NORMA
BRASILEIRA
ISO
XXXX
N011
Primeira edição
xx.08.2008
Válida a partir de
xx.09.xxxx
Non-Destructive Testing — Acoustic Emission
Inspection on Metallic Pressure Vessels During
Pressure Test
Descriptors: xxxxxx
ICS xxxxxxx
Número de referência
ISO xxxx:2008
9 páginas
© ABNT 2008
ABNT NBR ISO xxxx:2008
© ABNT 2008
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ISO xxxx:2008
Sumário
Página
Prefácio........................................................................................................................................................................v
1
PURPOSE .......................................................................................................................................................1
2
SCOPE ............................................................................................................................................................2
3
REFERENCES ................................................................................................................................................2
4
4.1
4.2
4.3
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.4.5
4.5
4.6
4.6.1
4.7
4.8
4.9
4.10
PROCEDURE..................................................................................................................................................2
Owner’s Responsibilities ..............................................................................................................................2
Personnel Qualification.................................................................................................................................3
Equipment and Materials ..............................................................................................................................3
Instrumentation Set-up .................................................................................................................................3
Sensor Spacing..............................................................................................................................................3
Sensor Mounting ...........................................................................................................................................4
Cabling............................................................................................................................................................4
Verification of Sensor Coupling and Circuit Continuity ............................................................................4
Instrument Settings .......................................................................................................................................4
Test Execution ...............................................................................................................................................5
Data Analysis .................................................................................................................................................7
Post-Test Filters.............................................................................................................................................7
Reporting of Source Locations ....................................................................................................................7
Interpretation of Results ...............................................................................................................................7
Follow-up Action............................................................................................................................................8
Report .............................................................................................................................................................8
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iv
ISO xxxx:2008
Prefácio
A Associação Brasileira de Normas Técnicas (ABNT) é o Foro Nacional de Normalização. As Normas Brasileiras,
cujo conteúdo é de responsabilidade dos Comitês Brasileiros (ABNT/CB), dos Organismos de Normalização
Setorial (ABNT/ONS) e das Comissões de Estudo Especiais (ABNT/CEE), são elaboradas por Comissões de
Estudo (CE), formadas por representantes dos setores envolvidos, delas fazendo parte: produtores, consumidores
e neutros (universidade, laboratório e outros).
Os Documentos Técnicos ABNT são elaborados conforme as regras das Diretivas ABNT, Parte 2.
A Associação Brasileira de Normas Técnicas (ABNT) chama atenção para a possibilidade de que alguns dos
elementos deste documento podem ser objeto de direito de patente. A ABNT não deve ser considerada
responsável pela identificação de quaisquer direitos de patentes.
v
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NORMA BRASILEIRA
ISO xxxx:2008
Non-Destructive Testing — Acoustic Emission Inspection on Metallic
Pressure Vessels During Pressure Test
1
PURPOSE
Acoustic emission is a phenomenon that occurs when a discontinuity is submitted to thermal and/or mechanical
stress. A region with failures is an area of stress concentration that, once stimulated, causes a redistribution of
localized stresses. This mechanism takes place, releasing stress waves transmitted in the form of transient
mechanical waves. The technique detects this change in the material with piezoelectric transducers placed on the
surface.
In pressure vessels, the early detection of flaws is of key importance. For the purposes of this standard, early
detection means detection of sub-critical sized flaws, and before they may cause leakages. These flaws are also
sources of acoustic emission, called areas of structural activity, potential areas for stress concentration and
propagation of internal and external flaws. This fact explains the predictive characteristic of an acoustic emission
testing.
It is desirable to conduct a study through fracture mechanics to assess the critical size of flaws and the right time
for the corrective intervention. The half value of the critical size has been considered the conservative standard, for
which repairs must be made.
