Removing Marine Growth

Virtually all inspection, maintenance, and repair operations on marine structures require some degree of marine growth removal. An underwater structure provides an ideal substrate for colonies of marine organisms. This marine growth, particularly if evident in large numbers, can have significant negative effects on the integrity of the structure. The presence of marine growth increases the size and mass of the structure, which causes the structure to un dergo greater wave and current forces, perhaps to the point of causing structural failure. The presence of marine growth can also cause accelerated deterioration of paint, steel, and concrete. However, in most cases, the organisms cause less damage than the process of removing them. Unless required for inspection, maintenance, repair, or reduction in weight or drag, the organisms should be left in place and not removed. Some typical growths found on underwater structures include kelp, seaweed, mussels, anemones, sponges, and barnacles.

There are several methods to clear structures of marine growth, generally divided into two groups: hand tools and power tools. Hand tools include such items as wire brushes and scrapers. Hand tools are good for general marine growth removal and are especially effective when a diver must be highly mobile, such as in the inspection of fleet moorings. They are generally not used when large areas of growth must be removed, such as in nondestructive testing (ultrasonic thickness measurement and magnetic particle inspection) or for maintenance and repair operations. Hand tools have an extra advantage — they are highly portable and involve minimum hazards in their use.

Power tools are useful for removing marine growth because they are faster and usually more effective than hand tools. The following types of Navy-approved, commercially available devices are recommended for cleaning underwater structures:

1. A reactionless water jet with variable flow rates and pressures for heavily fouled concrete and steel structures.

2. A rotary abrading device on concrete structures.

High Pressure Water Injuries

Figure 2-19 Reactionless high-pressure wateijet.

3. A hydraulic or pneumatic chipping hammer.

These devices are:

• Reaction!ess High-Pressure Water Jet, shown in Figure 2-19, is available with a number of fan nozzles varying in orifice size and fan angle. The retrojet is surrounded by a diffuser shroud with slots that force the exiting high-pressure water out the side holes to prevent injury from inadvertently passing the tool in front of the operator. The system operates within a wide range of flows and pressures limited only by die pump capabilities and includes a topside, foot-operated control valve that permits surface personnel to quickly shut off flow to the tool in case of emergencies or equipment malfunction. This device can effectively remove heavy marine growth and corrosion for most situations and satisfies most cleaning criteria and requirements.

Barnacle Buster

Figure 2-20 "Barnzcle Buster" tool.

• "Barnacle Buster" or "Whirl Awayn tool, shown in Figure 2-20, is a rotary abrading attachment that fits a standard hydraulic drill, sander, or grinder. Seven sets of hardened steel cutters rotate on their axles while the shaft of the tool attached to the hydraulic motor rotates in the opposite direction. Water displaced from the rotary motion creates a low-pressure area on the cutter side of the tool. This effect causes the tool to be pushed against the work surface but still allows movement in any direction under the operator's guidance. The Barnacle Buster is the most effective tool for removing fouling from concrete surfaces and is the safest cleaning device to operate because it does not require high-pressure water.

Figure 2-19 Reactionless high-pressure wateijet.

Figure 2-20 "Barnzcle Buster" tool.

• Water Jet Cleaning System - This system was developed by the NFESC and is available for the routine cleaning of structures, particularly in limited access areas. The system, shown in Figure 2-21, includes a:

gpm, 3,000-psi oil for powering oil-hydraulic diver tools.

• Noncavitating High-Pressure Water Jet-This device, without retrojet for surface-subsurface cleaning, is commonly used by the UCTs. This device, illustrated in Figure 2-22, develops more than 40 pounds of back thrust and may be equipped with a shoulder stock to provide support during operation. It operates at up to 10 gpm and 10,000 psi and is available with a number of standard and fan nozzles.

- Small hand-held water jet pistol

- Interchangeable cavitating fan and straight jet nozzles

- Diver-operated trigger valve with automatic safety lock

- Flexible, small diameter, high-pressure supply hose

- Foot-activated shutoff valve

- High-pressure swivel

Underwater Waterjet

Figure 2-22 Noncavitating high-pressure waterjet without retrofit.

