The generator is one of the most crucial parts of a power plant: this is where the electric energy is generated. It is therefore of major importance that the generator always remain in perfect condition. Among the critical components are the retaining rings at each end of the rotor. As a result of specific mechanical, chemical and electrical circumstances, flaw indications may appear in these rings. Replacing these rings involves substantial costs. KEMA has a much cheaper alternative, which is just as good: the KEMA Inspection system for Retaining Rings (KIRR).

A retaining ring has a long life span; it can even be used throughout the life of the generator. But no matter how small a risk it is, even a small crack in the retaining ring may have disastrous consequences and will result in safety risks and damage involving major costs.

In order to prevent such a catastrophe, retaining rings are -- often on the advice of the manufacturer -- replaced with new ones. Quite an expensive operation, since replacing them may cost up to USD 1,000,000. KIRR offers a perfect solution to these problems. A crucial advantage is that it is not necessary to disassemble the rotor and the retaining ring. This will mean a cost reduction of up to USD 200,000. Moreover, it takes less than 24 hours to measure two retaining rings. 

Benefits:

• Major savings, since rotor rings will not have to be replaced
• Constant awareness of the condition of the retaining rings
• Continuous monitoring
• Cost reduction because the rotor and the retaining rings do not need to be disassembled
• The measuring does not take long
• The system has a short delivery time.    

In most countries, authorities require a periodic visual / magnetic inner surface inspection of power plant pressure vessels such as steam drums.

Especially in the case of larger drums (L > 10 meters), the removal and remounting of its internals put these inspections on the critical path of the plant's outage. In the Netherlands, an extensive internal inspection is / was required once every two years.

For about 20 years, KEMA has been conducting automated ultrasonic steam drum inspections from the outside. The Dutch authorities accepted this methodology during this period as an alternative (rather than an addition) after several pilot projects revealed the advantages of this inspection, one of which is the recordability of the inspection results and possibility of thus trending these data. The resulting reduction of through-time turned out to be a major benefit for the plant owners!

Since the authorities adopted the RBI approach during the last 10 years, another advantage of the inspection methodology has become apparent: complete scanning and recording of the inspection data of circumferential & longitudinal (butt and fillet) welds, inspection of nozzle welds and inner radius as well as corrosion mapping have been covering all higher-risk areas in these drums. This enhanced inspection program, together with improved monitoring of operation parameters, has resulted in dramatic inspection interval extension in some cases. 

This attractive method for inspection interval extension has been applied by KEMA at several Dutch power plants.

Boilers are inspected at regular intervals; this often means that it is necessary to erect scaffolding. For the extensive replacements of parts of boiler wall tubing, there is no real alternative as yet. Sometimes, however, this can be avoided by using specialised personnel to conduct inspections and make small repairs. KEMA provides these services on a routine basis. Especially with unplanned shutdowns, this can help prevent high costs. Visual inspection is usually combined with ultrasonic testing to measure the remaining wall thickness. Computerized tabelizing yields clear insight into the corrosion pattern in the boiler and the severity of crack.

Benefits:

• No scaffolding necessary, saving outage time and cost
• Quick results on cause of damage and extent
• Recordable, tabelized results, to support management decisions
• Trending possibility: two short (weekend) stops will yield accurate results as regards corrosion speed
• Consultancy by KEMA (in one hand) in the field of corrosion and lifetime assessment.    

Corrosion and erosion affect the wall thickness of your pipework. Regular overhauls are planned to inspect the integrity. Expensive scaffolding has to be built for locations that are difficult to access. For these locations and critical components in your system, the KEMWAT (KEMA system for on-stream wall thickness measurement) is the right solution for you. KEMWAT accurately measures the wall thickness at temperatures up to 550ºC.

Applied method

An ultrasonic technique is applied to measure the wall thickness of pipes. Critical areas, which are mostly known from experience or inspections, are subject to monitoring. At the critical spot a stud is welded and an ultrasonic transducer is mounted at the free end of the stud just outside the insulation.

Cables are connected to a junction box at an easily accessible place so that readings can be taken at any time during operation. Measurements can be performed with standard ultrasonic equipment.

