IHI TRA350KW Compressor — Major Overhaul After 38,064 Hours
Second major overhaul of an IHI TRA350KW three-stage centrifugal air compressor at a manufacturing plant: intercooler and diffuser restoration, a new 1st-stage impeller, new low-speed bearings, all air & oil seals and a new discharge check valve.
Machine background
This IHI TRA350KW three-stage centrifugal air compressor was delivered in December 2008 and supplied plant air around the clock. By the time it came in for its second major overhaul the counter showed 38,064 running hours and 3,663 starts; the first intermediate overhaul had been carried out in 2012. The unit had started surging at its normal working pressure — a classic sign that efficiency had dropped because of internal fouling and eroded flow-path parts — so a full overhaul was scheduled.
| Model | IHI TRA350KW (three-stage centrifugal air compressor) |
| Discharge pressure | 0.9 MPa |
| Compression stages / gas | 3 stages / air |
| Motor | Siemens 350 kW, 2,986 rpm, safety factor 1.1 |
Condition found during overhaul
- 1st-stage impeller — surface damage beyond repair; replaced with a new impeller
- 2nd-stage impeller — cavitation pitting on the blade surface; dye penetrant tested, no cracks found, returned to service
- 3rd-stage impeller — cleaned and PT inspected; no cracking, returned to service
- 1st & 2nd-stage diffusers — corroded and eroded; replaced
- 3rd-stage diffuser — cavitation at the vane root, severe; replaced
- 1st-stage inlet scroll — corroded; replaced with a new part
- Scroll casings (volutes, all 3 stages) — rust in the flow path, heaviest in the 3rd stage; ground and re-coated
- Intercoolers (1st & 2nd stage) — heavy scale on the copper tubes and on the front & rear end covers
- Oil cooler — heavy scale on the water side
- Low-speed bearings (1st & 2nd stage) — replaced
- Air seals & oil seals — all three stages replaced, plus the bull gear oil seal
- Gearbox — bull gear, bull gear bearings and high-speed bearings in good condition; light carbon deposit on the high-speed shaft, cleaned
- Discharge check valve — valve plate damaged and no longer serviceable; replaced
Measured data — surge test, clearances & alignment
Every overhaul we document with numbers, not only photos. Below is the measured data recorded in the overhaul report for this machine.
Surge test — before vs. after overhaul
| Surge test point | Before overhaul | After overhaul |
| Surge point 1 | 0.901 MPa @ 44.5 A motor current | 0.801 MPa @ 45.1 A motor current |
| Surge point 2 | 1.257 MPa @ 63.7 A motor current | 1.034 MPa @ 64.4 A motor current |
Both surge points were re-tested after the overhaul and the anti-surge set points were verified against the new data. The machine no longer surges inside its working range.
Rotor & stator clearances (IHI TRA clearance table)
| Clearance position | Measured |
| A — bull gear | 0.25 mm |
| B — high-speed shaft / low-speed shaft | 0.18 mm / 0.17 mm |
| C — impeller ↔ inlet scroll, 1st / 2nd / 3rd stage | 0.44 / 0.43 / 0.39 mm |
| D — diffuser shim thickness, 1st / 2nd / 3rd stage | 1.70 / 1.65 / 1.20 mm |
| E — shaft & bearing clearance, 1st / 2nd / 3rd stage | 0.15 / 0.14 / 0.16 mm |
| E — bull gear bearing, drive side / non-drive side | 0.15 / 0.16 mm |
Coupling alignment (motor ↔ compressor, cold)
- Allowable deviation: ±0.15 mm (rim & face)
- Motor is set 0.12–0.15 mm high to allow for thermal growth of the motor bed — shafts must stay parallel
- Coupling face-to-face distance: 250 ± 0.5 mm
- Final dial-indicator readings after alignment: 0.00 mm at all four measuring points
- Vibration probe gap voltage: standard 8.5 ± 1.0 V — readings 8.74 / 8.85 / 8.91 V before adjustment, re-adjusted to 8.2 V
Control valve stroke test
| Valve | Close → open | Open → close |
| Inlet guide valve (IGV) | 18 s | 18 s |
| Blow-off valve | 23 s | 2 s |
Photos from the job
The photos follow the order of the overhaul report, row by row. Each row covers one stage of the work, so a component stays in the same column from one row to the next — as found, after cleaning / grinding / testing, then after coating or replacement — which makes the change directly comparable.
