TURBINE MAIN SHAFT REPAIRS

THE CHALLENGE

Providing a repair solution that extends life of main shafts

Wind turbine main shafts vary in metallurgical properties and the base material often varies between Original Equipment Manufacturers, OEM’s. Because of variances in materials, it was historically difficult to effectively repair main shafts and extend the life of the component.
Spray welding, or HVOF, was the industry standard for main shaft journal repairs and the most commonly used process. However, spray welding lacks strong bonding strength due to the differing mechanical properties from the existing shaft material. With a low bond strength, the spray weld process can lead to premature failure due to the material flaking from the original shaft.
Hard chrome plating has been another repair option with varying level of success and cost. Embrittlement can frequently occur when chemistry of the base material is not fully compatible with the plating process

Turbine owners and operators needed a better solution to repair main shafts that would last


IMPACT ON OPERATIONS

Keeping critical assets out of critical condition

The main shaft is a critical component of the drive-train assembly; likewise the life of this component impacts operations significantly when failures and premature replacements are needed.
Because many owner/operators have not budgeted or expected repeat main shaft repair for the life of the turbine, an upgraded or improved solution has been sought. When the bearing and lubrication upgrade is applied to a non-rehabilitated shaft journal, the fatigued shaft journal can be detrimental to the bearing and potentially cause repeat failure.
The industry needed a solution that was economically feasible, and equally strong to withstand the high-demand work the shafts undergo while in operation. L&H engineers analyzed the material properties of a variety of main shafts in an effort to develop rebuild options for customers’ specific operational needs and shaft designs.

 


THE SOLUTION

Main shaft repairs needed a more robust solution to extend component life


Metallurgy and shaft design were the main driving factors in determining the best repair options. Through a series of testing and analysis, L&H engineers developed two primary offerings.

Weld Overlay Journal Repair
Developed by L&H Weld Engineers, the weld repair process for bearing journals matches the base material’s metallurgy better than traditional spray weld processes. Additionally, the surface hardness was increased while decreasing premature cracking. After welding, the shaft undergoes a cold working process. This involves machining and deep rolling which creates a superior fit spec and leaves a mirror-like finish.

Roller Burnishing Journal Repair
The main shaft’s bearing journal is undercut to remove the fatigue zone which is followed by a high-pressure roller burnishing process. This cold working process leaves a hardened and superior surface finish while mitigating premature fatigue and minimizing flaking on the bearing journal. This repair method slightly undersizes the existing shaft journal while achieving the fit spec necessary for the new bearing.

The use of these enhanced repair methods with advanced bearings yields an overall assembly upgrade.


“L&H’s technical teams provide seamless and streamlined execution on the job. You can tell when jobs are breaking down, it’s often a breakdown in communication; with L&H that doesn’t happen.” – Greg Shelton, Vice President of Business Development, Run Energy


THE RESULTS

Taking quality to another level

These unique main shaft repairs provide longer life of the component and illustrate a much more viable repair option than others in the industry. In addition to the main shaft journal upgrade, all reused components go through a complete re-qualification process which includes various NDT and dimensional inspections. The utilization of improved material handling fixtures and methods ensures there is no damage to the bearing or other components during the L&H rebuild process. To ensure no contaminates are in the bearing after assembly, the bearing undergoes a thorough flushing process with industry leading equipment. After flushing, an automated grease pump is used to pack the bearing assembly through a multi-port process. A comprehensive rebuild report is provided to the customer documenting the disassembly, inspection procedures, rebuild solution, and assembly results.