S9074-AR-GIB-010/278
8.6.4 Postheating pressure vessels. Circumferential welded joints may be heat treated by uniformly heating a circumferential band having a minimum width of 6 times the material thickness on each side of the joint. Nozzles or other welded attachments for which post-heat treatment is required may be treated by locally heating a circumferential band around the entire vessel with the connection at the center of the band. The band width shall be a minimum of 6 times the material thickness on each side of the attachment. Local postheat treatment for applications other than those listed above will not be permitted without approval by the contracting activity of the detailed procedure. 8.7 Postheating repaired welds in Pressure vessels and piping. Unless otherwise approved, vessels or parts of vessels and piping that have been heat treated in accordance with section 8 shall again be postweld heat treated after repair or alterations have been made. 8.8 Heat treatment of titanium alloys. Protective (inert gas) atmospheres, vacuum, or molten salts can be used when needed, to protect surfaces from oxidizing or reducing reactions, and contamination, and changes in carbon content or embrittlement by undesirable elements such as hydrogen, oxygen, or nitrogen. Refer to MIL-H-81200.
8.8.1 Gases used for protective atmospheres shall be limited to argon or helium meeting the requirements of 30.2.1.
8.8.2 When parts are heat-treated in a vacuum furnace, the furnace shall be purged and backfilled twice before heating with pure argon or helium meeting the requirements of 30.2.1. The furnace may also be backfilled during cooling with the argon or helium. 8.8.3 When salt baths a n used for heat treating, the salt mixtures shall consist mostly of nonchloride oxidizing salts with chloride limited to 2000 ppm maximum. Reducing or nitriding salts shall not be used.
8.9 Temperature Measuring Methods
8.9.2 Locating thermocouples. Thermocouples shall measure the temperature at the anticipated hottest point on the weldment and at the anticipated coolest point. The number of thermocouples provided shall assure complete coverage of the weldment and adequate temperature history. If more than one weldment is to be stress-relieved at the same time. thermocouples shall be attached to each weldment. In no case, however, shall more than six thermocouples be required for a furnace charge. For local heating operations, not less than two thermocouples shall be attached to the weldment. When only two thermocouples we used, they shall be separated by a distance equal to 3 times the width of the weld reinforcement with the weld-centered 8.9.1 Pyrometric equipment. Pyrometric recording equipment shall be provided to indicate the temperature of the weldment and not the furnace except as specified in 8.9.4. The average of the observed temperatures of the weldment is considered to be the temperature of the weldment provided all observed temperatures are within the temperature range specified in Table VI .
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