Steam Turbine Inspection Checklist During an Outage

Before You Open the Machine

Inspection quality starts before the first bolt is removed. The following should be completed and documented before the casing is opened:

• Review of vibration history — any trends, events or alarms from the last operating period
• Review of oil analysis results from the previous months
• Review of known issues and open work orders from previous outages
• Definition of inspection scope: which areas must be inspected vs. which are conditional on findings
• Alignment measurements on the coupled rotor train before disassembly
• Bearing temperature baseline readings before cooldown

Rotor Inspection

The rotor is the most critical component in the turbine and the most difficult to repair or replace within an outage window. Inspection should be thorough and systematic.

Blades and blade attachments

• Visual inspection of all accessible blade stages for impact damage, erosion and deposits
• Blade tip clearance check where accessible — compare to original specifications
• Check for cracked or loose blades — visual and sound test (tap test on accessible stages)
• Inspect blade root fixings (fir-tree, T-root) for corrosion, fretting and cracking — dye penetrant testing where required by scope
• Inspect shrouds and tenons for cracks, looseness or contact damage
• Inspect interstage seals for wear, blowout damage and correct positioning

Rotor body

• Visual inspection of all accessible rotor surfaces for cracks, pitting or corrosion
• Check balance weight locations — document condition and ensure no weights are missing or displaced
• Inspect coupling flange and coupling bore for cracks, fretting and condition
• Check rotor journal surfaces — any scoring, roughness or damage to the bearing journal affects bearing performance
• Thrust collar inspection — check for scoring, discolouration or wear marks

Steam Path and Casing

Diaphragms and nozzles

• Inspect diaphragm vanes for erosion, cracking and deposits (particularly salt and silica deposits)
• Check diaphragm seal strips for correct positioning and condition
• Inspect nozzle blocks in impulse stages for erosion and cracking at nozzle throats
• Document erosion patterns — they indicate steam path flow patterns and can indicate moisture ingestion

Casing and casing joints

• Inspect casing bore surfaces for erosion, corrosion and contact marks (potential evidence of rotor contact)
• Check casing split joint for distortion — measure deviation from flat using feeler gauges at defined positions
• Inspect all casing bolting for condition, stretch and thread condition
• Check all thermowell, drain and seal steam connection penetrations for cracking

Journal and Thrust Bearings

Bearings tell you what happened in the previous operating period. Inspection findings — wear patterns, surface condition, clearance measurements — should be documented carefully.

• Measure journal bearing clearances — top clearance and side clearances; compare to OEM specifications and previous measurements
• Inspect Babbitt surface for wiping (smeared surface), cavitation erosion (pitting), corrosion and cracks
• Document any overlay of oil scoring patterns on the Babbitt surface — these indicate the operating oil film position and can indicate alignment issues
• Inspect bearing housing for correct clearances and pivot condition (tilting pad bearings)
• Inspect thrust bearing for pad wear and surface condition — measure pad thickness if replacement is planned
• Document thrust bearing clearance (end float) — compare to specification
• Inspect bearing instrumentation — thermocouples, proximity probes — for correct installation and condition

Labyrinth Seals and Clearances

• Measure radial clearances on all accessible labyrinth seal stages — compare to OEM specification and previous measurements
• Inspect seal strips for wear, damage and blowout
• Check for contact marks on rotor surface at seal locations — any evidence of rub should be recorded and assessed
• Inspect gland steam connections and gland steam condenser connections
• Check seal housing condition and seal ring fit in housing

Oil System and Lubrication

The oil system is often inspected under time pressure, but inadequate oil system attention is a leading cause of bearing problems after restart. Take the time to do it properly.

• Flush bearing oil supply lines during the outage — not just flush at standstill, but a dynamic flush at elevated flow rate if possible
• Inspect oil filter elements — note loading, colour and any particle deposits; cut open the element and inspect if any operational concern existed
• Inspect oil cooler for fouling and tube condition
• Check all oil supply and drain line connections for correct installation
• Take an oil sample for analysis before the outage and again after flushing
• Inspect the main oil reservoir for sludge, water and debris — clean if required

Coupling Inspection

• Inspect coupling bolts for condition and stretch — replace if any doubt
• Check coupling faces for fretting, cracks and perpendicularity
• For flexible couplings — inspect flexing elements, diaphragms or gear teeth as applicable
• Verify coupling alignment after reassembly before closing up

Documentation and Handover

What is found during inspection only has value if it is properly documented and communicated. The following should be completed before the machine is reassembled:

• All measurements recorded in the formal measurement protocol — clearances, dimensional measurements, alignment readings
• All significant findings photographed and logged with component location
• Each finding assessed for severity and assigned an action: repair now, monitor, or accept as-is
• The basis for each decision documented — not just what the decision was, but why
• A pre-close checklist completed before the casing is assembled