Kusile power station: absorber strakes: specialised fabrication and transportation

NATURE OF PROJECT

The purpose of the project was to decrease “Time to Site” as well as “Time on Site” as well as to ease onsite erection and improve quality of fabrication by manufacturing the Absorber Strakes to be installed at Kusile Power Station in the largest possible assemblies.The largest components to be moved were 120o segments of a 20m diameter, 9m high, circular absorber tower section, fabricated from 14mm steel plate.

The following considerations came into play when determining the feasibility of the “Large Assembly Transport”:

POSITIVE CONSIDERATIONS

Conditions inside the fabrication workshop at Genrec are controllable and assembly could take place without interference from the elements.Quality control is easier, and automated welding methods could be used.Time to/on site (read SITE COSTS) was drastically reduced.

NEGATIVE CONSIDERATIONS

Bespoke transport cradles, as well as lifting equipment would have to be designed and fabricated. This was mainly due to the flimsy nature of the 120o segmentsDue to the highly specialised nature of the design, specialist design expertise would have to be outsourced.It was decided that the positives outweighed the negatives and LSL Consulting Engineers were appointed to design the lifting and transportation equipment.

DESIGN PROCESS

Since the absorber towers are not constant in diameter, some sections were reducer sections and some were smaller sections. Therefore, a “one size fits all” system could not be used. All in all 4 different lifting arrangements and transportation cradles were used.However, due to a design process involving people from management right down to the factory floor, it was possible to design the different cradles and lifting beams in such a way that they could be disassembled and modified to suit the specific requirements of the particular component to be moved. Thus the same cradle components could be re-used.

As far as possible, standard hot-rolled structural sections were used (I-beams and H-profiles) due to ease of availability. Specialised spreader beams were however required to carry out the “top-and-tail” operations required to rotate the absorber segments from a vertical manufacturing position, to a horizontal transportation position. The spreader beams were manufactured using bespoke box girders due to considerations of lifting capacity.The most interesting” part of the process was that the spreader beams, as well as the lifting beams which clamped onto the shells, had to be positioned in such a way that the Centre of Gravity of each shell would act as the rotational pivot point.

FABRICATION & TRANSPORTATION

Fabrication of the cradles were done partly in-house and partly outsourced, and transportation and transport co-ordination was outsourced to a specialist contractor.

Tons of structural steel used 309
Structural profiles used Box Girders, I-beams, H-sections

Project Team

Project Team Role Company
Nominator GENREC
Client/ Developer GE (at time of project)
Structural Engineer LSL Consulting
Engineering Manager GENREC
Main Contractor GENREC
Steelwork Contractor Burger & Company
Steelwork Contractor Nessa Engineering
Steelwork Contractor One Steel

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