501FD2 users add thru bolts to their growing list of engine components to inspect regularly

Fig 1, ATS MB

1. Forward thru-bolt nuts are located between the second and third rows of compressor blades

It’s unlikely that many, if any, owner/operators of Siemens 501FD2 gas turbines would be surprised to learn that two units in the fleet suffered compressor thru-bolt failures during 2012—the first such failures experienced. The OEM has alerted its customers and shared available information—most recently at the 501F Users Group 2013 Conference in Charlotte a couple of weeks ago. Investigations of the incidents are on-going. CCJ Onsite will report on the 501F and 501G meetings (conducted in parallel) in early May.

SRP’s Mike Rutledge, chair of CTOTF’s™ Siemens 501F- and G-class Roundtable, knows first-hand about one of the failures so it’s not surprising the topic was included in that four-hour session on the final day of the spring meeting. A presentation by President Rod Shidler of Advanced Turbine Support LLC was the catalyst for discussion on inspection of thru bolts, the expectation being that early identification of a flaw could prevent a catastrophic failure such as that experienced by one unit.

Siemens has recommended its inspection of compressor bolts—for data-gathering purposes—during majors or any outage requiring a compressor cover lift. Note that the front ends of the bolts are located between the second and third rows of compressor blades (Fig 1) and inaccessible for inspection with the cover on. Shidler said his company collaborated with PSM in the development of an in-situ technique to identify thru-bolt flaws before they become critical and is now offering that service as an alternative to, or in addition to, the OEM’s inspection.

The Advanced Turbine Support presentation, which was developed by Dustin Irlbeck and also presented by him at the 501F meeting, began with an overview of the compressor arrangement, location and size of bolts, etc. Mentioned was that both failures occurred near the first engaged thread at the front end of the bolts. Also, that PSM and Advanced Turbine Support had developed a calibration/validation standard to confirm sensitivity and inspection reliability. Details are available in the presentation which can be accessed through CTOTF’s Presentation Library. Shidler said his company has inspected several sets of spindle bolts to date and found suspect indications only on two bolts in one unit. The owner can monitor these indications going forward; there was no cause for immediate concern in this case.

Inspection findings take center stage at aero-based roundtables

Prior to presenting at the Siemens 501F- and G-class Roundtable, Field Service Manager Mike Hoogsteden had shared Advanced Turbine Support’s inspection experience on LM2500s, LM5000s, and LM6000s at CTOTF’s GE Aero Roundtable. At the trade show, he and Shidler also discussed inspection experience specific to Pratt & Whitney FT4 and FT8 engines, as well as GE LMS100 and Rolls Royce RB211 machines.

Hoogsteden’s GE Aero presentation focused on the LM6000, a fleet with about 1000 engines in service. He noted that Advanced Turbine Support is an approved vendor for TransCanada Turbines, a 50/50 joint venture partnership between TransCanada Corp and Wood Group, which is licensed by both GE and Rolls Royce to provide global overhaul, repair, and maintenance services for their areo engines.

After a brief review of the state-of-the-art inspection equipment used by Advanced Turbine Support’s inspectors and its capabilities, Hoogsteden walked users through the LM6000, front to back, with highlights of recent inspections, including the following photos selected from among four dozen shared with the group and available through the CTOTF Presentation Library:

• Inlet gearbox spline wear (Fig 2), inspected in accordance with Service Letter (SL) 6000-04-01 R2.

• Variable-bleed-valve (VBV) clevis bolts, inspected in accordance with SL 6000-04-07. Fig 3 reveals less than one full thread of engagement.

• VBV actuator in Fig 4 has a broken safety tie wire.

• Case rubs and impact damage in the HP compressor. Note the precise location measurement in Fig 5.

• Loss of coating on secondary fuel-nozzle swirlers (Fig 6), inspected in accordance with SL 6000-03-04 R1.

• Base-metal erosion of first-stage turbine blade (Fig 7). Click images below to enlarge.

2. Wear pattern on inlet gearbox splines

2. Wear pattern on inlet gearbox splines

3. Clevis bolt has less than one full thread of engagement

3. Clevis bolt has less than one full thread of engagement

4. Broken safety tie wire

4. Broken safety tie wire

 

5. Compressor case rubs, airfoil impact damage

5. Compressor case rubs, airfoil impact damage

6. Coating loss on fuel-nozzle swirlers

6. Coating loss on fuel-nozzle swirlers

7. Base-metal erosion on first-stage turbine blade

7. Base-metal erosion on first-stage turbine blade

 

 

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