Inspection of reactor pressure vessels by zfr10000


                                                                                                 JOURNAL SEVENTH YEAR
                                                                                                 N ° 7 6 / O C TO B E R 2 0 0 6

       Dossier on non-Destructive testing
                                                                                                 Qualified inspection procedures for
                                                                                                 all plants
                                                                                                 Laborelec is active in the development
                                                                                                 of ultrasonic and eddy current inspection
                                                                                                 methodologies for detecting defects in power
                                                                                                 production equipment. Once qualified for a
                                                                                                 given sector and a given reference code, our
                                                                                                 procedures can often be transposed to other
                                                                                                 industrial sectors. This way, all plants benefit
                                                                                                 from our better knowledge and from the
                                                                                                 improved efficiency of the procedure, gained
                                                                                                 through the qualification process.

Inspection of reactor pressure vessels                                                 

An experienced eye for measurement analysis
Everything possible is done at nuclear power plants to guarantee
the safety of the reactor vessel. A reinspection of the vessel is
completed every ten years to look for defects that could endanger                                CONTENTS
vessel’s structural integrity. But detecting these defects requires an
experienced eye. Laborelec collaborates to this process on behalf of                             Qualified inspection procedures
Tractebel.                                                                                       for all plants                             p. 1
Belgian nuclear power plants must            Measurement results from these                      Inspection of reactor pressure
reassess the safety of their installations   techniques are often complex and                    vessels                                    p. 1
every ten years to confirm their             difficult to interpret. It is essential for plant
exploitation licence. Part of this           safety however, that no relevant defect             Close on-site follow-up of
assessment consists of inspecting the        is missed. This is why Tractebel asked              gas turbine vanes                          p. 2
reactor pressure vessel. The vendor,         Laborelec to add their expertise with
Intercontrôle which is an AREVA              Intercontrôle for analyzing measurement
                                                                                                 Assessing life expectancy of gas
subsidiary, is responsible for performing    results.                                            turbine blades                             p. 2
these inspections.                                                                               More efficient detection of
                                             Strong results in due time                          erosion on rotors                          p. 3
Extra safety guarantee                       Intercontrôle performs a first analysis of
Intercontrôle uses the best available        the measurement results, detecting and              Portable alloy analyser:
measurement techniques for inspecting        sizing the defects that could endanger              fast results                               p. 3
each part of the nuclear reactor vessel:     vessel’s integrity. Measurement results
●  Visual inspection for a global check of   are then transmitted to Laborelec for               Optimizing the inspection of
   the inner surface of the vessel           cross-examination and validation of                 steam generators                           p. 4
●  Eddy current measurements for             Intercontrôle findings.                             Condition monitoring of
   inspecting the internal walls of the      The compiled results – detection and
                                                                                                 condensers                                 p. 4
   nozzles                                   sizing of the indications - are handed to
●  Ultrasonic measurements for               the mechanical engineers in charge of
   inspecting welds and other zones of       the component assessment for further
   special interest                          investigation. This way of working has
                                             proved to be very efficient in providing
                                             strong results in due time.

    Close on-site                                                                           Assessing life expectancy
    follow-up of                                                                            of gas turbine blades
    gas turbine vanes
                                                                                            New NDT for monitoring base
    Laborelec regularly inspects                       Laborelec recently developed a Non-Destructive Testing (NDT)
    the first stage vanes at a gas                     technique for assessing the base material of hot gas path turbine
    turbine plant in Hungary to                        blades. After successful completion of the testing phase, it has now
    detect signs of ageing. The first                  proved its worth on a LM 6000 GE turbine. The technique significantly
    inspection was performed in                        improves the accuracy of estimating remaining blade life and the
    September 2004. Since then,                        decision whether or not to recoat a blade.
    Laborelec has followed up the
    quality of this set once every
    year to get an approximate                         The decision to recoat is particularly
    degradation status and ensure                      important for cost-efficient maintenance
    compliance with safety rules                       and reliable operation. Previously,
    and regulations.                                   decisions were taken based on a visual
                                                       inspection. That is good enough for
                                                       judging the state of the coating itself,
    In April 2006, Laborelec performed                 but yields no information on the state
    its third on-site NDT inspection on the            of the underlying base material. If the
    first stage gas turbine vanes. Laborelec           base material has deteriorated past a
    first visually inspected all of the vanes          certain point, the remaining blade life
    in the set to detect and document any              is too short to realize any significant
    abnormalities such as visible surface              economic benefit by recoating. In
    degradations. Then ultrasound testing              addition, attempting to recoat over a
    was conducted on 50% of the set to                 deteriorated base often results in a less
    identify coating detachment problems.              than satisfactory coating.
    Finally, Eddy Current (ET) tests were
    carried out on nearly the same amount              Measuring magnetic permeability
    of vanes to detect any internal cracks.            Laborelec’s new NDT technique
    In general, the vanes are degrading at             employs measurements of the magnetic
    a normal ageing rate. The May 2005                 permeability of the blades. When
    inspection had revealed two indications            structural damage first appears, the
    to assess. These indications did not show          initial paramagnetic structure of the base
    any significant evolution during this year’s       material transforms into a ferromagnetic
    inspection. However the new ET tests did           structure with a different magnetic
    uncover a third indication.                        permeability. Magnetic permeability
    Laborelec therefore recommended,                   is therefore a good parameter for
    the continuation of the periodic NDT               determining the degree of deterioration.
    inspections to follow up these indications         Laborelec has a special portable
    and to extend ET testing to a larger set           measurement instrument for magnetic
    of vanes.                                          permeability measurements.

