MIL-STD-1411B
reproducible up to a given predetermined pressure. A cylinder with known expansion characteristics for given pressures is used as a standard to calibrate a hydrostatic test setup.
3.4.2 Calibrated cylinder for ultrasonic examination (UE). The calibrated cylinder used in UE is typically a section of an actual cylinder that is used as a means of providing ultrasonic reflections of known characteristics. This is accomplished by precisely machining specified defects into the selected cylinder that simulate areas of corrosion, isolated pits, line corrosion,
and cracks. Cylinders with these simulated defects are used for the calibration of the UE system.
3.5 Color code. The government has developed its own system of color-coding for its pipeline and compressed gas cylinders under MIL-STD-101. These color identification codes are mandatory along with the name of the gas, as applicable, stenciled longitudinally and opposite on the exterior surfaces of a government-owned cylinder. When vendor-owned cylinders are used, MIL-STD-101 is not mandatory, except for medical gas cylinders, which are always color coded in accordance with MIL-STD-101.
3.6 Composite and fiberglass containers. Composite containers are generally cylindrical in design with enough metal in the sidewalls and heads to withstand the longitudinal stress of internal pressure ratings. The hoop stress of the cylinder is shared with fiberglass wrappings closely adhering to the exterior walls. High strength-to-density ratios are achieved by adding multiple layers of fiberglass filament at controlled tension and bonded into a composite unit with epoxy resin. The whole structure must be protected against moisture penetration to assure a stable design and extended life. The composite must undergo hydrostatic testing intact because removal of the fiberglass reinforcement would destroy the strength designed into the vessel. Fiberglass containers are also manufactured with gas-tight liners in which the liners are not depended upon to ensure the integrity of the pressure vessel.
3.7 Compressed Gas Association (CGA). The CGA is an industry association that is actively involved in preparing safety standards for the handling and shipping of compressed gases. Important CGA pamphlets that are referenced in 49 CFR include CGA C-1 and
CGA C-6. These documents are also referenced in this standard. Other CGA documents are referenced as applicable.
3.8 Compressed gas cylinders. Compressed gas cylinders are closely regulated by specification for construction and test in 49 CFR 178, subpart C. The government uses seamless cylinders in all high pressure applications (above 900 psig service pressures) and in some low pressure applications, such as in chlorine service. Seamless cylinders may be fabricated by billet piercing and plate drawing or by spinning processes in accordance with DOT 3A and DOT 3AA specifications. The government generally uses DOT 4 and DOT 8 cylinders in low pressure applications (not to exceed 500 psig). They are fabricated by welding or brazing shells drawn from plate stock for specified maximum service pressures.
3.9 Compressed gases. Compressed gases are defined as elements or compounds and mixtures of elements or compounds that will be contained in the gaseous state with a gauge pressure of at least 25 psig at 70 °F or 119 psig at 130 °F. If the gas is flammable, the lower pressure limit is 25 psig at 100 °F.
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