1、3-7SSPC-TR 2/NACE 6G198May 1, 1998Editorial Revisions November 1, 2004SSPC-TR 2/NACE 6G198JOINT TECHNICAL REPORTWet Abrasive Blast CleaningSSPC: The Society for Protective Coatings (SSPC) and NACE International (NACE) issue this report in conformance with the best current technology regarding the sp
2、ecifi c subject. This report represents a consensus of those individual mem-bers who have reviewed this document. It is intended to aid the supplier, the user and the general public. Its acceptance does not in any respect preclude any person or organization, whether they have adopted the report or n
3、ot, from manufac-turing, marketing, purchasing, or using products, processes, or procedures not in conformance with this report. Nothing contained in this report is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparat
4、us, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This report represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Neither is this repor
5、t intended to apply in all related cases. Unpredictable circumstances may negate the usefulness of this report in specifi c instances. SSPC and NACE assume no responsibility for the interpretation or use of this report by other parties and accept responsibility for only those offi cial in-terpretati
6、ons issued by SSPC or NACE in accordance with their respective governing procedures and policies, which preclude the issuance of interpretations by individual volunteers.Users of this report are responsible for reviewing ap-propriate health, safety, and regulatory documents and for determining their
7、 applicability in relation to this report prior to its use. This SSPC/NACE report may not necessarily address all safety problems and hazards associated with the use of materials, operations, and/or equipment detailed or referred to within this document.CAUTIONARY NOTICE: SSPC/NACE reports are subje
8、ct to periodic review and may be revised or withdrawn at any time without prior notice. SSPC and NACE require that action be taken to reaffi rm, revise, or withdraw this report no later than fi ve years from the date of initial publication. The user is cautioned to obtain the latest edition. For inf
9、ormation on this and other joint SSPC/NACE publications, contact either organization. The SSPC Publications Dept. may be reached at 40 24th Street, Pittsburgh, PA 15222-4656 (telephone +1 412-281-2331). The NACE International Membership Services Dept. may be reached at 1440 South Creek, Houston, Tex
10、as 77084-4906 (telephone +1 281-228-6200).ForewordThis joint report was prepared by the SSPC/NACE Joint Task Group C on Wet Abrasive Blast Cleaning, which is comprised of members of both the SSPC Surface Preparation Committee and the NACE Unit Committee T6G on Surface Preparation (now STG 04). It is
11、 intended to be used primarily by specifi ers, owners, painting contractors, inspectors, and others involved in surface preparation of industrial structures.1. ScopeThis document covers procedures, equipment, and mate-rials involved in a variety of air/water/abrasive, water/abrasive, and water-press
12、urized abrasive blast cleaning systems. Equipment usage and safety are also discussed. 2. Description and Use2.1 Air/water/abrasive blasting is a cleaning method in which water is injected into the air/abrasive stream generated by conventional air-pressurized abrasive blasting equipment. 2.1.1 Water
13、 helps to remove contaminants from the substrate, to wet the abrasive, and to substantially reduce dispersion of fi ne particulates (dust). Particulates are often caused by the breakup of the abrasives, surface corrosion products, and paint if the surface has been previously painted. Dust suppressio
14、n is achieved by thoroughly wetting the abra-sive and other particles to encapsulate them with a thin fi lm of moisture. The objective is to remove contaminants and suppress the dusting effect caused by the impact of the abrasive on the substrate, while retaining the blasting characteristics of dry
15、abrasive, including creation of anchor profi le.2.1.2 Air/water/abrasive blasting is an alternative to waterjetting, dry blasting, and water blasting with abrasive injection.2.1.3 Air/water/abrasive blasting is referred to hereafter as “wet blasting.”2.2 Water/abrasive blasting is a cleaning method
16、in which abrasive is injected into the water stream generated by conventional fl uid pumps.3-8SSPC-TR 2/NACE 6G198May 1, 1998Editorial Revisions November 1, 20042.2.1 Water is the primary agent to remove the contaminants from the substrate. The abrasive is injected to help remove brittle contaminant
17、s and create a profi le where necessary. Compared to wet blasting methods, water/abrasive blasting has a higher water to abrasive ratio. Dust suppression is achieved by the wetting of the abrasive and other particles. The objective is to remove contaminants with water and impact the abrasive on the
