DEVELOPMENTS
Mark Atkinson and Simon Slater,
MACAW Engineering, UK, and
David Teasdale and James Gilliver,
National Grid, UK,
discuss the
development of mechanised welding
for heavy wall hot-tap split tee
longitudinal seam welds.
H
istorically, the shielded metal arc welding (SMAW) process has been used
for welding of full encirclement split tees when making ‘live’ hot-tap
connections on pressurised gas transmission pipelines.
The National Grid high pressure gas transmission network currently
consists of pipelines up to and including 1219 mm outside diameter and up to
L555 (X80) grade steel pipe. Due to the size of the split tee assembly that is required
for large diameter high pressure pipelines, which can be up to 80 mm thick, the time to
manually weld these fittings to the pipeline can be considerable and requires multiple
welders to complete welding in one continuous operation.
The qualification of the semi mechanised gas shielded flux cored arc welding
(GSFCAW) process for welding the longitudinal seams on large diameter tee
connections would realise significant operational and cost benefits over the SMAW
method currently adopted, especially for tee thicknesses of 50 mm and above. The
equipment for mechanised or semi-mechanised welding is readily available for a large
number of applications across many industries. Recent advances in the technology
in welding
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