Introduction

The materials with which this book is concerned are used in the fabrication of process plant for power generation, or for structures such as steel buildings, bridges and offshore oil rigs. The joining method appropriate to this field of construction is predominantly fusion welding. Exceptionally a solid-phase process may be practicable, as for example in the longitudinal welding of pipe and tube using the electrical resistance welding process.

Amongst the more industrialized nations competition provides a spur to seek more economical methods of fusion welding. One route to greater productivity is through automation and by the use of robots, and to this end the process must be capable of operating consistently over as long a period of time as possible. When automatic techniques are not practicable the use of gas metal arc (GMA) welding, where wire is fed continuously, gives higher deposition rates than welding with coated electrodes as shown for the case of fixed position welding on an offshore oil rig in Table 1.1. ^[1]

Consequently there is a trend towards increased use of GMA welding and a corresponding decrease in that of coated electrodes. At the same time variants of the GMA process have been developed so as to widen the current range over which it can be used, make it applicable to all-position welding and...