Solvent cementing is an ideal and proven jointing method for numerous applications in industrial pipeline engineering. One particular example is pipelines used to transport aggressive chemical media. GF Piping Systems, one of the leading suppliers of plastic piping systems, has played a key role in developing and advancing the cement bonding technology.
In a crush test, the mechanical stability of a pipe-fitting connection is tested. The solvent cement joint is said to achieve practically the same stability as the pipe or fitting material. (photo: GF Piping Systems)
Cementing is one of the oldest known jointing methods. Even in the prehistoric era a distillate made of birch bark was used to fasten arrowheads. Since then, many materials have been used to manufacture adhesives. The first patent for adhesives was issued in the middle of the 18th century. In the early 20th century, the development of synthetic substances paved the way for industrial adhesives. The breakthrough for cement bonding in industrial applications, however, was the manufacture of cyanoacrylate adhesives, first achieved in 1960. Adhesives have become indispensable in both industry and private households. There are no fewer than 250,000 types of adhesives on the market today.
Jointing technology for high-demand applications
Cement bonding is a highly developed jointing technology and therefore used in applications with extremely stringent specifications, such as the automotive industry, aircraft construction or pipeline engineering. The primary focus is on quality and safety demands. In the past, only insulation and interior panelling were glued in automobiles; currently, however, body parts, brake linings and other bearing components are joined permanently with adhesives. In aircraft construction, adhesives were used even earlier, initially to join wood parts, later for metal and plastic components – on some new models large sections of the fuselage and wings are cement bonded. The applications in aircraft construction indicate that adhesives are indeed resilient; the joints withstand temperatures far below freezing, as well as intense UV radiation and the enormous forces caused in turbulence.
Adhesives for piping systems
Easy and fast installation, low maintenance costs and absolute resistance to corrosion and incrustation are what make plastic piping systems an attractive alternative to metal systems. ABS, PVC-C and PVC-U are solvent cementable plastics. When constructing industrial piping systems, it is essential that the connections between pipes and fittings or valves are not only easy and quick to assemble, but also 100% dependable under critical application conditions. The conveyed media can reach temperatures between -60°C in cooling applications and +70°C in chemical processes. Pressures up to 16bar are also not uncommon. When acids, alkalis and other chemicals are used, the solvent cement joint must be just as resilient as the piping component itself. A reliable and completely leak proof connection must be guaranteed throughout the entire lifetime of the system, which is often 20 years or more.
In a crush test, the mechanical stability of a pipe-fitting connection is tested. The solvent cement joint is said to achieve practically the same stability as the pipe or fitting material. (photos: GF PipingSystems)
Adhesive composition offers high cohesion
The cement bonding process with diffusion adhesives is often referred to as “chemical fusion”. The term accurately describes the process because the material of the pipes and fittings is liquefied and then bonded cohesively as in the fusion process. Such a homogenous joint is achieved largely through the composition of the cement. The solvent cements used by GF Piping Systems contain up to 20% of the raw material from which the fittings and pipes are made. In conventional fusion, heat is applied. In cement bonding, the solvent in the adhesive causes the liquefaction.
The cement bonding process
After prepping the surfaces by means of chamfering and cleaning, the cementing process may begin:
1) Applying solvent cement
The solvent cement is applied in an even layer on the fitting and the pipe.
2) Joining
Excess cement is expelled and cavities are completely filled.
3) Dissolving and swelling
The solvents soften the surface and cause the material to swell.
4) Chemical fusion
A homogenous joint is created from the fitting and pipe material together with the raw material in the cement.
5) Hardening
About 90% of the solvent evaporates. The residual 10% remains in the bond, thus ensuring flexibility. This also contributes to a reliable and tight connection under mechanical stress.
Over a billion successful connections
In 1952 Georg Fischer launched the first PVC fittings. During the development phase, intensive R&D efforts were dedicated to new jointing technologies. The formula for what was later to become the adhesive “Tangit” was developed. In 1964 GF Piping Systems formed a partnership with the world’s largest manufacturer of adhesives, Henkel, and they continue to work actively together to further develop jointing technologies. Over one billion successful connections worldwide rely on the cementing process. Additional features are easy handling – even in cramped spaces – as well as chemical and temperature resistance.
Cementing on a PVC socket fitting for a homogenous and cohesive bond
A direct comparison to socket fusion shows the consistently high quality of the two methods.
Wide range of application areas
Two projects realised in Austria illustrate the versatility of the cement bonding method in constructing industrial piping systems.
Körner Chemical Plant Engineering was commissioned to set up a plant to degrease and pre-treat metal parts prior to galvanisation. In the zinc bath treatment process, alkalis and acids are used in addition to a water bath, and suction lines are required to conduct vapours back to the air washer. GF Piping Systems’ solution comprised PVC-U piping systems, cement bonded with Tangit, manually operated ball valves and a range of services from material testing and recommendations for installation supervision and on-site support. Under these aggressive application conditions, PVC-U proved its worth with its high chemical resistance. The plant was brought on line in 2006 and has been in operation since without any problems.
For the international chemical supply group Donauchem, it was crucial that only maintenance friendly pipelines and valves with high chemical resistance were used in the new, automated mixing plant for flexible mixing and manufacturing of inorganic chemicals. The plant operates with various mixtures of acids and alkalis at temperatures between +10°C and +30°C as well as pressures up to 3bar. The solution offered by GF Piping Systems encompassed PE 100 pipes with butt-fusion joints and PVC-U pipes with solvent cement joints, including diaphragm valves and ball valves as well as fusion machines, adhesives and cleaners. The plant was successfully put into operation in 2010.
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