Figure 1 Kenyon Engineering has been orbital welding tubes
for the biopharmaceutical industry since 2002. Using an orbital
GTAW system from Arc Machines Inc., Kenyon has performed
at least 18,000 successful welds for customers such as Lonza and
GlaxoSmithKline in the past year. Photo courtesy of Kenyon Engineering,
Singapore.
Autogenous orbital GTAW
of large, high-purity tubes
How one company overcame major challenges
to achieve quality results
By Barbara K. Henon and Y.K. Tan
ince the early 1980s autogenous orbital gas tungsten arc welding (GTAW) has been the preferred
technology for joining of high-purity process piping for bioprocess, semiconductor, and other high-purity
applications. Over time millions of quality orbital welds
have been made, but new challenges arise even with the
widespread systemization of welding approaches.
Welding of the predominant 0.25-, 0.375-, and 0.50-
in.-OD tube sizes in the semiconductor industry and the
1 - to 4-in.-OD tube sizes used for bioprocessing equipment has become routine. However, welders in both industries occasionally need to weld 6-in.-dia. tubing and
fittings with a wall thickness of 0.109 in., which is at the
upper limit of diameter (but not wall thickness) for autogenous orbital welding with enclosed weld heads.
Because this size is near the edge of the process, orbital welding becomes trickier. The tube’s ovality can
make it difficult to maintain a constant arc gap with a
fixed tungsten length, which is needed for weld repeatability. Material differences between the tube and the fitting can present problems during welding. The location
of these welds also may present access problems.
S
Taking on the Challenge
of the 6-in. Weld
Kenyon Engineering (see Figure 1), a mechanical con-
tractor in Singapore, recently encountered a problem
with autogenous orbital GTAW of 6-in.-dia. tubing-to-T
fittings. The fittings were for REC Solar, a company that
specializes in designing and installing grid-tier solar pho-
tovoltaic systems, and the company’s $6.1 billion solar
panel production project, in which Kenyon played a very
small part. Kenyon reported that all of its weld problems
occurred at T joints done at high levels on a pipe rack.
An investigation uncovered several reasons why this
joint in this location presented a problem.
Figure 2 Kenyon Engineering developed this device for adjusting the circularity of 6-in. tubing before tack welding for orbital
welding.