                    First field success                          that visual inspections are sometimes              The new technique was tested                 misleading. For instance, contrary to
                                                       and calibrated over the past year            outward appearance, the new technique
                                                       by comparing the permeability                proved that the base material of the top
                                                       measurements with destructive tests on       blade pictured above is deteriorated less
                                                       the same blade. Following this testing       than the blade pictured below. These
                                                       phase, the first field service took place    results were of great help to MCC in
                                                       this summer. At request of the Electrabel    advising which blades are worth re-
                                                       Maintenance Competence Centre (MCC),         coating.
                                                       the nozzles of an LM 6000 GE turbine
                                                       were investigated. The results proved         

2      JOURNAL SEVENTH YEAR - N° 76 / OCTOBER 2006 - Dossier on non-Destructive testing
                          More efficient detection of                                           Portable alloy
                          erosion on rotors                                                     analyser:
                                                                                                fast results
                          Evaluation of the Phased Array Technology

                                                                                                Laborelec has purchased a
Laborelec has tested the ultrasound Phased Array Technology for                                 portable XRF-analyser that
detecting erosion on a power plant rotor. The technique appears to be                           simplifies the identification of
more accurate and faster than the conventional ultrasound method.                               metal alloys in power station
This tool will save plant operators time and money during equipment                             components. Knowing the
inspection.                                                                                     precise compound of an alloy
                                                                                                is important when choosing
                                                                                                the optimal welding procedure,
Erosion can cause permanent damage to
                                                                                                or when establishing an
                                             Faster and more accurate
power plant equipment if not detected
                                                                                                appropriate periodic inspection
                                             The conventional ultrasound technique
early. This is why power plants carry out
                                             works with a single sensor, which
regular erosion inspections.                 measures erosion on a specific spot and
Since this requires the complete             at a fixed angle. The rotor must pass              The new measuring device does not only
shutdown of equipment, plant operators       several times in front of the sensor to            make a chemical analysis of the alloy, it
are looking for ways to minimize             inspect a large area. The Phased Array             also right away identifies the constituting
inspection time as much as possible.         tool, on the other hand, utilizes several          material (= PMI or Positive Material
The ultrasound Phased Array Technology       elements to steer the measurement                  Identification). This significantly reduces
answers this request.                        beam, which measures erosion in a large            working time compared to the former
                                             area on one pass.                                  device Laborelec was using. Moreover,
                                             Our tests showed that the use of the               the new analyser is portable, so there is
                                             Phased Array technique increases                   no need anymore to remove pieces for
                                             preparation time, since a specific probe           analyzing in the lab.
                                             had to be build before inspection. But,            The new analyser has already proved
                                             at the opposite of the conventional                successful in a few cases. In the power
                                             technique, the rotor didn’t need to be             station of Rodenhuize (Ghent, Belgium),
                                             transported to an external workshop for            the chemical composition of several
                                             inspection and the actual measurements             steam pipes was determined before
                                             were accomplished a lot faster. In total,          choosing the best welding procedure.
                                             the inspection lasted ten to twenty                At the nuclear power plant of Doel
                                             times less compared to the conventional            (Antwerp, Belgium), alloy analyses
                                             technique.                                         are used in the erosion/corrosion
                                             Moreover, the Phased Array Technology              maintenance campaign of water and
                                             provided an image of much better quality           steam pipes. The periodic inspection
                                             than the conventional technique. It was            program for the pipes is drawn
                                             thus easier to detect and characterize             depending on the nature of the alloy.
Demonstrating method profitability           erosion areas, enabling better definition
Laborelec was asked to test this tool on     of necessary actions. These advantages             
a rotor in the field, in order to evaluate   clearly compensate for initial probe
and quantify its advantages compared to      development costs.
the conventional ultrasound technique.
Phased Array implementation costs    
are high, because a new probe must              
be developed for almost every type
of equipment inspected, so this must
be compensated for by other major
Our team tested both procedures at a
conventional power plant, measuring
steam erosion on damaged rotor blade
attachments. For these tests, we built
a Phased Array probe adapted to the
rotor type, with sixteen measurement

