In Service NDT for

Large Composite
Structures
Dr Martin Wall
ESR, National NDT Centre
NNDTC, Milton, Oxfordshire

IOM3 Workshop Living with Composites

NDT Methods for Large Scale Composites
Port Talbot, Wales 3 July 2007
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Introduction
Composites used in increasing range of applications
Comprehensive NDT at Manufacture
NDT in Service is more difficult and less widely done
Traditionally conservatively designed to allow for inservice damage
Perception of difficulty to inspect in service and
limitations of defect assessment methods have limited
uptake of composites
Increasingly used in large structural applications
With recent developments there are a range of NDT
methods that can be used in-service
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Scope of Talk
Introduction
Why inspect in-service
Challenges for in-service NDE
Defect Types
Standards
Current NDT practice
Potential NDE Methods
Examples
Information Sources
Future Developments
Conclusions
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Why inspect ?
Composites are used in an increasing range of
applications, increasingly structural, NDT in-service
cannot be ignored
Satisfy Quality Assurance
Legal/ Regulatory requirements
In-service damage
Extend product life
Safety critical
Condition of component

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What to inspect
Components
Tanks (above or below
ground)
Vessels
Pipes

Structures
Civil
Offshore

Systems
Pressure
Actuators
Rotating equipment
Safety
etc.
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Challenges - In-Service NDT

Thickness
Access
Coupling & surface condition
Area
Signal attenuation and scattering
Inhomogeneous and anisotropic structure
Lack of adequate standards
Interpretation of inspection results (PoD)
Familiarity with metallic structures
Increased reliance on operator experience
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Inspection Issues Large Structures

How much do we know?

Location of damage
What damage may occur

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Where to inspect

Time available for inspection.

Downtime.

Industry

Integrity required

Data analysis

Performance required
(Sensitivity, speed, coverage
and reliability POD, false calls)

Cost

Inspection Strategy Large Structures

Global inspection
methods
Monitoring (e.g. Acoustic
Emission)
Fast screening with
detailed inspection of
indications found
Risk-based inspection
Locations of likely
damage known
Slow crawler In its own
time
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Defect Types In Service and Installation

Composites are damage

tolerant.
Variety of in-service defects
are possible
Most significant are

Delaminations

Impact damage
Matrix cracking
Weepage
Environmental ingress

Thermal damage and

lightning strike
Disbonding joints and
repair applications

Courtesy CompositeNDT

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Courtesy NPL/Boeing

Loss of thickness due to

erosion or severe chemical
attack

Other failure mechanisms are

also present, e.g. fibre failure
but less of a concern.

Failure Example

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GRE pipe failure mechanisms

matrix cracking and delamination

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NDT Standards Composites

ISO14692
Norsok
In-house specifications (Shell,
BP)
Generic NDT procedures
Escape craft NDT procedures
CPD4D generic NDT procedures. Offshore
focus. Ultrasonics, thermography, laser
shearography (ESR, DTI)
NPL/ QinetiQ ultrasonic C-Scan
procedures, draft standard

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Example ISO 14692

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Potential NDT methods

Visual
Ultrasonics
Radiography
Thermography
Laser shearography
Courtesy Anne Birt QinetiQ

Coin and tap testing

Microwave
Acoustic
Other

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Data presentation
Image
C-Scan Map from above
surface
A-Scan Signal v arrival time
B-Scan through thickness
slice
Depth scan or Time-of-Flight
Digital data set

Courtesy NPL, QinetiQ

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Similar presentations used

irrespective of NDT method
used

Large area Inspections

Modern integrated
systems software
allows combination
of images for large
area inspections e.g.
Thermography
MOSAIC (TW Inc.)
Laser shearography
Ultrasonic C-Scan
Ultrasonic phased
array
Wheelprobes (e.g.
rapidscan)
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Rapid C-Scanning
Wheel
probes e.g
(RapidScan)
or Phased
Arrays
Air coupled
probes

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Laser Shearography

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Thermography

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Example Ultrasonic B-Scan and TOFD

Erosion and wall loss, liner Damage, GRP
vessels and pipe.

Pipe wall loss through

severe chemical attack

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Microwaves

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Acousto-Ultrasonics T-Scout

Courtesy Physical Acoustics

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X-Radiography

Courtesy Anne Birt QinetiQ

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Coin and Tap Testing

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Technique Selection

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Component

Geometry

Defect Type

Thickness

Access

Surface equipment

Material quality

Time available, no of components, area

Inspection performance (Sensitivity, speed,

coverage and reliability)

Cost

General advice in standards such as ISO

14692. More detailed advice MMS15 IKB
www.mms15.com
www.netcomposites.com/compositesndt

Example - Aerospace

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High percentage application of

composites
In structural applications
Up to 60% for aircraft structures
NDT well established. Fast and
global
Specialised NDT methods routinely
used in manufacture

Ultrasonic C-Scan, B-Scan image

processing

Laser shearography

Transient thermography

Laser ultrasound

Remote acoustic impact Doppler

(RAID)

