Anyone working around a UHP operation should exercise extreme care. Breaches in the hoses can cause very serious injury.
Operators may not realize anyone is in close proximity; a direct hit with the waterjet at these pressures can cause very serious injury or even death.
7.5.4 Safety
Safety systems include hose shrouds to pro-tect from high pressure hose bursts and
“deadman” controls to prevent the waterjet-ting system from being accidentally acti-vated (Figure 7.12).
Figure 7.12 Typical Braided Hose
Before beginning work, the waterjet team should ensure that:
• The work area is properly barricaded with appropriate warning signs.
• Electrical equipment is properly covered and protected from the water.
• Electrical connections do not sit in water.
• All fittings and hoses are in good condi-tion (not worn or damaged) and have the proper pressure rating for the working pressure to be used.
• Nozzles are open and free of obstructions.
• The complete system is flushed clean and air removed from the system before installing the nozzle.
• The dump system and all control systems are operational.
• All relevant moving equipment, such as conveyors, mixers, etc., are mechanically or electrically disabled, with appropriate lock-out provisions including the determi-nation of confined space entry
require-The joint NACE No. 5/SSPC-SP 12 stan-dard states that “all work shall be conducted in compliance with all applicable health and safety rules and environmental regulations.”
As a practical matter all personnel involved with the waterjetting, washing, and cleaning operation should obtain, study, and be famil-iar with, all regulations and safety proce-dures that apply.
The waterjetting unit shall have a pressure-control relief valve (deadman valve), which immediately interrupts the flow of water when the operator releases the trigger (this is similar to the deadman valve on a typical abrasive blasting hose). The operator may use a shrouded foot valve to control the flow of water to gun.
Figure 7.13 Foot Guard for Gun Trigger
Safety considerations require that only a well trained operator use the waterjetting equipment. Take the following precautions as well:
• Ensure the platform is stabilized when using swings, scaffolds, boson chairs, and similar riggings.
• Have an attendant present to monitor safety and functional conditions while the waterjetting unit is in operation.
• Ensure the operator wears the proper PPE when operating the equipment. This should include: (Figure 7.13, Figure 7.15)
— Head protection with full-face shield, and eye protection, such as goggles
— Body protection, such as water-proof or chemically resistant (if required) body suit
— Hand protection such as plastic-coated gloves, rubber gloves, or metal-mesh reinforced gloves
— Foot protection such as steel-toed boots and metatarsal guards
— A respirator as required, includ-ing full-face shield with sup-plied air
Specialized safety equipment is available for UHP waterjetting operations. One manufac-turer produces a system called TurtleSkin®, which uses specialized materials to protect workers from the high water pressures of waterjetting (Figure 7.14).
As previously stated, injuries caused by waterjetting or water-cleaning equipment can be life-threatening. It is a good practice to require every operator to carry a medical alert card to present to medical personnel prior to any treatment. The card should have information to this effect:
“This person has been waterjetting at pres-sures up to 60,000 psig (414 MPa) and/or a waterjet velocity up to 2,850 ft/s (870 m/s).
People injured by direct contact with high-or ultrahigh-pressure water typically experi-ence unusual infections with microaero-philic organisms. There may be gram-negative pathogens, such as those found in sewage. Before administering treatment, the attending physician should immediately con-tact a local poison control center for appro-priate information.”
Figure 7.15 Improper PPE (notice no gloves)
7.6 Special Considerations
Some of the advantages of waterjetting over dry abrasive blasting are:
• Less dangerous for crew
• Better air quality for workers
• Respiratory requirements may be less stringent.
• No dust contamination or clean-up
• Less damaging to the environment
• Relatively cost efficient
• Requires less clean up after surface prepa-ration
Some of the disadvantages of waterjetting over dry abrasive blasting are:
• The surface must have a prior anchor pat-tern or profile (waterjetting leaves no pro-file)
• Equipment is very expensive to purchase
• Dangers of a breached UHP hose
• Danger of water injection into the skin or serious cuts
• Collection and disposal of the contami-nated water (especially in ports when working on ship decks or hulls)
• Lack of proficient operators (however as waterjetting becomes more prevalent this issue subsides).
7.7 Inspection Concerns
Coating inspectors monitor the waterjetting operations and evaluate surface cleanliness in accordance with the descriptions set forth in the joint standards.
In addition to inspection and testing, the inspector may also be required to:
• Monitor clean-up of the waterjetting area
• Ensure that the water run-off from jetting operations is collected, treated, and/or dis-posed of according to applicable regula-tions
• Document carefully (with photographs, if necessary) each phase of the waterjetting operation
7.8 Inspection Checklist
The following is a general checklist that inspectors may find helpful during a water-jetting project:
• Attend the pre-job meeting to ask ques-tions, clarify issues, and contribute to the understanding of the specification, tools, and the methods of operation to be used.
• Read and understand the specification.
• Become familiar with the work schedule.
• Maintain all required forms of documenta-tion, including the weekly report.
• Get a broad understanding of equipment to be used.
• Confirm that the equipment is properly sized for the job.
• Check and verify operator qualifications if required in the specification.
• Know the surface preparation require-ments for the job and become familiar with the standards.
• Inspect and document the processes on the daily report.
• Ensure the job site is cleaned up on a daily basis, or as required by the contractual documents.
• Follow all safety requirements and encourage others to do the same.
• Immediately document and report all non-conformance with safety or quality.
Key Terms Definitions Non-Visible Contamination (NV): The
presence of organic matter, soluble ion materials, and/or sulfates that remain on the substrate after cleaning that cannot be seen with the naked eye.
Visible-Surface Cleanliness (VC): The vis-ible condition of the substrate, when viewed without magnification, after cleaning.
Waterjetting: The use of standard jetting water discharged from a nozzle at pressures of 10,000 psig (70 MPa) or greater, to pre-pare a surface for coating or inspection.
Study Guide
1. Specifiers must note specific requirements for both of the following per NACE No. 5/
SSPC-SP 12:
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2. A general description of robotic waterjetting includes:
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3. A typical waterjetting team consists of:
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4. Waterjetting is effective for removing:
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5. Describe two of the considerations with regards to “back thrust:”
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6. To ensure a safe work place before beginning the job, the waterjet team should ensure that:
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7. Waterjetting advantages include:
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8. Disadvantages of waterjetting include:
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