These recommended practices apply to the arc welding of the following base-metal combinations:

(1) Similar chromium-molybdenum steels

(2) Dissimilar chromium-molybdenum steels

(3) Chromium-molybdenum to austenitic chromium-nickel stainless steels

(4) Chromium-molybdenum to either carbon or carbon-molybdenum steels

In this document, the chromium-molybdenum steel alloys are referred to as Cr-Mo steels.

Cr-Mo steels are used extensively in the power, chemical, and petroleum industries. The properties of such piping and tubing materials and the applicable fabrication and inspection requirements are addressed in a wide range of documents, including:

(1) ASTM Material Specifications

(2) ASME Codes for Pressure Piping, B31

(a) Power Piping (ANSI/ASME B31.1)

(b) Chemical Plant and Petroleum Refinery Piping (ANSI/ASME B31.3)

(3) ASME Boiler and Pressure Vessel Codes (Sections I, IIA, IIC, VIII, and IX)

(4) NBIC National Board Inspection Code for Boilers and Pressure Vessels (ANSI/NB-23)

(5) API Piping Inspection Code (Inspection, Repair, Alteration and Rerating of In-Service Piping Systems), (API 570).

Abstract

This document presents recommendations for welding chromium-molybdenum steel pipe and tubing to itself and to various other materials. Subjects covered in detail are filler metal selection, joint design, preheating, and postheating. Particular emphasis is placed on the importance of maintaining interpass temperature and dangers inherent in interrupted heating cycles.