African Fusion

Earlier this year, GEA Aircooled Systems and GEA Nilenca became Kelvion Thermal Solutions and Kelvion Services, respectively. African Fusion visits the Roodekop premises of the two adjacent companies and talks to Alex Dreyer of Kelvion Thermal Solutions, Pieter Herbst of Kelvion Services and welding engineer Angel Krustev, who supports both entities.

Kelvion Thermal Solutions and Kelvion Services both have roots in the GEA group, which was founded by Otto Happel in Germany in the 1920s, as the ‘company for dust removal plants’, or in German, ‘Gesellschaft fur Entstaubungs-Anlagen’.

Kelvion Thermal Solutions Kelvion Services Angel KrustevGEA pioneered direct air-cooled steam condensation systems and became the world leader in this field as well as in the design and manufacture of finned tube heat transfer equipment. To supplement and complete this specialised engineering and product range, an evaporative cooling tower division was established.

In South Africa, GEA Aircooled Systems was founded 1975 to design, manufacture and service large contracts awarded by the power and petrochemical industries. Following a total technology transfer from the German parent company, the local GEA subsidiary became largely independent.

In recent times, the heat exchanger companies in the GEA Group were all moved into the GEA Heat Exchangers Group, which was then sold to an investor called Triton.

 “Globally, GEA Heat Exchangers’ businesses have been split into three: DencoHappel now represents the HVAC and filtration offering – which was never really a big part of our South African business; ENEXIO, now the conduit for the large power station solutions – wet and dry cooling systems, ash handling systems and components for water treatment – and Kelvion,” explains Dreyer.

In 2016, GEA Aircooled Systems changed its name to Kelvion Thermal Solutions, retaining substantial thermodynamic and mechanical design expertise as well as engineering, manufacturing and contract management capabilities. GEA Nilenca, formed in 2004 from the Service Division of GEA Aircooled Systems, became Kelvion Services at the same time, operating from its own premises adjacent to those of Kelvion Thermal Solutions.

“Here in South Africa, we continue to offer a full Kelvion suite of heat exchanger products and services, while also taking responsibility, on an agency basis, for ENEXIO-branded power station solutions, most notably, the large air-cooled condensing systems and services,” he adds.

“When building pressurised heat exchangers, the bending rolling and cutting of the steel is relatively simple, it is the welding that becomes complex,” says Dreyer. “Our in-house thermal engineering, pressure engineering and welding engineering capabilities – the welding of advanced material and material combinations to the exacting quality standards required – sets us apart from other equipment fabricators,” he tells African Fusion. “We have specialist know-how in welding applications that require high-levels of integrity for rigorous applications,” he adds.

He cites the recent construction of an acid scrubber column for the petrochemical industry, a 68 m column for removing acid from a process water stream. “This column is split into two sections with respect to materials. The base is made in carbon steel, explosively clad with Inconel, while the top sections are made with 316 stainless steel. During construction, therefore, we had to deal with the complexity of joining several dissimilar materials, particularly the seam connecting the clad carbon steel to the stainless steel upper section,” he says.

Krustev explains how this was done. “At the bottom of the vessel is a carbon steel dished end, which had to be weld clad with Inconel using submerged-arc welding. The carbon steel section of the column was made from sheet brought in with an explosively clad Inconel layer. Sections of plate were rolled into cans and, before joining the longitudinal seams, the Inconel layer along the seam had to be stripped away.

“The steel seams were then joined to make the cans. This process was repeated for the circumferential seams, and following carbon steel welding, the inside weld seams were re-clad with Inconel,” he tells African Fusion.

At the join between the carbon and the stainless steel sections, “an Inconel filler metal was used, which is austenitic and so compatible with all three of the materials at the joint,” he adds.

The stainless steel top section, according to Krustev, is made of relatively thin plate. “This creates challenges with respect to distortion. Complete penetration for all the welds was required, which had to be 100% verified by radiographic examination. We were able to successfully complete the welding using the submerged-arc process, but a careful weld sequence had to be developed, which almost completely eliminated distortion,” he reveals.

