Starenergy Geothermal Wayang Windu U1 110 MW FE Turbine Turn around 2012

1.      Executive Summary

Wayang Windu Power Station Unit 1 was shut down for the fourth major overhaul from June 9^th to June 20^th, 2012. The objectives overhaul of  mechanical  section are turbine general inspection and cleaning, turbine rotor replacement, MOP rotor replacement, main steam control valve inspection and replacement , main steam stop valve inspection, main steam strainer inspection, turbine oil replacement, condenser cleaning, hot well pump A and B overhaul and finish any outstanding works which could be conducted during outage only.

                                                                                                                            

It was noted the critical work is turbine rotor replacement due to the first time for WW team to conduct the work. Huge efforts were given to assure the turbine rotor replacement can be conducted safely with good quality work.  In overall, all the works can be completed safely with good quality work and time frame.

Note: This report does not contain detailed information on the inspections and measurements recorded by inspectors. The information can be found in the PT Sulzer Indonesia {PT SI} Report and Fuji Engineer’s report. In addition, generator and electrical components inspection was documented separately by E&I section.

2.       Results of Inspection:

In general, inspection methodologies carried out during this overhaul are visual inspection, dimensional inspection and Non Destructive Examination (NDE).  The inspections conducted by Turbine Supervisor refer to inspection procedures prepared by Fuji Electric.  

2.1.   Main Steam Strainers

Both left and right steam strainers are in excellent condition. There is  no fouling found and only very minor scaling noted; actually less scaling than in 2009. NDE does not reveal any cracks or flaws in the sieve base or top cover.

No remedial action is required. It is recommended to include examination of strainer’s body in main strainer inspection’s scope of next overhaul.

2.2.   Main Steam Stop Valves (MSSV)

Both Main Steam Stop valves are in acceptable condition. Prussian blue checks were done and results are substantially similar to 2009  inspection. The disc to seat surfaces on the main and equalizer pilot valve are still tight; providing a positive shut off on shutdown or emergency trip as designed.  No remedial action is required. These valves are critical for turbine safety and must be inspected at each overhaul. It’s recommended to monitor the actuator performance since there is no inspection of the actuator during overhaul.

2.3.   Main Steam Control Valves (MSCV)

On this occasion L1 and L2 valve and servo motor  are replaced , the other side R1 and R2 valves cleaned inspected , coupling and servo motor shaft replaced due to crack finding on the coupling and prevent leakage from the servo shaft  ,no evidence of excessive seat/disc wear found.  NDE revealed some small cracks in the disks and are similar in nature to those noted on the seats in 2009 when Fuji Inspector said they were “stress relief” cracking only in the stellite surface coating and should not propagate.

2.4.   Turbine Rotor

Change to new rotor

Commencing reaming work (for coupling turbine – generator) after alignment, duration 27 man hours equipped with 2 sets reaming tools.

Old Rotor:

The rotor and moving blades (buckets) are in acceptable condition.  There are minor scaling found on first stage blades with minor pitting or erosion on leading edges, similar to the as-found condition in 2009. The stellite strips on the freestanding L-1 and L-0 blades (7^th and 8^th stages) are holding up very well with no significant erosion noted.  The rotor was blasted clean with a finer grit than that used in 2009.  NDE on moving blade roots did not reveal any cracks. Refer to Contractor report for grit blasting and NDE details. Some of the rotary blades of LP carrier have “dent” defect (see the photograph), suspected coming from broken off 'J' strips.

2.5. Turbine Casing and diaphragms – Upper and Lower

The SBH and SBR were installed on the previous overhaul (2009). Found in good condition. The rim plate was repaired in a similar fashion as the HP carrier with Belzona. 

Steam inlet plenum (belly) drain line, and subsequent inter-stage drains are clean and clear of obstruction; this mitigates moisture accumulation and blade erosion from water droplet impingement.

Both rupture disks the on top casing were inspected and found  in good condition.

2.5.   Bearings – FIVE Each; FOUR Journal and ONE Thrust

The three of journal bearings and the thrust bearing are still in acceptable condition (No 1, 2, and 3).  It only requires polishing and cleaning process .Number 4 bearing was replaced, it is found linear scratch (about 23mm),

It is recommended to operate the coalescing oil purifier continuously except while cleaning and routine monitoring of lube oil quality is conducted.

2.7. Turbine Shaft Gland Packing – Labyrinth Steam Seals

The seal steam labyrinth fins (typically called “J-strips” because of their shape) are generally in fair condition. Based on these findings, the outer fin assembly was changed with refurbished packing. Top and bottom clearance of outer seals’ {both ends} were larger than clearance’s before its changed.. The center and inner labyrinth seal assemblies were changed. As found seal the tip-to-shaft clearances are slightly larger than in 2009 inspection. As overall the gap is back to standard O&M ( see detail report saparetely)

2.8. Main Oil Pump

The main oil pump (MOP) was uncoupled from the jackshaft, disassembled and internal inspection was performed. Pump’s rotor and bearing was replaced due to out of tolerance. Detailed results can be found in T-G contractor’s report.

2.9. Shaft Alignment  

Based on information obtained from measurement and calculation checks, all parties concluded that alignment adjustment was needed at this point.  PT. SI (Sulzer Indonesia) used laser alignment method. The alignment data of each method were discussed for acceptance.

(Please see alignment record of T –G).

  2.10 Turbine Lubricating and Hydraulic Oil System

The Lube Oil reservoir was supposed to have been pumped down and the reservoir cleaned and inspected.  It was not done due to concerns about the cleanliness of the transfer piping to and from the used oil storage tank.  This task must absolutely be done at next overhaul.

It’s recommended to develop a method to empty and clean the storage tank, flush the transfer lines and use a portable pump with fine filters to transfer the oil both directions (to and from the storage tank).  It may be practical to change out the lube oil with a new oil at next overhaul regardless of the condition of the oil.