API RP 571 emphasizes under Hydrogen Stress Cracking – Hydrofluoric Acid (HF):
“Cracking in carbon steel is influenced by high hardness and tensile stress in the presence of wet HF acid.â€
“Controlling weld and heat-affected zone hardness to below 200 BHN is a key mitigation measure, as higher hardness significantly increases susceptibility.â€
Steel hardness and strength are thus critical for cracking in HF environments, making option C correct.
