High quality PP-B pipe materials for sewage pipe systems

The latest generation of PP-B materials are the so-called PP-HM class (PP with higher modulus) which exhibit a higher stiffness have already been approved to the relevant European Standards. Currently an ISO standard isunder preparation, which also includes the PP-HM material class [1]. In this paper three practical installation examples demonstrate the versatility of the PP-HM material in different fields of application.

Introduction
In the past, rigid pipes made of conventional materials such as vitrified clay,concrete or cast iron were the preferred materials for sewage pipe works due totheir wide availability and their familiarity to the end-user. They were also perceived as low cost pipes with high strengthand stiffness.

Indeed this is still the case in some European countries whilst inothers, such as the Scandinavian countries, plastics pipes made from polyolefinsare the preferred choice for buried sewage and drainage applications.

Clearly, there is a major difference between countries and regions as far as selection of pipe materials is concerned. If a full assessment of network investmentis carried out including the totalcost of installation, maintenance and thepotential repair (including the cost ofconsecutive damage due to leakage),then the balance is changed strongly infavour of plastics pipes. In Germany these new non-pressure piping systems based on PP-B materials were first introduced into the market at the end of the1990’s [2 - 5].

The capabilities of these PP-B pipe systems were well-known formore than 25 years in Scandinavia and the benefits well appreciated by the installer and end-user. The development of the new PP-HM class of materials,which was especially designed forburied, non-pressure drainage and sewage pipe systems [6], has further accelerated the acceptance of polypropylene sewage systems.

Market development
Although the success story for buried PP-B sewage pipelines started in NorthernEurope, more recently they haveenjoyed strong growth in Central and Southern Europe. For example in Sicily,there has recently been some good experience not only for small diametersystems but also for very large diameter systems [7].

From a European perspective, the main reasons for the growing acceptance of PP-B and PP-HM for sewage applications are as follows:

• Greater knowledge of the sewer network condition due to more regularcamera inspection schemes
• Publication of failure statistics forpipes made of different material
• New plastic pipe developments, inparticular new innovative PP-B pipe systems
• New pipe material developments: PPHM,high impact PP-B with superior stiffness
• Progress in the European standards for PP-pipes for sewage applications
• Continued advancement in the machinery technology for structured wall
  pipes, in particular for pipes of medium and larger diameters
• Decision makers and civil engineers are showing greater awareness for the
  total life-time cost assessment and the real life-time performance of pipe
  systems
• Inherent performance benefits of pipe systems made of flexible thermoplastic
  materials compared to conventional rigid materials.

Flexible pipe systems made of thermoplastic materials like PP-B fulfil all the requirements of modern sewerage networks as has been demonstrated in the past [8]. Indeed the failure statistics of pipelines made of different materials clearly demonstrate a superior performance [9].

Recently leading communities in Germany, like the city of Göttingen, have used total quality management principles and a sustainable approach to the management of sewerage networks and decided for requirements which altogether can only be fulfilled by weldable thermoplastic pipe materials [10]. This approach has been supported by many leading companies from the plastics pipe industry in Germany through a nation wide road show to promote the total quality management principles to a broader audience [11].

PP-B piping materials and recentmaterial developments
Regular PP-B materials, typically with a modulus of elasticity in the range of 1,100 – 1,300 MPa, have been used for quite long time for the manufacturing of sewage and drainage pipes. Since several years a new PP-B class of materials, i.e. PP-HM (PP with higher modulus, E-modulus ≥ 1,700 MPa) has been available on the market. This class of materials combines high stiffness and high impact strength, also at low temperatures, whilst fulfilling the internal pressure resistance requirements.

The latter property is particular important to demonstrate the life-time of the pipe. From a material structure point of view, both the high stiffness and the high impact strength are based on a polymer matrix with high crystallinity, in which a finely dispersed rubber phase is embedded. Such PP polymers are produced by modern multi-reactor technology. In addition, PP-HM materials are characterized by excellent chemical resistance, very good short and long-term properties whilst retaining a low density.