Acoustic emission monitoring is used to map areas of greater structural activity and to recommend complementary
inspection with ultrasonic and magnetic particles, assuring continuity to structural integrity analysis, aiming to
assess the morphology and the sizes of present discontinuities, which will be useful in stress analysis and fracture
mechanics. Figure 1 is the flow chart recommended for the full integrity evaluation program
INTEGRITY EVALUATION PROGRAM
EA MONITORING &
ANALISYS
ACTIVE AREAS
RESULT
NO ACTIVE AREAS
LOCATION AND CLASSIFICATION OF ACTIVITIES
REPAIR
NDT – FOLLOW UP
FRACTURE MECHANICS
ANALYSIS
DECISION
PERIODIC
INSPECTION
Figure 1 — Título
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ISO xxxx:2008
A- Hydrostatic test or pneumatic test in-service, simultaneously monitored by the acoustic emission test in order to
control the integrity during the pressurization. This monitoring is intended to perform the pressure test in a safe way,
detecting, locating, and classifying the active areas associated with the presence of flaws.
B- Due to the result of the monitoring described above (A), in the presence of areas of high Acoustic Emission
activity source should be evaluated through the non-destructive test (follow up), in order to evaluate its critical
dimensions through fracture mechanics analysis.
C- Once guaranteed through calculation that the discontinuities remain at a sub-critical size and do not endanger
the structural integrity, the other inspection items shall be verified and the re-qualification report drawn up.
D- Should the contrary be included in item C, or rather, should the flaw present integrity problems, the execution of
repairs of these problems shall be recommended.
2
SCOPE
The objective of an Acoustic Emission inspection is to locate and monitor emission sources, which are generated
by internal or superficial discontinuities. The test could be applied during the first hydrostatic test, during periodic
proof test or in service.
All relevant indications generated by Acoustic Emission sources must be assessed by other non-destructive testing
methods.
3
REFERENCES
ASME Code, Section V, Article 12
4
4.1
PROCEDURE
Owner’s Responsibilities
Prior to setting up the test, the inspector shall be furnished with the following information, as applicable.
4.1.1 Material of Construction - A material specification of the vessel(s) and/or system(s) under examination,
such as material specification(s) and special heat treatments.
4.1.2 Lining and Insulation - Information on the type and construction of any lining, insulation, and internal
coating.
4.1.3 Design Basis - The design specification of the vessel(s) and/or system(s) under examination, including
applicable codes, e.g., ASME, API, AWS, and design pressure and temperature.
4.1.4 Geometry - A vessel or system assembly and/or layout drawings with sufficient detail to establish the
dimensions, nozzle locations and material thickness.
4.1.5 Maximum Loads - The maximum pressure, temperature, and other load considerations since the previous
test and during the last six months of operation.
4.1.6 The owner shall advise the Acoustic Emission system operator of special conditions that would influence
optimal placement of Acoustic Emission sensors. Such conditions would include a detailed stress analysis, recent
weld repairs, field welds, fire, mechanical upsets, or other historical parameters.
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ISO xxxx:2008
4.2
Personnel Qualification
Personnel operating Acoustic Emission equipment (Acoustic Emission operators) shall be certified according to
ISO 9712.
4.3
Equipment and Materials
4.3.1 General - The Acoustic Emission instrumentation consists of sensors, electronic signal processing and
recording equipment, and digital hardware and software for analyzing and displaying data in accordance with the
provisions of this procedure.
4.3.2 Sensors - sensors shall operate in the range of 100 KHz to 300 KHz. Each sensor shall be used in
conjunction with preamplifier circuitry including a band pass filter and shielding against electromagnetic and radio
frequency interference. It is preferred that the preamplifier circuitry be incorporated into the sensor casing.
4.3.3 Data Measurement and Recording - The instrumentation shall be capable of measuring and recording by
channel number and within a specific frequency range the following parameters for each Acoustic Emission hit; hit
arrival time, hit duration, peak amplitude, signal strength. A manually entered parametric value, or input data, may
also be recorded with each hit. The data acquisition system shall have sufficient channels to provide the sensor
coverage as required. Hit arrival time shall be measured to an accuracy of at least one millisecond.
