D.C. Mun. Regs. tit. 12, r. 12-E1020
Insert a new Section 1020 in the Mechanical Code to read as follows:
Repairs limited to specific types of steel. These rules shall be applicable only to repairs to steel having a known weldable quality, and are further limited to carbon steel having a carbon content of not more than 0.35 percent and to low alloy steel having a carbon content of not more than 0.25 percent. A welder shall not make repairs in a plate with thickness in excess of that permitted under the qualification tests in the ASME Code. A welder shall not make repairs on a material for which the welder is not qualified, or in a thickness of plate that exceeds that permitted under the welder's qualification conditions.
Groove welding. Groove welds shall completely penetrate the material being welded. If possible, welding shall be applied from both sides of the plate, or a backing strip or ring may be used to ensure complete penetration. Welds shall have a convex surface on both sides if applied on both sides of the plates being joined, or on the weld side if welding is applied from one side only. No valleys or undercutting at edges or welded joints shall be permitted. The reinforcement may be chipped, ground or machined off flush with the base material, if so desired, after the welding has been completed.
Defective weld repairs. In making a repair to a weld that has failed in service, the defective weld material shall be removed by chipping or grinding until sound material is reached on all sides. The resulting groove shall be filled as required by the applicable welding procedure.
Carbon steel stress-relieving. In the repair of carbon or low alloy steel, thermal stress-relieving shall be applied to the completed work when required by these rules and when considered necessary by the code official or insurance company inspector. The heat may be applied by any means that will raise the temperature of the material, in the region of the weld, gradually and uniformly, to approximately 1200°F (649°C). In the absence of a more accurate means of determining temperature, reaching a dull "red glow" in daylight will suffice. This temperature shall be maintained for a period of 1 hour/inch (1 hour/25 mm) of thickness of the joined material.
Circumferential joints. For circumferential joints, the area heated shall comprise a band extending completely around the cylinder and having a width on each side of the center line of the weld not less than three times the greatest width of the finished weld.
Nozzles. For nozzles, the heated area shall comprise a circumferential band of the shell of the vessel extending around the entire joint, including the nozzle of the welded attachment, and shall extend at least six times the vessel plate thickness beyond the weld that connects the nozzle or other attachment to the vessel.
Stress-relief cooldown procedure. Upon completion of the stress-relieving operation, the plate shall be allowed to cool at a rate not greater than 500° F (278° C) per hour divided by the maximum thickness of the welded part in inches, until the temperature of 500° F (260°C) is reached, after which normal cooling by exposure to air in a still atmosphere shall be permitted.
Thermal stress-relief alternatives. Where conditions are such that thermal stress relieving as outlined above is inadvisable, another method of stress-relieving acceptable to the code official or insurance company inspector shall be used. When deemed necessary, preheating shall be used.
D.C. Mun. Regs. tit. 12, r. 12-E1020