RR-C-901E
from a cylinder wall of greater thickness may be used if the source, processing, and heat treatment of the steel parallels the source, processing, and heat treatment of the cylinders under consideration.
3.3 Cylinder processing.
3.3.1 Preconditioning and internal preservation. After hydrostatic and any other testing, the cylinder internal surface shall be cleaned and dried to be free of moisture, oil, grease, grit, machining products, loose scale, slag, or other foreign materials. Rust bloom or particulate matter (approximately 1.0 to 1.5 grams) generated subsequent to inspection as a result of handling and shipping is acceptable. Cleaning agents used shall be compatible with the cylinder materials and the intended gas service.
3.3.2 Oil and hydrocarbon residue. Residual oil and other hydrocarbons resulting from the manufacture of the cylinder shall be removed to a level not greater than 2.5 milligrams (mg) per square foot of internal surface area, but shall not exceed 20 mg per cylinder regardless of the size of the cylinder. Trailer tubes shall not contain more than 40 mg of oil or residual hydrocarbons. Verification of cleanliness shall be measured by gravimetric or infrared analysis or any
equivalent chemical analysis method.
3.3.3 Moisture content. Cylinders tested hydrostatically and/or internally flushed for cleaning, or cylinders that were tested or flushed with moisture-laden air, shall be immediately dried with hot filtered air or nitrogen to insure the effluent air or gas has a dew point lower than 30 °F
(-1 °C). Immediately after internal drying, the cylinder shall be closed with the designated valve or plug (see table IV).
3.3.4 Internal cylinder preparation. When specified (see 6.2) or as needed, the internal surface of steel cylinders shall be cleared of all mill scale, rust, and oxidation to the reduced metal level by use of an abrasive process such as shot or bead blasting. Aluminum cylinders shall be cleaned free of residue by vapor degreasing or equivalent process.
3.3.5 Internal cylinder preservation. When specified (see 6.2), cylinders closed with a valve
shall be pressurized to approximately 5 psig with dry oil-free nitrogen, type I, grade A or B, class
1, in accordance with A-A-59503, or type I, grade L or better in accordance with CGA G-10.1. The cylinder shall then be tagged at the valve with "PRESERVED WITH NITROGEN GAS".
3.4 Tare weight. The cylinder's maximum tare weight shall be as specified in tables II or III and shall be stamped into the shoulder of the cylinder in a position other than in sequence with another DOT permanent marking (see 3.6.1). The marking shall be displayed as required by CGA TB-15. The marking shall represent the tare weight of the cylinder and valve with an accuracy of 1 percent and shall be displayed in pounds (lb.) and ounces (oz.) unless otherwise specified.
3.5 Delivery date. The cylinders shall be newly fabricated and delivered within one year from the date of manufacture.
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