![]() A better design of ball valve for throttling service is the characterized or segmented ball valve, shown in various stages of opening in the following set of photographs: Simple ball valves with full-sized bores in the rotating ball are generally better suited for on/off service than for throttling (partially-open) service. The following set of photographs shows a hand-operated ball valve in three different positions, from nearly full closed to nearly full open (left to right): When the passageway is parallel to the direction of fluid motion, the valve is wide open when the passageway is aligned perpendicular to the direction of fluid motion, the valve is fully shut (closed). In the ball valve design, a spherical ball with a passageway cut through the center rotates to allow fluid more or less access to the passageway. An important advantage of rotary control valves over sliding-stem designs such as the globe valve and diaphragm valve is a virtually obstructionless path for fluid when the valve is wide-open. Instead of sliding a stem into and out of the valve body to actuate a throttling mechanism, rotary valves rely on the rotation of a shaft to actuate the trim. ISSN: 2347-4718.A different strategy for controlling the flow of fluid is to insert a rotary element into the flow path. Gokilakrishnan G, Divya S, Rajesh R, Selvakumar V (2014)Operating torque in ball valves: a review. Young C, Budynas R (2002) Roark’s formulas for stress and strain, 7th edn. ASME Boiler and Pressure Vessel Code Section VIII, Division II, ASME, New York ASME Boiler and Pressure Vessel Code Section VIII, Division II, ASME, New YorkĪmerican Society of Mechanical Engineers (2004) Rules for construction of pressure vessels, alternative rules. Accessed 10 Sept 2018Īmerican Society of Mechanical Engineers (2017) Materials, part D. ![]() Piping Engineering (2018) Maximum allowable stem torque. International Organization for Organization (ISO) (2007) Pipeline transportation systems: pipeline valves, 2nd edn. ISO, GenevaĪmerican Petroleum Institute (API) (2014) Specification for pipeline and piping valves, 24th edn. International Organization for Organization (ISO) (2011) Petroleum and natural gas industries: mechanical integrity and sizing of actuators and mounting kits for pipeline valves, 1st edn. The stem key material is assumed to be the same as the stem material in this paper, which is UNS S41500, ASTM A182 F6NM before changing the stem material and Inconel 718 in case of upgrading the stem material.Īmerican Petroleum Institute (API) (2012) Standard for actuator sizing and mounting kits for pipeline valves, 1st edn. Changing the stem material will increase the stem torque values in other parts of stem including the rounded part with keys, the circular part, and stem keys to 468,958 Nm, 2,517,112 Nm, and 1,621,406 Nm, respectively. The MAST value in the rectangular area in Inconel 718 has been increased to 332,579.2 Nm, which is more than the actuator torque. Improving the material to Inconel 718 increases the MAST in all four parts of the stem which are rectangular area, rounded part with keys, circular part and stem keys. The average yield strength of this material is 130 Ksi equal to 896.3 N/mm 2. The alternative is to change the stem material from ASTM A182 F6NM, 13%Cr 4%Ni to Inconel 718. The second solution, which is more expensive, improves the MAST of the stem in all four sections of the circular section with stem keys, stem keys, the circular section, and the rectangular section. Two solutions are proposed in this paper one is to increase the rectangular section diameter, and the second is to upgrade the material to a higher strength option such as Inconel 718. The result of this calculation shows that the MAST in rectangular section of stem is less than the actuator torque. This paper provides a formula for calculation of MAST in different sections of a valve stem installed on an oil export pipeline. The actuator is a component or machine installed on the valve that is responsible for moving (e.g., opening or closing) the valve. The important point is that the actuator maximum output torque/thrust based on the maximum supply voltage or operating pressure generated by the actuator should not exceed the valve MAST at any point of travel. The valve train consists of all parts of the valve drive between the operator and closure member, including the closure member but excluding the valve operator such as the gearbox. Maximum allowable stem torque/thrust (MAST) is defined as the maximum torque/thrust that can be applied to the valve train without risk of damage, as defined by the valve manufacturer/supplier.
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