Vanguard completes challenging contract

The project was carried out by Vanguard, the heavy lift, abnormal transport and plant relocation specialist.

Two sets of 191 ton gas turbines, 231 ton generators and 140 ton transformers were transported from the Coega port to the project site, where they will help stabilise the national electricity grid from 2015.

The Dedisa peaking power plant, which will operate in times of high electricity demand or shortfalls of supply, will produce 335MW from the two open-cycle gas turbines. Eskom has contracted to purchase the electricity under a 15 year agreement.

The six heavy units arrived at the Coega port during August in two shipments, according to the Vanguard project manager, Dale Huddy. "After directly discharging the vessels, we staged the heavy units in our port yard in order to relocate the equipment in the required sequence for delivery," said Huddy. "The turbine needed to arrive at the Dedisa site first, and was loaded onto our 16 axle, three-file Goldhofer trailer."

Multi-axle suspension

Each Goldhofer muti-axle combination loaded with the heavy units was powered by a push-pull combination of Mercedes Actros horses. Passing under the N2 highway, the planned route for the convoy included only a couple of challenging corner turns.

"We managed to navigate the tight corners so that there was only one road island to traverse, and the trailer's sophisticated multi-axle suspension technology handled that with ease, distributing the load evenly despite the axles having to navigate different heights," he said.

To lift and place the heavy units into final position on their respective foundations, Vanguard had set up its 500 ton 'Power Tower' hydraulic lift system, commonly known as a gantry system, on site.

"This is a top-of-the-range gantry with a hydraulic drive system that allows easy travel along rails," said Huddy. "We manoeuvred the trailer in line with the foundations and between two sets of rails on which our gantry system was placed."

In this way, everything was lined up with the unit's foundations to facilitate quick and accurate placement to within a tolerance of just one centimetre.

Accurate placement

"After detaching the turbine's transport saddle, our gantries were able to lift and travel forward with the turbine over a distance of 40m to its final resting place - lowering the unit onto four threaded rods on either side of the turbine itself," he said. "Alignment was achieved by the accurate placement of slings over the header beams and lifting the unit in the correct position."

The generator and transformer were then relocated, offloaded and positioned on site in a similar fashion, using a second set of Vanguard's 600 ton gantries in the yard at the port to lift the units onto trailers.

"The use of our gantry system has several advantages over the traditional jack and slide technique, including speed and safety," said Huddy. "We were able to complete the transport, offloading and positioning on site of the first 'line' of units - turbine, generator and transformer - in just six days, while the second line took us only three days."