Ultrasonic testing helps improve safety at sea

Founded in 1983, Cygnus Instruments Ltd is a UK manufacturer of high-quality ultrasonic testing equipment. For the bulk carrier, Cygnus prides itself on making high quality ultrasonic thickness gauges (UTGs) and leak detectors that are entirely focused for the job in hand — and that are both highly ruggedized and simple to use.

 

At Periodical Survey, it is a Class requirement to carry out overall examination and thickness measurement of hull structures. With almost 40 years of close involvement with the marine inspection industry behind them, the team at Cygnus provide the industry with a small, dedicated range of UTGs that are entirely designed for the task.

 

Central to Cygnus’ place in the marine inspection industry was the company’s development and pioneering of the ‘multiple echo technique’. This is an ultrasonic technique that utilizes three back wall echoes to verify and error-check thickness readings. At its core, Cygnus’ multiple echo technique is extremely accurate and will ignore all coatings. IACS’ procedural requirements document URZ17 (IACS Req. 1997/Rev.13 2018) states that wherever there are coatings present during the vessel inspection, the multiple echo technique must be used. With the ever-increasing proliferation of coatings used in the marine industry, Cygnus has cemented its position as the number one choice for Class-Approved thickness measurement companies around the globe.

 

Taking a closer look at the equipment itself, Cygnus offers several options for bulk carrier, marine and shipping inspection. The Cygnus 2 and Cygnus 4 units use the required multiple echo technique — and will ignore coatings (up to 20mm thick) with no special technique or set up required.

 

The Cygnus 2+ and 4+ units also have single echo (SE) and echo-echo (E-E) modes (as well as multiple echo); the use of a range of twin crystal probe with SE and E-E modes adds flexibility to the units, and allows measurements to be taken in areas of extreme corrosion.

 

The Cygnus 4+ unit will also record (data-log) readings at the single press of a button; measurements can then be downloaded in to Cygnus’ easy-to-use software – or simply export in to Excel (as a .CSV file). The 4+ unit also features a live A-Scan and manual gain control to round out an exceptionally comprehensive UTG for bulk carrier inspection.

 

Drawing on its extensive experience in the market, it is natural that the Cygnus UTGs are very well designed. With environmental sealing to IP67 – US MIL STD 810G, all the units are waterproof, drop-proof and shock proof in order to cope with the very tough environment they will be used in. And the probe housings and cables that are made by Cygnus are exceptionally robust and durable too.

 

 

 

Poor maintenance of hatch covers, seals and coamings, resulting in water entering a ship’s hold can lead to highly expensive or even devastating consequences. Testing that hatch covers are weather-tight is a fundamental requirement for preventing damage to cargo and ensuring the safety of a vessel and its crew.

 

Ultrasonic testing is the most accurate, repeatable and convenient method of testing hatch covers, doors, ventilators and access hatches and is the preferred method of inspection by P&I Clubs; but there are other methods in use.

 

Light testing: hatches are fully battened down and a Surveyor will view the underside of the covers to see if any visible daylight is shining through gaps. This is the simplest method for identifying defects and their location but it may not be so easy to identify very small gaps.

 

Chalk testing: chalk powder is applied to the coaming compression bars and panel cross seams, the hatches are then closed and re-opened. The rubber joints are carefully examined. If there are irregularities in the chalk markings then it is assumed that these areas are not weather-tight. This method was the traditional way for testing hold cover compression but does not test the watertight integrity of the hold. IACS states that this test should be followed by a hose test.

 

Hose testing: the conventional technique for testing weather tightness of hatch covers is hose testing which uses large volumes of water sprayed at the rubber seals. Any water leaking into the hold should then be seen by the Surveyor inside, indicating a defect in the seams or joints. Although the most common method of testing hatch covers, this technique has many limitations when compared with using ultrasound:

 

* the hold must be empty;

* a minimum of two surveyors required;

* it cannot be performed in sub-zero temperatures;

* run-off from the deck which can lead to pollution — some port authorities will not permit this;

* it cannot accurately pinpoint leakages as water might travel along drainage channels and enter the hold at a different point or travel through the drain valves and back onto deck;

* variance in water pressure and distance of the jet can affect results; and

* time consuming.

 

 

 

Ultrasonic testing is an accurate, repeatable and convenient method of testing hatch covers, doors, ventilators, access hatches, etc.

 

A transmitter emitting ultrasound is placed in the hold and the hatches are then fully closed. On deck the surveyor wearing headphones will walk around the periphery of the covers using a hand-held receiver or detector and will be able to hear ultrasound leaking through any defective seams or joints — even through the smallest of openings.

 

A percentage scale is used with an open hatch emitting 100% of the ultrasound. DNV and ABS state that during an inspection any reading over 10% indicates an area of potential leakage.

 

When a vessel is at sea and is pitching and flexing, seals that were demonstrated to be tight when the ship was stationary might potentially leak. A benefit of the ultrasonic method is that the level of compression of a seal can also be detected and monitored through periodic maintenance checks. A higher percentage reading indicates a lower level of compression and could indicate a seal which will leak when the ship is in rough conditions.

 

While ultrasonic hatch cover testing has been available since the 1980s, Cygnus Hatch Sure has advanced the current technology with fully automatic Open Hatch Calibration (OHC) to set the Open Hatch Value (OHV). This ensures consistent results from hold to hold with a lightweight and extremely powerful 19 x 40KHz element transmitter. This is powerful enough to saturate the largest cargo hold with ultrasound. The variable output transmitter has six selectable power levels allowing the unit to also be used in confined spaces, such as for testing watertight doors. 

 

The Cygnus Hatch Sure system is comprised of two main components: a powerful ultrasound transmitter with 19 x 40 KHz elements and a hand-held receiver. Designed for ease of use and powered by standard rechargeable batteries, the whole system is extremely light and aircraft-friendly for passenger cabin transportation.

 

The Cygnus Hatch Sure leak detector is a purpose-designed, robust and very lightweight system; as such it has become the market leader for Ultrasonic Hatch Cover Inspections and is the preferred choice of multinational ship management companies across the globe who want to test hatch covers quickly, accurately and cost effectively.

 

Cygnus Hatch Sure is ABS Type Approved and accepted by all P&I Clubs. The Cygnus product training syllabus has been endorsed by the International Institute of Marine Surveyors (IIMS).