Orbital welding innovations

In support of its finned tube heat exchangers of various designs, Kelvion has patented a novel tube to tube-nipple welding technique that significantly raises productivity and quality levels. Describing a typical use for the technique, Krustev shows African Fusion a weld sample: “This shows a nipple welded onto a pipe header. We have developed and patented a fast and reliable way of butt-welding the ends of our finned tubes onto the header nipples or to the return U-bends,” he says.

These are commonly used for serpentine-type heat exchangers, which have the inlet and the outlet header pipe on the same side of the unit. Fluid passes from the inlet pipe, though finned tubes up the heat exchanger, around a bend at the top and then back again, into the return header pipe. “This design can take higher pressures – 186 bar at 700 °C for a recent fabrication – using thinner materials, because all of the interconnecting components are cylindrical,” says Dreyer, adding that conventional units with straight sided header boxes at each end have to be made of thicker section to cope with the high pressures.

Also with header boxes, the flow velocity decreases as fluid passes into the box from the tube. For media containing particles this can be a problem because suspended particles can drop out and accumulate in the header boxes. “The serpentine design ensures even flow velocity, which is better for preventing blockages,” Dreyer explains.

Turning attention back to the orbital welding technique, Krustev says that each serpentine heat exchanger contains more than 500 nipple-to-tube butt welds, and these used to be done in two passes. “In the past we would weld the first pass using the GTA process without filler material. But if filler is not used, there is always sagging, which compromises the material thickness at the joint. For an acceptable weld, a little reinforcement is required. So we would then do a second pass with filler to give each joint a visible cap.

“Our new orbital welding technique eliminates the need for the second run. We use special filler metal inserts, which are fused into the joint using the orbital welding system, creating a full penetration weld with a little overfill, guaranteeing integrity equivalent to unwelded pipe,” he explains

“The process has dramatically improved our production and quality and we have now developed the welding parameters to also suit carbon steel serpentine designs. I can safely say that Kelvion is now a world centre of excellence for serpentine heat exchangers,” he adds.

Kelvion Thermal Solutions also makes extensive use of automatic orbital tube-to-tubesheet welding technology. A modified orbital welding technique has recently been developed, based on the use of specially designed copper weld retainers. This innovation allows the weld to be executed in a single pass, without any overlap into the tube bore, thus increasing productivity and weld quality.

Kelvion Services

The welding expertise from Kelvion Thermal Solutions is also shared with sister company, Kelvion Services, which operates its own service and repair workshop on an adjacent site. “We are frequently contacted by companies in the petrochemical industry to perform weld repairs,” says Herbst, citing a current case where the Monel cladding repair on a vessel has failed. “We believe the process and the cladding materials were not correctly specified and we are currently busy solving this problem by seeking a more suitable cladding material and weld repair process – and we have the process, welding and metallurgical skills necessary to evolve a better solution,” he assures.

“We also have a strip cladding capability that allows us to deliver solutions such as these more cost-effectively,” adds Dreyer.

Herbst cites another success in Qatar for Dolphin Energy. “We were asked to refurbish a sulphur crystalliser condenser during the plant shutdown. These had a knuckle-type tube sheet heat exchanger to take the high pressure. After removing the internal components and baffles, we did our usual integrity test, only to find that the casing was severely eroded and the wall thickness compromised.

“Because of our welding expertise, we were quickly able to develop an onsite weld repair procedure for the Inconel build up required, which we successfully performed before rebuilding the unit – without delaying the shutdown.

“A few years ago, we also participated in the return-to-service project for the Komati power station. We were contracted to do the HP and LP heat exchanger pressure vessel refurbishments, but ESKOM also wanted the same contactor to supply all of the associated high-pressure pipework. So we developed this expertise and can point to the successful completion of this work, nearly a year ahead of schedule, as a reference,” he points out.

“We pride ourselves on our ability to find and overcome the complications that are often associated with routine refurbishment work. We have thermal design specialists, pressure vessel engineers, welding engineers and metallurgical expertise, all in-house. We are therefore able to produce successful turnkey solution, on the service and refurbishment side and for new installations,” Herbst concludes.

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