How welding consumable improvements can reduce pipeline construction time

1. Marcel Stemvers, Global Energy Segment
Manager and Gordon Eadie, Global Pipeline
Segment Manager, ESAB, Sweden, explain
how welding consumable improvements can
reduce pipeline construction time.
T
here are continual developments in the field of pipeline welding products and
those involved in the ownership, design, installation and maintenance of pipelines
need to be fully aware of such improvements.
Manufacturers of welding consumables and machines, such as ESAB,
have continued to invest in research and development. They offer solutions that are
technologically advanced, acknowledge the need to keep costs as low as possible and
reflect the important criteria of safety, quality and environmental requirements. ESAB is
the only welding company to have achieved ISO 14001 and OHSAS 18001 standards in
environmental, health and safety management systems across all of its global manufacturing
facilities.
Every day vast distances of steel pipelines are installed worldwide for the most varied
civil engineering and industrial uses, carrying essential fluids and gases. To comply with
all pipeline technical specifications and fulfil the necessary safety requirements, welding
Figure 1.
ESAB welders
demonstrate the
versatility of the
Pipeweld DH
range of vertical
down basic
electrodes.
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2. materials and processes continue to evolve. Whilst welding
consumables may represent only a small fraction of the
overall cost of pipeline construction, the combination of these
consumables and welding processes is critical to a project’s
success.
Within the industry, the onus is on the pipeline contractor
to propose a welding process that meets the mechanical
requirements of the pipeline designer or owner. Pipeline
contractors often design the welded joint to suit their
preferred welding technique, then approach manufacturers
of consumables for tailored welding electrodes or wires that
perform as required for the proposed process.
Meeting targets
ESAB has recently succeeded in supporting pipeline contractors
with a welding technique that significantly reduces welding
time and is easy to adapt to specific project demands. The
contractors are able to utilise existing staff and equipment
as well as meet more demanding requirements. The drive for
this change came from increasing demands on weld metal
strength as well as the need from the contractor to improve
competitiveness by reducing the man-hours on the job. It was
clear that adopting the same welding technology would not
deliver both targets. However, a fundamental change in welding
technology would push the operations into another dimension,
with all risks associated.
The technology adopted uses several classical welding
solutions, which have recently been upgraded to deliver
improved weld metal properties as well as enhanced welding
productivity and process control. After depositing the classical
cellulose root, filling commences normally with a ‘2 run’
procedure. The suggested alternative is a ‘3 run’ procedure where
a modified vertical down basic electrode is used, to overcome
the typical shortcomings of the ‘2 run’ procedure, as explained in
more detail later.
Thanks to its ease and versatility, the main welding
process used to install pipelines is manual welding with
coated electrodes. However, to limit costs and increase
welding productivity – particularly on long routes – pipeline
constructors have adopted the semi-automatic or completely
automatic welding process with solid and flux-cored wires. Since
protective gases can also be difficult to find in certain countries
– and these are necessary in welding with solid or cored wires –
manual metal arc (MMA) remains attractive.
Characteristics
To describe the benefits of the recently modified ESAB Pipeweld
DH series the typical process characteristics should be reviewed.
These Pipeweld DH products are offering 120% recovery, against
90% of the cellulose electrodes. This leads to deposition rates
over 3 kg/hr in vertical down position, very close to flux-cored
wire vertically up. The main added benefit from welding vertical
down is the inherent safety against excessive heat input. Impact
toughness and tensile properties of weld metal and heat
affected zone are generally better than when welding vertical
up, which is further supported by the low oxygen content of the
basic weld metal. Another benefit is the low hydrogen content
of the deposited weld metal, the Pipeweld DH range is classified
H4R, providing the highest possible security against cold cracking
or porosity. This low hydrogen content is guaranteed from the
ESAB VacPac electrode packaging, avoiding costly baking and
electrode handling.
The practical limitations from using vertical down basic
electrodes has been the requirement to apply a starting
technique perpendicular to the pipe, after which the electrode
has to be tilted to get the appropriate
dragging angle. This requires dedicated
skills and does not entirely avoid
starting porosity. The Pipeweld DH
series use a patented tip design that
allows the welder to start with the
electrode already in the proper
welding direction, without the risk to
generate starting porosity.
This special tip design is
furthermore supported from enhanced
coating strength. The projects supplied
so far have reported a complete
reduction of electrode scrap rates,
which has been on average as high
as 30% for the classical tapered tip
designs, due to transport damage.
These modifications are now
enabling pipeline contractors to use
Figure 2. Deposition comparison (kg/hr at 100% arc time).
Table 1. Pipeweld WPQR tests
Test
No.
