of the contents of this material; however, Harrington Industrial Plastics LLC shall not be liable or responsible for any loss whether direct, indirect, incidental or consequential arising out of the use of or reliance upon any of the contents of this material.

There are several recommended methods of joining thermoplastic pipe and fittings, each with its own advantages and limitations:

SOLVENT CEMENTING

The most widely used method in Schedule 40 PVC, Schedule 80 PVC and CPVC piping systems as described in ASTM D-2855. The O.D. of the pipe and the I.D. of the fitting are primed, coated with special cement and joined together. Knowledge of the principles of solvent cementing is essential to an excellent job.

NOTE: The single most significant cause of improperly or failed solvent cement joints is lack of solvent penetration or inadequate primer application.

There are various methods to join pipe and fittings when installing chlorinated polyvinyl chloride (CPVC) piping systems. One of the most common ways of joining is by solvent cementing. Solvent cement is not a glue — it is a process that uses solvents and resin to chemically fuse the pipe and fitting together at a molecular level.

Article: Solvent Cementing CPVC – The Dos and Don’ts of CPVC Piping Solvent Cement Welding – Corzan (External Link)
Article: Solvent Cementing CPVC – The Complete CPVC Solvent Cement Guide – Corzan (External Link)

THREADING

Schedule 80 PVC, CPVC, PVDF, and PP can be threaded with special pipe dyes for mating with Schedule 80 fittings provided with threaded connections. Since this method makes the piping system easy to disassemble, repair, and test, it is often employed on temporary or take-down piping systems, as well as systems joining dissimilar materials. Threaded pipe must be derated by 50% from solvent-cemented systems.

NOTE: Threaded joints are not recommended for PP pressure applications.

FLANGES

This technique is used to assemble PVDF and polypropylene pipe and fittings for high-temperature, corrosive-service applications. (See each manufacturer’s data for recommended joining techniques.)

SOCKET FUSION

This technique is used to assemble PVDF and polypropylene pipe and fittings for high-temperature, corrosive-service applications.

NOTE: See each manufacturer’s data for recommended joining techniques.

BUTT FUSION

This technique is used to connect all sizes of polypropylene (Proline), PVDF (Purad™) and other larger diameter materials. Butt fusion is an easy, efficient fusion method especially in larger diameters.

IR (INFRARED)

Fusion Improving upon conventional butt fusion, IR welding uses a noncontact method. IR welding uses the critical welding parameters of heat soak time, change over time, and joining force as found with butt fusion. By avoiding direct contact with the heating element, IR fusion produces a cleaner weld with more repeatable and smaller bead sizes. The end result is a superior weld for high-purity applications.

HPF Fusion

The HPF welding technology is an electric socket fusion system that joins Purad™ PVDF piping components, providing a smooth internal surface.

SMOOTH INNER BORE (S.I.B.)

S.I.B. offers state-of-the-art technology for sanitary piping systems construction. The “smooth” interior surface of the weld eliminates all beads, crevices and intrusions into the fluid system. Materials cannot become entrapped, and the possibility of bacterial growth and contamination is virtually eliminated. S.I.B. reduces pressure loss due to friction and improves system hydraulics. Available in Kynar® (PVDF) and polypropylene.

ELECTROFUSION

Electrofusion fittings are manufactured with an integral resistance wire, molded in place using a proprietary manufacturing process. The wire is electrically heated by means of a microprocessor controlled control unit. This results in fusion and bonding of the pipe to the fitting.

MECHANICAL JOINT

Traditionally mechanical joint polypropylene and PVDF drainage systems are used extensively for accessible smaller sized piping areas. The system, as the name implies, is a mechanical sealed joint that consists of a seal-ring and nut. It is quick and easy to install and can be disconnected just as easily. This joining method is most suitable for under-sink and under-counter piping.

SANITARY MECHANICAL JOINT

The Sani-Tech Division of Saint-Gobain Performance Plastics offers a sanitary mechanical joint similar to the Ladish® tri-clamp sanitary joint systems found in the pharmaceutical, food and beverage industries. This system requires that rigid tubing (pipe) and fittings are formed with a sanitary flange and gasket be joined together with a special mechanical clamp.