Ask X3What does 49 CFR 178.44 (Specification 3HT seamless steel cylinders for aircraft use) require?
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As an Ask X3 fleet-compliance assistant, here is what 49 CFR 178.44 requires for Specification 3HT seamless steel cylinders for aircraft use:
* Type, Size, and Service Pressure: Cylinders must be seamless steel with a nominal water capacity of not over 150 pounds and a service pressure of at least 900 psig.
* Authorized Steel: You must use uniform quality open hearth or electric furnace steel (specifically AISI 4130, with defined chemical analysis limits and check analysis tolerances), with a maximum grain size of 6 or finer.
* Identification: Material must be suitably identified, but steel stamping of heat identifications cannot be placed on the eventual side wall, and stamping depth must not compromise the minimum wall thickness.
* Manufacture: Equipment and processes must ensure compliance. Cylinders must be free of fissures or weakening defects, with a general surface finish roughness no greater than 250 RMS (machining or treating is allowed to remove defects). Spun closures must have a point of closure at least twice the prescribed wall thickness, and end contours must be hemispherical or ellipsoidal.
* Welding and Brazing: Welding or brazing is strictly prohibited, except for spinning to close the bottom of spun cylinders.
* Wall Thickness: The minimum wall thickness is 0.050 inch, and wall stress at the minimum specified test pressure must not exceed 75% of the steel's minimum tensile strength (and cannot exceed 105,000 psi). Hemispherical bottoms may be reduced to 90% of the sidewall thickness, but not below 0.050 inch.
* Heat Treatment: Completed cylinders must be uniformly heated, quenched in oil or a suitable medium (at a steel temperature not exceeding 1750 °F), and tempered at not less than 850 °F. You must inspect all cylinders using the magnetic particle or dye penetrant method to find quenching cracks; any cylinder with a crack must be rejected and cannot be requalified.
* Openings and Connections: Thread openings must be clean-cut, even, crack-free, and to gauge. Tapered threads must meet NGT length requirements, while straight threads require at least 6 engaged threads, a tight fit, a calculated shear stress of at least 10 times the test pressure, and leak-prevention gaskets.
* Pressure Testing: Every cylinder must pass a water-jacket or direct expansion pressure test to a minimum of 5/3 times the service pressure. The test pressure must hold for at least 30 seconds, and permanent volumetric expansion cannot exceed 10% of the total volumetric expansion at test pressure.
* Cycling Tests: Before initial shipment, cyclic pressurization tests (between roughly zero psig and service pressure at no more than 10 cycles per minute) must be performed without failure on at least three representative design samples, and repeated on one random sample per lot.
* Burst and Flattening Tests: One random cylinder per lot must be hydrostatically burst-tested to destruction. Additionally, a flattening test must be performed on one random cylinder per lot (or on an 8-inch ring cut from the cylinder for lots of 30 or less) using wedge-shaped knife edges.
Source: 49 CFR 178.44.