The power source, which delivers up to 5 gpm at 12,000 psi, is driven by a diesel engine. The power unit operates on either freshwater or sea water. The system also provides 12-

Figure 2-22 Noncavitating high-pressure waterjet without retrofit.

Jet Skin And Bones

CAUTION Exercise extreme care while using any high-pressure cleaning systems. The water jet is capable of cutting skin and bones. Never point the jet at anyone, even underwater.

Figure 2-2lb NFESC waterjet cleaning power source.

Figure 2-2 la High-pressure wateijet cleaning nozzle.

Many different commercial high-pressure waterjet systems are available. Also commercially available are high-pressure waterjet systems with abrasives injected into the fluid stream. These systems are primarily designed for abovewater use for cutting material and are especially hazardous to use both underwater and on land.

The best operating technique for all high-pressure jets includes a standoff distance of 1/2 to 3 inches, an impingement angle of 50 to 90 degrees, and quick and agitated translation. Each tool has an optimum operating technique that should be established prior to any actual cleaning.

Cleaning rates for the various cleaning methods differ. In addition, the cleaning rate depends on the type of structural material, fouling amount and type, water visibility, temperature and surface condition, size of area to be cleaned, operating pressure and flow rate, and operator experience. Assuming good working conditions, an average experienced diver will achieve the cleaning rates given in Tables 2-8 and 2-9 for steel and concrete structures, respectively. Since most of the time required to completely clean underwater surfaces is spent removing die last remnants of stubborn shell growth and fouling, two cleaning times are indicated in the tables.

A "preliminary cleaning" to remove moderate to heavy marine fouling consisting of weed growth, algae, rust, and loose barnacles or tubeworms is sufficient for most routine inspection and maintenance operations. A "final cleaning" to remove all heavy fouling including stubborn shell growth and any protective coating is required for other situations. A diver should not be expected to work longer than the time indicated in the table; fatigue could render the diver unsafe.

2.4 THERMAL CUTTING/WELDING

There are two general categories of underwater cutting techniques: mechanical and thermal. The equipment used for mechanical cutting includes hydraulically-powered chain saws, band saws, and shears. Thermal cutting techniques employ the use of a thermal arc with and without oxygen.

2.4.1 Thermal Cutting

A brief description of thermal cutting methods is contained below and a full discussion can be found in the U.S. Navy Underwater Cutting and Welding Manual, NAVSEA S0300-BB-MAN-010.

All underwater thermal cutting methods are potentially hazardous to personnel. Divers performing underwater cutting and welding must have greater skill and stamina than those doing the same work topside. The use of the correct techniques and equipment becomes extremely important underwater. Diving apparel, depth, currents, low temperature, poor visibility, and suitable footing are all factors that make underwater cutting and welding difficult.

Only personnel trained and qualified in underwater welding may be assigned to those jobs. Dives must be carried out in conformance with the U.S. Navy Diving Manual (NAVSEA 0994-LP-001-9010). Cutting and welding must be carried out in accordance with die procedures described in the Underwater Cutting and Welding Manual using equipment that has been approved for Navy use.

WARNING Serious injury or death may result when adequate precautions are not followed during underwater cutting and welding operations. Supervisors shall ensure that all personnel are trained and qualified in underwater cutting and welding and are thoroughly familiar with the safety précautions covered in the U.S. Navy Underwater Cutting and Welding Manual.

Table 2-8

Marine Growth Removal from Steel Structures

Table 2-8

Marine Growth Removal from Steel Structures

0 -1

Responses

  • Sophia
    What can be expected for cleanng area and rate with barnacle busters?
    6 years ago
  • TRAHAND
    Does marine growth have to be cleaned off before concreating?
    6 years ago
  • JESSIKA
    How to remove marine growth?
    4 months ago

Post a comment