18、substrate to retain the blasting characteristic of dry abrasive, including creation of anchor profi le.2.2.2 Water/abrasive blasting is an alternative to dry blasting, wet blasting, or waterjetting.(1)3. Procedures and Parameters3.1 Wet blasting is generally considered suitable for use on any substr
19、ate for which the use of abrasive is appropriate. Wet blasting can often be adjusted to clean delicate substrates.3.2 Some wet blasting systems can utilize the same wide variety of available abrasives as conventional dry abrasive blast systems. Wet abrasive is more diffi cult to recycle than dry abr
20、asive. In some cases, recycling of wet abrasive may not be possible. In some cases, the water may be recycled.3.3 The water fl ow rate and the ratio of water to abrasive are usually adjustable so that a wide range of applications, from washing of surface contaminants to white metal blast, can be acc
21、omplished.3.4 After wet blasting, all traces of abrasive and other loose particles are brushed, blown off with clean dry air, vacuumed, washed, or otherwise removed from the surface. Cleanliness of the surface cannot be overemphasized.3.5 The injection of water to the air/abrasive stream helps to re
22、move contaminants such as dirt and water-soluble salts, including ferrous, chloride, or sulfate salts.(2)3.6 Inhibitors can be used to control fl ash rusting during wet or water/abrasive blasting. Many coating manufacturers prefer that inhibitors not be used in wet or water/abrasive blasting. (See S
23、ection 6.)3.7 Production rates vary due to variations in surfaces being blasted, the type of abrasive used, and the level of fi ne particulate dust suppression desired. Systems introduced since 1985 claim production rates equal to or higher than conventional dry blasting, but independent studies hav
24、e not been published as of this publication date.3.8 Wet blasting is a process that can produce surface cleanliness and anchor profi les (surface roughness) similar to those obtained with dry blasting. The level of surface prepa-ration specifi ed is the same as that specifi ed if dry blasting was th
25、e process being used. However, because the visual appearance of wet blasted surfaces is not necessarily the same as the visual appearance of dry blasted surfaces, care and judgment should be exercised by inspectors. It is common to encounter diffi culty when visual inspection standards or aids prepa
26、red for dry blasting are used as inspection or judgment criteria for wet blasted surfaces. This visual diffi culty can be lessened by preparation of a test patch which is agreed upon by the concerned parties during a pre-job conference.4. Wet Blasting Equipment4.1 The equipment used for wet blasting
27、 generally consists of conventional dry abrasive blasting equipment supplemented with modules to inject water into the abrasive stream. Ideally, the water encapsulates the abrasive particles with a thin fi lm of moisture to suppress and contain the dust generated by the impact of the abrasive with t
28、he substrate. Abrasive injection into water blast equipment will also be discussed.Systems are available that allow the operator to select adjustable rates of air, water, or abrasive as necessary to achieve optimum results. Some systems allow independent adjustment of each of these parameters while
29、the system is in operation. Some systems also allow independent adjustment for each nozzle for multi-nozzle setups. 4.2 TYPES OF WET BLASTING SYSTEMS 4.2.1 General Requirements of Wet Blast Units: Most systems under the general classifi cation of wet blast units contain a conventional dry abrasive b
30、last pot with OSHA/NIOSH required deadman and other safety features, plus the normal complements of abrasive metering valve(s), compressed air inlet valve(s), blast hose, dry abrasive blast nozzle, etc. With these systems, the compressed air volumes and pressures are the same as for conventional dry
31、 abrasive blasting. Each of these systems can clean to SSPC-SP 5/NACE No. 1 (White Metal) and create a suitable anchor pattern for paint adhesion. 4.2.2 Radial Water Injectors: Some of these are commonly referred to as “water rings,”and are available in three basic confi gurations. In the fi rst con
32、fi guration, water is injected at an angle toward the center of the blast stream as the air/abrasive stream enters the blast nozzle. The water is normally injected at or just above the pressure of the compressed air (see Figure 1). The second confi guration is a “donut” that fi ts over the outside o
33、f the dry blast nozzle. Water is injected from around (1) Waterjetting is defi ned in NACE No.5/SSPC-SP 12 as “the use of standard jetting water at high or ultrahigh pressure to prepare a surface for recoating using pressures above 70 mPa.” Standard jetting water does not contain sediments or abrasi
34、ve media.(2) See NACE Publication 6G1-86 (latest revision), “Surface Preparation of Contaminated Steel Surfaces,” and other items in the Bibliography.3-9SSPC-TR 2/NACE 6G198May 1, 1998Editorial Revisions November 1, 2004the outside of the blast stream radially inward at an angle toward the center of
