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API RP 6HT-2013 pdf free download

API RP 6HT-2013 pdf free download.Heat Treatment and Testing of Carbon and Low Alloy Steel Large Cross Section and Critical Section Components.
1 Scope This recommended practice (RP) may supplement the API equipment specifications for carbon and low alloy steel large cross section and critical components. The recommend practice described herein suggests the requirements for batch-type bath quench and water spray quench-type heat treating practices. 2 Normative References Standards referenced in this specification may be replaced by other international or national standards that can be shown to meet or exceed the requirements of the referenced standard. Manufacturers who use other standards in lieu of standards referenced herein are responsible for documenting the equivalency of the standards. Referenced standards used by the manufacturer may be either the applicable revision shown in Section 2 and herein or the latest revision. When the latest edition is specified it may be used on issue and shall become mandatory six months from the date of the revision. API Specification 6A, Specification for Wellhead and Christmas Tree Equipment ASTM A255 1 , Standard Test Methods for Determining Hardenability of Steel NACE MR0175 2 /ISO 1 51 56 3 , Petroleum and natural gas industries—Materials for use in H 2 S-containing environments in oil and gas production SAE AMS-H-6875 4 , Heat Treatment of Steel Raw Materials 3 Terms and Definitions For the purposes of this document, the following definitions apply. 3.1 critical section components Any part having a cross section thickness with an equivalent round (ER) that exceeds the depth of hardenability of the alloy selected for the part. 3.2 large cross section Any part having a cross section thickness with an equivalent round (ER) greater than 5 in. (125 mm).
The final stage of heat treating carbon and low alloy steel is tempering. This consists of reheating the steel to an elevated temperature, but below where it would again transform into austenite, and letting it soften. This lowers the strength but greatly increases the ductility and toughness of the steel. Tempered martensite exhibits the best combination of mechanical properties (hardness, strength, ductility, toughness, fatigue, etc.) of any of the transformation hardening microstructures. As indicated above, in some cases an additional operation is utilized prior to the austenitizing cycle. This process is called normalizing. Normalizing consists of heating uniformly to temperature at least 1 00 °F (56 °C) above the critical range and cooling in still air to ambient temperature. The treatment produces a recrystallization and gives refinement and uniformity to the grain structure. The redistribution of the elements that occurs during normalizing produces a microstructure that responds to heat treatment in a more uniform manner. For many low alloy steels, normalizing prior to austenitizing can improve the toughness of the material and reduce the tendency toward a banded structure. The mechanical properties of carbon or low alloy steel are dependent on the type, relative amounts, and distribution of the various microstructural components that form in response to a heat treatment. The surface of a part always heats up or cools down at a faster rate than the center. Thus, some variation in microstructures and properties can be expected within the same part, particularly if there is variation in section thickness. The variation in microstructure can be reduced and the desired microstructure obtained by selecting an alloy grade with appropriate hardenability and performing rough machining to near net shape prior to heat treatment. Heat treating is the controlled heating and cooling of a metal to obtain a desired microstructure. Furnaces must be adequately sized for the load to be heat treated. The load must fit entirely within the calibrated working zone. The furnace must be capable of bringing the load up to temperature within a reasonable time period. The furnace must be adequately insulated to prevent heat loss and maintain temperature uniformity. Electric furnaces should have some mechanical means of circulating the air during heating. Furnaces shall have automatic temperature indicating, controlling, and recording devices. The controlling and recording instruments used for heat treating shall posses an accuracy of ±1 % of their full scale range. Furnaces shall be properly calibrated no less than once a year to an internationally recognized standard such as SAE AMS-H-6875 or API 6A. Furnaces shall be capable of maintaining a uniform temperature within the working zone of ±25 °F (±14 °C) of the set point temperature for austenitizing and normalizing and ±1 5 °F (±8 °C) of the set point temperature for tempering. Temperature controlling and recording instruments shall be calibrated at least once every three months. Thermocouples also shall be calibrated or replaced at least once every three months. Equipment used to calibrate production equipment shall have an accuracy of ±0.25 % of full scale range and shall be traceable to an industry recognized industry standard such as the National Institute for Standards and Technology (NIST).

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