Ultrasonic Testing

General description of the equipment

The SHERLOG ultrasonic detection equipment has been designed to perform non-destructive weather-tightness inspections of hatch covers, doors, ramps, covers, windows, bulkheads or any other on-board or offshore -related tightness control.



The flexibility of ultrasonics has been successfully applied to a wide range of applications that are of direct interest to numerous sectors of industry. Norwegian Marine & Cargo Survey performs mainly hatch cover leak detection and tightness testing within the maritime industry.


Tightness and leak detection testing

The most efficient way to ensure tightness is to test it using ultrasonics. The testing can be either fully integrated into the production process, or carried out later as a control. In the case of hatch cover tightness and leak testing a transmitter is placed in the cargo hold and the hatch is closed. Ultrasonic waves are transmitted throughout the hold and with the detector, leaks or weak points between the rubber packing and compression bar, will be detected to exact location. The strenght of the signals received will reveal the extent of the problem.

Ultrasonic is more than just another form of testing tightness. It offers a complete, global solution with unheard-of accuracy and reliability.
Accuracy that has received Classification Society Type Approval.

Hose and chalk tests demonstarte whether or not there is contact between the rubber packing and compression bar but give no indication of the actual compression. Once at sea, it is often too late to see the shortcomings of this methode. Only ultrasonic testing can show you when you have the required or acceptable compression.


Basic Principle of ultrasonic testing

The principle of ultrasonic testing is remarkably simple. An ultrasonic transmitter is placed in the hold (empty or with cargo) and emits ultrasonic waves. The hatch cover is then closed, fully cleated and bettened. The surveyor or operator then uses the Sherlog ultrasonic detector to listen from the outside and pick up all "leaking" ultrasonic sounds that pass through the sealing arrangements, vents and/or cracks. Ultrasonic testing is far more accurate than other testing methodes, enabling operators and surveyors to pinpoint leaks that are a problem - or are likely to become one.

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements. Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more. A typical UT inspection system consists of several functional units, such as the pulser/receiver, transducer, and display devices. A pulser/receiver is an electronic device that can produce high voltage electrical pulses. Driven by the pulser, the transducer generates high frequency ultrasonic energy.

In the case of a leak detection test of a ship’s cargo hold the transmitter is placed in the cargo hold and the sound energy is propagated through the volume space in the form of waves. The waves will be reflected by surfaces covering every point in the space. When there is a leak or weak point, typically along the hatch coming the ultrasonic waves will escape through the crack. The wave energy can be picked up by a receiver and the signal is transformed into an electrical signal by the transducer and is displayed on a screen. The leakage point is now located exactly.

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