I would expect the amount of diffusible hydrogen available to influence the time required for the hydrogen cracks to propagate to the point where they are detectable. So, in an environment that is hydrogen rich, i.e., the acid pickling bath, the potential for introducing diffusible hydrogen is relatively high.

Then the ratio of the thickness of the base plate versus the thickness of the mast would come into play as well. The thickness of the base plate would influence the potential for cracking in at least two ways. The first would be the increased in alloying constituents required to maintain the required mechanical properties. Thick plate experiences less mechanical work, i.e., the number of passes through the rolling mill for thicker material is less than for thin materials, thus there is less grain refinement for the thicker plates. The lesser amount of mechanical work required for thick plates would necessitate an increase in the amount of alloy required to produce the required tensile strength. The increased the alloy content would increase the carbon equivalency and the potential for hydrogen sensitivity and it lowers the ratio between tensile strength and yield strength, i.e., a low ratio of tensile strength to yield strength (approaching 1). That would mean there is little plastic deformation before failure, thus there is little opportunity for crack arrest. The second condition that results from a high ratio between the base plate thickness to mast wall thickness would result in increased rigidity and increased residual stresses because the residual stress cannot be easily redistributed by plastic deformation, i.e., distortion in the base plate. The magnitude of the residual stress increases the potential for cracking due in the presence of diffusible hydrogen.

There are times when it is beneficial to use lower strength steel (less alloying) and thicker is not always better. Contrary to the belief held by some designers, stronger is not always better.  

Best regards - Al