Reliability of dissimilar metal weld ultrasonic examination

© 2019 Electric Power Research Institute, Inc. All rights reserved.w w w . e p r i . c o m

Greg SelbySenior Technical Executive

QNDE short courseJuly 2019Portland

Reliability of

dissimilar metal weld

ultrasonic

examination

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© 2019 Electric Power Research Institute, Inc. All rights reserved.w w w . e p r i . c o m2

Outline

Background

POD development

Brush with reality

Measures to improve reliability

POD in the field



Background



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



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



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



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



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



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



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



Performance

demonstration

facility



POD development



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



Stainless steel pipe examination (mean POD, several studies)

1980s: Administrative qualification

Today: Performance-based qualification

POD studies have shown improvement through

the qualification process



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



Manual examination from the outside surface:

Pressurizer surge nozzle

611 attempts1675 attempts



Brush with reality



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



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



Measures to improve reliability



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.



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




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?




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




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



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



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.”



NDE process: Flowchart to keep management calm

“Nondestructive Evaluation: Indication Characterization,

Evaluation, and Disposition Guideline”, 1025225 on epri.com



POD in the field



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



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



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



discussion



Together…Shaping the Future of Electricity


Documents

Reliability of dissimilar metal weld ultrasonic examination