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Automated pipeline welding
CAPS – "Cranfield Automated Pipewelding System", is a special GMA welding process based on
tandem technology and developed specifically for pipeline construction by Cranfield University. CAPS
is intended to make pipeline welding faster and more economical while coping with harshenvironmental conditions and temperatures which can often become bitterly cold.

Stephen Blackman, Director of Welding Engineering at Cranfield University’s Welding Engineering
Research Centre in England has been using Fronius Tandem GMAW equipment since 1997. In 2001,
BP were looking for a welding process that could significantly reduce the cost of pipeline construction.
Laser welding and one-shotwelding had failed to deliver and BP consulted a group of industry experts
for guidance. As an acknowledged expert in the field, Stephen Blackman, had the answer in tandem
GMAW. BP liked his ideas and set Cranfield a challenging target – to develop and field test a
mechanised tandem GMAW pipeline welding system within 18 months. BP had one other requirement,
the field trials had to be performed inwinter under Arctic conditions.

This latter requirement was based upon the target pipeline project. The new process had to be
suitable for use on the proposed large-diameter, long-distance gas pipeline known as the Alaskan Gas
Pipeline. This is a 5700 km long pipeline between Alaska and Chicago and at a predicted cost of
US$16 billion this will be the largest private financed project inNorth America. Due to environmental
considerations, most of the construction work in the Arctic will have to be carried out in winter, at
temperatures of down to minus 50o C.

Cranfield University realised that they would only be able to deliver BP’s project objectives if they
worked closely with industrial partners. They approached a number of potential partners but only
Fronius and RMS WeldingSystems of Alberta, Canada were able to provide the necessary expertise
and technology. Fronius accelerated their TimeTwin Digital development programme and provided
this welding system to the project. RMS Welding Systems provided automatic pipeline welding
equipment to carry the welding torch around the pipe and conducted the field trials.

The welding engineering requirements for theAlaskan Gas Pipeline are very stringent:
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The pipes can only be laid (and thus welded) in winter when the ground is solid enough to
hold the weight of the construction equipment and the snow and ice protects the tundra from
permanent damage by the vehicles.

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The 24 m long pipes must be welded inside a special shelter. This protective enclosure is
transported from "weld-seam to weld-seam"suspended from a side-boom tractor. Each

welding shelter needs to be self-sufficient carrying all equipment and consumables for the
welding operation and powering the welding power sources from a diesel generator.
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To get the highest welding speeds, welding is performed vertically downwards with one
machine on each side of the pipe.

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Each welding machine carries two tandemwelding torches spaced 70mm apart so two weld
passes are deposited simultaneously. This dual-tandem welding process with two pairs of
arcs allows high deposition rates to be maintained at the 130cm/min travel speeds used.

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The Alaskan Gas Pipeline is being designed using X100 linepipe. This high strength material
allows high operating pressures at reduced wall thicknesses and significant costsavings are
obtained over comparison with conventional linepipe. However, X100 has never been used in
a long-distance pipeline before and the 690MPa of the pipe must be overmatched by the
strength of the weld metal. BP require a minimum weld metal strength of 810MPa for X1000.

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The pipeline will be 1321mm diameter with a 22.9mm wall thickness.

The field tests were intended to...