RENOVATION OF OLD WATER PIPELINE AND CASE STUDY IN CHINA

Transcription

1 Proceedings of the 17 th Plastic Pipes Conference - PPXVII September 22-24, 2014, Chicago, Illinois, USA RENOVATION OF OLD WATER PIPELINE AND CASE STUDY IN CHINA Xiao Lei 1, Cheng Liang 1 and Fang Dongyu 2 1 Changzhou CGE Water Co.,Ltd.; 2 Borouge Sales and Marketing (Shanghai) Company ABSTRACT The renovation of old water pipes in a big city, such as Shanghai in China, is always a challenging job due to huge population, heavy traffic and high demand for drinking water. Due to these problems No-Dig technology has become common practice, particularly relining using plastic pipes, to repair corroded metallic or concrete pipes. This paper describes the pipe renovation technology currently being used for drinking water supply pipelines and covers several real cases in China. This includes a recent project carried out by the Changzhou CGE Water Company which is responsible for the supply of fresh water to 2 million of local inhabitants. This case concerns the renovation of a leaking large diameter (1000mm diameter) cast iron main, which is buried 3.5 meter under a high speed railway bridge. Continued leakage of this main would erode the soil which could potentially damage the foundations of the bridge. One effective solution for the leakage of the corroded iron water main is to insert a close-fit PE100 pipe into the bore of the main. It is the first project in such a large size for both engineering and water companies in China. This solution is attractive in terms of both of economic and environmental aspects causing the least disturbance to the neighborhood. However there are a number of challenges including the jointing and forming process and the potential damage to the outer surface of the PE pipe. The success on this project has subsequently been shared with other water companies who are facing with similar problems in China. KEYWORDS: PE100, high stress crack resistance, relining, water pipe, renovation INTRODUCTION As the Chinese economy has grown over the last 30 years the urban population has increased dramatically from 10% to 40% of the total population, which has compounded water shortages and water pollution problems. Despite increasing investments in new water and sewage systems in many of the major cities the leakage rates remain high as many of their systems are heavily corroded and Copyright 2014 by PPCA

2 leaking. These new infrastructure projects have to take place in cities that are getting more and more crowded and compete for space with the many expansion projects taking place, such as airports, bridges and high speed railways. Therefore it becomes very difficult for the cities to install new pipes or replace old pipes in open trenches due to the heavy traffic, potential public safety risks and the huge cost. Therefore, no-dig technology is taking a major position in China. For example in Shanghai recently two major Swagelining projects have taken place in addition to the first U lining project. The U-lining technique is still new in China and there is a lack of experience with the engineering practice. In this paper, the first U-shape relining project in China and its engneering solutions are presented and discussed. CHALLENGE OF THE PROJECT Changzhou City is situated on the southern bank of the Yangtze River just 165km west of Shanghai. The Changzhou Water Company was founded in 1927 and is now a joint venture with Veolia and the Citic Pacific Group. Veolia and Citic Pacific Group own 49% of the company for 30 years and the remaining 51% is owned by the Changzhou municipality. The water company is responsible for providing fresh water to 2 million of the local inhabitants but like many other water companies they have many problems with their existing network of iron pipes. One particular concern for the water company was a leaking 1000mm diameter cast iron main which was installed in 1998 under the Wanfu Road. Where the road drops 3.5 metres to pass under a railway bridge the misaligned pipe joints were leaking and the concern was that this could ultimately damage the foundations of the bridge which carries the high speed Beijing to Shanghai rail link. The high level of internal corrosion in the pipe was also contaminating the water and therefore it was decided to replace or renovate a 400 metre section of the main. THE CHOSEN SOLUTION One effective way to overcome leakage and contamination from a corroded iron water main is to insert a close fitting PE100 liner pipe into the bore, which will effectively provide a new pipeline at a considerably lower cost and without the disruption caused by installing a replacement pipe. Whilst this is an attractive option from an overall economic and environmental viewpoint, trenchless installation techniques can introduce scratching and scoring on the outer pipe surface. This damage can develop into cracks which gradually make their way through the pipe wall, eventually leading to a brittle failure of the pipe. To overcome this concern it was decided to use a High Stress Crack Resistant (HSCR) PE100 material to produce the liner pipe. This type of material provides a much higher resistance to crack initiation and growth, thereby giving engineers greater confidence to use the lining technique. Most of these HSCR bimodal PE100 materials use hexene as a co-monomer rather than butene which is used in most standard PE100 materials. Under the right polymerisation conditions this leads to a PE molecular structure that has many more and longer side branches. As shown in Figure 1 this results in stronger tie molecules that resist the growth of the crack through the pipe wall and dramatically slow down the process. In the Notched Pipe Test described in the PE water pressure pipe standards ISO 4427 and EN HSCR PE100 pipes typically achieve failure times in the region

