Zetec, Inc

Ultrasonic Hull Inspections: How to Find the Right Equipment

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Courtesy of Zetec, Inc

Hull inspections keep crew, ship, and cargo safe at sea. Not only is it plain good sense to periodically ensure the seaworthiness of any vessel, but it can also be required by law for ships registered in the U.S. and other countries. Hull inspections can be conducted visually in some cases, but for the best results, ship owners rely on nondestructive testing.

Marine nondestructive testing, such as ultrasonic hull inspections, improve technician’s abilities to detect deterioration, damage, or defects. Ultrasonic testing, in particular, allows ship owners to more effectively map corrosion and measure hull thickness than visual inspections. The primary benefit is the ability to image the interior of the hull, which no visual inspection can achieve. This allows ship owners to detect hull issues before they become leaks (and lost dollars). 

Ultrasonic Hull Inspections Augment Visual Inspections

If a ship’s hull is corroding, it will likely be easy to see (at least in drydock). Technicians will spot rust, pitting, grooving, and patches where coatings have worn off. What they won’t be able to see is how deep the damage goes. Minor surface issues can obscure major internal decay, which can worsen with little or no warning.

As such, ultrasonic hull inspections should be used to augment visual inspections. Even apart from the periodic, legally required inspections, ultrasonic can be used to perform spot checks for potential corrosion based on crewmember observations. Visual inspection offers suspicions; ultrasonic offers certainty. 

How Ultrasonic Testing Equipment Inspects Hull Plates

Ultrasonic testing equipment uses high-pitched acoustic waves to examine the interior of objects. Probes transmit and receive waves, then calculate interior irregularities based on the returning signal’s delay. (In time-of-flight-diffraction ultrasound, the waves do not return, but are received on the other side after they have passed through the object). Longer or shorter delay times indicate the presence of internal cracks or voids.

The entire extent of the internal damage can be mapped using ultrasound, giving shipowners a precise indication of what maintenance is required to keep the hull sound. Ultrasonic testing equipment can also be used to directly measure the thickness of hull plates, ensuring safe margins. 

Additional Benefits of Ultrasonic Inspections 

The equipment’s software records and displays data from each scan, allowing workers to see corrosion in real-time, or anytime after. This recordkeeping ability also simplifies proof of compliance, for regulatory bodies.

In addition, it enables companies to compare apples-to-apples records of their ships. While visual inspections can be conducted under grading criteria, visual inspections are inherently subjective. Even with printed aides and guides, one inspector’s “fair” can be another’s “poor.” Ultrasonic testing, by contrast, provides objective data that can be compared directly to other data sets taken from the same ship or a different one.

These data sets provide a detailed look at the way corrosion spreads in specific ships. Such knowledge allows ship owners to better prepare predictive models for maintenance. More knowledge of how corrosion spreads can help identify where it may spread next, and when it will spread too far. 

Choosing the Right Ultrasonic Testing Equipment for Hull Inspections

The right ultrasonic testing equipment ‘for hull inspections shares certain characteristics:

Advanced software.
Full software packages for ultrasonic testing equipment simplify scanning for their operators. Software features may include guided probe positioning, calculation of all parameters, coverage overview, simple calibration routines and status for all channels, phased array and time-of-flight-diffraction analysis, and reporting tools.  Intuitive user interfaces and touchscreen ensure smooth operations in the field.

Durability.
Even drydock can be a difficult environment. Ultrasonic testing equipment should be moisture resistant, encased in a rugged protective shell, and able to withstand a wide range of temperatures. Equipment without air intakes prevents damage from airborne particulate matter.

To ease inspection of large hulls, technicians should turn to ultrasonic scanners. These tools aid the scanning of large surfaces. Scanners designed to work on flat or curved surfaces are ideal for hull inspections. Top-level scanners track the position of their wheels, allowing technicians to identify areas they haven’t yet covered in real-time.

Ultrasonic testing equipment improves the ability of shipowners to meet regulatory demands and protect their crews, ships, and cargo. Ultrasonic hull inspections provide information that simple visual inspections cannot, such as the extent of internal corrosion. By taking the guesswork out of hull corrosion mapping, ultrasonic testing equipment provides ship owners peace of mind, whether their ship is in Miami or Malacca.

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