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Pipe Welding and Coating
The most critical aspect of a pressure pipe system is the care taken in metal preparation, cutting and
welding. Without sophisticated testing, poor welding is hard to differentiate from good welding. For insight
into good welding, take a “welding” tour of EFI’s new 54,000 sq. ft Metal Preparation/Cutting/Welding/Coating
facility. See the steps that make good welding practice, superior product life and the lowest product life cost.
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Pipe ends for butt welding are bevel cut to produce the
“V” groove necessary for a full penetration weld.
Likewise, a smooth bevel cut facilitates the proper
mounting of compression couplings to avoid their damage during installation.
Computer controlled, rotating and traversing cutting beds
produce precisely cut (by plasma or oxy-acetylene) and
aligned pipe pieces.
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Holes and saddle cuts are CNC cut to mate exactly and allow
full penetration cope welds free of crevices, gaps and
inclusions. The well formed cope weld lessens piping head
loss and energy use.
Hole cuts and saddle pieces are staged for welding to
make piping assemblies. The pipe pieces have been
abrasive blasted to keep impurities out of the weld
formation. These impurities cause pinholes, inclusions
and corrosion sites leading to premature joint failure.
Engineered Fluid, Inc. PO Box 723, Centralia, IL 62801 618-533-1351 Fax: 618-533-1459 or info@engineeredfluid.com
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Platen tables are used to square up and align pieces for
tack welding. Squareness is important for proper alignment and bolting so undue stress is not placed on the
piping assemblies.
The tack welded flange-elbow is chuck clamped into a
motorized, variable speed, welding positioner. The positioner turns the weld piece at a constant, settable speed to
assure the weld is of repeatable, consistent high quality.
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For slip-on flanges, full fillet welds are made on both the
interior and exterior of the joint. Strength is maintained
by multiple pass, fillet welds with final cross-section
equal to or greater than the thickness of the pipe wall.
Butt welds begin with two pieces aligned in a
positioning fixture. At least four tack welds are made
around the joint. Note the proper “V” groove and gap
forming the weld joint set-up.
Engineered Fluid, Inc. PO Box 723, Centralia, IL 62801 618-533-1351 Fax: 618-533-1459 or info@engineeredfluid.com
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Fill Pass
Root Pass
Root Pass
For each pipe diameter and wall thickness the weld parameters of weld heat, weld filler wire feed rate, and positioner rotation rate are digitally set for weld repeatability. The
root pass is laid down first, filling the gap and creating a
smooth, continuous weld at the pipe interior.
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To continue to build weld thickness, at least one fill
pass is laid down over the root pass.
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Finish Pass
Fill
Pass
Finally, the finish pass is laid over the uppermost fill pass.
Weld thickness and strength equal to that of the pipe are
achieved.
The finished MIG weld shows smoothness, uniformity, and a complete lack of any inclusions. The inert,
arc shield gas keeps oxygen away from the weld joint
as it forms and cools thereby eliminating corrosion.
Engineered Fluid, Inc. PO Box 723, Centralia, IL 62801 618-533-1351 Fax: 618-533-1459 or info@engineeredfluid.com
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A butt weld between a neck flange and an elbow is set into
the positioner. This will be a three pass weld where the
gap at the base of the “V” groove is set at 1/8” when tack
welded.
This weld assembly of two butt welds and a cope weld is
correctly aligned and square. The EFI weld process is controlled and repeatable for consistent high quality. No stick
welding is done, only MIG.
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Complete quality control is achieved. All the parameters
of the MIG (Metal Inert Gas) weld process are controlled
- weld method (pulse, short-circuit or spray), weld heat,
wire feed rate, shield gas mixture, shield gas flow rate,
weld rotational speed, and weld position. Weld position
is important to avoiding the effect of gravity causing the
liquid metal pool to sag or flow.
There are five pipe welding stations at EFI, each
equipped with MIG welders suspended from swings for
an easy approach to the work. Weld gas is selected from
a central gas mixing facility and dialed in at the
individual welding stations. Weld wire is fed to the weld
head and into the arc from a reel feed unit. The work is
supported by the positioner and roller stands for use with
longer assemblies.
Engineered Fluid, Inc. PO Box 723, Centralia, IL 62801 618-533-1351 Fax: 618-533-1459 or info@engineeredfluid.com
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Welded assemblies are shot or grit blasted either
manually (as shown) or in automatic blast chambers.
The blasting achieves a surface finish exceeding
SSPC-SP6, it removes surface oxidation and achieves
the correct surface profile for proper coating adhesion. Optimum surface profile is especially important
for coating the pipe interior.
Once all weldments for a job are complete, they are
abrasive blasted again. Once the blasting achieves the
proper profile, each piece is sent to the fusion bonded
epoxy coating process - an EFI standard.
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For fusion bonded epoxy coating the pipe pieces are
placed in a conveyorized oven and heated to 400F.
When at temperature, pieces are removed from the oven
and coated with an electrostatically applied epoxy powder. The powder fuses as it contacts the hot pipe. This
fusion results in a high adhesion strength, 12 to 16 mil
coating of impervious fusion bonded epoxy. The procedure is performed according to AWWA C-213-91.
Note the uniformity of this cope weld. A smooth fluid
flow pattern is achieved. The lack of crevices, cracks and
steps in the weld allows complete coating coverage to
prevent corrosion and to assure a long service life.
Engineered Fluid, Inc. PO Box 723, Centralia, IL 62801 618-533-1351 Fax: 618-533-1459 or info@engineeredfluid.com
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