Automated Tap testing

In-Service Same approach

possible in-service if at
maintenance facility

Field and difficult access

inspections may need different
approach: e.g. phased array or
wheel probes

Example Marine Hulls

Significant wave
loading

Range of potential
defects
Impact damage
Disbonding from
core
Delamination
Core splice

Images courtesy Roger Gregory, www.compositendt.com

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Laser shearography
has become accepted
as main inspection
method using
vaccuum hood. e.g.
RNLI Lifeboats

Particularly good for

repairs. Sensitive to
level of adhesion

NDT Methods Offshore Composites

Visual
Manual ultrasonics
Radiography
Thermography
Specialised NDT methods trialed
in some applications
Microwave inspection
Acousto-ultrasonics (T-Scout)
Laser shearography

NDT Applicability depends on

thickness, and surface and
material quality

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Example NDT Composite end Connections

Different types - Adhesive,

threaded, keylock ISO 14692

NDT options currently limited,

particularly for adhesive joints
Focus on good joint preparation
Reliance on proof testing

Important to integrity
NDT required all parts of connection
(GRP, metallic)

Access difficult for NDT,

particularly for adhesive joints

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Nozzle and flange connections can

also be an issue

Example - Composites Offshore

Applications include
pipelines
risers and piping systems (e.g. firewater mains)
tubings and casings;
process equipment; tanks and
vessels
Structures- access equipment (stairs
and gratings);
lifeboats
Mud mats (sub-sea)
protective covers (sub-sea)
Tanks and vessels
Lifeboats
Repairs to metallic pipework
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Example - NDT of Composites Offshore

(Cont)

Mainly GRP

Variable wall thickness (2-50mm) and

section

Connections, nozzles and flanges an Issue

Variable material properties and quality

NDT may be affected by high porosity or

poor surface finish
NDT methods difficult to apply in thicker
sections

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Access for NDT an issue. Piping often

close packed e.g water treatment
Special issues in some applications
escape craft, firewater mains, lined vessels
etc.

Composites in FPSOs
Floating Production Offloading and
Storage Vessels (FPSOs) are used
increasingly for offshore
Significant increase in use of
composites on FPSOs
Firewater mains

Water treatment
Pipes and vessels etc
e.g Petrobras P50 FPSO

Lightweight and efficient use of space

a particular issue.
Long GRP Lengths. Significant
movement. Fatigue failure an issue
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NDT of Composites FPSO Background

Minimising topside weight is a key

issue for FPSOs and floating
installations.
This together with good corrosion
resistance, flexibility and continuous
manufacture has lead to an increased
use of fibrereinforced composite
materials (FRP).
Limited guidance is available on NDT
of composites in offshore GRP
standards notably ISO14692 and
NORSOK.
NDT is not widely used. Increasing
requirement due to service issues.

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NDT Composites Information Sources

Offshore standards ISO, Norsok

MMS15 Knowledge Base
www.mms15.com or via
NetComposites site
MMS13 Defect Assessment of
composites (NPL, ESR)
NPL/ QinetiQ ultrasonic C-Scan
procedures, draft standard
CPD4D generic NDT procedures.
Offshore focus. Ultrasonics,
thermography, laser shearography
(ESR, DTI)
Adhesives Toolkit (ESR, NPL, DTI)

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Defect Assessment - Oil & Gas

Defect type
Matrix cracking

Defect assessment
procedure
Damage mechanics
approach to estimate
density

Lack of adhesive Simply area of de-bond

(< 30% of bond area OK)

Comment
Procedure in
development and under
test
Used in ISO 14692

Loss of
thickness

Simple 1-D assessment

Very conservative for
using estimated minimum localised defects
wall

Delamination

Linked to damage
mechanics plus also
fracture mechanics
approached

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Damage approach under

development. For fracture
approach difficult to
quantify critical values

NDT Simulation and POD models

Simulated ultrasonic C-Scan data from ultrasonic POD Model (ESAPOD)

developed by NNDTC for ESA [42]. On the left is the POD curve obtained from a
spot the ball POD trial carried out using the simulated ultrasonic C-scan data on
the right.Body text goes here (Arial 28 - font size can change as required)

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Future Developments
Improvements in rapid screening methods and
monitoring techniques
Improved defect assessment methods
Application of risk-based methods. Identify critical areas
Reliability and performance of composite NDT Methods
POD
Use of simulation and NDT reliability models
Improved standards for in-service composite NDT

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Conclusions

A range of NDE methods are now available for in-service NDT of

composites
The position has advanced significantly since 5 years ago
In-service NDT is more difficult than in manufacture
Large structures pose particular difficulties for inspection
The choice of NDT method will depend on a number of factors including:
access, defect type, thickness, surface condition, material quality
Potential strategies include fast screening, global methods, monitoring or
application of risk-based inspetion methods depending how much is
known on type and location of damage and integrity requirements.
Most procedures are proprietary. A number have been standardised.
Information is limited in industry standards such as ISO 14692
A number of information sources are available to assist industry users.
Including the MMS15 IKB www.mms15.com or
www.netcomposites.com/compositesndt
More work is needed on development of defect assessment methods

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END

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