Requalification of LPG tanks in Europe: Verifying the structural integrity by monitoring the pressure test with acoustic emission

摘要

The requalification of LPG tanks usually requires a set of inspections and tests defined by national regulations or by other applicable rules. To assess the structural integrity of the pressure equipment is the main objective of these activities. Historically, the combination of hydrostatic testing and visual inspection (external and/or internal) was the first widely-accepted procedure. Its regular application led to tremendous safety improvements. However, since the end of the 19th century, safety considerations have been extended. Degradation by cracks and corrosion, as well as manufacturing defects leading to local stress accumulations, have to be detected in time in order to prevent failure. Entering into a confined space for an internal inspection is considered to be a high-risk activity. Safe disposal of polluted water from the hydrostatic test requires a high level of effort and carries a substantial risk regarding environmental pollution. Acoustic emission testing on LPG tanks has been developing since the late 1980s to offer an alternative to the traditional approach. It allows the detection of corrosion damage, cracks and weld defects activated by the applied test load. Online monitoring of the pressurisation enables severe defects to be indicated, while the structural integrity is still given. Thus, a pneumatic test may be performed instead of a hydrostatic test. Furthermore, it provides information regarding the tank condition usually obtained by internal and external inspection. After the first 1000 tanks had been tested in Austria in 1993, LPG tank testing was applied in Germany, France and other European countries, such as the Czech Republic, Slovakia and Slovenia. In the early 2000s, further European countries updated their national legislation to enable the application of acoustic emission testing, including Italy, Portugal and Spain. The EN 12817 and EN 12819 standards, which address the requalification of LPG tanks, were improved by adding acoustic emission testing for tank requalification. This paper describes how this kind of LPG tank testing was established in Europe and shows, with the help of case studies, the capabilities of the method and provides information on the latest developments.