The Development of a Mains Pressure Test for PE & PVC Pressure Pipes [PVC, PE]

# 1995 Edinburgh

Many UK Water Companies are now using PE pipe systems because it 1s believed that use of an all-welded pipe will minimise the number of mechanical fittings employed and therefore will reduce potential sources of leakage. With pipes such as ductile iron and PVCu, which are joined in short lengths, it is often postulated that the rubber seal within the joint may eventually become ineffective and will allow leaks to develop. There is little hard evidence that this is true and indeed, the welded PE system has experienced considerable leakage problems due to the failure of electrofusion joints. Such failures do not need a sensitive test procedure to discern leakage, the fitting failure is normally of such a magnitude that the pressure drops rapidly to zero instantaneously. There have been almost no failures of butt fusion welds. The leakage problems with PE have centred on poor tightening of flange connections where the gasket provides a poor seal.

With ductile iron the test procedure is regarded as being straightforward and simple. The main is charged with water and raised to the test pressure and a valve closed to seal the system.
After allowing the main to stand for at least lhr any pressure decrease is noted and the volume of water necessary to raise the main back to the test pressure is measured. The current UK specifications allow for an acceptable leak rate of 0.02litres/day/bar pressure/mm dia./km length.

This test procedure 1s simple, but the interpretation of results may be in error if air 1s contained in the system. Because water has a very high bulk modulus a small leak will reduce the pressure very quickly. Where air is present however, the pressure will drop very gradually since gases decompress very slowly and a significant leak may reduce the pressure by only a small amount. In the UK, there is no requirement to ensure that iron mains are free of air prior to test and it is believed that many mains are declared to be leak-free when test results are rendered insensitive by the presence or air.

The iron pressure test 1s completely inappropriate for either PE or PVC materials which will creep and extend in dimensions under constant stress conditions and will suffer stress relaxation under constant strain. Hence the pressure would naturally decay without leakage and it is thus not possible to use the simple iron test for plastics pipes, since molecular rearrangement within the pipe wall will confuse interpretation of results.

Because of the non-linear behaviour of plastics under stress, it has been necessary to develop new test procedures for the testing of MDPE and HPPE pipe systems and this was recognised in the production of the WRc MDPE Manual. New procedures attempting to account for the viscoelastic deformation behaviour were proposed. Although PVCu was excluded from the new approach and WRc have decided to adopt the iron procedure, there is no reason in principle why the Type 2 test should not apply. PVCu does deform in a viscoelastic manner and has time dependent properties, albeit at a less marked level than for PE.

Please note that the whole article content is available on PPCA website onlySource : 1995 Edinburgh


Related papers

Very High Molecular Weight Polyethylene Resins with Improved Chemical and Abrasion Resistance

Author(s) : Dr. Dane Chang, Dr. David Marshall, Chris Cox 2014 Chicago

Plastic pipe applications often require polymers to have adequate abrasion resistance during usage. Although typical polyethylene resins have reasonably good resistance to abrasion and can be broadly used with a variety of chemicals, there are some demanding applications that require a resin with enhanced abrasion and...

Evaluation of the Surge and Fatigue Resistance of PVC and PE Pipeline Materials for use in the UK Water Industry

Author(s) : Marshall, Brogden, Shepher 1998 Gothenburg

Many early brittle failures in PVC water and sewerage pipelines, where repeated surge events are thought likely to induce embrittlement, were attributed to fatigue. The concerns of pipeline engineers led to the adoption of the British Standard Code of Practice CP 312 (ref. 1) by the UK water industry, which gives...

Smart Solutions for the Design of Rehabilitation with Plastics Pipes

Author(s) : Marshall, Morley, Pearson 1998 Gothenburg

The Water Industry in England and Wales has responsibility for an approximate length of 300,000km of water main, ~nuchof which was laid over 70 years ago using cast iron.Subsequently, asbestos cement, PVCu and cement lined ductile iron have been used. The old iron pipe systems that were installed in many of the...

Improvements in Electrofusion Welding in the UK Water Industry

Author(s) : Marshall, Hepburn, Netherwood 1995 Edinburgh

The adoption of polyethylene as a pipe material by both the gas and water indusmes has undoubtedly led to several sigruf~cant economic and operational advantages. The development of narrow trenching techniques and insertion refurbishment methods only became viable once a complete fusion jointed polyethylene system was...

The Crack Growth Resistance of PVC and PE

Author(s) : Marshall, Ingham, Brogden 1995 Edinburgh

When clients purchase plastics pressure pipes, they have frequently made that decision because they know that plastics do not corrode and they assume that if they do not exceed the pressure rating then a long lifetime should be assured. (Low cost has also been known to be a factor). It is thus of concern for the...

The Abrasion Resistance of Polymers Used in Slurry Transport Systems

Author(s) : Lowe, Marshall 1988 Bath

A Rotating Pipe Drum Test has been developed to assess the abrasion performance of plastics pipes to an extpnt where most test variables are understood. The procedure involves the rotation of relatively short pipe lcngths containing slurry on a conventional bail mlll. In the rest, the pipe surface repeatedly passes...

The Correlation of Fast Fracture Resistance of Polyethylene with Impact Toughness

Author(s) : Marshall, Birch-Kisbenyi, Youd 1988 Bath

A complete analysis of the Charpy impact system has been made to relate measurements of impact toughness to the geometry of samples. Using data obtained on pipe grade polyethylenes, Gc values at 20°C and 3°C have been found to correlate wel! with measurements of resistance to fast fracture in pressurised pipe...

The Renovation of Trunk Mains and Distribution Pipes in NWWA by Cold Drawn Swage Lining with MDPE

Author(s) : Young, Thomas, Marshall 1988 Bath

Within the Water Industry in England and Wales, there is an estimated length of 295,000 km of water main, much of which was laid in unlined cast iron prior to 1940. Subsequently, asbestos cement, UPVC and cement lined cast/ductile iron has been uscd....

Specifying High Toughness in PE Pressure Pipes

Author(s) : Marshall, Birch 1985 York

It is proposed that present Specifications for PE Pressure pipes are essentially undemanding and tests do not simulate service conditions. Perfect pipes are assessed rather than pipes which have sustained handling and installation ‘damage’.Flaws and defects have caused many problems with other thermoplastics pipes...

The Abrasion Resistance of Polymers in Slurry Environments

Author(s) : Lowe, Marshall 1985 York

A new test has been developed to evaluate the abrasion performance of different pipe materials. The Rotating Pipe Test simulates sliding bed flow of a slurry and gives quite excellent data reproducibility. The influence of sample geometry and slurry changing frequency and particle size have been assessed. The...

Members of the Association

BOREALISBOROUGEINEOS O&PIRPCKorea Petrochemical IND. Co., LTDLyondellBasellPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE
TOP