4.3.4
Instrument Displays - The instrumentation shall be capable of providing the following real time displays.
a)
Bar Chart - This plot shows cumulative signal strength Vs channel number.
b)
Amplitude Per Hit Versus Time.
c)
Hit Duration Per Hit Versus Time.
d)
Log Duration Per Hit Versus Amplitude Per Hit.
e)
Cumulative Signal Strength Per Channel Versus Time.
4.3.5 Waveguides: Acoustic waveguides may be used to minimize damage to the Acoustic Emission sensor on
high temperature environments. Waveguides shall be of either one-piece construction or with press-fit sensor
cones. Alternate designs may be used provided that performance attributes meet or exceed the requirements of
this procedure.
4.3.6 High temperature waveguide couplant, if required, shall ensure positive coupling throughout the period of
monitoring.
4.4
4.4.1
Instrumentation Set-up
Sensor Spacing
The location and spacing of sensors shall be determined following review of owner information, and with
consideration of the damage mechanism anticipated. A primary consideration in choosing sensor locations is the
need to detect structural defects at critical sections, e.g., high stress areas and geometric discontinuities. As a
minimum, sensors shall be placed as follows: Sensor spacing for pressure vessels shall ensure that the entire
structure is properly monitored during the stressing sequence. Sensor spacing shall ensure that at least one
sensor may detect a lead break from a 0.3 mm pencil at any point of the structure, or at least 4 sensors may detect
the signal from a mechanical punch at any point of the structure. In all cases, sensor spacing shall provide for
proper monitoring of the area of interest for the damage mechanism(s) anticipated. Attenuation measurements
may be required.
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ISO xxxx:2008
4.4.2
Sensor Mounting
Sensors shall be mounted with the center of the sensor face directly coupled to the structure.
4.4.3
Cabling
Signal cables should be verified for continuity and to avoid short circuit. All signal cables should be constrained to
prevent stressing the sensor or loss of coupling and to avoid extraneous noise from wind or thermal induced
movement of the cables. Additionally, a provision to protect the cables from hot surfaces shall be made.
4.4.4
4.4.4.1
Verification of Sensor Coupling and Circuit Continuity
Local Sensor Verification
Each sensor shall be checked for coupling and circuit continuity prior to beginning of the monitoring procedure.
A 0.3 mm 2H graphite lead break may be used to provide a source of Acoustic Emission. Checks shall be carried
out for each sensor. The average amplitude of three such successive checks shall equal or exceed 85 dB.
All sensor/channel combinations shall not present variations greater than +/-3dB from the average of amplitudes
detected by all sensors.
Corrective actions In the event that a sensor/channel combination does not meet the verification requirements
above, it may be necessary to re-check sensor coupling, change signal cables, or re-position the sensor. In the
event that a sensor, cable, or pre-amplifier is considered to be sub-standard, the suspect equipment shall be
clearly identified, segregated, and shall not be used for monitoring until performance attributes are verified.
4.4.4.2
Global Verification
Global verification of coupling and circuit continuity shall be performed before testing, following completion of
testing, and after delays exceeding 12 hours.
4.4.4.3
In the event that a sensor/channel combination is found to be non-responsive during the monitoring period, the
sensor/channel shall be temporarily de-activated, and substitute instrumentation installed. De-activation should be
as short as practicable to minimize data loss. A local Sensor Verification, as described in 4.4.4.1 shall be carried
out on the substitute instrumentation prior to resuming the monitoring. The time of such instrumentation
substitution shall be noted in the test log.
4.4.5
Instrument Settings
4.4.5.1
Fixed threshold levels shall be the preferred method of triggering data acquisition. Thresholds shall be
as low as practicable, and be in the range of 40 dB to 55 dB. Monitoring areas presenting a background noise
level unsuitable for any sensor/threshold combination shall be recorded and reported to the owner prior to testing.
