Hydrocarbon Processing - June 2021 - GP-16

SPECIAL FOCUS: PIPELINES AND TRANSPORT
TABLE 1. Comparison between ERW and DSAW/LSAW pipes
Parameter
Raw material note: Pipes should
be normally fully killed,
continuously cast steel
Grades
Pipe size
Wall thickness
ERW pipe characteristics
Normally hot coils.
DSAW/LSAW pipe characteristics
Normally plate, but hot coils can also be used.
No difference; however, depending on the mill, market conditions and required thickness, there may be a limit
on pipe production for specific grades. The mill's confirmation is required at an early phase of the project.
Normally 1 NPS-26 NPS.
Since hot coils are used as the starting material,
thinner wall-thickness pipe can be manufactured.
The maximum thickness may reach 1 in.; however,
mill confirmation and mill past production experience
for similar service are recommended to be verified.
Welding process
Two electrodes, usually copper, are used to apply
pressure and current. The electrodes are disc-shaped
and rotate as the material passes between them.
This allows the electrodes to stay in constant contact
with the material to make long, continuous welds.
Weld seam surface quality
The weld seam is flat, which may cause difficulty
and impact productivity of work during construction
for field bending.
Weld seam defects
Weld seam chemical
composition
Lesser defects, but a high risk of oxide air in the
seam, which impacts the chemical composition
and microstructure.
Since no filler metal is used to complete the weld
seam, there is usually little difference in the chemical
composition of the weld metal and the base metal.
It is formed from the same material and is considered
more homogenous in chemical composition with
the base metal.
Heat treatment of the
weld seam
Weld seam length
Normally, the weld seam is heat-treated before the
shop hydrostatic test, creating a similar zone of
microstructure. This must be confirmed by the mill,
especially for sour service.
The weld length of ERW pipe is the same as for
DSAW/LSAW pipe; however, the risk of defects in
the weld seam is lower than for DSAW/LSAW pipe.
Fracture toughness-
weld and heat-affected zone
Pipe length
Normally 16 NPS-64 NPS; check with the mill for
special-order pipe sizes.
Normally 0.5 in.-2 in., depending on grade and
pipe size; however, mill confirmation and mill
past production experience for similar service are
recommended to be verified.
In this method, a welding arc is submerged in welding
flux. A continuous solid filler wire is fed from the outside.
The pipe is first welded from the inside and then welded
from the outside. The welds penetrate 100% of the pipe
wall and produce a strong bond of the pipe material.
The weld seam is not flat, and is higher than the steel
plate surface. The tolerance of the weld seam height
should be agreed upon initially, as this impacts the pipe
coating performance.
Whether or not defects are present depend on the
definition of defects, as well as on the pipe grade,
pipe thickness, mill's quality control, etc.
DSAW pipe requires a filler metal. When filler metal
is used, the weld seam local region is somewhat
different in chemical composition to that of the
surrounding base metal.
Normally, the weld seam is heat-treated before the
shop hydrostatic test, creating a similar zone of
microstructure. This must be confirmed by the mill,
especially for sour service.
The weld length of ERW pipe is the same as for
DSAW/LSAW pipe.
Fracture toughness-pipe body Impact testing commonly can be done by reputable mills up to M45.
Impact testing commonly can be done by reputable mills up to M45 for the fusion line. However, subject to
the pipe grade, the specified toughness value and minimum metal design temperature (MDMT), some mills
may have limitations.
Reputable mills can produce either triple random
lengths (approx. 18 m) or special-order quadruple
random length (approx. 24 m).
Y/T (yield to tensile) ratio
Pipe-making process
productivity
Higher production productivity compares to that of
DSAW/LSAW pipes, mainly because ERW pipes can
form pipe continuously from an entire coil, while SAW
plates are limited in length by the dimensions of the
associated pipe-welding presses.
Dimensional accuracy
Non-destructive testing
Normally higher than DSAW/LSAW pipes.
Normally, ultrasonic tests will be performed for the
coil, weld and pipe as a whole. In addition, eddy
current and magnetic particle testing may be carried
out. Detail must be clarified with the mill before the
order is placed.
16 MAY/JUNE 2021 | GasProcessingNews.com
Reputable mills can produce triple random lengths
(approx. 18 m) with no jointers (girth weld) for DSAW/
LSAW pipe, assuming availability of plate with suitable
length at the time of order.
Reputable mills can produce pipe based on the pipe datasheet and specification.
Lower production productivity compares to ERW pipes,
mainly due to welding the pipe from the inside and
outside.
Reputable mills can produce based on the agreed
design tolerances.
Ultrasonic tests will be performed for the plate and
weld. In addition, radiography will be performed for the
weld seam and pipe ends. Magnetic particle testing
may also be carried out. Detail must be clarified with
the mill before the order is placed.

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Hydrocarbon Processing - June 2021

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