Marshall, Williams
Drainage and Sewerage # 1974 Southampton
During the last ten years, it has often been predicted that plastics will be used in increasing quantities as true engineering materials, Whilst there has been an increased acceptance of GRP as a positive alternative to metals in many applications, the use of thermoplastics for major load bearing structures has been more restricted, with the exception of the piping. industry, where the use of thermoplastics pressure and drain pipe has increased very significantly.
Manufacturers’ data sheets on various types of plastic would suggest that they are ideal materials for pressure piping, since very large “extensions to failure” are quoted (~100%) and uPVC in particular has a ee high “ultimate tensile strength” (~50 MN/m2 [~8000 Ibf/in2]). These properties, coupled with cost advantages (c.f. metals), acknowledged resistance to many environments which corrode metals, increased speed of pipe laying and easier handling characteristics have made thermoplastics attractive alternatives for use in sewage, water carrying and general chemical plant applications. The range of use has been extended recently into higher pressure piping by employing thermoplastics (particularly uPVC) overwrapped with GRP, the thermoplastic effectively acting in place of a gell coat resin.
It must be emphasised that with the majority of plastic pipe which is at present in service use, the materials have behaved in a satisfactory manner and there have been no problems apart from leakages at joints, etc., which are to be expected on a random basis, However, it is unfortunate to have to report that there have been a number of cases where uPVC pressure pipes have failed by cracking of the main section of pipe and various UK water and sewage undertakings have suffered failure problems which have been extremely expensive to repair. Indeed, in two cases the whole lines have been scheduled for replacement with metal pipes.
Of over 100 cases of failures known to the authors, the majority of fractures have occurred on a few systems which would suggest that in these cases either a faulty batch of material had been used or the line had not been laid according to specification. By careful excavation of failed sections, it is possible to check on the degree of care with which the pipe had been laid (backfill, etc.), but it is not quite so easy to check on the condition of the material since, as yet, there are no written standards by which to judge the fracture behaviour of plastic materials. Indeed, the present ASTM and British Standards demand elongations to failure of 80% as a requirement for uPVC, suggesting that the material is highly ductile and should not be subject to brittle failure. Unfortunately, in practice this 1s not the case, since the failures are invariably brittle in nature as shown in figures 1 and 2, which illustrate a practical failure on uPVC sewage pipe. In the close-up view of the failure (figure 2) it can be seen that there is no sign of any macroscopic deformation or yielding and the extension on the material at fracture must have been less than 5% (there was no likelihood of impact failure in this case).
Related papers
Author(s) : Bruce Mowry, PhD, P.E., Brian Dorwart, P.G., P.E., David Mancini, Bryan Fletcher, Roger Williams, P.E., Rene Brito, EIT, Arnelio Alfonso, P.E .
The City of Miami Beach owns and operates a 54-inch sanitary sewage PCCP force main (FM) that was built in 1977. This FM is the only transmission pipeline for conveying about 22 million gallons per day (MGD) of raw sewage to the wastewater treatment plant. In 2012, the City identified structural deficiencies in the...
Author(s) : Peter Hubbard, Linqing Luo, Andrew Yeskoo, Kenichi Soga, Krista (Moita) Araica, Gus Cicala, Marshall McLeod
Seismically active faults pose a risk to buried water pipelines that can be complicated to quantify. Fault type, slip rate, pipeline geometry, and soil conditions all factor into a complex soil-pipeline interaction. For critical pipelines that cross faults, high-density polyethylene (HDPE) has become an attractive...
Author(s) : Dr. Dane Chang, Dr. David Marshall, Chris Cox
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...
Author(s) : SKM Ting, JG Williams and A Ivankovic
Recent experimental data (Ting et al (1-2) and Ting (3)) has shown that the onset and subsequent evolution of the damage (craze) was found to be sensitive to constraint effects, in addition to rates. In particular, the effect of notch depth was found to exert a greater influence on the material response than through...
Author(s) : Marshall, Brogden, Shepher
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...
Author(s) : Marshall, Morley, Pearson
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...
Author(s) : Williams
A review of the Fracture Mechanics methodology for characterising toughness is given. It is shown that the fracture resistance R is derived by computing an energy difference. It is noted that R is dependent on the constraint in the crack tip region and that this leads to the very complex behaviour observed in Charpy...
Author(s) : Marshall, Hepburn, Netherwood
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...
Author(s) : Marshall, Ingham, Brogden
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...
Author(s) : Marshall, Birch, Morley
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...
Author(s) : Lowe, Marshall
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...
Author(s) : Marshall, Birch-Kisbenyi, Youd
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...
Author(s) : Young, Thomas, Marshall
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. It is kn-that a substantial number of...
Author(s) : Marshall, Birch
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 and...
Author(s) : Lowe, Marshall
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 effects...
Author(s) : Marshall, Taylor, Dickinson
A study has been carried out which has sought to establish the influence of processing conditions on the properties of medium and high density polyethylene. Residual stress and fracture toughness measurements have been carried out on hdpe pipe, from which predications of the influence of diameterlwall thickness on the...
Author(s) : Birch, Marshall
The mechanics of failure of uPVC pipe materials have been investigated using fracture mechanics test methods to induce brittle failure. It has been found that brittle failure can be quantified and test procedures have been developed which are capable of being used as quality control methods for classifying pipe. High...
Author(s) : Birch, Howarth, Marshall
The paper is a brief resum of a large project which has sought to investigate the use of fracture mechanics in evaluating the failure properties of a number of common thermoplastics pressure pipe materials. In this outline, the results of tests made on uPVC and YDPE pipes are described. Pre-notched pipes have been...
Members of the Association
