Location: Kusile Power Station
Owner and Specifier: Eskom
The Stopaq ETFE corrosion protection system was selected for the protection of the Stainless Steel Flues at the top of the stacks at the Kusile Power Station. The application requirements of the system, require no blasting, only minimal surface preparation as well as no specialised machinery for the application. The Kusile Power Station is a coal fired station with a wet scrubber and the three cans at the top of each smoke stack and other parts such as taps and trays were manufactured from 316L stainless steel. Processing of coal for the provision of energy causes a gaseous mix which is emitted from of the top of the flues. This gas contains high levels of corrosive chemicals such as sulphides and chlorides. Because of the corrosive environment (pH1, 30,000ppm chlorides) at the flue outlet, the 316L was likely to sustain damage over time. Eskom tasked Stopaq to assist in specifying a suitable coating system to protect the Stainless Steel flues and other Stainless Steel ancillaries, including the inspection hatches, the drains at the lobster backs, the stairs, and the access door at the 200m level from chlorides in particular.
Coating materials manufacturer and type:
The Stopaq Polyisobutene material is co-extruded with a film of ETFE (Ethylene tetrafluoroethylene) which is a fluorinebased plastic, forming a single layer system. The ETFE is the outer layer of the single system. ETFE is designed to have high corrosion resistance and mechanical strength over a wide temperature range of -200 to +165ÅãC. The Stopaq ETFE system is extremely chemically resistant; handling PH levels of 0 to 12. ETFE has excellent weathering characteristics, is UV stable and due to its low surface energy it is non wetting and self-cleaning.
End user: Eskom
Project team: Corrosion Control Services, ASP Rope Access and Stopaq
Main contractor: Concor Karrena JV
Applicator: Corrosion Control Services and ASP Rope Access
3rd Party inspection: Eskom
Action taken to complete scope of work:
The application took place at the 200m level of the stack and all personnel, material and equipment had to go through a hatch measuring 900mm x 600mm in order to get to the construction site. The lobster back drains were in the lobster backs at 50m and only accessible by rope access or scaffolding and the inspection hatches were at different levels within the flues accessible by the platforms at the relevant levels.
The Alimax elevator hoisted all the material, equipment and applicators up to the top platform at 180m inside the stack, and from there a safety ladder was used to get to the 200m platform. This platform was surrounded by a 1.8m wall from the stacks and this outdoor area was from where all activities took place.
The Stopaq material was packaged in wooden crates and these were hoisted through the hatch. Careful planning had to take place to ensure that sufficient material was available at all times, so as not to cause any delays in the application.
There were times when the elevator was out of order and the team faced the challenge of having to walk up to the top, using the spiral staircase within the stacks.
An additional challenge was that the Concor Karrena team were also completing various other work at the top of the chimneys at the same time and working in such a restricted space took a measure of mutual cooperation and tolerance of one another.
The application was completed largely by rope access teams and often the weather conditions were an added challenge, since the application took place in the severely cold weather conditions of winter, including extremely strong winds and high humidity levels.
The choice to use the Stopaq system proved to be practical, cost effective and time efficient above any standard liquid applied coating system, which would have required abrasive blasting, which in itself would have been a challenge with limited access at 200m above ground level.
Holiday tests were conducted once application was complete to ensure full coverage of the surface.
Project size: 3300m.
Project starting date: March 2015
Project end date: September 2015
Project value: R20 Million
Coating warranty: The client required a 50 year life expectancy from the system and a 30 year corrosion guarantee.
Technical development :
The Stopaq ETFE system was specially designed for the application at Kusile and has resulted in a new and innovative system having been developed worldwide, the benefits of which extend far beyond this application. Combining the benefits of the Stopaq Polyisobutene material with the ETFE film to form a single layered coating has resulted in a new and unique coating solution over a wide range of applications where previously extremely costly and difficult to apply systems were utilised.