Corrosion constantly threatens the safety and lifespan of ships. Ultrasonic thickness measurement (UTM), a non-destructive testing (NDT) method, is now crucial for identifying and evaluating hull corrosion on ships.
But what is this technology, and why is it so important in the maritime industry?

UTM employs high-frequency sound waves to measure material thickness, such as steel plates and structures in a ship's hull. By measuring the time needed for sound waves to travel through the material and return, thickness can be precisely determined. This non-invasive method enables the detection of corrosion, erosion, and damage without the need for invasive procedures or removal of protective coatings.
The maritime industry has adopted UTM as a dependable method for evaluating ship hull integrity. Most instruments used are handheld, this enables convenient & fast on-site inspections. UTM is invaluable for monitoring critical structural areas (such as the outer hull or the internals of ballast tanks), which are prone to corrosion.
Regulatory bodies (e.g IACS) have set Unified Requirements for UTM testing on vessels. These standards are more rigorous for larger vessels, highlighting the necessity of regular hull corrosion monitoring.
Key Takeaways
Ultrasonic thickness measurement (UTM) is a non-destructive testing method used to detect and assess hull corrosion on ships.
UTM utilizes high-frequency sound waves to measure the thickness of materials without causing damage or requiring the removal of protective coatings.
The maritime industry relies on UTM to monitor critical structural areas
Regulatory bodies, such as IACS, provide Unified Requirements for vessels regarding UTM testing
Advanced ultrasonic testing technology enable accurate and efficient hull corrosion assessments for steel, aluminum, and composite structures.
Understanding Ultrasonic Thickness Measurement (UTM) in Marine Environments
In the maritime sector, the structural integrity of ships is crucial for safe and efficient operations. Ultrasonic thickness measurement (UTM) has become a vital non-destructive testing method. It assesses the thickness of ship hulls and identifies potential corrosion issues. This technique is essential for ship hull maintenance and corrosion monitoring.
Definition and Principles of UTM
UTM is a non-destructive testing technique that employs high-frequency sound waves to measure material thickness. It involves sending an ultrasonic pulse through the material and measuring the time for the pulse to reflect back. By calculating the round trip time and knowing the sound velocity in the material, the thickness is determined accurately.
UTM instruments used on vessels are handheld, portable devices. These devices enable precise measurements of steel thickness, detecting corrosion, pitting, and structural defects.
Applications of UTM in the Maritime Industry
UTM is widely used in the maritime industry for assessing ship and offshore structure integrity. Key applications include:
Monitoring critical structural areas prone to corrosion
Identifying suspect areas with rapid wastage and substantial corrosion
Complying with classification society requirements for thickness measurements
Extending vessel lifespan and reducing maintenance costs through early detection of corrosion
Vessels classed by the International Association of Classification Societies (IACS) must adhere to specific UTM rules outlined in Unified Requirements. Regular thickness gauging on ships ensures compliance with these regulations, maintaining vessel safety.
The Importance of Monitoring Hull Corrosion on Ships
Maintaining the structural integrity of a ship's hull is paramount for maritime safety and adherence to marine safety standards. Unchecked hull corrosion poses severe threats to the vessel, its crew, and the environment. Advanced techniques, such as ultrasonic thickness measurement (UTM), are vital for effective maritime corrosion control. Regular monitoring and assessment of hull thickness are essential.
Consequences of Hull Thinning & Corrosion
The gradual thinning and deterioration of a ship's hull due to corrosion can lead to numerous structural issues. These include:
Reduced structural strength and integrity
Increased risk of hull cracks
Compromised watertight compartments and bulkheads
Advantages of Ultrasonic Thickness Measurements over Traditional Methods
Ultrasonic thickness measurement (UTM) is an excellent option for assessing ship structural integrity. This non-destructive testing (NDT) technique offers numerous ultrasonic testing benefits, making it an essential tool in the maritime industry.
One major advantage of UTM is its non-destructive nature. Unlike traditional methods that might require invasive procedures, UTM uses high-frequency sound waves to measure thickness, without causing any permanent damage. This feature allows for comprehensive inspections while preserving the vessel's structural integrity.
UTM allows technicians to quickly evaluate the hull's condition and identify areas of concern in real-time, enabling prompt decision-making and corrective actions.
Another notable feature of UTM is its ability to perform single-sided measurements. Technicians can accurately determine thickness by accessing only one side of the hull plate, avoiding the need for access to hard-to-reach areas that would require extensive scaffolding or entry into confined spaces. For instance, the main deck plating can be measured directly from the main deck instead of inside the Cargo Holds or Cargo Tanks, which would be very difficult due to the heights of Cargo Holds.
Ultrasonic Thickness Measurements Ships Non-Destructive Test Hull Corrosion
Accuracy and Reliability of UTM for Hull Corrosion Assessment
UTM surpasses traditional methods in assessing hull corrosion. Its main advantage is that it can measure metal plate thickness without removing paint.
Representative readings should be taken at various areas and spaces on board the vessel. This includes Critical Structural Areas and where uneven corrosion, pitting, or other defects are visually obvious. Proper recording and identification of the number and locations of measurements are crucial.

