A corrosion solution to ‘pig-out’ on
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Significant time and money could be saved in the mechanical and
chemical cleaning, surface preparation and recoating of underground
water reticulation pipelines in South Africa, through the use of
on-site pipe-pigging technology, says corrosion engineering
specialist Corrocoat South Africa’s MD Louis
Pretorius says that maintenance of the internal surfaces of pipes
is far more problematic than the external surfaces, owing in part
to severe access constraints. South African municipalities have
already identified that large amounts of water are being lost every
day owing to pipe leaks caused by corrosion.
He says that when corrosion protection is required, it is often
too expensive and time consuming to dig up underground pipes and is
more practical and cost-effective to fix the pipes while they are
Pipe-pigging technology has been designed to specifically tackle
the effects of access limitations as well as the high costs of
internal pipeline coating, maintenance and refurbishment.
Initially, mechanical scraper pigs are applied to the internal
surfaces of pipelines that are too small for conventional blasting
and painting techniques. It is used extensively to clean pipeline
systems when they are too small for human access, too long to clean
adequately or too expensive to have sediment blasted out with
high-pressure water, says Pretorius.
The pigs are launched into the pipeline, through the use of either
compressed air or the use of the medium already in the pipe, as a
vehicle. Scraper pigs of different configurations remove the
corrosion and sediment build-up in the pipes, resulting in an
increase in flow through the pipeline.
The pigs are inserted into the pipeline either by the use of a
fabricated Y-piece introduced into the pipeline or through the use
of an in-line launcher bolted to the pipeline wherever there is a
break. It is therefore used, for example, at a valve point or bend.
Once the pigs travel through the pipeline section, they are caught
at the other end using a pig ‘trap’. Electronic pig
signallers assist with the pig detection and progress while in the
pipe and indicate when foreign matter is to be expelled at the
After mechanical cleaning, ‘intelligent pigs’ can be
run for pipeline assessment, or the pipeline can be further cleaned
in preparation for lining. Chemical cleaning involves repeated runs
with detergents, solvents, and acids. When the pipeline is
thoroughly clean internally, it is ready to be coated with a
seamless internal liquid glass reinforced polymer (GRP)
In normal circumstances, a pipeline would be taken out of service
for 10 to 20 days while the corrosion protection oper-ation is
being undertaken, says Pretorius. He says that in certain
conditions, one can use the pigs for cleaning and desilting
purposes, without stopping the flow of process liquid in the
pipeline. This is accomplished by using the same liquid as a
vehicle to carry the pigs, coupled with a filtration system to
prevent any contamination of the process liquid further down the
Pipeline pigging has existed in the petroleum industry in South
Africa for over 25 years. The technology has been modified and
further developed for introduction to the water supply industry
over the last 18 months.
“As a direct response to the South African government
spending more money on infra- structure and reticulation, a company
decision was made to further develop the technology with the aim of
offering this service to the water-supply industry at national
level,” says Pretorius.
South African company Magnaflux originally developed the technology
in conjunction with US-based Union Carbide Corporation in the
early-1980s, he says. The technology was then sold to another South
African company, Bateman Engineering, and Corrocoat was enlisted to
carry out joint research and development with Bateman for two
years, researching pigging techniques and the use of better types
of coating materials to seal leaking pipelines. Thereafter, Bateman
withdrew from the sector after considering pigging technology as a
noncore business and many of the Bateman staff involved in the
pigging technology joined Corrocoat, says Pretorius. Corrocoat then
developed the technology further, advancing thick and
ultrathick-film technology, which is one step further than
corrosion protection, he adds.
Thick and ultrathick-film technology involves a range of different
aspects, including the relining of pipe lines for corrosion
protection purposes and the application of ultrathick (6-mm to
12-mm) GRP linings, effectively creating a ‘pipe within a
pipe’, in which GRP is created within an existing corroded
To create the GRP, a thick, liquid, cold-curing polymer resin,
is applied to the internal pipe surfaces using specialised coating
pigs, controlled by compressed air. The resultant GRP lining cures
within 24 hours, effectively creating a polymer pipeline within the
existing corroded steel pipe line. The GRP can be installed over
distances of up to 45 km on a single pig run, says Pretorius. The
coating technology has also evolved from 50
Edited by: Laura Tyrer
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