Different standards were applied to calculate the minimum necessary wall thickness of bent tube extrados for tubes in 1 000 MW unit boilers.The results showed that

the thickness calculated by GB/T 9222 was very close to that by DL/T 5054

and they were both thinner than that by JB/T 1611 or JB/T 6509.During the manufacturing inspection

the thickness of the bent tube extrados should be controlled according to JB/T 1611-93 and JB/T 6509-92.If the wall thickness thinning rate was a little higher than the control value in JB/T 1611-93 and JB/T 6509-92

the thickness of the bent tube extrados can be controlled according to the minimum necessary thickness calculated by GB/T 9222 or DL/T 5054.For the in-service running boilers

the thickness of the bent tube extrados can be controlled according to DL/T 438

but the performance deterioration caused by creep damage of the material should be considered.