A LACT (Lease Automatic Custody Transfer) unit is an arrangement of skid mounted products and piping designed to make a system that will accurately measure the quality and quantity of the liquid passing through it.
It is used to automatically transfer the custody of a liquid from one responsible party or location to another. And most important, all the components used to measure the quantity and quality of the fluid must be able to be checked for proper and accurate operation. We can compare the operation of a LACT Unit to a cash register. Like the cash register a LACT Unit must be able to prove to the party receiving the material that the information on the product supplied by the seller, is correct.
Some of the factors that effect the design of a LACT Unit are; type of liquid to be measured, flow rate, viscosity, temperature, pressure, and location.
The type of liquid and its chemical components will determine such things as; the operating range of the meters, use of NACE materials, type of sampler and sample container, and pipe and flange material.
The flow rate will determine the pipe and meter size, and the size of many of the components. The piping must be designed to provide for minimum pressure drop across the LACT Unit.
This is usually accomplished by limiting the maximum velocity of the fluid in a LACT Unit to 12 to 14 feet per second. There is also a minimum velocity, which must be maintained for the proper operation of the static mixer.
The static mixer is placed upstream of the liquid sampler and water content monitor. The minimum velocity, for the proper operation of the static mixer is usually 3 ft. per second.
The viscosity of the measured fluid will affect the pipe sizes of the LACT Unit, but the main effect of the fluid viscosity is on the flow meter. Fluids with a higher viscosity will require the use of a Positive Displacement type meter, while fluids with a low viscosity can be measured with a Turbine Meter. Follow the manufactures recommendations on viscosity when selecting the meter.
The temperature of the measured fluid will determine if special components are required on the LACT Unit. For example if the temperature is high, special seals will be needed on many of the components like the meter, sampler, water monitor, valves etc. If the temperature of the measured fluid is low special alloy materials may be needed in the piping and components.
The pressure of the liquid in the LACT Unit will determine the pipe, and its wall thickness, the ANSI rating of the flanges, and the pressure rating of the various other components. Most LACT Units are built with 150# ANSI flanges, but it is not uncommon today to see pressures requiring 300# and 600# ANSI flanges. If at all possible try to place the LACT Unit so 150# flanges can be used. The cost of the LACT and prover goes up when 300# and 600# pressure rated ANSI flanged components are used.
L.A.C.T. Units are used on-shore and offshore, in wet and dry climates and in cold and hot locations. The location of the L.A.C.T. Unit will determine the use of heat tracing and insulation, the protective coating, and if the L.A.C.T. Unit will need to be placed in a building for protection from the elements. It is not unusual for L.A.C.T. Units to be placed in buildings for ease of maintenance and protection from the elements. After all the L.A.C.T. Unit is the cash register.
LACT Unit Components
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