reliability of dissimilar metal weld ultrasonic examination
TRANSCRIPT
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Greg SelbySenior Technical Executive
QNDE short courseJuly 2019Portland
Reliability of
dissimilar metal weld
ultrasonic
examination
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Outline
Background
POD development
Brush with reality
Measures to improve reliability
POD in the field
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Background
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UT in the nuclear power industry
UT techniques in the 1970s were driven by the ASME Boiler and Pressure Vessel Code, Section XI
Through the 1970s and early 1980s field and laboratory experiences cast doubt on the effectiveness of these techniques
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Pressure vessel
Hatch Unit 1 RPV
– Preservice UT in the early 1970s detected three crack-like indications in nozzle-to-shell welds; later confirmed destructively
– Construction radiography (RT) hadn’t seen them; performed again in the plant, RT again didn’t see them
Programme for the Inspection of Steel Components (PISC)
– Laboratory round-robin study using RPV specimens with defects, manufactured by the Pressure Vessel Research Committee (PVRC)
– Severe defects were not detectable using Code techniques
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Primary coolant piping
1970s – intergranular stress corrosion cracking (IGSCC) detected by leakage was not detectable using Code UT techniques
– Led to wholesale replacement of boiling water reactor (BWR) piping systems in the early 1980s
Early 1980s – round-robin studies at Pacific Northwest Laboratory (PNL) showed poor detection performance for realistic cracking in stainless steel and cast stainless steel piping welds
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Industry and regulatory response
Industry and the Nuclear Regulatory Commission (NRC) agreed that UT capability was significantly dependent on equipment, procedure and personnel
ASME Section XI Appendix VIII was published in 1989, defining the qualification requirements for UT of the RPV, nozzles and primary piping welds
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Industry and regulatory response
Industry formed the Performance Demonstration Initiative (PDI) to implement Appendix VIII
EPRI was tasked to develop and administer the qualification program
Qualifications commenced in the 1990s
Dissimilar metal weld requirements were added in the late 1990s
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Generic Process for Developing New PD Programs
Determine the Need
Determine Failure Mechanisms
Develop Acceptance Criteria
Survey the Fleet
Design and Fabricate
Specimens
Develop Procedures
Qualify Procedures
Qualify Personnel
Tasks performed by other
EPRI Programs, or locally
by members and
regulators
Tasks performed by
the EPRI NDE Program
Industry
decision
The entire process may
require several years of
work
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Types of performance demonstration
Each country’s requirements are different, but always it is some combination of two primary approaches:
Practical
demonstration
(physical trials)
Technicaljustification
(theoretical argument)
USA:
ASME
Code
Europe:
ENIQ
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Performance
demonstration
facility
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POD development
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PD Program has generated a lot of data
Over 20,000 qualifications have been performed
Over 1,000 qualification candidates (personnel)
Over 100 procedures have been qualified
– Pressure vessels
– Piping
– Bolting
– RPV penetrations
High quality data
– Controlled conditions
– Using the same procedures, equipment and personnel that perform the examinations in the field
– Qualification program operates under the nuclear QA program, frequently audited
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Stainless steel pipe examination (mean POD, several studies)
1980s: Administrative qualification
Today: Performance-based qualification
POD studies have shown improvement through
the qualification process
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Dissimilar metal
weld geometry
The welds and the buttering are acoustically attenuative and anisotropic
Scanning access is limited
UT is optimized to focus at the weld root
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Manual examination from the outside surface:
Pressurizer surge nozzle
611 attempts1675 attempts
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Brush with reality
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North Anna
W 3-loop PWR
North Anna Unit 1 planned to install overlays to mitigate steam generator DM welds– Mitigation, not repair
Pre-overlay inspection performed– No defects reported
30mm machined off the outside surface– Part of the overlay design
1
2
~130 mm
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North Anna
After machining, two leaking axial cracks were seen
Inspections were repeated, and three more deep, axial crack-like indications were detected
Total 5 cracks, all axial, all deep,
none detected during the
initial inspection
2
3
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Measures to improve reliability
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BAM Modular Reliability Model
Intrinsic Capability
– Physics
Application Parameters
– Application in the real world
Human Factors
– Those humans again …
Organisational Context
– Business and operational impacts
BAM – Bundesanstalt für Materialforschung und –prüfung1: Paradigm Shift in the Holistic Evaluation of the Reliability of NDE Systems. C. Müller et al., 2013, Materials Testing, 55(4), p. 264.2: Conclusions of the 6th European American Workshop on Reliability of NDE. C. Mueller et al., 2015.
