For the first time in the industry, Steinmüller Africa, a leader in high-pressure steam generation equipment, with eNtsa, engineering consultants, successfully used rotary friction welding. This innovative technique was applied to fabricating four headers used for high-pressure water heater boiler units installed on Tutuka power station in Mpumalanga.

The duo used a hybrid of rotary friction welding and friction hydro-pillar processing (FHPP) to attach 448 heat exchanger nozzles onto each of the four high-pressure headers used in the final fabrication of the high-pressure heat exchangers. This process needed to be developed as an alternative to the already used submerged arc welding method.

 “The nozzles need to be precise, to ensure a proper fit between the tube and nozzle weld,” explains Friedrich Schwim, Senior Welding Engineer, Steinmüller Africa.

The initial welds using the submerged arc welding method found defects in the first four headers and although the submerged arc welding process was further refined to have no defects, these four headers still needed to be repaired. To repair these defects, the two companies used a hybrid application of FHPP and rotary friction welding to weld the nozzles to the headers.

100% defect free

“All necessary code compliances were developed, and the welding has proven to be 100% defect-free and a huge success,” says Schwim. He points out that there are numerous advantages to this new welding method. “There was almost zero distortion in the nozzle orientation; the automated process ensures that all the welds are the same;  welding time is 75% less compared to submerged arc welding; and, most importantly, the cost of manufacturing remained the same,” he says.                                                                                                                                                                            WeldCore® technology

WeldCore®, which formed the basis of this welding technique, is a novel sampling and repair technique that involves removing a cylindrical metallurgical sample from a pipe wall and repairing the site in the steam line using taper friction hydro-pillar processing. This reduces the risk of unexpected catastrophic failure and increases uptime, which leads to substantial cost savings.

“There are various friction welding technologies in the industry,” says Schwim, “but for this specific application, they have never been used. It also becomes a difficult and expensive process when developed from scratch.” The company’s collaboration with eNtsa, which had developed the fundamentals of this process, led to its application and approval. “There is a health and safety standard for this welding process, but without a baseline project where this technology was used anywhere in the world, we had to persuade the client and the Association of Inspection Authorities (AIA) to accept it for the project,” says Schwim.

Applications and IP

This welding technique can be applied to the petrochemical, nuclear, and power generation industries, where nozzles must be welded to pipes to create a forged-like bond. It now forms part of Steinmüller Africa’s and eNtsa’s intellectual property. “Our two companies are the only ones currently in the world that introduced it for this specific application,” says Schwim.

To bring the project to fruition, eNtsa provided the welding technology, the machines, and expertise in the process itself. Steinmüller Africa provided the technical knowledge on welding and required compliance including the final machining of the stub to header welds. For the duration of this project, eNtsa was appointed as Steinmüller Africa’s sub-contractor under its ISO 3834-2 quality certificate. “We took full responsibility for the welding,” Schwim concludes, “and provided the technology to perform the final machining and post-weld heat treatment”.