3 of 10,000 hours or higher. This compares to the 500 hours required for standard PE100 pipes. Figure 1 The action of the tie molecules in HSCR PE100 in resisting slow crack growth THE INSTALLATION OF THE PIPE For the project, a non standard 983mm diameter pipe with a 15mm wall thickness was manufactured by Shanghai Chinaust using a HSCR PE100 material. On site the team from the Shanghai Water Special Engineering Co.,Ltd. butt welded the pipe sticks together and removed the external bead prior to passing the pipe through a folding machine that formed it into a U shaped section. Strapped in this form the effective diameter of the liner pipe is greatly reduced and it could be easily inserted into the bore of the old pipe. Once in position the PE100 pipe was pressurised to break the strapping and to form a close fit liner, which will eliminate leakage and prevent further contamination of the drinking water, thereby providing the water company with a very cost effective solution to their problem.

4 Figure 2 Butt welding the pipes together prior to forming them into a U shape for insertion into the leaking iron water mains SOME PROBLEMS ENCOUNTERED AT LOW AMBIENT TEMPERATURES However, things didn t go as smoothly as planned in the early stages. After the installation site was prepared, the engineering company and the pipe company laid the pipes on the ground along the road. The road is very narrow so they decided to do the installation at night or in the early morning to minimize safety risks to pedestrians. Unfortunately the weather in Feburary in Changzhou suddenly got colder and the temperature down as low as -3 C during the night and early morning. The pipe was therefore unusually stiff and the engineering company found it was very difficult to fold the pipe into a smooth U-shape. The sharp angles caused some local buckling of the pipe and some small cracks were observed around these sharp corners as shown in Figure 3. Figure 3 Sharp corners and local buckling caused by forming the pipe at low temperatures Table 1 Material properties at different temperatures Properties -4 C 0 C 5 C 10 C 23 C Tensile stress at yield, MPa Tensile strain at yield, % Tensile stress at break, MPa Nominal tensile strain at break, % >150 >150 >150 >150 >600 Tensile modulus, MPa The engineering company therefore stopped the installation to make checks on their pipe folding equipment and of course the pipe material. Tensile properties were

5 measured at different temperatures ranging from -4 C to 23 C as shown in Table 1. It can be seen that tensile modulus is increased dramatically with the decrease in temperature, which means the PE100 material becomes considerably stiffer at lower temperatures. Tensile strain at break at lower temperature is also lower which indicates why the environment temperature plays such an important role in the technical solution. IMPROVED PERFORMANCE AT HIGHER AMBIENT TEMPERATURES The problem was solved by waiting until the cold weather had abated and the project was restarted in March. At the higher ambient temperatures the U form could be produced at much lower stresses and a smooth profile was formed with no evidence of cracking. Under these conditions the project was completed in very quick time and the HSCR PE100 liner pipe prevented any further damage to the foundations of the bridge. Figure 4 Pipe successfully folded and strapped being inserted into the old leaking water main CONCLUSIONS During this first large diameter U-shape relining project, the Chinese engineering company learned a lot and was able to further improve its technology. Clearly the technical solution has to consider all the possible factors in order to provide the optimum solution under all conditions. The use of a high stress crack resistance PE100 material will effectively protect the pipe from failure due to any surface scratches or scores sustained during the installation. The successful development of this and other no-dig technologies will surely support the development of the urbanization that is taking place in China and other Asia countries.