The general properties of PP-B materials and the new PP-HM class are given in Table 1, illustrated by commercial products. All these grades fulfil the material requirements of the European standards for buried solid wall sewage and drainage pipes according to EN1852-1 [6]. The PP-HM materials also meet the additional requirements for materials with an E-modulus of ≥ 1,700 MPa and for structured wall pipes in accordance with the draft prEN13476 [12].

BorECO™ BA212E and BA222E, both PP-HM materials, facilitate the design of stiff, robust solid wall pipe systems that are easy to install because of their high stiffness and low product weight. These properties together with high impact strength and the possibility of longer pipe lengths provide a cost-efficient, economic pipe system for sewage networks. BorECO™ PP also offer major benefits for the production of ribbed, structured, multi-layer and spiral wound pipes as well as for foamed pipe solutions, injection- moulded fittings and for chambers and manholes. For all these designs BorECO™ PP offers an economically attractive material choice which out perform other materials.

The increased short-term and longterm modulus of elasticity (i.e. extrapolated to 50 years) of the new PP-HM class of materials also provide an increased resistance against creep and stress relaxation [13, 14]. These materials also exhibit an excellent stress crack resistance which ensures a long service life.

In order to demonstrate long-term pipe performance and to ensure that the lifetime is more than 100 years at a typical operating temperatures of a sewage pipe system, internal pressure tests are carried out in accordance with DIN 8078 (quality control requirements) for in excess of 1 year (at 110 °C), these test results are then extrapolated on the basis of the standard extrapolation method ISO 9080 [13].

Installation examples
In this section three examples are given of the installation of sewerage systems manufactured from higher stiffness PP-HM materials. The projects utilise readily available pipe designs, namely solid wall pipes in accordance with DIN EN 1852-1/A1 for new installations and for short pipe relining and spiral wound pipes in accordance with the European standards and guidelines. Although not covered here these PP-B and PP-HM materials are also used extensively for the manufacture of continuously extruded twin-wall and ribbed structured wall pipes.

Piping system made of PP-HM at the airport of Cologne/Bonn (Germany)
The airport of Cologne/Bonn is the fifth biggest airport in Germany based on passenger frequency. In the year 2004, an average of 450 plane take-offs and landings took place per day. When based on cargo traffic, this airport is second only to Frankfurt/Main. In 2002, the seven terminals handled a total of 542,400 tons of cargo.

In the course of the operations of the airport, it was necessary to install a drainage pipeline crossing under one of the runways with a total length of 2 km. Therefore in addition to the standard performance the pipeline had to fulfil a number of specific requirements:

• High resistance against static and dynamic load, also under the extreme condition "Aircraft with a total weigh of 550 tons"
• High chemical resistance in particular against aggressive de-icing media,
  e.g. glycol or sodium acetate
• Safe, proven jointing technology
• Safe and fast installation
• Lowest possible level of maintenance.

Due to these requirements, the heavy duty solid wall pipe system Awadukt PP SN10 Rausisto manufactured from BorECO BA212E by Rehau was chosen (Figure 1). This system fulfils all the requirements including the high static and dynamic load even at a shallow laying depth. The high intrinsic stiffness of the system and the special jointing technology was also greatly appreciated during installation. The jointing system comprised an elastomeric gasket which was locked into the socket during the manufacturing process thereby preventing any movement during installation.

Short pipe relining with pipes made of PP-HM
In the city of Einbeck in Lower Saxony, Germany, the sewer network is installed as separate foul and rain water systems to prevent rain water from mixing with foul water. However during heavy rainfall it is still possible for the central sewage treatment plant to reach its capacity limits due to rain-water intake from private property. With this background, a number of selective measures were developed to minimize the risk of rain water infiltration.

One such measure was to connect the private property along the Gleiwitz street to the public drainage and sewage network. Due to the very narrow streets and the need to minimize open trench works, it was not possible to use pipes of normal length and therefore relining with short pipe lengths was chosen. An additional requirement was to install a system with leak-tight joints.

