Relationship Between Thermophysical Properties of Carbon Pipe Steel and Hydrogen-Induced Structural Transformations

The article presents the results of experimental studies of the temperature distribution and thermal stresses arising during the heating of carbon steel specimens, in their relationship with microstructural hydrogen-induced transformations. Samples of radiant heating surface tubes experiencing the maximum temperature gradient during boiler operation are examined (the front (fire) side of the tube faces the radiating medium of the furnace, and the rear side faces the refractory lining). Under the influence of hydrogen, the ferrite-pearlite microstructure on the front side transforms into a predominantly ferrite structure, while the microstructure on the rear side remains unchanged. This microstructural gradient across the cross-section of steam-generating tubes results in a 35 % difference in thermal stresses between the hydrogenated and undamaged walls (front/rear) at the initial moment of heating. Subsequently, as the tube wall heats up, this difference decreases to 10 %. The obtained results can explain the facts of destruction of hydrogen-embrittled pipes during boiler start-up, and not in steady-state operating mode.