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API 599:2002 pdf download

API 599:2002 pdf download.Metal Plug Valves-Flanged,Threaded and Welding Ends.
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 ductilily and toughness of the steel Tempered inartensite exhdits 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 100 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 dunng normalizing produces a microstructure that responds to heat treatment in a more uniform manner. For many low alloy steels, normalizing poor 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 microstnctural 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 microstructuros and properties can be expected within the same part, particularly if there is variation in section thickness. The variation In rnicrostructure can be reduced and the desired microstructure ob(ained by selecting an alloy grade with appropriate hardenability and performing rough machining to near net shape prior to heat treatment.
Heat treating Is the oowitroled heating and cooling of a metal to obtain a desired microstructure. Good heat treat practice Involves having the proper equipment and procedures m place to ensure that the necessary control Is maintasied.
6.2 RequIrements for Heat Treating Equipment
6.2.1 Requirements for Heat Treat Furnaces
Furnaces must be adequately sized for the load to be heat treated. The load must fit entirely within the caiibrated 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 mccaIIng, controlling, and recording devices.
The controlling and recording instruments used for heat treating shall posses an accuracy of ±1 % of their fuN 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 ±15°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 10 calibrate production ecjment 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).
When oil quenching as perlormed. only oil formulated by the quencti oil manufacturer specafically for heat treat quenching operations shall be used. Additionally, oil quench media shall be maintained within the manufacturers recommended temperature range. These requirements are necessary to minimize the possibility of oil quench tank tires.
Polymer cjench media shall be maintained within the manufacturers’ recommended temperature range, and the concentration of ttie polymer stiall be routinely monitored and adjusted as necessary.
ray quencti facilities shall consist of one or more high pressure arid high volume spray quench nngs. These spray quench facilities are normally used for quenching cylindrical cross section parts sucti as bar arid tubing. Essential parameters such as nozzle size. jet spacing, standoff, flow rate of quench medium, and traverse rate of component shall be quantified and controlled.


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