NACE 2 ( Chapter 7: Waterjetting )

(NV) - • Non-visible contamination (VC) - • Visible surface cleanliness NACE No. 5/SSPC-SP 12 - describes the use of a high-energy water stream to strip off existing coatings and remove contaminants on a substrate being prepared prior to coatings application. When compared to abrasive blasting, And water jetting - this method has certain advantages particularly for safety and environmental control. Respiratory protection requirements are less stringent and waste (abrasive) disposal is not an issue because water is the medium. The term waterjetting denotes - the use of "water only," without the addition of solid particles such as sand or garnet in the water stream. Modern waterjetting equipment produces pressures of up to 90,000 psig. However, In the marine industry, waterjetting - is widely used to remove marine growth, depleted antifouling coatings, Data also proves it is effective - in removing marine growth on offshore structure's jackets (submerged sections). waterjetting - will remove contaminants and millscale at varying pressures, it will not create an anchor profile, which plays a critical role in coatings adhesion. In maintenance and repair operations, waterjetting exposes the existing anchor profile there is no direct correlation between dry abrasive blasting standards and - the capabilities and results of waterjetting. surface preparation utilizing waterjetting, the visual - (WJ-1 to WJ-4) non-visual surface preparation definitions - (NV-1 to NV-3) Visual reference photographs or visual standards such as - NACE VIS 7/ SSPC-VIS 4. The specifier, inspector, and contractor must agree on the test methods to - determine the amount of non-visible contaminants that can be left on the prepared substrate. Consult the manufacturer of the specified coatings to determine the coating's tolerance to the surface conditions after waterjetting, commensurate with the in-service conditions. Two terms synonymous with cleanliness after waterjetting are - visible and non-visible contaminants. Non-visible contamination (NV) - is the presence of organic matter, such as very thin films of oil and grease, and/or soluble ion materials such as chlorides, ferrous salts, and sulfates that remain on the substrate after cleaning that cannot be seen with the naked eye. Visible surface cleanliness (VC) - is the visible condition of the substrate when viewed without magnification and after cleaning. WJ-1 Clean to Bare Substrate: - The surface shall be cleaned to a finish which, when viewed without magnification, is free of all visible rust, dirt, previous coatings, mill scale, and foreign matter. Discoloration of the surface may be present (A, B, C). WJ-2 Very Thorough or Substantial Cleaning: - The surface shall be cleaned to a matte (dull, mottled) finish which, when viewed without magnification, is free of all visible oil, grease, dirt, and rust except for randomly dispersed stains of rust, tightly adherent thin coatings, and other tightly adherent foreign matter. The staining or tightly adherent matter is limited to a maximum of 5% of the surface (A, B, C). WJ-3 Thorough Cleaning: - The surface shall be cleaned to a matte (dull, mottled) finish which, when viewed without magnification, is free of all visible oil, grease, dirt, and rust except for randomly dispersed stains of rust, tightly adherent thin coatings, and other tightly adherent foreign matter. The staining or tightly adherent matter is limited to a maximum of 33% of the surface (A, B, C). WJ-4 Light Cleaning: - The surface shall be cleaned to a finish which, when viewed without magnification, is free of all visible oil, grease, dirt, dust, loose mill scale, loose rust, and loose coating. Any residual material shall be tightly adherent (C). The inspector and contractor should know that surfaces prepared by - LP WC, HP WC, HP WJ, or UHP WJ After waterjetting, - The matte finish color of clean steel surface immediately turns to a golden hue unless an inhibitor is used or environmental controls are employed Color variations in steel - can range from light gray to dark brown/black. The gray or brown-to-black discoloration - seen on corroded and pitted steel after waterjetting cannot be removed by further waterjetting. A brown-black discoloration of - ferric oxide may remain as a tightly adherent thin film on corroded and pitted steel and is not considered part of the percentage staining. Waterjetting at pressures in excess of 35,000 psig (240 MPa) - is capable of removing tightly adherent mill scale, but production rates are not always cost effective. Mill scale, rust, and coating are considered tightly adherent - if they cannot be removed by lifting with a dull putty knife (see NACE No. 4/SSPC-SP 7). No Flash Rust: - A steel surface that, when viewed without magnification, exhibits no visible flash rust. Light (L) - a surface which, when viewed without magnification, exhibits small quantities of yellow-brown rust layer through which the steel substrate may be observed. The rust or discoloration may be evenly distributed or present in patches, but it is tightly adherent and not easily removed by lightly wiping with a cloth. Moderate (M) - A