For the first time in the industry, Steinmuller Africa, has successfully applied rotary friction welding to fabricate four headers used for high-pressure water heater boiler units installed at Tutuka power station in Mpumalanga.
A hybrid of rotary friction welding and friction hydro-pillar processing (FHPP) was employed 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 current submerged arc welding method.
Proper fit
“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 do so, the hybrid application of FHPP and rotary friction welding successfully welded 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 Friedrich. 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% that of submerged arc welding; and, most importantly, the cost of manufacturing remained the same.”
WeldCore, which forms 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,” adds Friedrich, “but for this specific application, these methods 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.
Technical knowledge
“There is a health and safety standard for this welding process, but without a baseline project where this technology was used elsewhere in the world, we had to persuade the client and the Association of Inspection Authorities (AIA) to accept it for the project,” says Friedrich.
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 to introduce this technology for this specific application.”
Quality certificate
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,” Friedrich concludes, “and provided the technology to perform the final machining and post-weld heat treatment”.
