Application of Ultrasonic NDT in Marine Structures

Email: NDT@marineresults.com Telephone: 02380 454 666

Application of Ultrasonic NDT in Marine Structures

•  Crash course in ultrasonic NDT •  Why use NDT (Benefits/Limitations) •  Key inspection areas on boats •  Reporting and use of reporting

•  Aerospace grade flaw detection equipment •  Modified aerospace inspection procedures

•  Metallic and composite •  Monolithic and cored structures

Non Destructive Testing

EN 4179, NAS 410 and SNT-TC-1A Pending: Nadcap & Germanischer Lloyd/DNV

Rigging Project Management

Sailing Campaigns Repairs

Background

Crash course in ultrasonic NDT

•  Defect Types •  Appropriate Techniques •  Frequency Selection

Ultrasonics

Good signal

Porosity Delamination

Inclusions Disbonds

Layer Porosity

Defect Types

Defect Types

Clean Laminate Layer Inclusion

Impact Damage Porosity

Appropriate Techniques

Standard ultrasonics Low frequency ultrasound (Cored laminate: Nomex, Rohacell). Low frequency ultrasound (Thick section monolithic wet laminate) High frequency ultrasound (Thin section wet laminates, autoclaved laminates, metallic parts and welds)

Appropriate Techniques

Advanced ultrasonics: Phased array (Autoclaved laminate: porosity, fibre wrinkling, impact damage) (Cored laminate: Nomex skin to core disbonds, core crush) (Composites with radius corners or rod components)

!

A-scan ultrasonics

Phased Array – B Scan

Phased Array – C Scan

Appropriate Techniques

Acoustic pitch catch resonance (Cored laminates: Nomex, Rohacell)

Thermal imaging (Cored laminates: Nomex, Rohacell) (Cored laminates: Water ingress)

•  Potential for supporting other NDT methods)

Appropriate Techniques

Mechanical/Digital tap test (Cored laminates: Nomex, Rohacell)

Manual tap testing (Cored laminates: disbonds and core damage) (Monolithic laminates: Near surface voids/delaminations)

Frequency selection Very Low Frequency Low density Foam Sandwich Construction 0.5MHz GRP (Glass Reinforced Plastic)

Lower quality, hand laminated Carbon Difficult to inspect or thick section laminates Often used to help classify indications in high quality laminates

1MHz Specialist sandwich construction

Moderate thickness laminates Often used as secondary check on thicker sections of high quality laminate

2.25MHz Moderate quality Carbon

Often hand laminated with vacuum consolidation Infused carbon laminates Low to medium thickness

5MHz High quality carbon products

Often pre-preg, autoclaved construction Masts

Why different frequencies

•  Low frequency •  Long wavelength

Passes through material easily

•  High frequency •  Short wavelength

Will not penetrate material

•  Medium frequency •  Medium wavelength Penetrates material but

with some difficulty

In the case of indications close together indications

Why different frequencies

High Frequency

Low Frequency

Why different frequencies

0.5MHz Transducer 5MHz Transducer

Screen images from handover between 4mm and 8mm thicknesses.

Clearly increased resolution at higher frequency even at 4mm difference in thickness.

Why use NDT (Benefits/Limitations)

•  Quality Assurance •  Warranty/Repair •  Pre-Purchase •  Risk Management •  Research and Development

Quality Assurance

Applied throughout the build phase of a vessel, mast or structure NDT can ensure that quality standards are met throughout the process. In a multi-phase build it is recommended to inspect critical parts at key stages in the build. •  Ensure quality standards and design expectations are met in

production.

•  Ensure quality expectations of sub-contracted components prior to installation or delivery.

•  Detect construction issues at an early stage enabling remedial action at the most suitable opportunity.

•  Potentially save cost of expensive re-works or warranty issues.

Warranty/Repair

Inspections take place once an issue is discovered through use or another inspection means. NDT is used to determine the extent and severity of the issue and, potentially, assist in determining the root cause. Once reparation or modification is completed NDT is utilised to assure quality of repair. •  Understanding of extent and severity of damage prior to

destructive work.

