Q. Explain about Surface Preparation?
All oil, grease, salts, and any other contaminants detrimental to the formation of a good coating bond or coating quality must be removed prior to the coating operation. Prior to blast cleaning the pipe shall be preheated to remove moisture. The pipe temperature shall be maintained at a temperature at least 5°F (3°C) above the dew point, but less than 300°F (150°C), during blast cleaning and inspection.
Suitable provisional caps shall be applied into both pipe ends in order to prevent abrasive and coating material from entering into the pipe. Care shall be taken to avoid damage to weld bevels and steel surfaces.
The blast cleaned surface shall be visually inspected for defects which would impair proper coating application. Defects shall be removed by grinding or hand filing. If defect removal is not possible, the joint shall be set aside for OWNER's inspection. The surface profile, measured from peak to trough, shall be 1.6 to 3.9 mils (40 to 100 μm), inclusive, and in accordance with the powder manufacturer's recommendations.
Residual blast products shall be suitably removed from the pipe surface by Clean Air Wash, or by High Pressure Water Wash followed by an air blast to remove excess water on the pipe. The internal surface of the pipe shall be cleaned by vacuum or blown with compressed air to ensure that no traces of blasting media remain in the pipe. Air shall be dry and free of oil and grease contaminants.