A Pressure Vessel subject to Internal Corrosion shall be defined as any metal Pressure Vessel using a processed product that can cause Corrosion, Erosion, Pitting, Cracking, or Deterioration, as defined in Part 2, 3.3 of the National Board Inspection Code. The intent is to verify the vessel is safe to operate. Pressure Vessels subject to internal corrosion shall receive a Certificate Inspection every three (3) years. Owner-Users qualified in accordance with Section 15 of the Illinois Boiler & Pressure Vessel Safety Act (430 ILCS 75) shall have the option of using API-510 or the NBIC for inspection intervals. This inspection shall be external and internal where conditions permit,* however, small air receivers and domestic hot water supply storage vessels, or vessels without man-way openings, may substitute thickness readings compared to original material thickness values when the internal inspection is impractical. CLICK HERE (pdf) to see this DRAFT Document.