Gas Turbine Alignment

Mechanical Dynamics & Analysis (MD&A) experts offer specialized gas turbine services, such as Gas Turbine Alignment, as a global full-service provider to the power generation industry.

Gas Turbine Alignment

Unlike steam turbine alignment, gas turbine alignment is performed with the upper halves installed, also called “Tops-On” alignment, and moves must be made in a specific sequence, adding to the overall challenge.

MD&A Alignment Engineers have experience with a variety of OEM’s allowing them to service a large portion of the installed fleet.

The most common issue with three bearing gas turbine models, such as the GE® 7B, 7E, and 7EA, is with casing slippage in the turbine/exhaust frame casing joints. The casings serve an important function as they support the bearings, rotor, and hot gas path hardware. It’s necessary that casings stay in position to keep the unit’s performance and efficiency at an optimal level.

On affected turbines with this issue, the casing slips downwards in relation to the exhaust frame. This causes misalignment of the #2 and #3 bearings, as well as, causing a vertical step change in the stationary component positions near the joint.

Two bearing gas turbine models, such as GE’s® 7F turbines, can also become misaligned over time. This is due to conditions including gravity sag, casing slippage, and thermal creep. These conditions cause shifting for both the casings and the T2 bearing, requiring the unit and its components to be precisely realigned.

Occasionally, turbine compressor discharge casings need to be replaced on older machines. Originally, these casings were fabricated with welded joints, which have been shown to be susceptible to casing creep. As the metallurgy changes over time, the casings distort, leading to significant performance issues. This is resolved by completely replacing the compressor discharge casings.

The process for our specialized Gas Turbine Alignment starts with an internal inspection of the unit. Partial disassembly is required to identify the issues. The most common signs of misalignment are blade rubs. These are caused when the rotating blades come in contact with the casings after they have slipped or become distorted. This condition is visually evident on both the casings and the blades themselves. This type of damage can only be seen and assessed if the unit is taken apart. Rotor position to casing measurements is also taken and recorded. Once the cause of damage is understood, the repair phase begins.

The typical Gas Turbine Alignment consists of realigning the bearings and changing the dowel pins in the turbine/exhaust casing vertical joint. On the 7F series units, only the T2 bearing is alignable, since the T1 bearing is secured within a cylindrical fit. Alignment is a fairly complex undertaking due to very small clearances and tight tolerances. The process requires specific expertise, equipment, and experience to properly diagnose and resolve the casing alignment issues.

In decades past, on earlier models, misalignment was less of an issue. Older units were more forgiving and kept running even when misaligned. Today, it’s much more of a concern. Alignment affects clearances and clearances affect output and air quality, which is now heavily regulated.  With today’s modern units and high-efficiency levels, even small rubs of rotating blades with the casings open clearances and degrades the efficiency and output of the unit.

Our Alignment Engineers have the knowledge needed in order to interpret the data. Each engineer’s broad base of experiences contributes to the overall value MD&A provides to our customers. You can expect dependable and accurate results every time you hire MD&A to align your turbine.

MD&A’s specialized services range from Compressor & Turbine Rotor Repairs to Plant Performance Testing and Analysis. We provide immediate access to expert help when you need it, where you need it. For every repair job, large or small, the speed and effectiveness of our response team is matched only by the depth and breadth of our engineering expertise.

Call our Gas Turbine Services at (518) 399-3616 or use our Contact form.

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