An Investigation of the Factors Influencing the Formation of Hollow Bead Pores in Pipeline Girth Welds

Hollow bead is an elongated linear pore aligned with the weld axis. The sporadic appearance of epidemics of hollow bead defects during the construction of pipelines has for years been responsible for increasing the cost and time required for completion of a number of projects in many parts of the world. The inability to identify the cause of this defect has been one of the major obstacles in attempting to reduce its occurrence. As a result of this situation, following an important pipeline construction project which was seriously disrupted by problems with hollow bead, a number of Australian companies contributed to a major three year programme of research undertaken by the Cooperative Research Centre for Materials Welding and Joining. A systematic study of the effects of a range of parameters including welding variables, parent metal composition, joint geometry, surface condition and welding consumables has been undertaken. The data obtained has been used to ascertain their influence on the occurrence of hollow bead pores, and to provide guidelines for field welding practice which provide a high level of confidence that hollow bead can be eliminated as a practical problem in pipeline construction.