4.4.5.2
Front end filters, when needed, should be set with consideration of the observed background noise
level. Suggested values for front end filters are:
4
Frequency
70 - 400 KHz
Duration
5 - 70000 microseconds
Risetime
5 - 1000 microseconds
Counts
5 - 70000
Energy
5 - 70000
Total Gain
60 dB
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ISO xxxx:2008
4.5
Test Execution
4.5.1 The Acoustic Emission operator shall maintain a test log recording data file names, times of various phases
of testing such as the start and end. The test could be applied during the first hydrostatic test, during periodic proof
test or in service with increment on the operating pressure. Examples of test sequence are in figure 2 and 3.
Figure 2 — Sequence for hydrostatic pressure test and proof tests
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ISO xxxx:2008
Figure 3 — Sequence for in service tests
4.5.2 All Acoustic Emission data shall be stored on appropriate media. In the event that the test situation
requires more than one data file, the Acoustic Emission operator shall record the start and end time for each data
file.
4.5.3 Temperature and pressure data shall be recorded on appropriate media or in the test log, as applicable. It
is preferred that continuous recording of temperature/pressure be enabled; however, in the event that automated
acquisition is not available, the Acoustic Emission operator shall ensure that such parameters are recorded at the
beginning and end of the monitoring and at intervals not to exceed 30 minutes or 25% of the test duration,
excepting long delay periods.
4.5.4 All recorded data (Acoustic Emission hits, temperature, pressure, etc.) shall be correlated to the elapsed
test time.
4.5.5 No sensor/channel combination may be disabled during the course of the test, unless the Acoustic
Emission operator identifies a sensor/channel failure.
4.5.6
Background noise may be present as a result of factors other than process flow.
4.5.6.1
Movement: False emissions can be caused by movement of the component under test.
emissions are generally sporadic and can be identified and filtered out in post-test analysis.
Such
4.5.6.2
Wind and Vibration: Visually examine the sensors, cables, and other hardware to verify the equipment
is securely mounted and will not be subject to wind or vibration induced movement.
4.5.6.3
External Nois: Uncontrolled noise caused by conditions such as rain, sleet, hail, snow, wind blown
particles, air hoses, leaks, blasting, etc., shall be evaluated as they occur. The effects of such sources shall be
minimized by acoustic isolation where practical.
4.5.6.4
Communication between the Acoustic Emission operator and the owner shall be available to alert the
owner in the event that Acoustic Emission activity indicates a potentially serious condition.
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ISO xxxx:2008
4.6
Data Analysis
4.6.1 Acoustic Emission data presentations should be overlaid with parametric data, (temperature, pressure)
where possible. Guideline for analysis is described below:
4.6.2 A general assessment of the raw data shall be made to identify emissions considered to be arising from
flaws, and to assess the need for post-test filtering. The following paragraphs describe plots which are, in
combination, useful in performing the general assessment:
4.6.2.1
Duration Vs Amplitude: Active discontinuities are characterized by a single data distribution with high
amplitude hits in the range of 100 - 3000 microseconds in duration.
4.6.2.2
Counts Vs Amplitude: Active discontinuities are characterized by a single data distribution of amplitude
values greater than 60 dB with counts in the range of 500 to 1500.
4.6.2.3
Cumulative Energy Vs Time: Active discontinuities are characterized by an exponential increase of
cumulative energy with a clear ‘knee’ in the curve that may be correlated with a corresponding rapid stressing
change.
4.6.2.3
Overall duration of active discontinuity hits may fall in the range of 100 to 2000 microseconds.
