Maintaining the health of a steam turbine is primarily about diagnosing issues before they take you down. A borescope (https://en.wikipedia.org/wiki/Borescope) allows you to peer a long way down into the turbine, without having to disassemble it, thus saving time and risk. With excellent visual and measurement capabilities, borescopes provide a step beyond assumptions and evidence-based maintenance.
What Is Borescope Inspection?
Borescope inspection involves steering a slim probe fitted with a camera through pre-existing access ports to visually access internal components. The lighting on the probe allows you to see into tight spots, and the steering controls allow the camera to move around stators, rotors, seals, etc. Since you are inspecting instead of disassembling, this method is considered non-destructive testing (NDT), allowing for safer and faster inspection cycles.
Before seeing a single blade, it’s worthwhile to understand how a modern scope works in practice:
- Flexible or rigid scopes can be maneuvered through any inspection port to view buckets, nozzles, and diaphragms.
- High-definition video can be captured as high-res stills, or video, which can be annotated and saved as part of your asset history.
- On-screen measurement capabilities can be used to estimate crack length, pit-depth, tip clearance, etc. to help measure change over time.
- Remotely articulated scopes can be used to scan 360° around features that are impossible to see directly.
Benefits of Using Borescope Cameras
Using borescopes will decrease outage time, reduce labor cost, and limit the risk of collateral damage by unnecessary teardown. You are able to check the condition of hot-section parts, verify the quality of repairs, and establish a visual trending line of the parts from run to run. Lots of plant’s combined the scope results with condition-based maintenance to do the right work at the right time. If you do not have your own in-house equipment, consulting steam turbine inspection services, results in the utilization of very specialized tools and technicians who are wise to each model’s access paths and common failure modes.
Finding Hidden Turbine Defects
Even the most seasoned crew can miss something when there is limited line of sight. A borescope will show what the naked eye will not see, thereby giving the opportunity to detect pre-existing issues early, and without significant costs. Pictures of the images of defects make it easier to collect and communicate your observations to stakeholders and justify the case for both targeted and system-wide repairs instead of a broad and expensive upgrade.
Watch for trends like:
- Nicks on the leading edges of blades, and erosion on both the rotor blades due to carryover, and beyond that linked to foreign object damage.
- Cracks attributed to thermal fatigue at the blade roots, platform fillets, and tenons.
- Deposits and pitting on the nozzle and diaphragms which could cause restriction and degradation in overall system efficiency.
- Wear on seals with evidence of rub conditions and liberated fragments that yield increased clearances, which increases leakage.
- Water wash streaks, corrosion under what appears to be deposits, and a lack of steam chemistry.
Examples of Failure Risk Analysis
The data from the borescopes lends itself to basic, defendable, and practical determinations of the likelihood of the risk (how quickly a defect could grow) and consequences of failure (what happens if it fails). For example, a short crack growing in a non-critical component is likely safe to monitor until your next minor inspection, but if it is growing the tip quickly and is near resonance, you are more likely better off changing it out now.
If you link a picture with vibrating analysis running, and the detailed history of the asset, your likely confidence in the likely action is greatly increased. From there, you are able to align the work scope with your outage planning, order the parts early on, and educate the contractors with scope of repairs, concerns with defects, and exact locations. All with the intent to have the contractors minimize time on tools.
Why Early Detection Matters
Detecting and assessing issues early provides safety for individuals, and profitability for the plant. A small blade and seal issue will quickly turn into either efficiency loss, forced outages, or secondary damage. By utilizing a planned PM program (see here for more) with no scope gaps, you remove surprises and unknowingly protect your most expensive rotating asset.
Here is what early detection, and identified risks returns in real terms:
- Reliability: Less forced stops, and accelerated reliability after planned maintenance or outage work.
- Efficiency: Better heat rate, based on tighter clearances and clean flow paths.
- Budgetary: Smaller projects, scoped work, and generally trending away from emergency overhauls and major repairs.
- Documented: Visual history of images that build as a historical data set to support warranty claims and audit trails back to the customer.
Above all, make borescope inspection part of your routine than a tracking strategy or method to rescue the turbine. When you apply the work expertise, batteries of images and size of defects, and disciplined follow-up routine, your privilege to internal knowledge turns into informed decisions and turns into turbine alignment and longevity.