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TECHNICAL SPECIFICATION NO. 3 <br />NEAR-WHITE BLAST CLEANING <br />3.01 SCOPE <br />This specification covers the procedure required for the near-white blast cleaning of <br />structural steel surfaces prior to painting or coating. <br />3.02 DEFINITION <br />Near-white blast cleaning is a method of preparing metal surfaces for painting or <br />coating by removing mill scale, rust-scale, paint, or foreign matter to the degree <br />hereafter specified, by use of abrasives propelled through nozzles or by centrifugal <br />wheels. <br />A near-white blast cleaned surface finish is defined as one from which all oil, grease, <br />dirt, rust-scale and foreign matter are removed completely from the surface and all rust, <br />mill scale, and old paint have been completely removed except for very light shadows, <br />very slight streaks, or slight discoloration caused by rust stain, mill scale oxides or <br />slight, tight residues of paint or coating that may remain; if the surface is pitted, slight <br />residues of rust or paint, may be found in the bottom of pits; at least.95 percent of each <br />square inch or surface area shall be free of all visible residues and the remainder shall <br />be limited to the light discoloration, slight staining or tight residues mentioned above. <br />Photographic or other visual standards of surface preparation may be used as provided <br />in the Appendix to modify or further define the surface if specified in the contract. <br />The overall blast cleaning effort expended (nozzle time) shall be not less than (2/3) of <br />that required to produce a White-Metal Surface Finish on the same surface; nor should <br />it be more than 95 percent of such effort required. This limitation shall not be construed <br />as a waiver of any of the above requirements. <br />3.03 PROCEDURES <br />Near-White blast cleaning shall consist of the following sequence of operations: <br />A. Heavy deposits of oil or grease shall be removed by the methods outlined in <br />Specification SSPC-SP 1-82, "Solvent Cleaning". Small quantities of oil or <br />grease maybe removed by the blast cleaning operation. If oil or grease are <br />removed by blast cleaning, the abrasive shall not be reused if such reuse is <br />detrimental to the surface. <br />TS3-1. <br />- ~ 449 <br />