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Jun 01, 2007

A corrosion solution to ‘pig-out’ on

© Reuse this 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.

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 underground.

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 other end.

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) lining.

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 line.

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 steel pipe.

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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