The mild steel in this AWS standard refers to lowcarbon less than 0.25 carbon steels such as ASTM A 53, A 106, A 135, A 179, A 524, A 587, and API5L, Grades A25, A and B, and X42. It covers pipe sizes of DN 200 NPS 8 and under, with wall thicknesses of 13 mm 0.5 in. and under. You'll find Guide for Welding Mild Steel Pipe especially useful for piping system applications such as low pressure heating, air conditioning, refrigeration, water supplies, and some gas and chemical systems. It explains techniques for procedures such as preheating, joint preparation, alignment and positioning, fittings, and root and hot passes for SMAW, OAW, GTAW, and GMAW. Tables include Required Filler Metal per Joint for Mild Steel