Row 1 — intercooler cores and 3rd-stage scroll, as found
1st-stage intercooler core — relatively clean
2nd-stage intercooler core — heavy rust on the cold side
3rd-stage scroll casing & impeller — heavy rust
Row 2 — intercooler cores after grinding; 2nd-stage impeller under PT
1st-stage intercooler core — ground
2nd-stage intercooler core — ground
2nd-stage impeller — dye penetrant applied
Row 3 — intercooler cores re-coated; 3rd-stage impeller PT result
1st-stage intercooler core — coated
2nd-stage intercooler core — coated
3rd-stage impeller — no cracks found
Row 4 — diffusers and 2nd-stage impeller, as found
2nd-stage diffuser — heavily rusted
3rd-stage diffuser — heavily rusted
2nd-stage impeller — wiped for inspection
Row 5 — diffusers after grinding
2nd-stage diffuser — ground
3rd-stage diffuser — ground
Row 6 — diffusers re-coated; 2nd-stage impeller PT result
2nd-stage diffuser — coated
3rd-stage diffuser — coated
2nd-stage impeller — no cracks found
Row 7 — cooler end covers, as found
1st-stage front cover — heavy scale
2nd-stage front cover — heavy scale
1st-stage rear cover — heavy scale
Row 8 — cooler end covers, ground and re-coated
1st-stage front cover — ground & coated
2nd-stage front cover — ground & coated
1st-stage rear cover — ground & coated
Row 9 — scroll casings, as found
1st-stage scroll casing — light rust
2nd-stage scroll casing — light rust
Row 10 — scroll casings, re-coated
1st-stage scroll casing — coated
2nd-stage scroll casing — coated
3rd-stage scroll casing — coated
Row 11 — stage inlet pipes and the new 1st-stage inlet scroll
2nd-stage inlet pipe — coated
3rd-stage inlet pipe — coated
1st-stage inlet scroll — new part
Row 12 — new bearings, oil seals and air seals
Low-speed bearings, 1st & 2nd stage — new
Oil seals, all stages & bull gear — new
Air seals, all stages — new
Row 13 — bull gear parts, motor side
Bull gear shaft & thrust face — good condition
Bearing thrust face — good condition
Bull gear bearing — good condition
Row 14 — bull gear parts, main oil pump side
Bull gear shaft & thrust face — good condition
Bearing thrust face — good condition
Bull gear bearing — good condition
Row 15 — check valves, as found
Main oil pump check valve — worn
Auxiliary oil pump check valve — worn
Discharge check valve — damaged, unusable
Row 16 — check valves, replaced with new parts
Main oil pump check valve — new
Auxiliary oil pump check valve — new
Discharge check valve — new
Full inspection record
The overhaul followed the IHI inspection checklist for the TRA series. Every item below was opened up and checked, and the work actually carried out on each part is listed here.
| Item inspected | Work carried out |
| Air end & gearbox | |
| Bull gear, tooth contact & meshing flank | Inspected, cleaned — good condition |
| High-speed / low-speed pinion gear & shaft | Inspected; light carbon on high-speed shaft cleaned |
| Bull gear shaft bearing | Inspected — good condition |
| High-speed pinion bearings | Inspected — good condition |
| Low-speed pinion bearings | Replaced |
| 1st / 2nd / 3rd stage impellers | 1st stage replaced; 2nd & 3rd cleaned & PT tested (no cracks) |
| 1st / 2nd / 3rd stage scroll casings | Cleaned, ground & re-coated |
| 1st / 2nd / 3rd stage diffusers | Replaced, with new diffuser shims |
| 1st / 2nd / 3rd stage air inlet piping | Cleaned & re-coated |
| 1st-stage inlet scroll | Replaced |
| 1st / 2nd / 3rd stage air seals | Replaced |
| 1st / 2nd / 3rd stage oil seals + bull gear oil seal | Replaced |
| Coolers | |
| No. 1 / No. 2 intercoolers | Cleaned; end covers ground & re-coated; new stainless gaskets |
| Oil cooler | Cleaned; scale removed |
| Drain traps & drain trap check valve | Inspected & cleaned |
| Lubrication system | |
| Oil tank, heater & vacuum gauge | Inspected & cleaned |
| Main / auxiliary oil pump | Inspected; main oil pump coupling replaced, O-rings renewed |
| Oil filter, oil circuit check valves | Replaced |
| Controls, piping & other | |
| Inlet guide valve & blow-off valve | Stroke tested & adjusted |
| Air filter element, oil filter element | Replaced |
| Main coupling alignment | Re-aligned, within ±0.15 mm |
| Protection devices & vibration probes | Function tested; gap voltage re-adjusted |
| Discharge check valve | Replaced |
Scope of work — parts replaced
- 1st-stage impeller
- 1st & 2nd-stage diffusers
- 3rd-stage diffuser
- 1st-stage inlet scroll
- Low-speed bearings (1st & 2nd stage)
- Air seals, 1st / 2nd / 3rd stage
- Oil seals, 1st / 2nd / 3rd stage + bull gear oil seal
- Diffuser shims, all stages
- Cooler stainless steel gaskets
- Main oil pump coupling & O-rings
- Oil circuit check valves
- Discharge check valve
- Air filter element & oil filter element
In addition: grinding and protective re-coating of the intercoolers, scroll casings, diffusers and inlet pipes; dye penetrant inspection of the 2nd and 3rd stage impellers (no defects); cleaning of the oil cooler and intercooler copper tubes; coupling alignment within ±0.15 mm; vibration probe gap voltage re-adjustment; control valve stroke test; and a surge re-test after reassembly.
Post-overhaul operation record
The machine was restarted immediately after the overhaul. Discharge pressure, motor current, bearing temperatures and vibration all came back to normal, and the unit has run without surging since. All parameters were normal at restart.
Root cause & our recommendation
The rust and cavitation came from years of operation with moist intake air and a cooling-water side that was not treated: scale built up in the intercooler tubes and on the end covers, air-side dirt blocked the flow path, and the resulting higher inlet temperatures pushed the machine towards surge. For the next overhaul we recommend checking the impellers, diffusers, scroll casings and coolers, keeping the cooling water treated and the tube side cleaned, and holding the following spares: 1st-stage impeller, diffuser set, air and oil seals, low-speed bearings, intercooler gaskets, air filter and oil filter elements.
Planning an overhaul or need IHI TRA spare parts?
Turbomax supplies alternative spare parts and overhaul service kits for the IHI TRA and other IHI centrifugal compressor series — impellers, diffusers, inlet scrolls, scroll casings, air seals, oil seals, journal and thrust bearings, bull gear bearings, intercooler and aftercooler cores, air filters, oil filters and check valves — and supports overhaul projects worldwide. Our founder has 10 years of IHI field service experience.