Process Bead location Consumable Diameter Passes Welding
time
1 Cellulose Root Pipeweld 6010 Plus 4 mm
6 13.5 minsCellulose Hot pass Pipeweld 9010 Plus 4 mm
FCAW Fill & cap Pipeweld 71T-1 1.2 mm
2 Cellulose Root Pipeweld 6010 Plus 4 mm
6 14.5 mins
Cellulose Hot pass Pipeweld 9010 Plus 4 mm
DH Basic First fill pass Pipeweld 90DH 4 mm
FCAW Fill & cap Pipeweld 71T-1 2 mm
3 Cellulose Root Pipeweld 6010 Plus 4 mm
17 28.5 mins
Cellulose Hot pass, fill & cap Pipeweld 9010 Plus 4 mm
4 Cellulose Root Pipeweld 6010 Plus 4 mm
10 19 mins
Cellulose Hot pass Pipeweld 9010 Plus 4 mm
DH Basic First fill pass Pipeweld 90DH 4 mm
DH Basic Fill & cap Pipeweld 90DH 4.5 mm
114 World Pipelines / JUNE 2014

3. vertical down basic electrode welding to their full benefit
and seriously reduce rework and welding time whilst
meeting high requirements on the weld metal. The Pipeweld
DH range is available for pipe steels up to API-5L: X80.
‘2 run’ procedure
The ‘2 run’ procedure uses filling with a rutile cored
wire directly after the cellulose hot pass. This method is
regularly causing issues with gas pops or blowholes coming
from the cellulose layer underneath the first FCW fill pass.
Deep grinding to clean the weld metal does overcome most
of this problem, but not entirely. This grinding is both time
consuming and removes quite a bit of weld metal, adding to
the further completion time.
‘3 run’ procedure
The ‘3 run’ procedure uses a basic vertical down first fill
pass. This avoids heavy grinding and leaves a clean basis
for the FCAW process without the need for any other
treatment than slag removal. Filling commences with a rutile
flux-cored wire that is specially formulated for mechanised
pipe welding. This style was originally developed for tie-in
welds where, due to physical restrictions (fittings etc) or
connecting into the main line at road crossings, the use of
the internal line-up clamp and or internal welder was not
possible. Contractors soon realised that with the correct
manning and number of welding stations this technique
resulted in a similar number of joints per day at a lower
cost.
Table 1 explains the details of the techniques described
with their economical characteristics.
Field welding results have given the following
productivity rates:
) 1 pair of welders for root, hot pass and fill using
cellulose, Basic DH and FCW resulted in 3 welds/d on a
48 in. 25 mm wall pipe.
) 1 pair of welders for root cellulose, one pair for 1st
HP with cellulose, 1 pair for 2nd HP with basic VD
and 6 pairs with welding bug and FCAW resulted in
60/65 welds/d on a 48 in. 21.3 mm wall pipe.
) On a 24 in. mainline 14 mm wall thickness with 9 pairs of
welders (as above) 120 - 130 joints/d were achieved and
65 joints/d on a 48 in. 17 mm wall thickness with the
same crew formation.
Practical conditions
The main requirements for successfully mechanised pipe welding
have to do with the practical conditions under which the wire
has to perform. Arc voltage has to be set low in order to get a
smooth weld bead in all the pipe positions. However, this low
arc voltage shall not create excessive spatter or contact tip
damage. At the same time the welding parameters should not be
so low that productivity is affected.
The Pipeweld FCW’s are designed to work in mixed gas and
overcome all the hurdles above. They are class leading in their
productivity, which can reach 4 kg/hr, they have a good welder
appeal and have proven themselves to be very robust in field
conditions. Their strength levels go up to X80 with overmatched
weld metal.
Flux-cored wires are nowadays well suited for pipeline
applications. Low-hydrogen operation is possible as well as good
impact toughness down to -60 °C. It is easy to obtain flat welds
with a good penetration and smooth wetting onto the pipe
edges. The brittle slag is easily removed leaving behind a smooth
rutile weld appearance. Typical positional welding defects, such
as lack of fusion and slag inclusions, are avoided due to the
spray arc operation. The wires have a good tolerance to poor
joint fit up, which understandably makes then especially suited
for tie-in welds.
The combination of cellulose, basic vertical down electrodes
and the cored wire from the Pipeweld range has proven to be as
cost-effective as automatic solid wire welding, even when using
an internal root pass welding clamp. This is mainly due to the
relatively low cost equipment and avoiding the high rental costs
of internal welding line-up clamps and the additional equipment
and technicians to support joint completion. However, this
statement is restricted to light to medium wall thicknesses.
On heavy wall thicknesses narrow gap pulsed MIG is the most
productive solution.
Figure 2 demonstrates the deposition rates that can be
expected from the various processes, when using these under
ideal pipe welding conditions. What is often not recognised is
the productivity of the vertical down electrodes.
This technique is receiving a warm interest due to the
global trend to use cellulosic electrodes for root and hot pass
applications only. This will not change overnight, however once
the pipeline owners requests for limitations on weld metal
hydrogen content are heard, appropriate alternative solutions
must be found. The technique described here allows the existing
skilled welders to make the change with no issues as both
processes are high speed vertical down MMA welding processes.
From these field results it can be learned that the use
of modified basic vertical down electrodes can significantly
reduce welding time and enhance flexibility. The welding
time reduction of more than 30% against cellulose is very
attractive, especially since savings can be realised with
existing skills. It is obvious that filling with FCAW delivers in
terms of productivity. Here the modified basic vertical
down electrode enables a process switch whilst enhancing
productivity and weld quality.
Figure 3. Macro examination of Pipeweld FCAW 15.9 mm wall
thickness. Root and hot pass with cellulose, fill and cap with
FCAW.
116 World Pipelines / JUNE 2014