                                                       JOURNAL SEVENTH YEAR - N° 76 / OCTOBER 2006 - Dossier on non-Destructive testing       3
    Optimizing the                                                                      Condition monitoring of
    inspection of steam                                                                 condensers
                                                                                        Development of a Knowledge Centre

                                                    In recent years, Electrabel Group power stations have increasingly asked
                                                    Laborelec for advice and help on the maintenance of their condensers.
                                                    Recently, Laborelec established a Knowledge Centre to offer power
                                                    stations full support in this specialized domain.

    Nuclear power plants work                       A power plant condenser, which converts
    hard at maintaining the                         steam back into water, consists of
    structural integrity of their                   10,000 up to 120,000 tubes. Small
    steam generator (SG) tubes.                     water droplets in the steam, the chemical
    Detecting the degradations and                  quality of the water, and living organisms
    characterizing them precisely                   in the water can all cause corrosion or
    is essential to guarantee                       erosion in the tubes. This leads to micro-
    plant safety and availability.                  pores, holes, or a general decrease of
    Laborelec tested the various                    the wall thickness, which can eventually
    expertise probes available on                   result in leaks.
    the market and determined
    their efficiency in characterizing              Advice on Eddy Current
    several types of defects.                       measurements
                                                    Monitoring the general condition of
    Accurate characterization of defects in         tube wall thickness using Eddy Current
    SG tubes is essential to identify the most      measurements can help prevent leaks.
    suited repair procedure.                        Usually this procedure is executed by
    Basic SG tube inspections at nuclear            subcontractors under the supervision
    power plants are performed with                 of power plant staff. Recently however,
    eddy current bobbin coil (BC) probes.           several power plants turned to Laborelec
    While these enable fast and reliable            for advice. This was a natural choice,
    detection of many degradations,                 since it was Laborelec experts who
    such as corrosion and erosion, their            originally developed the Eddy Current
    configuration makes them incapable of           measurements protocol back in the
    completely characterizing some defects.         1970s.
    Complementary examinations with                 By bundling its know-how on Eddy
    expertise probes are often required. For        Current measurements, visual inspection,     Laborelec also purchased a special
    example, BC probes efficiently detect           destructive testing, and water analyses,     software that reduces the working time of
    corrosion on tube support plates, but           Laborelec becomes a knowledge centre         the experts by structuring and archiving
    complementary measurements with an              offering power plants comprehensive          the measurement results. Moreover,
    expertise probe are necessary to evaluate       advice.                                      power plants can turn to the Knowledge
    the azimuth extent of the corrosion.                                                         Centre for advice on choosing
    Laborelec recently started a study to           New inspection guidelines                    subcontractors, and on actions to take in
    evaluate the efficiency and accuracy            The first task of the Knowledge Centre       the event of critical damage.
    of the most recent expertise probes             was to re-examine the pipe inspection
    available on the market. The purpose is         method, incorporating Laborelec’s many
    to identify which probe gives the most          years of experience with critical cases.
    reliable signal depending on the type and       New guidelines are being written for
    location of the defect. In the future, this     Eddy Current measurements. They clearly
    will enable Laborelec experts to choose         define which tubes must be investigated
    the most appropriate probe, depending           and when, as well as how to perform the         Responsible editor: André Even
    on the defect they are looking for.             measurements and interpret the results.
                                                    These guidelines guarantee the quality
                                                    of the inspections and in this way reduce       Rodestraat 125
                                                    the risk of leaks.                              B-1630 Linkebeek
                                                                                                    Tel: + 32 (0)2 382 02 11
                                                                                                    Fax: + 32 (0)2 382 02 41


4   JOURNAL SEVENTH YEAR - N° 76 / OCTOBER 2006 - Dossier on non-Destructive testing

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