C A S E S T U D Y and building of turbine rotor a first Don Pedersen had a problem. The Norske Skog Tasman mechanical engineer was dealing with a troublesome turbine rotor in the company’s energy centre, which generates steam and electricity to run the Kawerau paper mill, as well as supply power to the national grid. There was ongoing damage to the turbine, with blades which were falling off and cracking. “We were facing, at minimum, a two month shutdown of the turbine if we had to replace all the blades. That’s a lot of wasted energy. But, if we had a catastrophic failure we could be down for six months, and there’s a lot of cost to do that,” he says. After considering the expensive option of purchasing a new proprietary turbine rotor, Pedersen instead opted to engage Allied Industrial Engineering (AIE) to manufacture a completely new rotor. The project turned out to be a complete success that both Don Pedersen and AIE turbine engineer Steve Sands describe as the most significant project either of them has worked on. “It’s the first time something like this has been done in New Zealand,” Sands says. Talks began as far back as 2008 between Carter Holt Harvey Tasman, as it was then known, and AIE to determine whether the manufacture of a new rotor or a major repair of the original rotor would be the best solution for ‘TA3’. By 2012, Carter Holt Harvey Tasman (Paper) had become Norske Skog, and AIE was asked to develop a proposal. Drawings and scopes of work went back and forth, an agreed price was negotiated, delivery was defined and the go button was pushed in January 2014. Don Pedersen says that moment was “no leap of faith”. “My dealings with AIE in the past meant I knew exactly what their capability was so I had no doubt about their ability to deliver quality work. I had full confidence the project would be delivered on time and on budget.” So began the highly technical, zero tolerance, reverse engineering of the existing TA3 rotor. Meticulous manufacturing drawings were produced to a particularly high standard with the full knowledge that errors could make or break the project. Extensive material tests were undertaken on the existing rotor and blading and material specifications agreed to by both AIE and Norske Skog for the new build. Rotor forging and rotor blading was ordered, and 12 March 2016 component orders placed. The rotor blading and shrouds arrived from the Netherlands in November 2014, and the forging from Germany early 2015. Steve Sands says it took three months of planning to produce timelines which both Norske Skog and AIE agreed on for the manufacture of the rotor at the AIE workshop. “In discussion with Norske Skog it was decided we would manufacture all of the components for the thrust end and assemble them to the new rotor. We would only re-use the existing coupling which would be exchanged during the shut.” At AIE a project manufacturing team was put together that included the operations manager, project manager, machining supervisor, workshop planner, machinist and a turbine fitter to facilitate the smooth manufacture of the TA3 rotor. From this two smaller teams were set up; one, consisting of a project manager, supervisor and machinist looking at the machining of the rotor, the other focused on the fitting of the blades to the rotor consisting of project manager, supervisor and turbine fitter. The brief for these two teams was to look at the length of time it would take for each operation and any specialist tooling required. “Our two key machinists came up with their plan as to how to machine the parts. I put together the process for fitting. The process for peening was done in conjunction with the fitters on the job. It was a cooperative team effort and it worked really well.” A full project team approved and ratified all aspects of the project plans and allocated machining and fitting resources along with manpower. Sands says this was critical to the successful outcome. Once the blades, shrouding material and rotor forging arrived they were inspected thoroughly for any transport damage. The rotor forging went into the CNC lathe for a full ITR and truth check to confirm the rough machined sizes were to the drawing. Machining commenced with constant reference to drawings throughout the process. Initially, both ends were centered; the shaft ends outside diameters and stages 1-4 outside diameters were machined to size. This was an important step as stages 1 and 4 outside faces would then act as datum throughout all of the machining processes that followed. At each hold point, the finished dimensions were recorded and, once accepted by the project manager, the machining process could continue. As the blades were unpacked they were laid out in the manufacturer`s numbering sequence and the oversize blades identified. Each individual blade was weighed and documented with each blade positioned around the disc for optimal theoretic balance, using a balancing program developed by AIE to determine blade position. This process was repeated across each stage. On completion of fitting the blades an ITR was completed to ensure all blade root blocks were tight. The pitch of the tenons was then taken for the machining of each shroud piece. Shroud pieces were machined to suit each packet of blades and each individual shroud section fitted to its designated position. Clearance around the tenon was checked, adjusted and again ITRs completed prior to peening commencing. Various processes for peening the tenons were applied on several samples. This was then examined microscopically, process adjusted, and further samples completed and examined microscopically. Peening of the tenons following the established process ensued and each packet of blade tenons was completed in sequencing order. With all peening completed an ITR was performed on shroud to blade connections. Once all of the above inspection was complete an NDT examination of the tenon and cover bands REVERSE ENGINEERING
EN feb16-HR-nocrops
To see the actual publication please follow the link above