Low temperature stainless steel wire cut off valve caused by the cause of the failure

Published on:

2019-02-28

Low temperature stainless steel wire cut off the valve used in the test system, there can not move the fault. After the disintegration of the valve, it was found that the stem and the bonnet were engaged, and there were two deeper scratches at the center line of the stem surface, and there were two corresponding positions in the lower flange of the bonnet Scratches. After analysis, there are two reasons for the failure.

(1) Storage period: the valve placed during the horizontal and placed in the open state, hydraulic control valve stem and valve to form a cantilever beam structure, cantilever length 147mm, cantilever weight 418kg. Due to the role of gravity caused by the lower valve rod bending, making the lower stem and flange flange flange coaxial deviation increases. The maximum deviation of the coaxiality in the original design is 0.1mm, and the measured coaxiality deviation after removal is about 0.4mm. As the two pieces of materials are OCr18Ni9 stainless steel, low temperature can not be lubricated, the action due to coaxial deviation occurs large bite phenomenon.

(2) Processing period: After inspection, the pin groove on the bonnet is not processed according to the drawings. The square groove is machined into a circular groove, which affects the normal fit of the pin and pin groove, and the lower stem is subjected to lateral force, resulting in interference between the lower stem and the valve cover.

In view of the existing problems in the analysis, the structure of the low temperature cut valve has been improved:

(1) Stem and bonnet mating parts Lower stem [51mm H62 OCr18Ni9 160HB H62 56HB 51mm 57mm H8 f7

(2) stem anti-rotation device pin and pin groove with the role is to avoid stem rotation. As the valve valve, stem, cylinder and piston, etc. for the rotating body, the stem is rotating its sealing and opening and closing performance will not have an impact. The electric actuator eliminates the pin in order to avoid the lateral force of the lower stem due to improper pin and pin groove.