Tony Dale reports on enclosure integrity testing using acoustic ultrasound
Rig operations have numerous challenges. Accidental release of gases, operating in extreme environments or when being towed during a heavy sea state are just a few. A common and often-overlooked concern among the above, is the assurance of enclosure integrity against gas or water ingress.
Gases and excessive water entering into open enclosures, are a recipe for disaster. With likely outcomes being power outages, engines over revving, fire, explosion, intoxication and potential stability concerns.
Whenever drilling or when under way to the next destination, exterior doors and hatches should remain shut and effectively sealed from the elements, with an internal positive pressure present to prevent gas or water ingress.
Similarly, below the waterline hydraulically operated watertight doors should be permanently closed to function as a safety barrier, preventing water ingress from one compartment to another during an accident or flooding. When enclosures are shut, daylight, noise and smells should never be sensed.
Yet wear and tear, poor maintenance, paint and the environment can all contribute to seal integrity losses. Invariably, the hardening of neoprene seals becomes commonplace and an indentation of the enclosure becomes permanent, causing a significant portion of the seal’s surface contact area to become ineffective against gas or water ingress.
Using the services of a Class-registered, third-party inspector, one can actively find leaking sites to assist the Rig Maintenance Supervisor (RMS) enclosure and maintenance compliance needs, using high-frequency emission ultrasounds. The acoustic leak detection method generates frequency emissions greater than human audible hearing range, over 20MHz.
The ideal solution
Purposely designed to ensure enclosure compliance, professional equipment such as the ABS Class-approved Cygnus Hatch Sure provides the safe and direct means of closure integrity assurance, in a timely manner and with pin-point accuracy.
This non-invasive method does not disrupt rig operations and can be performed at any time of day, in any conditions.
Mounted on a tripod behind a closed door or beneath a hatch cover, a high-frequency transmitter inundates the enclosed space with ultrasound. After heterodyning (the process where the high-frequency sounds are modulated in real time for listening), the inspector – wearing a set of headphones – scans the other side of the shut enclosure with the ultrasound probe, tracing around the enclosure to listen for and mark where the leaking ultrasounds are emanating from.
Returning ultrasound levels are dependent on seal compression. Typically, the higher the pitch, the greater the leak.
When performing vessel cargo hatch inspections, an open hatch value (OHV)
is obtained, a value >10% denotes seal failure.
After repairs or seal replacement, a valve <10% of the OHV the enclosure is considered weathertight.
A pass result of <10% means water will not penetrate through the enclosure in any sea condition, and by extension, air and gaseous emissions at atmospheric pressure.
Regardless of surrounding decibel noise levels, the ultrasonic acoustic emission works just as well in noisy engine rooms. Furthermore, the system is applicable for all enclosure types, i.e. water and weathertight doors, deck hatches, manhole covers, scuttle ways and tank hatches, etc.
Ultrasound emission and its detection is so effective that classification societies and P&I clubs have accepted it for locating leakage sites around ship cargo hatches and coamings, to mitigate multi-million-dollar cargo losses due to faulty seals and openings.
Noise, smells and water ingress, no matter how small, are unacceptable. Ingress of gases into a hold, machinery space or into the accommodation, including the loss of stability from water ingress does not bode well for any MODU or floater.
Keeping enclosures closed and proactively testing seal integrities with ultrasonics is
the pitch perfect and cost-effective means for your RMS to call out an approved inspector before the next drilling campaign or rig move.
Tony Dale is managing director of Geotherm.