Directing against the problems existing in aspects of solidity of bolts and nuts

impact ductility of bolts

and metallographic examination of 20CrlMolVNbTiB steel

which were discovered in the inspection process of high - temperature bolts at thermal power plants

some recommendations have been put forward

such as requirements for solidity of bolts

which had been stipulated in standards DL438 - 2000 and DL439 -91

should be unified* and solidity inspection for new nuts should be carried out

and be numbered and applied with corresponding bolts

etc. . It is hoped to be considered in the process of revising the above - mentioned standards.