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About cause surveys such as leak of water accidents

Last update date March 5, 2019

 We report causes investigation such as leak of water accidents.

2, Tarumachi valve damage cause working papers

 This report gathered examination contents in "2, Tarumachi valve damage cause investigation Exploratory Committee" carried out in November, 2017.

Report

Summary

 We received leak of water by damage of valve of diameter 800mm that occurred in 2, Tarumachi, Kouhoku-ku on January 22, 2016 and showed directionality of future correspondence for prevention of recurrence with cause of damage. For setting of investigation item, we assume damage cause from the findings using FTA investigation technique. Finally we receive assumed damage cause and show directionality of correspondence in two viewpoints.

Progress of correspondence for prevention of recurrence

 From 4,281 diameter 400mm or more valves, we carried out extraction work of 100 valves installed on condition like damaged valve.
 We classified in C from priority A to prioritize, and to cope for 100 engines.

The number of the valves according to priority

The number of the valves according to priority
Priority Classification The number of the valves
A Valve which influence caused by subsidence is big, and has top priority, and needs investigation Seven engines
B Valve which will need monitoring that progress of subsidence is assumed, and is continuous in future 73 engines
C Valve that it is assumed that there is not influence of the ground and the plumbing caused damage 20 engines
The total 100 engines

 About seven engines (one engine of them has been removed by superannuation pipe update construction of 2017) classified in "priority A", we investigated crazing of protection concrete which we could confirm in cause of damage quickly, but crazing connected for damage promptly was not confirmed.
 We will perform investigation by trial boring and viewing of the valve room in future for the purpose of choosing four engines assumed that quantity of subsidence of the neighboring ground is big from six valves of "priority A" and valve of "priority B", and actually confirming the plumbing from quantity of subsidence and valve of the ground which is cause to be connected for damage.
 In addition, we perform correspondence such as update immediately when abnormality is confirmed in the investigation by trial boring and viewing.

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