Through analytical study on bolt breakage of the valve body for motor-driven master valve of unit NO.1 in a power plant

it is considered that the main causes leading to end-cover fly-out of the motor-driven master valve at this time are as follows: （1） unreasonalble bolt structure; （2） the quality of screw thread fabrication isn’t up to standard; （3） unsuitable process of bolt installation. For these

relevant measures and recommendations have been put forward

namely: the high temperature bolts used in thermal power plants should be that with high flexibility; the farication quality of bolts should be strictly controlled; the method of bolt installation with big hammer striking should be seriously prohibited

etc.. The above-mentioned measures and recommendations can be used for guiding practice in the power plants.