What is the minimum preheat and inter-pass temperature required when plug welding a 1-1/4" thick ASTM A572 GR.60 plate?

The minimum preheat and inter-pass temperature required when plug welding a 1-1/4" thick ASTM A572 Grade 60 plate is indeed 150°F. This requirement is significant for several reasons.

Preheating is essential to control the cooling rate of the weld, which helps to minimize the risk of cracking. For thicker materials like the 1-1/4" plate in question, a preheat of 150°F is specified to achieve adequate ductility and reduce residual stresses during cooling.

Additionally, maintaining this temperature during the welding process at inter-pass stages ensures that the weld metal and the base metal do not cool to a point where undesirable metallurgical changes occur. Such changes can lead to brittleness in the heat-affected zone, which is particularly critical in high-strength steels like ASTM A572 Gr. 60.

Choosing a preheat temperature that is too low could increase the likelihood of issues such as cracking and reduced toughness, particularly in thicker materials, so 150°F serves as a balanced approach for this application.