The hardness of base material and welding of T91 steel small-diameter pipe with different wall thicknesses were tested by leeb hardness tester and brinell hardness tester

respectively.The results show that the error between the direct reading HBHLD and the measured HBW of base material decreases with the increase of wall thickness.The error between the direct reading HBHLD and the measured HBW of weld initially increases and then decreases

eventually stabilizing with the increase of wall thickness.Based on the regression analysis

a new conversion relationship between the leeb hardness and brinell hardness for base material and weld of T91 steel small-diameter pipe is established.The absolute error between the calculated HBW and the measured HBW is within the range of 0 to 6 HB.The research results can provide a basis for the strength assessment of boiler small pipelines in thermal power plant.