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Using PE 100-RC in trenchless pressure installations

As the global population grows, utilities are forced to come up with cost-effective solutions to meet demands for reliable water and energy supplies. One of the easiest solutions is to expand utility networks and rehabilitate existing assets using Trenchless Technology.

However, trenchless pipe installations are often demanding and exceed common capabilities of pipe materials. Enter PE 100-RC: a specially engineered material with special requirements set in PAS 1075 and successfully applied in a wide variety of trenchless installations.

Born and raised in Germany
The first test manufacture of polyethylene (PE) took place in Germany in 1955. Over the next twenty years the material was refined and adapted for the manufacture of PE pipes. By the 1970s PE pipes were being used in all kinds of applications including water supply, gas supply and slurry transportation.

Since that time PE pipe has seen an exponential growth in usage, with the material becoming an increasingly popular choice for trenchless installations across Europe and around the world. The last 10 to 15 years have been particularly important for the growth of PE pipe – further development has led to improved pipe characteristics, ensuring the material can stand up to modern utility installation and rehabilitation techniques.

Fast forward to today and PE pipe is still one of the most popular materials for trenchless installations. The features and benefits of the product include:

  • High reliability
  • Proven service performance
  • High resistance to impact, surge, fatigue and low ambient temperatures
  • High ductility, toughness and elasticity
  • Smoothness of bore, ensuring optimal flow
  • Ease of assembly
  • .

The easy fusibility of PE pipe means that long lengths with highly reliable joints can be assembled ahead of installation. These joints are typically made with heat fusion – using either butt-fusion or electro fusion techniques.

Tough installation conditions
As with any aspect of trenchless installation, correct installation starts with selecting the correct tools and materials. In the case of PE pipe this means determining the optimal pipe type to meet the installation conditions and the fitness for purpose of the pipeline afterwards.

There are two pipe characteristics that determine the pressure capability of a pipe for pressure pipe applications: geometrics and material strength.

Geometrics refers to pipe thickness – the thicker the pipe, the higher the pressure capabilities. The pipe thickness is classified using the standard dimension ratio (SDR). Regarding material strength, pipes are classified by the minimum strength (MRS) at 20å¡C over a time period of 50 years. PE pipes for use in pressurised pipelines are usually made from a material with an MRS value of 10 N/mm squared.

New technology for a new millennium
As PE pipes were increasingly applied with trenchless installation techniques like horizontal directional drilling and pipe bursting, they were exposed to rough treatment and possibly continuous point loading – conditions that could potentially lead to pipe cracks and leakage.

In the late 1990s the need for extra resistant materials was recognised and dedicated investigations took place at HesselIngenieurtechnik GmbH in Germany into the crack resistance of PE pipe materials. The investigations revealed that continuous point loading to the installed PE pipes led to craze initiation that could eventually develop into through-wall cracks.

To avoid multiple pipeline failures the trenchless industry needed a new PE material: PE 100-RC (resistant-to-crack) pipe. PE 100-RC answered the growing demand for pipe materials with improved capabilities – such as resistance to outside damages and protection against point loads – while still remaining as easy to install and maintain as regular PE pipe. The minimum requirements for PE 100-RC are laid down in the publicly available standard PAS 1075 (with dedicated standards drafting work ongoing still in ISO). According to PAS 1075, compliance to the higher set requirements of PE 100-RC material requires three characteristics to be tested (in addition to the tests required for regular PE 100).

Notch test: This test measures the slow crack growth (SCG) of notched pipes. Lengths of pipe with machined longitudinal external notches are subjected to a hydrostatic pressure test while submerged in water tank at 80å¡C. The test method is outlined in ISO 13479.

Point loading test (PLT): This test, developed by Hessel, is used to determine the SCG of pipe with a continuous external point load. The test uses a point loading with a tip radius of at least 5 mm to determine if the pipe has internal yielding. The test method is outlined in PAS 1075.

Full notch creep test (FNCT): This test is less time consuming that the PLT and delivers comparable results. As such, it has seen a more rapid uptake across the trenchless industry. The test method is outlined in ISO 16770.

These tests demonstrate that compared to traditional PE materials PE 100-RC has a much higher resistance to notches and point loads.

The Wavin Group was one of the early adopters of PE 100-RC. The company used this material to develop TSDOQ pipes, which were introduced into the market in 2000. TSDOQ pipe is manufactured with three co-extruded layers: a middle layer that uses PE 100-RC material (50 per cent); an outer layer (25 per cent) and an inner layer (25 per cent) made with Total XSC50, a specialised PE 100-RC material with superior resistance to cracks.

Since 2000 approximately 20 million metres of Wavin’s TSDOQ pipe has been installed across Europe. The uptake in Germany has been particularly strong, with PE 100-RC pipe accounting for 25 per cent of all new pipelines installed.

With its efficacy determined PE 100-RC is being increasingly adopted for trenchless pressure pipe installations around the world. The upward trend is expected to continue in the coming years.

Case studies
In Klingenberg, Germany, just south of Frankfurt, water and gas supply pipelines had to be re-installed in 275 m lengths. In addition some 135 m pressure sewer (rising main) had to be installed.

All the lines had to cross a major river, the Main.

Directional drilling was selected as the installation technique. Pipe materials and sizes were PE100 RC SDR11, diameter ranging from 180 to 355 mm. The pipes were colour-coded blue for water, orange for gas and green for sewer. Impressively, construction was completed within a few days only.

In Ì_dz, the third-largest city in Poland, a substantial rehabilitation and extension program of the city’s water systems took place 2008-09. The project involved installing 65 kms of pipe DN160 to 400 mm were using pipe cracking and horizontal directional drilling (HDD). PE100 RC pipe was also used to avoid any risk of possible negative effects of point loading.

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