Cost-Effectiveness of UTM Compared to Other Methods
UTM's accuracy and reliability make it a cost-effective method for hull corrosion prevention. Regular inspections using UTM can extend a vessel's lifespan and reduce maintenance costs over time. This is crucial given the marine environment's corrosive nature, which affects metal hull plates. Corrosion progresses from the interior, often undetectable by visual inspections.
Method | Accuracy | Cost |
Ultrasonic Thickness Measurement | High | Moderate |
Visual Inspection | Low | Low |
Radiographic Testing | High | High |

UTM Equipment and Procedures for Ship Hull Inspection
To guarantee accurate and dependable results, it is crucial to employ the correct ultrasonic testing equipment. It is also essential to adhere to best practices when conducting UTM surveys on marine vessels.
Types of UTM Devices and Probes Used in Marine Surveys
UTM equipment are available for ship hull inspections from various manufacturers, each tailored to specific requirements and conditions. Most instruments used on board vessels are handheld & portable. To use them during Class Surveys, the equipment must be type-approved by Class & the UTM Operator shall possess the relevant Certifications.
The equipment utilizes probes placed on the material's surface (usually by applying grease between the probe & the steel plate, which ensures proper coupling for the ultrasonic wave transition)
Calibration and Operation of UTM Instruments
Accurate readings depend on proper calibration and operation of UTM instruments. Ultrasonic gauge calibration must be performed regularly, adhering to the manufacturer's guidelines and industry standards. The use of a reliable, properly calibrated instrument is critical for precise results. UTM instruments should be operated by certified individuals who have received the necessary training and possess the required skills and knowledge.

Best Practices for Conducting UTM on Ship Hulls
Multiple readings should be taken at various locations to minimize possible measuring errors and enhance accuracy. Technicians must also consider factors such as surface conditions, coupling mediums (grease, etc), geometry, and curvature issues that may affect the measurements.
Interpreting and Reporting UTM Results for Hull Corrosion
Analyzing UTM Data to Identify Areas of Concern
UTM data analysis involves comparing the measured thickness values with the original "as-built" thicknesses and the maximum allowed diminution. Proprietary reporting software must be used from the ship's Class Society (e.g Bureau Veritas, DNV, Lloyd's Register, etc). Each Class Society has its own software to accurately record, assess, and report wall thickness information. This ensures a consistent way of reporting, efficient workflow and up-to-date vessel certification.

Documenting and Communicating UTM Findings to Stakeholders
Clear documentation and communication of UTM findings are essential for stakeholders to make informed decisions regarding ship maintenance and repairs. Reports should include the following information for each measurement location:
Original "as-built" thickness
Measured/gauged thickness
Maximum allowed diminution (in % or mm)
Calculated diminution (in % or mm)
Integrating UTM into Ship Maintenance and Inspection Programs
Ultrasonic Thickness Measurement (UTM) is a crucial tool for evaluating the structural integrity of ships, notably in monitoring hull corrosion. Incorporating UTM into routine ship maintenance protocols enables vessel owners and operators to preemptively tackle potential issues. This ensures the safety of their fleet.
Developing a Comprehensive Hull Corrosion Monitoring Plan
A thorough hull corrosion monitoring plan necessitates regular UTM checks on critical structural elements, such as main deck plating, beams & girders. Establishing a baseline measurement and tracking changes allows for informed maintenance and repair decisions.
Combining UTM with Other Non-Destructive Testing Methods
Other non-destructive testing methods, like magnetic particle inspection for instance, can detect cracks on welding seams (but is not mandated by Class Societies, unless an obvious crack - visible by naked eye- is noticed during an inspection onboard).
Advancements in UTM Technology for Enhanced Hull Corrosion Detection
Recent years have witnessed significant advancements in ultrasonic thickness measurement (UTM) technology. These advancements have greatly enhanced its capabilities for detecting hull corrosion in ships and inspecting composite boats and spars. The improvements in UTM have not only increased its accuracy and reliability but have also broadened its applications within the maritime industry.

Ultrasonic testing is now invaluable for inspecting not only steel hull corrosion but also aluminium hull thickness and the integrity of composite boats. On boats, it can detect various issues such as laminate thickness uniformity, delaminations, voids, porosity, bonding quality, and the presence of inclusions or alien materials in composite structures. This comprehensive evaluation is crucial for ensuring the safety and performance of these vessels.
Training and Certification for UTM Operators in the Maritime Industry
Industry standards require UTM operators to be certified at least to Level II according to SNT-TC-1A or similar standards. This certification confirms their knowledge, skills, and experience for precise thickness measurements. UTM survey providers must also gain approval from classification societies and ensure their equipment meets these requirements.
Importance of Skilled and Qualified UTM Personnel
The significance of skilled UTM (Unmanned Traffic Management) personnel cannot be overstated, as their expertise plays a crucial role in ensuring the safety and efficiency of maritime operations. A UTM assessment for a single ship can yield over 20,000 data points collected from various critical areas of the vessel.
However, the mere collection of data is only the first step in the process. Analyzing this vast array of information requires a high level of expertise, as skilled UTM personnel must sift through the data to identify patterns, anomalies, and trends that could impact hull integrity.
Available Training Programs and Certifications for Marine UTM
Marine surveyor training programs are available for those aiming to become certified UTM operators. These programs cover ultrasonic testing principles, equipment operation, data interpretation, and reporting. Participants gain practical experience with UTM instruments and learn to conduct assessments according to industry standards and regulations.

