There Are Numerous Ways to Weld High Yield Pipe in The Field

ABSTRACT Today there are numerous ways to weld high yield pipe in the field. It is necessary to understand these various processes to insure that the process selected with meet the quality and productivity requirements of a pipeline project. Several prcocesses are discussed, with emphasis on shielded metal arc welding with cellulosic electrodes and self-shielded flux cored arc welding. INTRODUCTION In today world cross country transmission pipelines have to address many issues including higher service pressures, sour products, new high strength steels, more severe operating environments, tighter governing codes, and a host of environmental concerns. These conditions must be balanced by the needs of the pipeline contractor to control costs and complete the project in a timely manner while still meeting more stringent quality requirements. A knowledge of welding processes can help the contractor meet his needs and deliver the required quality. This same knowledge can help the specifying engineer understand that there are numerous ways to meet his quality and design needs without imposing unnecessary costs on the contractor. Several processes and combinations of processes currently used for the field welding of cross country line pipe. These include shielded metal arc welding (SMAW), self shielded flux cored arc welding (FCAW-S), and gas metal arc welding (GMAW). With GMAW transfer mode must also be consider, short arc, controlled short arc as in Surface Tension Transfer®, spray, and globular. Attention will be placed on those processes which lend themselves to high quality and high productivity field welding with conservative capital investment. REVIEW OF PIPELINE STEELS Today pipe steels are higher strength than those used previously and are today designed with weldability in mind. The most common steels used for oil and gas cross country pipelines conform to API 5LX or similar such standards. Strength levels can be achieved by several methods including gross chemistry, micro-alloying, and cold expansion of the pipe when produced at the pipe mill. In higher strength grades the trend is to use cold expansion and micro-alloying so that carbon and manganese can be kept at relatively low levels, thus reducing heat affected zone hardness and helping reduce, though not eliminate concerns about weld metal hydrogen. For example, it is typical to see carbon contents of less than 0.05% in modern X70 and X80 steels with some X80 steels having Pcm values of less than 0.20. Source: smitweld.be