On choice of allowable stresses on the basis of data on minimum practible strength of the 12Kh1MF steel

Studies of the 12Kh1MF steel with minimum practible strength have been carried out in order to choose allowable stresses during the Cr-Mo-V steel steam pipeline operation. The thermal treatment of specimens included annealing at 980 deg C with the following slow cooling and ageing at 610 deg C during 5000 and 7000 hours. It has been established that at operating temperatures of 570 deg C and higher it is possible to take minimum practible values of long-term strength corresponding to a ferrite-carbide structure as allowable for tube metal stresses. At operating temperatures of 510-540 deg C allowable stresses may be increased that will permit to use tubes with thinner walls and to diminish the scarce steel consumption