4.6.2.4
The nominal calculated frequency of hits from active discontinuities should be in the range of 100 to
300 KHz when 150 KHz sensors are used.
4.6.1
Post-Test Filters
4.6.3.1
Time Filters - Time filters are used to eliminate bursts of data caused by unavoidable circumstances as
the test proceeds. Such circumstances include wind gusts or other types of mechanical noise. These sources of
interference should be noted in the test log along with their time of occurrence. A time filter can then be used to
reject the interference noise from the data set, leaving only genuine Acoustic Emission. Time filters can also be
used when it is necessary to closely examine data characteristics within a known time range.
4.6.3.2
Amplitude Filter and Signal Strength Filter - Amplitude and signal strength filters are used less
commonly than the previously described filter. Their function is to allow the user to more closely examine data
characteristics within a given range of amplitudes and signal strengths.
4.7
Reporting of Source Locations
Sensor/Channel combinations considered to exhibit data indicating flaw growth shall be reported, and ranked in
terms of relative priority, where possible. Suspect areas shall normally be reported to the owner as soon as
possible.
4.8
Interpretation of Results
A written procedure for processing, interpreting, and evaluating the Acoustic Emission data shall be prepared and
approved by the Acoustic Emission Inspector Level 3. This procedure shall be made available to the personnel
responsible for operating the Acoustic Emission system, the personnel responsible for Acoustic Emission data
interpretation and evaluation, and a representative of the owner of the equipment being monitored.
This procedure shall be tailored to recognize and accommodate unique requirements associated with the plant
system or component being monitored.
A recommended presentation and interpretation of the results could be given by ranking the detected acoustic
emission source during the test in different categories, related with the level of the Acoustic Emission source
intensity, based on the activity detected during the loading. The ranking could be through letters A, B, C, D and E,
(see the example in table 2). The analysis must be carried out individually for each sensor, reflecting the view of the
zonal location of active areas. When the results show consistency with the methods of exact localization, they must
be used for refinement on localization of active areas.
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ISO xxxx:2008
Table 1 — Example of source classification
AE source Intensity
A
Recommended Action
NO ACTION RECOMMENDED
B
REGISTER FOR REFERENCE IN FUTURE MONITORINGS
C
ATTENTION LEVEL: RECOMMENDED TO REDUCE INSPECTIONS INTERVAL
D
PRESENCE OF DEFECTS
APPLY NDT*
E
PRESENCE OF SIGNIFICANT DEFECTS; APPLY NDT*
* APPLY NDT means to evaluate using Non-Destructive Tests at the locations with the objective of characterizing and sizing the
existing defects.
4.9
Follow-up Action
Follow-up actions shall be proposed for all tests carried out. Consideration must be made for the test item service,
the known inspection history, the type of anticipated degradation mechanisms expected, Acoustic Emission test
characteristics, and the appropriateness of follow-up inspection methodologies.
4.10 Report
The following information shall be included with each test report.
4.10.1 A complete identification of the vessel(s) including:
a)
Equipment Identification, i.e., name and item number
b)
Material of Construction
c)
Test Location
d)
Test Date
e)
Applicable Codes or Standards
4.10.2 Sketch or drawing showing overall dimensions and sensor locations.
4.10.3 Test fluid and fluid temperature.
4.10.4 Stressing sequence including fill, temperature, or pressure level(s), and the starting and ending times of
hold periods, as applicable.
4.10.5 A comparison of the test data with the appropriate interpretation and evaluation criteria.
4.10.6 A statement of conclusions on the basis of the Acoustic Emission test results. This may be a brief
statement that the vessel contains no significant defects, or it may include a list of areas of concern.
4.10.7 A list of recommendations. This may include follow-up inspections and complementary Non Destructive
Evaluation methods, or it may be a brief statement that no follow-up is necessary.
4.10.8 Any unusual effects or observations during testing.
4.10.9 Name(s) and level of certification of test operator(s).
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ISO xxxx:2008
4.10.10 Test instrument, including serial number.
4.10.11 Sensor Model(s).
4.10.12 Procedure with interpretation and evaluation criteria used.
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