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A major urban rail project in southeast China uses new welders to get the job done on time.
By Christophe von Arx
Introduction
Guangzhou, previously known as Canton, is a thriving city in the southeast of China with an estimated population of more than 10 million, with an estimated 15 million living in the entire Pearl River delta region.
Due to its proximity to Hong Kong, this area in Guangdong province has played a decisive role during the recent years of economic boom in China and is still an important gateway to the West today. In addition to being home for the world’s highest television tower (610m / 2,001ft), currently under construction, a complex but well-organized public transportation system has also developed.
Guangzhou Metro
With the large number of commuters in this sprawling metropolis—the third-largest in China—a systematic public subway network has been developed during the last two decades.
Four rail lines are already operational, with a fifth under construction. Much of the Guangzhou Metro travels underground. Since August 2004, builders have been working on this east-west line around the clock. Line 5, almost 27 miles (43km) long with 29 stops, is expected to be completed this year in an effort to provide additional relief for above-ground traffic.
The entire rail grid is operated by the state-owned Guangzhou Metro Corporation (GMC) and was the fourth metro system built in mainland China, after Beijing, Tianjin, and Shanghai. Construction began in 1993 and the first line opened in 1997. Today, there are four completed lines in operation with 60 stations and more than 116km (72 miles) of tracks.
The Guangzhou Metro delivered 601 million rides in 2008 and set a daily record of 2.47 million rides on May 1, 2008, according to a Chinese report released in December 2008. The metro system has a total operational capacity scheduled to grow to 191km (118 miles) by 2010 and eventually will exceed 600km (372 miles).
Working below ground
During the strenuous welding work to connect geomembranes in the tunnels, there were problems with the Chinese welding equipment. The heating elements could not cope with the continuous 24/7 stress. Welding temperatures were difficult to control, often increasing during the subtropical heat and burning the PVC material. The machines failed regularly.
A further disadvantage of these devices was a susceptibility to corrosion from the PVC that required welding. The quality of connection of the geomembranes did not satisfy the client’s high demands. Therefore, the risk of penalties for delay also increased for the company carrying out the work, the China Railway Tunnel Group (CTG). In short, CTG was forced to source better machines in an expedient fashion.
New equipment
CTG contacted a sales partner located in Guangzhou, and Digital Steel Welding Equipment Ltd. said it could quickly supply the necessary machines.
Hot-air welding machines, handheld welding devices, and associated accessories were also ordered. An important quality criterion of the new equipment was their resistance to corrosion, for the welding machines as well as handheld devices. This is a real plus, particularly when working with PVC, as in this project. The five CTG welders also received comprehensive training with the purchase of the new equipment.