Hydrocarbon Processing - June 2021 - GP-15

SPECIAL FOCUS: PIPELINES AND TRANSPORT
Evaluate ERW and SAW pipes
for onshore buried gas pipelines
S. ZARDYNEZHAD, TurboTech Consulting Corp., Calgary, Alberta, Canada
The question of whether to use electric resistance welding
(ERW) pipe or submerged arc welding (SAW) pipe for an onshore
gas pipeline project arises frequently. Each type of pipe
has different advantages and disadvantages, which should be
studied in detail to make a rational and reliable decision.
The quick answer may be to perform an internet search for
a comparison of the two types; however, most of the resources
readily available on the internet about this subject are based on
advertising and sales efforts. Good engineers use hard data and
factual experience to make equipment purchasing decisions.
In this article, ERW and SAW pipes-the latter of which
may be double (DSAW) or longitudinal (LSAW) style-for
onshore gas pipelines are explained. A general comparison between
ERW and DSAW/LSAW is developed. Finally, selection
criteria are proposed to help engineers and project managers
decide which type of pipe to use in their project. Note: This
article does not recommend or address spiral SAW pipes for
buried natural gas pipelines, as this type of pipe is not acceptable
by many clients' specifications.
Examples of pipeline failure. Examples of pipeline failure
for both ERW and DSAW/LSAW due to weld seam fracture
illustrate the many possible causes for pipeline failure. Many
similar failure examples for each type are available from different
regions around the world. These incident reports suggest
the need for bias-free studies to determine all potential
factors and classify them as contributing causes, direct causes
and root causes.
ERW seam weld failure.1
Williams Gas Pipeline experienced
an incident caused by a brittle failure. A long split along
or near a seam weld caused a catastrophic failure of the 16-in.
(outside-diameter, or OD) pipeline at 1.5 mi downstream of
the compressor station. The pipeline was manufactured of API
5L Grade X46 ERW pipe.
FIG. 1 shows (a) a large piece of the failed ERW pipe containing
the origin of failure, (b) the same piece marked with
flow direction and the distance from the other end of the failed
piece, and (c) a mockup reconstructed from the failed piece
with a split along a seam. The white circle indicates the failure
origin at 52.5 in. from the other end of the failed piece (upstream).
The insert shows a photo of the fracture surface. FIG. 2
shows more detail of the fracture surface of the pipe.
DSAW/LSAW seam weld failure.2
Enbridge experienced
the rupture of a 34-in. (OD), API-5L-X52 crude oil pipeline
and oil release near Cohasset, Minnesota. A fatigue crack along
the DSAW/LSAW pipe's longitudinal seam weld generated
during the transport of pipes caused the failure, based on the
incident report.2
The project used ERW pipe from Canadian
FIG. 1. The failed ERW pipe containing the origin of the failure and
the reconstruction mockup for the failure.1
FIG. 2. Failure origin of the ERW pipe showing a three-zone feature:
Zone 1: initiation sites, Zone 2: subcritical crack growth region,
and Zone 3: final fracture area.1
Gas Processing & LNG | MAY/JUNE 2021 15
Hydrocarbon Processing - June 2021

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