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Reliability improvements in the US: Mapping to the BAM model
Probe
verification
(receipt
inspection)
Intrinsic capability
Very little change
The techniques work well; they simply weren’t applied correctly, or didn’t match the field condition
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Reliability improvements in the US: Mapping to the BAM model
Plant walkdown
Simulation on
mockups
Application Parameters
Make sure that you really understand the configuration
– Does it match the NDE procedures that you plan to apply?
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Reliability improvements in the US: Mapping to the BAM model
Improved written procedures
Pre-job brief
Hands-on practice
Awareness of relevant operational
experience
Proper use of team scanning
Sense of the urgency and importance of
the inspection
Human Factors
A much longer list
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Reliability improvements in the US: Mapping to the BAM model
Effective long-term planning
Preparation far in advance
Communicating expectations to the
NDE company and technicians
Selection of NDE technologies – cost or quality?
Contingency planning – are you ready for bad
news?
Change management
Crisis management
Organisational Contextmight be the most important factor of all
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Organizational Context: advance planning for a reliable
examination24 months
Day of exam
- Examination plan and scope
- MRP or BWRVIP guidance
- Walkdowns at N-1 outage
- Review T & Cs, procedure
options
- Procedure qualification review
- Prepare bid specification
- Vendor selection
- Detailed procedure qual
review and coverage calc
- Plan alternative techniques or
site specific quals as needed
- Scope and coverage
review with vendor
- Review plans for
alternative techniques or
site-specific quals
- Review equipment
selection & status
- Establish work plans to
support surface
conditioning, and
contingency exams
- Review qual status with
vendor
- Review status of
alternative or site-
specific quals
- Review equipment
availability & status
- Retrieve and review
previous examination data
- Obtain data analysis
software; train personnel for
data review and oversight
- Review status of:
- Procedure, alternative technique, or site-
specific qualifications
- Work plans for additional surface
conditioning and contingency
examinations
- Personnel availability, qualifications, training
- Equipment availability
- Review previous automated data for
assessment of previous conditions,
indications and contact
- Readiness
review with
vendor
- Identify
actions to
address any
issues identified
in readiness
review
- Prepare pre-job brief
- Verify:
- Procedure and personnel
qualifications
- Personnel training, availability,
contingencies
- Equipment availability,
contingencies
- Plan to perform vendor oversight
- Site support readiness
- Complete pre-
job brief
- Address any
actions resulting
from pre-job
brief
- Perform additional surface
preparation as required by
examination personnel
- Complete prompt review and
disposition of examination
results
- Perform rescans in a timely
manner as required by
examination personnel
- Implement examination
contingencies, if required
18 months 12 months 6 months
3 months 2 months 1 month 1 day
Post-exam
- Perform post-job
briefing and
document results
- Update inservice
inspection
documentation
Major themes:
Communication
Readiness reviews
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More Organizational Context
There are problems even when the NDE is done correctly
The problems arise because many people who are affected by the NDE results, do not understand NDE processes; this results in terrible pressures for the NDE team
“Hey, I might have found a
crack. Give us some time
to work through the
process to see if it’s real.”
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NDE process: Flowchart to keep management calm
“Nondestructive Evaluation: Indication Characterization,
Evaluation, and Disposition Guideline”, 1025225 on epri.com
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POD in the field
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Probabilistic fracture mechanics tools need quantitative POD values
Initiation
Crack Coalescence
t=ti
t=t+Dt
yes
Inspection/
Mitigation
Crack Growth
StabilityLeakage
Rupture, tf
Category A(P)- Surge Line POD
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100
Flaw size %T
PO
D
A(P)
Lower 95%
Upper 95%
Surge
line
POD
Inspections
provided
1000x
improvement
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Developing POD for inspections in the field:
Automated or encoded examination
• Encoded examination is thoroughly documented and auditable
– Coverage
– Data quality, probe contact
– Data can be re-analyzed
•Should be feasible to show that the POD in qualification is representative of the POD in the field
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Developing POD for inspections in the field:
Manual examination
Manual examination is less documented and auditable
– Manual examination may become more auditable with improvements in inspection implementation and oversight
– But, we may not be able to show that POD in qualification is representative of POD in the field
Developing those values will be a challenge
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discussion
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