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58 TUBE PRODUCTS INTERNATIONAL July 2017
will meet 316L composition. When Alloy 625 is used (as it is
in the vast majority of clad pipelines), the usual acceptance
standard for chemical composition is either 5% Fe or 10%
Fe. While this measure does not give an absolute indication
of corrosion resistance, it is a good indicator of the quality
control mechanism in place during welding – a high level
of iron means that the weld has penetrated too deeply into
the base metal, causing the higher dilution. It is not a direct
measure of corrosion resistance.
Figure 1 shows an example of pipe weld overlay cladding.
The component is a riser and, for this application, there were
concerns regarding fatigue resistance. As a consequence, the
acceptance standard for inspection was reduced to 1mm. The
bores were machined smooth and the cladding was tested
with dye penetrant and compression wave angle probes.
Pre-production qualification testing will include corrosion
testing to ASTM G48 practice A, at 50°C for Alloy 625 and
ASTM A262 Practice E for 316L. Cladding is invariably
undertaken with the gas tungsten arc process using hot wire
addition to the wire consumable.
Post-welding NDT for weld overlay clad pipe comprises
visual inspection using video cameras, plus ultrasonic, dye-
penetrant inspection. Acceptance standards are extremely
tight (UT, Ø1.5mm flat bottomed hole; DP, Ø1.6mm indication).
Testing also includes PMI, clad thickness measurement and,
in some cases, laser surface recording.
Corrosion monitoring
Corrosion performance within pipes is monitored by means
of intrusive devices such as smart pigs, which are intelligent
sensing devices that are introduced into a pipeline and usually
carried by the product along the length of the pipe. The
devices are able to measure and transmit dimensional data
regarding the pipe bore, and will highlight heavily corroded
areas.
Ring pair corrosion monitoring equipment – such as that
provided by Teledyne and manufactured by Arc Energy
Resources – is specified when high resolution, real-time metal
loss measurement on the full pipeline diameter is required.
Figures 2 and 3 show examples of Teledyne ring pair corrosion
monitors – complete and in production. These are good
examples of both weld overlay clad and fabricated products.
Arc Energy Resources
Arc Energy Resources’ weld overlay cladding services are
used by clients in a large number of industry sectors where
service conditions require corrosion-resistant properties. The
company’s weld overlay and weld inlay service offers a reliable
and high quality product. The scope of supply includes
flanges, elbows, tees, reducers, pipes, dished ends, valves,
vessel strakes, heat exchanger tubesheets, fabricated sub-
assemblies and various other geometries.
Cladding can be carried out on components as small as 20mm
and as large as 4m in diameter. Overhead cranage exists up
to 15T, though heavier components can be accommodated.
In addition to the cladding workshops, Arc Energy Resources
maintains a radiographic-quality fabrication facility and
segregated stainless steel workshop, allowing it to project
manage more complex structures such as pressure vessels
and spools (both clad and unclad). The company also holds
ASME U and U2 stamps, so can provide a full range of
services in compliance with the ASME code.
Arc Energy Resources’ machine shop provides CNC milling,
turning and drilling to tight tolerances. It specialises in flanges,
connectors and other subsea components.
In-house NDT incorporates visual inspection, dye penetrant
inspection (DPI), ultrasonic testing (UT), magnetic particle
inspection (MPI), radiographic testing (RT), dimensional
inspection and CNC coordinate measurement (CMM). This,
along with in-house procurement, design-for-manufacture,
project management and heat treatment facilities, allows Arc
Energy Resources to provide a complete one-stop shop for all
cladding, fabrication and machining requirements.
Summary
Corrosion continues to challenge the oil and gas industry. The
control of corrosion requires a combination of calculation and
prediction of likely product content, design of the pipeline,
protection of the pipe bore and monitoring of the actual
corrosion activity. With a comprehensive combination of these
disciplines, successful control of corrosion can be achieved.
Arc Energy Resources has over 22 years’ experience in the
protection of pipeline equipment from corrosion and is happy
to discuss solutions to any corrosion problems a client may
be facing.
Arc Energy Resources Ltd – UK
Figure 3: Corrosion monitor during weld
Figure 2: Teledyne
ring pair corrosion
monitor