Raising the standard

Failing to maintain the integrity of standards could prove costly to the water industry, argues Frank Jones, director of the BPF Pipes Group

As the UK, and indeed the global economy, struggles to find its feet, the AMP5 investment programme appears to be bucking the trend in the construction sector and is building up a head of steam. One worrying aspect that seems to have appeared within this cycle has been some water companies’ change of procurement strategy to a competitive tender process as opposed to the partnering ethos that was used in previous phases. Of course, the fiscal problems have meant that we are all counting the pennies, but at what cost to our utilities. It is a well known fact in commerce that the definition of “value” is not “cheapness.”

In order to protect us all from the old “cheap and nasty” adage there are numerous international, European and UK national standards and in many cases national regulations / requirements. The water industry and the products and services used therein are no different, and compliance with applicable standards ensures that customers can be safe in the knowledge that money has been spent on products that comply and are approved to applicable standards.

Plastic pipes
One such standard that has recently come to the fore, taking over from the incumbent WIS 4-35-01 is the European Standard BS EN 13476 – Plastics piping systems for non-pressure underground drainage and sewerage – structured wall piping systems of unplasticised poly vinyl chloride (PVC-U),  polypropylene (PP) and polyethylene (PE). This standard took many years to develop and involved most of Europe’s plastic pipe manufacturers to ensure commonality across the whole industry when it comes to ensuring the quality, reliability and longevity of the product.

In simple terms, it has raised the bar for structured-wall plastic pipe system standards right across Europe. The standard was specifically written for structured wall pipe systems made only from one of three materials: HDPE, PP or PVC.

As stated by the CEN TC 155 committee (the European Committee for standardisation), it is not applicable to, and therefore cannot be used, as a standard for pipes made from other materials, combinations of materials (composite pipes) or pipe systems that do not belong to the clearly defined structured wall family.

Reassurance
BS EN 13476 covers all aspects of the system for foul and surface water sewers, some of the main points that provide comfort and reassurance to the end users are:

Raw Materials
BS EN 13476 details a very stringent testing regime for the raw materials used in manufacturing. In fact, the pressure resistance requirement that has to be met in order to comply with the standard is so demanding that it is very unlikely that anything below a specific pipe grade material, for example, PE 80/100, in the case of HDPE, would pass. This gives end users reassurance that only premium grade materials are used.

As Jan-Ake Sund, head of laboratories at KWH Pipes Finland, and one of Europe’s leading experts on materials puts it: “It is strange, but you hear this more and more these days, that unclassified PE materials are said to be PE 63 material. If no classification according to ISO 9080 has ever been made for a material, then it is not acceptable to use a classification number for it.”

It is an unfortunate state of affairs that even some test houses bow to commercial pressures and state classifications such as PE 63 which are so clearly incorrect and misleading to potential users.

Wall thickness
BS EN 13476 has a clearly defined a waterway wall thickness for the pipes that gives the installer and end user satisfaction in the knowledge that it will provide extended design life and longevity. HDPE, PP and PVC are generally regarded as the most abrasion resistant of all the pipe materials but by specifying a minimum wall thickness, the standard provides for excessive wear.

Vagn Salling Poulsen, convener of the original CEN committee, was one of the main driving forces behind the European Standard BS EN 13476. He said: “The waterway wall thickness is specified in order to give a minimum of guarantee that the foul water does not enter the hollow sections of a pipe construction, either as a result of excessive pressure in connection with surges or as a result of wear.”

Impact resistance
Of course, Poulsen’s comments also touch on the necessity for adequate impact resistance that both the construction of the pipe wall and thickness of it provide in the new standard. If any pipe product were to have a single, very thin wall construction then not only would it be impossible to gain approval to BS EN 13476, but ultimately the high risk of failure to the end user would be unacceptable.

Ring flexibility
In order to comply with BS EN 13476, manufacturers of plastic structured wall pipes must test their products in accordance with a number of methodologies listed therein. One of the most important tests that demonstrate the structural integrity by BS EN ISO 13968 - Plastics piping and ducting systems thermoplastics pipes determination of ring flexibility.

This procedure enables the producer to determine the deflection and force at which physical damage, if any, occurs within 30% diametric compression.

The visco-elastic behavioral properties and strainability of the structured wall plastic pipes generally allows them to deform to over and above 30% without any issues in their structural integrity or performance in practice.

This is contrary to products such as composite pipes which have proven in independent tests to buckle and fail at small deflections of 5%. Indeed, in one particular composite product, failure continues without increasing the load.

Structural design
BS EN 13476 also gives clear guidance on structures involving fully plastic pipes should be designed by referring to industry accepted standards such as BS EN 1295 - Structural design of buried pipelines under various conditions of loading general requirements as well as national design standards such as the German ATV A 127E. These give clear instruction and assurance on how to design for structured wall plastic pipes and give the designer a guarantee on how pipes that fully comply with BS EN 13476 will perform.

Standards take away both the uncertainty and the ignorance of how structured wall plastic pipes perform under buried conditions.

Epilogue
In principle, new products should always be encouraged into a marketplace to drive innovation and development. However, they must be regulated, tested and approved in the proper manner using methods that are recognised across the industry.

More worryingly, the fact that all industries have been so badly affected has meant that even those bastions of rules and bureaucracy, the approvals bodies, are giving way to commercial pressures. This has led to a trend of products receiving approval certificates against selectively chosen individual requirements taken from recognised European and national standards that have been designed for completely different products.

This “pick and mix” approach does not necessarily ensure that that all aspects of the reference standards are met. By ignoring these tried and tested systems, dangerous precedents can be set that could have a longlasting and damaging effect, not only on the reputation of the approvals bodies and their ability to provide trust and safety in the water sector, but on the plastic pipe industry as a whole.


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