The trend towards data-driven digital class programs in the maritime industry is gaining momentum, allowing for enhanced ship monitoring and improved operational performance.
The maritime industry's evolution and adoption of digital technologies highlight the importance of certified UTM operators. Digital platforms like the UTM Digital Platform by Bureau Veritas enable multiple users to collaborate on a single report. This streamlines data submission and report generation. The data collected through UTM assessments contributes to a database for analytics, offering insights to charterers and owners. This ultimately enhances the longevity and safety of ships.
Conclusion
Ultrasonic thickness measurement (UTM) has become essential for monitoring hull corrosion and ensuring ship structural integrity. It uses advanced ultrasonic technology to provide accurate and reliable hull thickness measurements. This is crucial for early corrosion and metal loss detection, vital for vessel safety and regulatory compliance. Regular UTM use for corrosion monitoring also cuts down long-term maintenance costs (related to hull repairs).
The maritime sector heavily depends on UTM for ship structural integrity assessments due to its non-destructive and precise nature. During ship inspections, detailed visual checks and non-destructive tests are common. UTM is a key tool in these processes. It helps identify corrosion early, enabling timely repairs and preventing further damage.
It is strongly recommended to incorporate regular ultrasonic thickness measurements into the maintenance and inspection schedules of ships. The timing of these inspections should consider the vessel's type, age, operational characteristics, and previous inspection results. Generally, UTMs are performed during the vessel's Intermediate and Renewal Surveys. However, if significant corrosion is detected, the Class Surveyor may also require annual verification of the measurements during Class Annual Surveys.
FAQ
What is ultrasonic thickness measurement (UTM) and how is it used in the maritime industry?
Ultrasonic thickness measurement (UTM) employs high-frequency sound waves to gauge material thickness. This includes ship hulls, piping, and structural steel. It's a non-destructive testing method, vital in the maritime sector for tracking corrosion, erosion, and damage. This ensures vessels remain safe and structurally sound.
Why is monitoring hull corrosion important for ships?
Hull corrosion monitoring is essential for ships' safety and seaworthiness. Excessive corrosion can cause hull thinning, threatening the vessel's integrity. This could lead to accidents or failures. Regular monitoring allows for timely maintenance and repairs, crucial for vessel safety.
What are the advantages of UTM over traditional methods for assessing hull corrosion?
UTM surpasses traditional methods in several ways. It's non-destructive, offers immediate on-site evaluations, and requires only one side of the material for measurement. This method is cost-effective and provides precise corrosion assessments. It enables proactive maintenance, reducing long-term costs.
What types of UTM equipment are used for ship hull inspections?
Ship hull inspections employ handheld portable devices with adjustable software. These devices feature probes for surface contact, ensuring ultrasonic wave transmission. Accurate readings depend on the use of reliable, calibrated instruments.
How are UTM results interpreted and reported for hull corrosion assessments?
UTM results are analyzed for corrosion, pitting, or grooving. Reports detail measurement locations, original thicknesses, and calculated diminution. Documenting and sharing these findings is critical for effective maintenance and repair planning.
What training and certification is required for UTM operators in the maritime industry?
UTM operators need proper certification and skills for accurate inspections. Training programs and certifications cover equipment operation, data interpretation, and industry standards. Qualified personnel are crucial for reliable hull corrosion assessments.
Source Links
What are the most effective methods for inspecting and monitoring ship structures? - https://www.linkedin.com/advice/3/what-most-effective-methods-inspecting-monitoring-oourc
Non Destructive Testing on Ships & Boats – Marine NDT | Eddyfi - https://www.eddyfi.com/en/application/ships
Ultrasonic Thickness Tests Ensure Infrastructure Viability | Zetec - https://www.zetec.com/blog/ultrasonic-thickness-tests-ensure-infrastructure-viability/
Lloyds Register ART Validation for Hull Thickness Measurements - TSC Subsea - https://www.tscsubsea.com/acoustic-resonance-technology-quantitative-hull-thickness-measurement/
Hull Marine Services - https://atslab.com/nondestructive-testing/hull-marine-services/
Metal Hull Inspections and Corrosion Measurement with Ultrasonic Testing - https://marinesol.org/metal-hull-inspections/
Cm ppt - https://www.slideshare.net/slideshow/cm-ppt-78568107/78568107
Fixed Platform ROV Inspection - Hull Cleaning | Geo Oceans - https://www.geooceans.com/services/fixed-platform-inspection/
Ultrasonic Thickness Measurement Market Outlook: Complete Industry Analysis (2024 to 2031 - https://www.linkedin.com/pulse/ultrasonic-thickness-measurement-market-outlook-complete-uyiye
The more you know: digital tools to unlock UTM data analysis - https://marine-offshore.bureauveritas.com/more-you-know-digital-tools-unlock-utm-data-analysis
Commentaires