Page 606 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

606 CHAPTER 22 It’s the Little Things That Matter
There are, however, several advantages to deploying ROV systems at night for underwater port security, including:
• Lower harbor traffic that could inhibit operations
• Easier sighting of the submersible’s lights below the water, assisting in visually locating the
vehicle
• Better discrimination of items by the camera due to higher lighting contrast
22.1.3.5.2 Extreme temperature operations
For operations in Arctic and desert conditions, special considerations are needed to protect the equipment from malfunctioning due to temperature damage.
High temperatures are especially hard on electronic components due to the printed circuit board’s and conductor’s normal heating, plus the local high temperature, exceeding the maximum temperature limits of the materials.
Low temperatures are especially hard on seals, O-rings, plastics, and other malleable compo- nents (most of which are consumables).
Shock temperature loading of components happens when the components are left in air and allowed to settle to the local extreme ambient temperature. Once the components are temperature- soaked to the local extreme ambient air temperature, the possibility exists of shock temperature damage. If the submersible is then operated in water with a large temperature difference from the local air, shock loading of the components will be experienced.
An example of this in the Arctic would be a cold-soaked submersible left out overnight in
40F/ 240C air and then deployed into 132F/0C water, causing a total shock temperature loading of 72F/22C. This mistake, in all likelihood, would shatter the domes and cause seal failure, with the
resulting ingress of seawater into air-filled spaces of the submersible.
A similar instance happened recently in the Gulf of Mexico aboard a derrick barge during a hot,
windless August day. Prior to an operation, the vehicle was left out on the steel deck without shade while the crew relaxed in the air-conditioned operations shack. When the time came to dive, the vehicle (now heated to approximately 150 F/65 C) was lowered into the 75 F/24 C water, unevenly contracting the faceplate on the lights, thus allowing saltwater incursion into the light housing. Once the salt water penetrated the light housing, there was an immediate ground fault, tripping the GFI circuit and shutting down the vehicle electronics. Upon vehicle recovery, the light- ing circuit had been destroyed due to metal oxidation through the ground fault.
Practically all temperature-related issues are resolved on the submersible by gradually matching the temperature of the submersible with the temperature of the water before deploying the vehicle. Extreme temperature problems with the control console are more easily resolved since it will be with the operator, normally, in a temperature-controlled environment.
22.1.4 Predive operations and checks
22.1.4.1 Crew briefing
Any team effort requires a full understanding of the operation to be conducted by all team mem- bers. Before the start of any ROV operation, a full crew briefing is essential so that efficient tasking