•  Potential to adapt repair schedule to retain existing structure or include visually un-detected damage.

•  Assure quality of repair method once complete.

Pre-Purchase

•  Gain quality assurance prior to vessel/part purchase and put in place a baseline for future inspections if required.

•  Potential to detect anomalies in structure that may impact integrity creating a case for rejection of purchase or a standpoint for negotiation.

Risk Management

Increasingly required by insurers but of equal use to vessel owners to establish baseline condition of structures and provide a reference for future inspections at key stages.

•  In conjunction with manufacturers structural engineers provides a baseline understanding of the condition of the inspected areas.

•  Provides quality assurance at initial inspection stage.

•  Sets baseline for future inspections, enabling accurate monitoring of detected anomalies extent and severity and identification of new indications at subsequent inspection cycles.

Research & Development

•  Evaluate quality of laminates or metallic in new construction processes potentially helping determine how improvements can be made to processes.

•  Determine location and severity of anomalies from build process enabling forensic consideration to determine cause and develop processes to improve final product.

•  Monitor anomalies during fatigue cycling or other load testing to determine impact on structures integrity and/or lifespan.

Why NDT

•  Baseline for future inspections •  Track changes to anomalies

•  Detailed analysis of detected anomalies •  Assess type of defect

•  Cost savings:

•  Detect potential failures before they happen •  Understand extent of damage prior to destructive work

and repair

Key inspection areas on boats

•  Mast, Boom and Rigging •  Hull, Topsides and Deck •  Internal Structure •  Appendages

Mast and Rigging

Options of: •  100% baseline •  Representative survey at regular locations •  Evaluation of high load areas surrounding stay and

spreader attachment points.

•  Ensure expected reinforcement patching in place.

•  Evaluate laminate quality for engineering consideration and set baseline of anomalous areas for future monitoring.

•  Assess condition of standing rigging including solid carbon fibre stays.

Hull, Topsides and Deck

Generally representative survey of larger areas in grid pattern scan or more detailed evaluation of localised areas.

•  Provide general assurance of laminate condition with representative grid inspection.

•  Bespoke grid pattern dependent on quality acceptance criteria under advice from structural engineers if required.

Internal Structure

Evaluation of general construction and installation of bulkheads, stringers, keel trays, bowthruster housings, retracting propulsion wetbox etc following construction.

•  Quality assurance of internal structures prior to installation.

•  Quality assurance of secondary bonding following installation process.

Appendages

•  Quality assurance of keels, daggerboards and rudders which are often sourced externally.

•  Evaluation of laminate structures of daggerboard and rudders. •  Evaluation of forged or fabricated keels for construction

defects or following grounding incidents.

Reporting and use of reporting

•  Identification and location of anomalies •  Supporting evidence (Scan Images) •  Higher level analysis •  Consultation with designer/engineers

Reporting and Recording

Unbiased •  Facts rather than opinion

Calibration and strategy •  How calibrated •  How inspection carried out Recording

•  Location and classification as baseline for comparison

Provide evidence for future comparison •  Scan Images

Recommendations for how to treat the information •  Refer to designer •  Destructive testing •  Independent design review

What next? Damage event or Defect

present

Assess damage/defect

size/location

Defect – Significance

uncertain Large defect Insignificant defect

Contact Designer/Manufacturer

Agree assessment method

•  Visual Check •  Tap Test •  NDT Method

•  Laminate Analysis •  FEA Method •  Fracture

Mechanics (Crack Growth Tests)

•  Buckling Checks

Produce and test representative

section

Re-inspect feature after agreed period

Growing

Issue Completion

Repair and re-inspect

Re-inspect after agreed period of service

Classify Damage

Re-inspect feature after agreed period

Y

N

Large defect

Insignificant defect

Significant Minor

Unsure Concerned

Recording Data

Recording Data

Further Analysis

•  Micrograph •  Experimental testing •  Modeling

Any Questions?