The system chosen was a short pipe relining system made from PP-HM (BorECO BA212E) produced by Karl- Schöngen AG (Figure 2). The total pipe length of the installed pipeline was 51 m, using DN 200 mm pipes with individual length of 1.0 m, respectively. The pipes were connected with the so-called "multi-raster-fusion technology". Basically, this method is practically a socket connection, using supporting elements (so-called rastern) combined with additional inductive fusion of the remaining wall thickness. Installation of the 51 m length took only 3.5 hours which included the time for the fusion welding of the pipes.

PP-HM for an ID 2000 mm spirally wound pipe system in Canicattì, Sicily, Italy
This project in Sicily is described in more detail because it was a remarkable project from many points of view.

Firstly, the pipeline was originally designed using 2.0 m pre-cast concrete pipes, based to past practice. However, after considering the long term leak tightness and durability requirements for the system, the project was carried out using both pipe and manhole systems manufactured from PP-HM material.

This was even more remarkable as in Italy, unlike Scandinavia and some countries in Northern Europe, PP-HM materials had only just been introduced to the market, therefore a project of such size is all the more remarkable. The successful production of such high quality large diameter pipes is also a testament to the technical capabilities of the PP-HM material.

In the case of this project, the requirements for the pipe system were specified in a way that the special benefits of flexible pipe systems made of PP could be exploited. Simplast S.p.a. produced the high quality pipes and manholes using a spiral winding technique called Weholite, which is licensed from KWH Pipe. BorECO BA212E was chosen as the raw material for the manufacturing of the system [7].

The town Canicattì, has 34,000 inhabitants and is located in the province of Agrigento, Sicily, 40 km from the South West Coast, see Figure 3. The region is a large agricultural centre and Canicattì is well known for the production of almonds, olives and grapes.

System requirements
A range of requirements for the pipes and systems components was defined by the municipality as follows:

• Designed and installed based on European or International standards and guidelines
• Easy, fast and safe to install
• Have high hydraulic capacity
• Show excellent resistance towards substances found in municipal sewage
• Excellent resistance towards corrosion, stress cracking and abrasion
• Easily installed flexible and leak tight joints
• Flexible to soil movements and leak tight also under tough conditions
• Designed for a service life exceeding 80 years
• With low total cost and low maintenance costs.
  
   

System description
The project is based on a combined solution for both sewer and rain water (see Figure 4). It is designed as a SN4 system and has in total a length of 3.3 km. Pipe dimensions vary between ID 500 to ID 2000 mm (Figure 5), i.e. main collectors are included but not the house connections.

Installation and jointing technology
In the Canicattì project, the normal pipe length is 13.5 m, i.e. only one joint or connection per 13.5 m compared to the concrete alternative based on circular prefabricated pipes, with normally 7 - 14 joints per 14 m. Clay and ductile iron pipes are not available in the large pipe diameters involved in the project. Another important factor is the weight of the system. An ID 2000 mm Weholite PP pipe length of 13.5 m weighs approximately 2400 kg. The same diameter of concrete pipe weighs around 4000 kg per meter (i.e. approximately 25 times heavier).

The installation was carried out with standard excavation equipment. The installation of 4 x 13.5 m of an ID 2000 mm pipe took approximately one day. This is possible based on the low pipe weight and easy connection of the system parts. A PP-HM pipe of this diameter is still very flexible; hence no problems due to potential soil settlement need to be expected.

In this project it was crucial to secure good jointing of the pipes and system parts, especially because of the difficult ground and soil conditions. The two jointing solutions chosen for the Canicattì sewer were extrusion welding and a flexible mechanical connection. For the larger diameters, the pipes were jointed using extrusion welding, the ultimate leak tight solution. For the smaller diameters, e.g. 500 and 600 mm, the flexible mechanical solution was normally used. In general, push-fit jointing is often used in these dimensions for sewers.

Manholes
The complete system was made from the new generation PP-B materials. The manholes were up to 8 m of depth with a diameter of 2.4 m (Figure 6), they were connected to the larger pipe sections mainly by extrusion welding. This method provides the best means for leak-tight connections following soil settlements to minimize the risk against leakage to the environment.