surface that, when viewed without magnification, exhibits a layer of yellow-brown rust that obscures the original steel surface. The rust layer may be evenly distributed or present in patches, but it is reasonably well adherent and leaves light marks on a cloth that is lightly wiped over the surface. Heavy (H): - A surface that, when viewed without magnification, exhibits a layer of heavy red-brown rust that hides the initial surface condition completely. The rust may be evenly distributed or present in patches, but the rust is loosely adherent, easily comes off, and leaves significant marks on a cloth that is lightly wiped over the surface. NV-1: - surface shall be free of detectable levels of soluble contaminants, as verified by field or laboratory analysis using reliable, reproducible test methods. NV-2 - surface shall have less than 7 μg/cm2 (0.0007 grains/in. 2 ) of chloride contaminants, less than 10 μg/cm 2 (0.00 1 2 grains /in. ) of soluble ferrous ion levels, or 2 less than 17 μg/cm 2 (0.00 17 grains/in. ) of sulfate contaminants as verified by field or laboratory analysis using reliable, reproducible test methods. NV-3: - surface shall have less than 50 μg/cm 2 2 (0.005 grains/in. ) of chloride or sulfate contaminants as verified by field or laboratory analysis using reliable, reproducible test methods. Waterjetting (WJ) is the use of - water discharged from a nozzle at pressures of 10,000 psig (70 MPa) or greater to prepare a surface for coating or inspection. Low-Pressure Water Cleaning (LP WC): - Cleaning performed at pressures below 5,000 psig (34 MPa). This is also called "power washing" or "pressure washing. • High-Pressure Water Cleaning (HP WC): - Cleaning performed at pressures of 5,000 to 10,000 psig (34 to 70 MPa). • High-Pressure Waterjetting (HP WJ): - Waterjetting performed at pressures from 10,000 to 30,000 psig (70 to 210 MPa). • Ultrahigh-Pressure Waterjetting (UHP WJ): - Waterjetting performed at pressures above 30,000 psig (210 MPa). A commercial waterjet unit can be - skid, trailer, or truck-mounted and usually consists of pumps, hoses, a prime mover (diesel,electric, etc.), along with various tools such as guns, nozzles, lances, etc nozzle, should have minimum burst strength - of 2½ times the capability of its maximum-rated operating strength High-pressure hoses are fitted with a safety device known as - a whip-lock or whip check. This is a short length of cable or wire looped over each end of two hoses connected by - connected by a coupling The whip-lock or whip check - prevents the ends of the hoses from whipping around if the coupling breaks. hose shroud - which usually is a short length of heavy-duty hose placed over the high-pressure hose to provide instantaneous protection if the hose bursts. A hose shroud also can be used over other hose connections. The shroud, however, does not form a permanent barrier to the flow of water from a damaged hose or broken connection. Waterjetting equipment types generally fall into one of two basic categories: - • manual • robotic Technology is quickly improving and a new kind of equipment recently developed is a robotic water jetting unit. - It is a cleaning vehicle that attaches itself, using vacuum, cables, or magnets to a vertical, horizontal or overhead surface. It is controlled by a single operator A Robotic unique features is that - it collects in excess of 95% of the water, removed coatings and rust (waste generated) Robotic cleaning This unit is used on - used on vertical surfaces such as ship hulls and tanks on horizontal surfaces such as flat decks and on overhead surfaces such as the bottom of ship hulls. It also works well over weld seams, doubler plates, lap joints and riveted seams, and moves easily in and around keel blocks and other common obstructions. For straight-line work, it uses an "autopath" control feature. Robotic The equipment sends a concentrated stream of water through the hose and nozzle at pressures of - 10,000 to 60,000 psig (70 to 414 MPa). With current technology, the most practical pressures are - 10,000 to 35,000 psig (70 to 240 MPa). At working pressures of 4,000 psig (28 MPa) or higher, the waterjetting team consists of: - • The nozzle operator • The pump operator • Additional operators or workers The nozzle operator - controls the operation while waterjetting is taking place by holding the gun and lance or delivery hose and controlling the motion and direction of the waterjets. The pump operator - monitors and controls the pressurizing pump during the jetting operation, and watches the nozzle operator at all times to be able to react if any difficulty arises, or if the operator begins to show signs of fatigue. The pump operator also monitors the working area and its surroundings in case anyone tries to enter the area or if a potentially hazardous condition occurs. Depending upon the size and scope of the project - other operators or workers may be required to assist in handling a jetting gun if it is fitted with more than one jetting extension or if the hose must be fed to the work piece. Waterjetting is effective for removing: - • Surface oil and grease • Rust • Concrete (shot-crete) spatter • Existing coatings