35、 the blast stream as the air/abrasive stream exits the nozzle. The third confi guration utilizes a wet blast venturi nozzle which allows water and atmospheric air to be inducted at midpoint in the nozzle behind the bore restriction. 4.2.3 Coaxial Water Injectors: In these systems the water is inject
36、ed directly into the throat of the blast nozzle. The direc-tion of water injection is parallel to the fl ow of the air/abrasive stream. The air/abrasive stream and the water stream have the same axis or center line (see Figure 2).4.2.4 Slurry Blasters: The term “slurry blasting” is commonly used for
37、 the systems described in Sections 4.2.4 and 4.2.5. In these devices, the water is injected into the air/abrasive stream at some point substantially upstream from the blast nozzle. This allows the air/abrasive/water mixture to tumble for some distance in the blast hose to mix with and wet the abrasi
38、ve. Typically, the water is injected at the blast pot abrasive metering valve or at a blast hose connection. Sometimes the water is injected at the connection point of the whip hose to the main blast hose (see Figure 3, Confi guration 1).In Figure 3, Confi guration 2, the abrasive is loaded into a p
39、ressure vessel and simultaneously mixed with water. The vessel, loaded with the abrasive/water combination, is then pressurized using an integrated pump and the mixture is injected into the air stream. The unencumbered air fl ow reduces overall water consumption rates and provides good dust suppress
40、ion. Wet abrasive can be reused in the confi guration 2 system as long as the abrasive has not been crushed during the cleaning process and the material being removed in the blasting process is non-hazardous.4.2.5 Water Blast with Abrasive Injection: These devices differ from the units described in
41、Sections 4.2.2 through 4.2.4 in that the propelling force is the water stream, not compressed air. This method is commonly referred to as “abrasive wet jet” or “AWJ”, or “slurry blasting.” The typical devices consist of a fl uid pump with a venturi nozzle of some type in which the water fl ow draws
42、the abrasive into the water stream or the abrasive media is injected into the water stream under pres-sure. Because the fl uid stream is well defi ned, these devices usually cut a narrow blast pattern (see Figure 4).4.3 WATER DELIVERY SYSTEM4.3.1 Purity of Water: The purity of the water used for wet
43、 abrasive blasting (or any wet cleaning method) can affect the quality of the cleaned substrate. To achieve a clean substrate, demineralized, potable, or other water that will not impose addi-tional contaminants on the surface being cleaned is acceptable. There is no current defi nitive number for a
44、cceptable levels of water purity. The quality contamination of the substrate may be tested and confi rmed. Recycled water may contain a buildup of contaminants. FIGURE 13-10SSPC-TR 2/NACE 6G198May 1, 1998Editorial Revisions November 1, 2004FIGURE 2FIGURE 3, Confi guration 1FIGURE 3, Confi guration 2
45、3-11SSPC-TR 2/NACE 6G198May 1, 1998Editorial Revisions November 1, 20044.3.2 Water Flow Rates Requirements: The system has suffi cient water inlets with fi lters at the suction side of the pump to provide an adequate supply of water to the pump . The pump is capable of providing the water pressure a
46、t the required fl ow rates of the type of wet blast injector being used. Typical water fl ow rates and water pressures are:a. Radial Water Injectors: 0.5 to 31 L/min (0.2 to 8 gpm) at 0.2 to 21 MPa (25 to 3,000 psi) b. Coaxial Water Injectors: 2 to 4 L/min (0.5 to 1 gpm) at 0.7 to 21 MPa (100 to 3,0
47、00 psi) c. Slurry Blasters (Figure 3, Confi guration 1): 2 to 4 L/min (0.5 to 3 gpm) at 0.7 MPa (150 psi); Figure 3, Confi gu-ration 2, 0.02 to 1.6 L/min (0.0005 to 0.4 gpm) at 0.2 MPa (25 psi)d. Water Blast with Abrasive Injection: 10 to 38 L/min (2.5 to 10 gpm) at 34 to 280 MPa (5,000 to 40,000 ps
48、i) 4.3.3 Inhibitors: Where inhibitors are used, typical inhibitor/water ratios range from 1:1 to 1:1000. The inhibitor injector can be positively interlocked to the water pump to provide a uniform metered supply and constant concentration of inhibitor in the blasting water or mixed in a reservoir wa
49、ter supply. Other techniques, such as addition of inhibitor to a reservoir, can be equally effi cient. The inhibitor or wet blast equipment supplier or manufacturer sometimes sets forth special recommenda-tions (see Section 6). 5. Selection of Abrasives5.1 GENERAL: Virtually any type of abrasive com
50、monly used with conventional dry blasting can be utilized with the radial and coaxial injection type wet blasting devices (Sections 4.2.2 and 4.2.3), because they are supplemental to conventional blast equipment and the abrasive is not wetted in the blast hoses (see SSPC-AB 1, “Mineral and Slag Abra