It is known that large diameter thermoplastic manholes and chambers perform well in the soil (15). However as with pipes, manholes also respond differently to soil movements if poorly installed and this is why special efforts have been put on design, preparation and installation technique. For the installation, ASTM D2321 (16) has been followed and for the manhole design, the guidelines according to ASTM F1759 (17) and the German guideline ATV A 127 have been used.

Conclusions and outlook
Starting in Northern Europe, people have gained more than 25 years very positive experience with the material PPB
used for buried sewage and drainage pipe systems. The new PP-HM class of materials offers an additional opportunity to manufacture pipes of reduced weight compared to existing pipes made from thermoplastics.

Well designed pipe systems made of high-quality PP-B and PP-HM materials fulfil all the requirements for pipe systems used for non-pressure sewage and drainage applications, including some that are not achieved by all the conventional rigid pipe materials. The new PP-HM materials provide the system producer with the best opportunity for future innovations.

Developments in pipe production machinery technology also contributes to the variety and types of systems that can be produced using PP-B, and in particular PP-HM materials. It is up to the plastics pipe industry, including raw material manufacturers, test institutes and machinery manufacturers, to further utilize the potential of PP-B and the new PP-HM for new exciting sewerage system innovations.

References
[1] ISO/DIS 8773:2005, Plastics piping systems for underground drainage and sewerage – Polypropylene (PP)

[2] N. Jansen, Polypropylen – A tried and proven pipe material, 3R international, February/March 1998

[3] L. Bosche, Polypropylene drainage piping system, 3R international, September 1998

[4] D. Scharwächter, Neu auf dem Markt: Abwasserohrsystem aus PP – Eigenschaften, Produktdesign u. Wirtschaftlichkeit, Anwendungsbeispiele aus der Praxis; Wiesbaden Pipe Days ´99, Wiesbaden, 26-27 April 1999

[5] K. Ebner und C.-G. Ek, Der Rohrwerkstoff PP: Schlagzähes PP-B hoher Steifigkeit: Eigenschaften und Anwendungsgebiete, Wiesbadener Kunststoffrohrtage ´99, Wiesbaden Pipe Days, Wiesbaden, 26-27 April 1999

[6] DIN EN 1852-1:2003-04, Plastics piping
systems for non-pressure underground drainage and sewerage - Polypropylene (PP) - Part 1: Specifications for pipes, fittings and the system

[7] C.-G. Ek, S. Barresi, Plastics Pipes XII, Large diameter spirally wound PP sewerage pipe installation in Sicily, Milano, 19-22 April 2004

[8] G. Kania, Überzeugende Alternative: Polymere Abwasserrohrsysteme in der Abwasserentsorgung, Wiesbaden Pipe Days '03, Wiesbaden, 23-24 April 2003

[9] ATV: Zahlen zur Abwasser- und Abfallwirtschaft, Hennef, 1996

[10] M. Fiedler, Sanierungsstrategien im Vergleich, 5. Göttinger Abwassertage, Göttingen, 23-34. February and 1.-2. March 2005

[11] Leaflet for the road-show: To the point – Practical experience with pipes, Technische Akademie Hannover e.V., 2005

[12] prEN 13476-1, 2005, Plastics piping systems for non-pressure underground drainage and sewerage - Structured-wall piping systems of unplasticized poly(vinyl chloride) (PVC-U), Polypropylene (PP) and polyethylene (PE) - Part 1: Specifications for pipes, fittings and the system

[13] C.-G. Ek, Plastics Pipes XI, Stiff PP: The new generation polypropylene block copolymer for non-pressure pipe applications, Munich, 3-6 September 2001

[14] L.-E Janson, Plastics Pipes for Water Supply and Sewage Disposal, 4. Edition, Majornas Copyprint, Gothenborg/ Stockholm 2003, p108-112 and p216- 232

[15] F. Alferink, Performance of plastics manholes, Plastics Pipes XI, Munich, 3-6
September 2001

[16] ASTM D2321, Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity Flow Applications

[17] ASTM F1759, 1997, Standard Practice for Design of High-Density Polyethylene (HDPE) Manholes for Subsurface Applications BorECO™ is a trademark of Borealis A/S