Steel fabrication, steel erection and corrosion protection specialist Betterect and engineering, equipment and services solutions company FLSmidth have collaborated to deliver several 45-m-diameter modular bolted thickeners for an undisclosed mining project in Southern Africa.

The thickener project entailed the fabrication of several precisely engineered, carbon steel, very large diameter dewatering tanks or thickeners designed for exact alignment in accordance with the highest quality and design codes.

This is to ensure the client receives the best possible design and fit for their requirements.

The robustly fabricated thickeners will be transported to site as modular sections and bolted together in situ, eliminating the need for “hot work” on the site.

Modular Sections

In contrast with fabrication methods where tank sections are welded together during the site installation, a bolted thickener design allows for the thickeners’ modular sections to be bolted together on site.

This will also ensure a safer erection and assembly process, which will take about three weeks, compared with the traditional welded thickener process.

This also allows for significantly smaller, lesser skilled installation crews who can complete the installation in a much shorter duration with completely accurate alignment and a perfect fit.

“This translates into an overall project saving of about 30% compared with a traditional welded thickener supply and installation project,” says Betterect MD Nicolette Skjoldhammer.

The tanks were completed in less than half the usual time taken to fabricate thickeners of this size.

Fabricating a thickener of these dimensions normally takes 16 to 20 weeks; however, Betterect’s unique fabrication process significantly reduced the fabrication time on this project, explains FLSmidth project manager procurement Pieter Pretorius.

“One of the greatest challenges was ensuring that the very large welded modular sections, once bolted together, are aligned with, and bolted to, their adjoining sections with mathematical precision, working to extremely tight tolerances of 1 mm over as much as 25 m. Any deviation, even that of a millimetre within the flanges over the massive surface area, would not have been acceptable,” Skjoldhammer explains.

In total, the thickeners comprise several hundred tons of platework and structural steel, representing a total of more than 60 km of welding for the project.

At Betterect, each weld undergoes 100% nondestructive testing conducted by a permanent, onsite third-party.

“This entails each weld passing either visual, dye penetrant, magnetic particle, radiographic or ultrasonic testing, where the radiographic testing checks for defects inside the weld, while ultrasonic testing conducts a full volumetric examination of the components,” Skjoldhammer explains.

“While it is extremely labour-intensive, the process certifies that every weld and joint withstands the harsh environment in which the tanks will be deployed,” she adds.

Over the last five years, Betterect has invested significantly into the latest pulse arc welding technology from Finnish original equipment manufacturer Kemppi.

“The decision to use the Kemppi range of welding equipment was based on it being one of the best available, with the highest inherent safety factors, as well as being user-friendly for the welders and operators.

Pulse arc welding technology is extremely effective in ensuring high-quality welds. The technology reduces defects, porosity, cavities or cracks, lack of penetration or lack of fusion.”

This results in excellent weld quality, strength and integrity while significantly reducing the welding duration, which improves productivity and ultimately reduces cost for the end-user client.

The successful project is a demonstration of the concept and practice of Betterect’s ‘Team Africa’ concept, where local suppliers and manufacturers collaboratively supply mining, industrial, power generation and other sector projects throughout the continent, she highlights.

“The successful collaboration with our client FLSmidth and the supply to the end-client in Southern Africa exemplifies the ‘Team Africa’ concept in action, whereby companies are able, through forming synergistic partnerships, to supply and process massive equipment, to the highest specifications, within record time,” Skjoldhammer says.