Measurement resolution of less than 0.1 mm is achieved using a thermocouple wire mounted near the stud weld. Measurement intervals can vary, depending on the decrease of the wall thickness monitored. Results can also be used in condition-based maintenance.

Your benefits - Cost savings:

• no scaffolding necessary
• fewer inspections
• higher availability
• imput to improve maintenance planning. 

Boiler evaporator walls (water walls) of power plants and waste incineration plants bear a heavy load due to corrosion and erosion. Therefore these components are inspected during shutdowns. The integrity of boiler wall tubing can be monitored with KEMCOP’s®   corrosion probes. The KEMA corrosion probe (KEMCOP®) was developed in 1997 in order to monitor the corrosive conditions in a high-temperature environment.

In order to perform ultrasonic wall thickness measurements from the inside, many costly & time-consuming preparations and provisions are necessary: scaffolding, grinding of the tube surface and often inspection of the radiation level and special protective clothing. Especially at the larger plants, this is a major budget-consuming activity. KEMA has developed KEMBUS, an ultrasonic scanning system for wall thickness measurements from the outside to minimize these costs & problems.

Benefits:

• No need for scaffolding in the boiler
• No need for grinding, grit blasting
• No need for radioactive radiation control
• Less cost for inspection
• Accurate wall thickness trending possibility
• Better reliability for exact reproduction of measurements.    

Gas turbines can be fully opened for inspections. However, it is often possible to save the expense of disassembling the housing as well as the power outage time. Therefore, inspection holes are commonly integrated into the gas turbine housing. Most gas turbine owners have their own endoscope nowadays, specifically for this reason. To determine whether there is a total blade failure, missing parts, major damage of blades, vanes and shrouds and colouring of the blade surface, this is usually an adequate method. Once smaller linear flaw indications in blades or vanes are detected, it may be a different case: then an often heard discussion may arise: "Is this something trivial, or is it a crack in the base material?" Now there is a problem: should we open the housing and perhaps conclude that nothing is amiss, or should we continue operation (and if so, for how long?) and risk a possible crash?

VINSPEC will help you out!

To check on flaw indications detected via the regular endoscopic inspections, it is possible to verify defect (crack) depth and length. The VINSPEC system enables us to provide you with this service. The inspection is conducted through the inspection holes (>6 mm). The instrumentation and the specialists can be on site within the shortest response time.

Benefits:

• In case of doubt, upon finding flaws such as indications on blades, vanes or other hot gas path parts in gas turbines, the character and size of the indication can be established instantly with endoscopic inspection through limited access inspection holes
• A clear decision can be made by the owner to further open the gas turbine in order to repair/replace a blade or to leave it in place and postpone repair/replacement until a better moment in time arises or even forget about it altogether
• After leaving the blade unrepaired/unreplaced there will be a trending possibility (crack progression monitoring)
• Before opening the gas turbine housing for further inspection, you will be sure that the flaw indication is not just a trivial, superficial crack
• The possibility of rapid deployment around the world.

Gas turbine rotors may be susceptible to life limitations due to creep and/or fatigue. This may (eventually) lead to critical cracking and catastrophic failure. Assessment of critical areas is necessary to determine opportunities for continued operation. KEMA can perform this assessment and inspect rotors non-destructively with high reliability and at low cost.

Benefits:

• Independent assessment on how to continue operation with a GT-rotor
• Reliable NDI results -> less uncertainty, improved
• Cost savings: decrease of direct cost through cheaper inspection method; lifetime extensions of the rotor, deliberate postponement of investments
• One-stop shopping for both ND inspection and FFP evaluation.

KEMA has developed a method to check extruder barrels quickly and quantitatively. It can be applied to barrels of conventionally hardened steel, or to steel produced according to HIP (Hot Isostatic Pressure). Extruders can be assembled as a chain of blocks or out of one piece. This method can be applied during outages, and in addition to visual/endoscopic inspections without spending too much extra time.

Benefits:

• A quantitative method
• Eearly warning of wear
• Recordable results, trending possibility
• High accuracy (starting from 0.1 mm)
• Independance of extruder length
• Minimal chance of missing abnormalities/degradations
• Short measuring time (less than ¼ hour).