ENGINEERING: Tripper Cars Replaced at Saldanha
Recent Western Cape Business News
WHEN one of the old tripper cars at the Port of Saldanha failed it became critical to quickly replace both this tripper car and its companion. DCD-Dorbyl Marine was awarded the contract to manufacture, erect and assist in the commissioning of the two tripper cars.
The project was of importance as, in terms of export revenue, the entire iron ore export in South Africa goes through Saldanha. Dorbyl Marine had to reserve current fabrication capacity and acquire additional fabrication capacity to ensure that it could meet the delivery deadlines and schedule.
“We were on a tight delivery envelope and undertook to do whatever was needed to ensure successful and timeous completion of the project. From receipt of the first engineering drawings in February 2007, it took 12 months to fabricate and erect the two trippers,” Bill Flear, industrial manager at Dorbyl Marine, says.
“This project period included the trial assembly of tripper 2A and we achieved our targets despite the inclement weather,” Flear says. Another constraint experienced by the company was working around the tanker movement in the bay, which necessitated careful planning of this 24 hour operation.
Flear claims Dorbyl Marine is the only engineering facility in the Western Cape offering such a full turnkey facility. The facility had the cranage available to handle the heavy components and structures required for this project and the height under hook of 11 metres means that the company can fabricate girders up to 60 metres in length.
The company’s facilities conform to ISO 9001:2000 quality systems and are accredited by Lloyds. “Transnet also sited permanent QC inspectors at our premises and all quality procedures were monitored in tandem with comprehensive data packs in place to ensure that all specifications were met,” Flear says. The scope of Dorbyl Marine’s work included the supply, manufacture, machine, shop trial assembly and disassembly, shot blasting and painting, transporting, cranage on site, scaffolding on site, supply of management, supervision and labour, including the necessary site tools, rigging and restraining equipment, site transport, accommodation, messing, ablutions, offices and stores, own security to erect the complete structure including the assembly of mechanical components.
The company was also contracted to strip and demolish the old tripper 1A which has been replaced with the new 1A.
“The mere size of these components was something to behold. The longest girder fabricated was 45 metres and therefore it necessitated special transportation on extendable low-bed trucks. Wind conditions also tested the mettle of all those involved in the transportation,” Flear says.
The tripper was engineered in a way that facilitated fabrication and transportation to site where it was then erected in its final configuration. “Essentially, each tripper comprises two portal girders, two box girders (connected to the box girders using high tensile friction grip bolts), two fixed legs, two pivot legs, stairway support structures and the yard conveyor supported by a trestle structure,” Flear explains. Included in the scope of work was the installation of all free issue items including head pulleys, drives, motors and installation of the conveyor belt itself.
“On the erection side of the project, challenges were posed by the space constraints on site where the trippers were both installed in existing quay spaces. This was overcome through careful planning whereby components were delivered to site in the erection sequence,” Flear says.
This type of planning also eliminated any unnecessary delays in terms of erection as the appropriate components were available on site as required. Planning began from the fabrication stage of the project to ensure that the final delivery to site dovetailed with the erection schedule.
“A vital design consideration was the erection length of the beams. This was necessary because of the lifting capabilities on site, coupled with the tight space in which erection was done,” Flear adds.
The entire girder structure was erected on temporary support trestles, and only after the fixed and the pivot legs had been bolted to the underside of the portal girder frame was the entire structure lifted in order to remove the trestles. The entire structure was then lowered onto the bogies and bolted into place. “Hydraulic mobile jacks were used for the lifting and lowering of tripper 2A, while because of time constraints, a mobile crane was used in the case of tripper 1A,” Flear says.
“Unique to tripper 2A is a large spiral feed chute which feeds ore from the yard conveyor to the intermediate conveyor, both of which are bolted to the portal frame. The intermediate conveyor then in turn feeds the ship loader,” Flear says.
The spiral chute has been lined with high alumina ceramic tiles to ensure optimum wear life under the abrasive operating conditions. In order to fabricate the spiral chute to the degree of accuracy required a full jig was designed and fabricated by Dorbyl Marine to accommodate the correct offset and ensure that the tight tolerances were met.
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