Reporting Section Added Section 10 7. What Happens after Near-White Blast Cleaning? Power abrading tools also acceptably remove mill scale according to the standard. Note that any variation on the surface caused by the original steel conditions do not factor in the no more than five percent of each unit area of the surface that can have the staining. A hot dip-galvanized coating is said to be fully weathered when the ss;c surface consists mainly of water-insoluble zinc carbonates, some zinc oxides, and rarely, zinc hydroxides. Just as important as pre-solvent cleaning, post-solvent cleaning is just as important as the step following solvent cleaning. The sandblasting process should not be done if the surface temperature is less than 5-degree Fahrenheit or 3-degree Celsius above the dew point.
This enables the specifier to select from five different restriction levels related to spot and area measurements. Figure 11 Table 1 Coating Thickness Restriction Levels Thickness Gage Reading Spot Measurement Area Measurement Level 1 Minimum Unrestricted As specified As specified Maximum Unrestricted As specified As specified Level 2 Minimum Unrestricted As specified As specified Maximum Unrestricted 120% of maximum As specified Level 3 Default Minimum Unrestricted 80% of minimum As specified Maximum Unrestricted 120% of maximum As specified Level 4 Minimum Unrestricted 80% of minimum As specified Maximum Unrestricted 150% of maximum As specified Level 5 Minimum Unrestricted 80% of minimum As specified Maximum Unrestricted Unrestricted Unrestricted Level 1 is the most restrictive and does not allow for any deviation of spot or area measurements from the specified minimum and maximum thickness, while Level 5 is the least restrictive. Feathering the edges of adhered paint surfaces is also required. A test certificate or other documentation showing traceability to a national metrology institution is required. D states that painting should be performed as soon as possible after power-tool cleaning or surface grinding. Dry film thickness gages are calibrated by the equipment manufacturer, their authorized agent or an accredited calibration laboratory under controlled conditions. Materials and work areas shall be accessible to the inspector.
D also considers the two methods interchangeable during the surface cleaning phase of the process. Also, uncoated shims of flat plastic sheet with assigned values traceable to a national metrology institution. If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy should be rechecked. It is important to recognize however that simply because all of this has been researched and the technology is in place to measure quantify it, does not make it contractually binding. On welded work removal of all welding flux, slag, and fume deposit are necessary as those are the contents that promote paint failure on welding joints. You are purchasing a downloadable pdf of this standard covers the requirements for power tool cleaning of steel surfaces.
Acceptable spot measurements are defined by the minimum and maximum values in the contract documents. The amount of surface profile depends on coating specification, but most of the specifications require 2 thru 3 mils. Please fill this form, we will try to respond as soon as possible. Here is a list and brief summary of the surface preparation standards used in the hot-dip galvanizing industry with a brief summary of each. If the recently blasted surface is exposed to salts, moisture, contamination or a corrosive environment, rust can occur quickly. For these gages, a permanent magnet is brought into direct contact with the coated surface. We will be updating and growing this site with more and more of industrial inspection related articles.
Near-white metal blast cleaning allows staining on only 5 percent of each unit area of surface, while commercial blast cleaning allows staining on 33 percent of each unit area of surface. The best way to avoid spreading the contaminants is to use contaminant free solvents for the final steps. The average of the three acceptable gage readings is the spot measurement. A780 allows uncoated areas to be power-tool cleaned before repair with zinc rich paints in areas of less critical field exposure conditions. Relative humidity should be less than 85% since the higher value can cause moisture condensation on the surface. We make our mailing list available for purchase. This fact makes power-tool cleaning an acceptable method for surface preparation of a hot-dip galvanized coating after it has been cleaned.
On complex structures or in other cases where making spot measurements at 5-foot intervals is not practical, spot measurements are taken on repeating structural units or elements of structural units. Oil, grease, and dust must be removed both before and after the cleaning procedure. The coating specification documents are part of the contract and have established requirements that must be met per project. The standard has been updated on multiple occasions 2004, 2009, and 2012. This fact makes power-tool cleaning an acceptable method for surface preparation of a hot-dip galvanized coating after it has been cleaned. If after solvent cleaning still, the soluble salt content is higher than allowable limit, then specification might call for high-pressure water jetting.
This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. This blasting method cleans less aggressively than an industrial blast clean. It depicts an approximate 100 square foot area containing gage readings and spot measurements. In order to select an appropriate abrasive, the type, grade, and surface condition of the steel need to be considered. An area is defined as approximately 100 square feet.
A hot dip-galvanized coating is said to be fully weathered when the exposed surface consists mainly of water-insoluble zinc carbonates, some zinc oxides, and rarely, zinc hydroxides. There are three categories of coated area: less than 300 square feet; 300-1,000 square feet; and greater than 1,000 square feet. Unperfected surfaces may lead to premature paint failure. Depending upon the application, the individual gage readings may also be recorded. The standard also provides requirements for random staining on the surface which shall not exceed five percent of each unit area of surface. Therefore, always be certain to remove visible rust prior to continuing with the new coating system. You can produce one without the other.
A surface profile of no less than one mill between peaks and valleys is required. List Updated: May 17, 2019 1. The remaining two-thirds of each square inch of surface area must be free of all visible residues. If after solvent cleaning still, the soluble salt content is higher than allowable limit, then specification might call for high-pressure water jetting. Note that as supplements, every project will have its conditions that need to be met.
Usually occurring around after six months of weathering, a finely etched and roughened profile acceptable for paint covers the surface of the galvanized coating. Should is used to state that which is considered good and is recommended but is not absolutely mandatory. Three sets of four circumferential spot measurements should be obtained on pipe spools less than 10 feet in length. After a galvanized surface has been acceptably cleaned of oil, grease, and similar products, this brush blasting can be applied in order to create an acceptable profile. May sspcc, Authored sspc sp1 Daniel Barlow. For emulsion, alkaline sp11, and steam be sure to finish the method by s1 the surface with fresh water or steam. Adjustment of Type 2 gages to compensate for substrate characteristics described later is typically performed using certified shims.