An overhaul can restore individual bearings, diaphragms and seals to their specified condition while leaving a separate question unanswered: how do those internal features relate once the turbine is assembled? Steam turbine bore alignment addresses that geometry. It records the relationship of internal locations to a chosen reference so the overhaul team can review the machine as an assembly, not a collection of isolated repairs.

The critical detail is the machine state. A reading taken with casing tops off may be valid for that state, yet it can mean something different after the casing is closed. Useful turbine overhaul measurements therefore connect the measured feature, reference, assembly condition and any correction in one record.

Internal geometry is a chain of relationships

The rotor passes through a succession of stationary features. Depending on turbine design and the work scope, those features can include bearing bores, diaphragms, packing or seal locations, nozzles, inner shells and casing bores. Each feature may have its own repair or inspection history, but its position also affects the geometric path through the machine.

Bore alignment asks where each measured location sits in relation to the selected reference line or reference points. That is a different question from external shaft alignment at a coupling. Both can matter to a turbine train, although one cannot stand in for the other.

The wider relationship becomes important after work that disturbs an internal element or its support. A local repair can be carefully completed and still leave a review question if a reference point changed, a diaphragm was repositioned, or a casing condition altered the observed centre line. The purpose of the measurement is to make that relationship visible before the record is reduced to a final result.

When the unresolved question is whether a bore-alignment result can be delivered as a traceable report, require the report to identify the datum, internal feature sequence and casing state. That reporting boundary matters more than a bare set of coordinates because it tells the outage reviewer what can genuinely be compared at final assembly.

Casing condition changes what a comparison means

The casing is part of the measurement condition, not background detail. With tops off, access and support conditions differ from the assembled state. With tops on, the casing and its connections may change the measured relationship of internal features. A result is therefore meaningful only alongside the state in which it was collected.

That point changes the review conversation. Instead of asking only whether a bore moved, the team can ask whether the reference was stable, which assembly state applies to each set, and whether the difference was investigated before the next decision. A measurement sequence needs to suit the turbine, outage scope and reference strategy; no one sequence applies to every machine.

A sound geometry record should keep these elements together:

  • the internal features included and their machine positions;
  • the selected reference line, datum or reference features;
  • casing, support and assembly state at each reading;
  • setup details that affect repeatability or interpretation;
  • corrections made between readings; and
  • access limits, incomplete work or unresolved differences that need review.

This is not paperwork added after the fact. It gives the next reviewer enough context to compare like with like and stops a bare coordinate from being reused as though the machine state were unchanged.

Before measurement begins, agree which features are genuinely accessible, where the reference will be established and when the casing condition will change. That short planning conversation can prevent a later comparison between readings that look numerically compatible but were taken from different support or assembly conditions. It also makes it easier to identify whether a second measurement set is required before the outage team disperses.

One overhaul illustrates the assembly-state issue

In a 550 MW steam-turbine overhaul case, the internal geometry was measured three times with casing tops off and three times with tops on across a 30 metre housing. The project covered 42 diaphragms and nine stuffing boxes. The reported centre line changed between those assembly states, so the team used the comparisons to agree corrections and then checked alignment parameters again at recommissioning.

That is a project example, not a template for another turbine. Its housing length, number of components, outage sequence and achieved result belong to that installation. Its lasting lesson is narrower and more useful: the state of the casing can alter the meaning of an internal-alignment result, so that state belongs in the evidence.

Select measurement capability around the geometry question

The instrument and arrangement should suit the features, access and reference needed for the job. Geometric measurement equipment for bore alignment covers bore alignment alongside other geometric tasks. PRUFTECHNIK’s current geometric-measurement range includes straightness, flatness, level, inclination, plumbness, parallelism and right-angle checks. The equipment choice should follow the geometry, not an assumption that one historical setup fits every turbine.

The result also needs to be readable by people who were not present. A traceable report can show which features were measured, how the reference was carried through the work, which condition applied to each result and what remains outside the measurement. It supports an informed review of the overhaul evidence; it does not by itself approve assembly or return to service.

Where the outage needs independent rotating-machine or bore-alignment measurement and reporting support, the laser alignment measurement and reporting service includes rotating-machine alignment, CENTRALIGN bore alignment over large distances and traceable reports. The owner and its authorised engineering process retain the decision on the reference, any acceptance requirements and turbine operation.

Compare assembly states on one reference

Comparable turbine states depend on a reference established at the right assembly stage. Commission CENTRALIGN bore-alignment measurement and reporting through Aquip and scope the named turbine measurement dates. Each casing, bearing or rotor-related result must retain its assembly state and setup reference so dimensional change is not confused with a changed basis.

The resulting work boundary should identify which internal features are accessible and when the reference can be established, while the owner retains the reference strategy and acceptance requirements. Declare the reference line before the first state is captured. Each later casing, bearing or rotor-related measurement must retain its assembly state and setup reference so that a dimensional change is not confused with a changed measurement basis.

The overhaul record should compare successive states only where that reference remains traceable. Its final anchor is the common line that allows those states to be compared.