Katsutaka Nakagami, Takahiro Kasatani
Papers # 2018 Las-Vegas
Osaka Gas improves various approaches to the improvement of polyethylene piping construction quality and executes the approaches. As a result of that, polyethylene pipes in Osaka Gas maintain high-quality and withstand the earthquakes. This paper shows these methods and performance against earthquakes in Japan.
In Japan, examination of the usage of medium density polyethylene (MDPE) pipes started in 1970, and its Japanese Industrial Standard (JIS) was established in 1979, though this was late compared to other countries. It reflected the frequency of earthquakes and the concentrated land usage in Japan, and addressed the concern for possible damages caused by other construction works and accidents caused by leakages. The most significant difference between this and the standards of other countries was the number of areas covered by the quality assessment test. In Japan where earthquake and breakage caused by other construction works are frequent, standard that could withstand these were necessary. After the establishment of this standard, usage of PE pipes is promoted in Japan. Today, its total length is 101,500km, which is approximately 39 % of the piping extension in Japan. In future, further expansion of gas pipes in PE will continue. (Osaka Gas [OG] supplies gas to 7.3 million households. Thus far, 1,8500 km of PE pipes, approximately 30% of all gas pipes, have been installed.)
PE pipes must have specifications that could withstand possible future earthquakes so that they may be used forever. Thus OG realized practical applications of ultrasound examination and traceability function of EF controller and utilizes them in order to maintain the quality of its conduit network. Moreover, PE pipes sampling inspection is conducted after their installation in order to assure their quality. When a pipe does not pass the test, efforts such as further sampling tests are made to assure the quality. We shall discuss various measures for quality guarantee.
Furthermore, evaluations of construction companies were carried out based on the result of this test. The amount of construction contracts awarded is regulated based on the evaluation result. Moreover, energy is invested in the improvement of various tools, such as scraper, in order to prevent the deterioration of quality caused by workers. The installation specifications/process is defined in detail from the perspective of quality control, and we conduct regular instruction based on this. In addition, the earthquake resistance of PE pipes compared to pipes made of other materials was proved through the record of recent earthquakes in Japan, namely 2011 Tohoku earthquake and 2016 Kumamoto earthquakes. This will be discussed in the following part.
Finally, our recent activities will be discussed. In Japan, there is a high risk of breakage caused by other construction work because various underground facilities are concentrated due to Japanese land usage habit. Moreover, as building density is also higher than other countries, it is deemed that there is a high likelihood of human damage in the case of medium pressure breakage. With this background, the responsibility of gas business operators is more serious than the situations in other countries. Therefore historically, PE pipes have hardly been used for medium pressure conduit in Japan. However, our company makes limited use of PE pipes for medium pressure conduit by using an IS method that utilizes existing pipes as protection in order to improve cost performance and workability. We shall also discuss these examples.