What is the maximum permitted diffusible hydrogen for welding without preheat on ASTM A913 steel thicker than 1 1/2 inches?

The maximum permitted diffusible hydrogen for welding ASTM A913 steel that is thicker than 1 1/2 inches, without the need for preheat, is set at 8 ml/100g. This specification is crucial as hydrogen can lead to hydrogen-induced cracking, especially in high-strength steels like ASTM A913, which is often used in structural applications requiring superior strength.

Managing the amount of diffusible hydrogen is essential to ensure the integrity and durability of the welds. The limit of 8 ml/100g is established based on studies and industry standards, which consider the potential for cracking in heavier sections of this steel. Preheat can reduce the risk of such problems by allowing better diffusion of hydrogen, but the thickness of the material also plays a critical role in determining allowable levels of hydrogen without preheat.

In contrast, options like 4 ml/100g, 6 ml/100g, and 10 ml/100g do not reflect the established limits for this specific material thickness, thus making them not suitable for welding under these conditions without preheat. Hence, the correct answer signifies a balance between weld quality and precautions taken to prevent defects in the weld joint.