Orifice plates are on of the most economical devices of measuring flow. SEIKO´s production range extends from standard size orifice plates, through orifice carrier and flange assemblies to customized meter runs.
Typical orifice plate are supplied with a data tab welded to the plate. The majority of plates used in all orificed based devices is the concentric design. The bore is sharp-edged on the inlet and parallel or chamfered on the outlet of the plate. For very low Reynolds Numbers the inlet shall be chamfered (conical or radius). Concical or quarter-Circle Type of orifice plates can measure flow at low velocity and high viscosity and can be used for low-density gases.
With a standard orifice plate, the user must arrange the tapping points in the pipe in the positions requested by the ANSI / ISO standards. This is often problematic for customers, so SEIKO has an orifice carrier assembly available, with the correct tapping points and ring chamber already included. Using a split ring chamber design the orifice can be replaced without replacing the carrier assembly.
Concentric orifice plates are not suitable for dirty fluids. Eccentric and segmental orifice plates are designed such that solids can pass through the bore.
Orifice plates can be designed to fit beween flanges that have ring-type joints (RTJ). The coross section profile of the plate is designed to fit inside the recess of the RTJ flanges and is used as flange sealing.
Orifice plates can be integrated to a complete meter run assembly.
Three types of tapping points are used for orifice plates. D and D/2 taps are located in the pipe wall one pipe diameter upstream of the face of the plate and half pipe diameter downstream from face. Flange taps are located in the pipe flange in a distanced of 25,4 mm(1 in.) distance from upstream face of the plate and same distance from downstream face. Flange taps maybe also designed as corner taps.
Depending on customer requirements, the typicall 1/2 in. or 3/4 in. tappings have a but or socket weld, screw thread or flange connection. Tappings maybe equiped with condensate chambers and shut-off valves.
The standard materials used by SEIKO for orifice plates is stainless steelaccording to ASME A240 316/316L. Other materials can be used as well including Duplex Steel and ASME A182 F91.
The plate thickness is selected based on the application and design conditions, typically between 3 mm (0,12 in.) to 10 mm (0,4 in.).
The flow calculation is performed according to the ISO 5167- Part1.
The typical uncertainty of uncalibrated orifice plates is +/-0,5%.
Orifices have a typicall pressure loss between 40 to 95% of the gernerated differential pressure. The actual permanent loss of pressure depends on the Beta-Ratio.
Orifices can be best used for clean and non-corrosive fluids, if sufficent straight inlet pipe section is available and a higher pressure loss is allowed.