Plastic pipe fittings and joining technology

A review of the AMI Plastic Pipe Fittings and Joints 2007 conference, where there was a real buzz in the debate over new technology starting with scepticism and finishing with plans to check it out

Pipe joints require a high level of guaranteed performance and as a consequence the industry uses advanced technology in both fitting manufacture and joint sealing: the conference heard about many developments from the different manufacturers.

AMI has reviewed the state of the European pipe industry - around 3.5 million tonnes of plastics are used per annum.

With fittings, the market is growing in applications in sewer, water, plumbing, road drainage, gas and soil and waste.

"The fittings industry in Europe has enjoyed strong growth in recent years", remarked consultant Jon Nash, "and can look forward to a robust future despite the predicted slowdown in construction".

The production of fittings is a precise moulding operation, even involving large item rotomoulding for exceptionally large joints.

AMI organized a conference in Cologne in December 2007 to debate production methods for fittings, and pipe joining technologies.

Crosslinked polyethylene (PEX) is making inroads into the plumbing market and avoids issues such as theft of valuable copper pipe.

It can be installed more quickly and at lower cost.

The material must be protected from abrasion and UV exposure, according to expert Camille Rubiez of the US Plastic Pipe Institute.

PEX can reduce the number of fittings in the system and a variety of types of fittings can be used.

Aliaxis are experts in producing PVC pipe fittings for a range of applications from water distribution to drainage and sewage.

Ramix Moulds specialises in pipe fitting tooling.

Energy is a significant factor in moulding and NRG Control have worked with fitting manufacturers to improve profit by cutting this cost.

66% of the energy used is in processing, particularly the electric motors and barrel heaters.

Simply using motor speed control can cut unnecessary work - this was illustrated with a Demag machine making a fusion coupling.

Barrel temperature control can save 30-70% of heating costs according to Fred Pratt.

Pipe extrusion requires a high viscosity material, while injection moulding needs improved flow.

The Borealis Borstar polymerisation process has generated a better grade of PE100 for pipe fitting manufacture.

Prime Polymer (Japan) has been working on a similar project and also has a high flow PE100 material, produced using a new single-site catalyst to control molecular structure.

It moulds 30% faster than conventional grades because of the high MFR.

High performance materials such as polysulphones are used in fittings.

Solvay Advanced Polymers has carried out extensive research into mould flow and cost comparisons with metal fittings.

For example, the Udel P-1700 grade is said to offer a 75% saving compared to brass.

The material has been used in crimp, sliding sleeve, screw, push fit and manifold systems.

Solvay Solexis has fluoropolymers for applications such as industrial pipe and pressure pipes.

These fluoroplastics are found in hot water systems and fittings and have exceptional chemical resistance.

Foma Engineering has modified the injection moulding equipment to cut costs in fitting production.

It has also examined methods of socketing corrugated pipes and developed injection moulding of the socket on to a corrugated pipe.

Agru Kunststofftechnik has examined polypropylene pipes after 21 years of exposure to 20% sulphuric acid.

PP offers good toughness, chemical and temperature resistance.

The aged pipes showed a white brittle inner layer deposit (from Zn-S pigments reacting with acid) and an outer chalky brown layer.

Tests showed that the material was still in good condition with impact properties similar to new pipe - the outer layer simply flaked away.

SKZ has also studied aged PP pipe using FTIR and examined oxidation in relation to failure.

ENSAM has studied the adverse effects of a change in disinfection chemicals in water in France on polyethylene pipes.

TWI has looked at different joining methods for plastics pipe.

Hot plate welding is used for PE, PP and PVDF (63-1600 mm OD) in applications such as gas and water distribution and can be automated.

Socket fusion welding is used with the same materials at diameters up to 1500mm mainly in industrial pipework - the equipment is portable and the technique is manual.

Electrofusion welding is used mainly for PE up to 710mm OD and is useful in narrow trenches.

Infrared welding (up to 225 mm OD) is employed in pipework in the semiconductor and pharmaceutical industries.

Solvent welding is employed in PVC, cPVC and ABS joining and requires very little equipment.

Extrusion welding is used in non-pressure systems to join PP and PE pipes and to fabricate fittings.

TWI has also worked on ultrasonic inspection systems for butt fusion and electrofusion joints in PE pipes.

Fast Fusion from the USA, has demonstrated technology for joining HDPE pipes.

It uses standard butt fusion equipment inside the moving cab that follows the pipeline and picks up and joins the pipe ends as it travels.

Georg Fischer described the issues of joining of large diameter PE pipes, where ovality of the pipe can cause unacceptable gaps.

There are various solutions: primarily the pipe can be re-rounded, or the coupler can contract down during the welding process.

The company has extensive field experience and developed practical technology to solve this problem cost-effectively.

Friatec has worked on fusion of high pressure plastic pipes including polyamide, reinforced thermoplastics and polyethylene.

The pipe should fail before the joints in test conditions.

Kiwa Gas Technology has extensive experience in testing and has examined electrofused PE pipes using the standard peel test and a slow peel test.

The studies showed that even first generation PE pipes could be joined using the new PE100 and PE80 couplers.

Slow peel testing picked up joint failures in PEX pipe that were not evident using the standard short-term methods.

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