To prevent inefficient fuel usage, moisture, corrosion, and to meet official safety regulations the oil and gas industry has a number of critical requirements to the process. Differential pressure is one extremely important part of measuring gas flow through pipelines, pressure at compressor stations, filter, and many other applications.
Furthermore, fluctuations in the temperature have a big influence on cost and performance. Ametek Calibration specializes in producing test and calibration equipment for utilization throughout the oil and gas industry. From high accuracy dry block temperature calibrators to intrinsically safe digital test gauges and data recorders, Ametek Calibration produces a wide scope of equipment to aid many applications.
Gas Distribution - Compressor Stations
Situated around every 30 to 60 miles / 50 to 100 km along each pipeline, compressor stations boost the pressure which is lost through the friction of the natural gas moving through the steel pipe. The equipment can be started or stopped from a central control room as many stations are automated. The control stations can remotely operate shut-off valves and their operators store detailed data on every station.
Gas Distribution - Processing Plants
To generate pipeline quality dry natural gas, processing plants clean the raw natural gas by separating contaminants such as carbon dioxide, water, and hydrogen sulfide. A fully operational plant produces natural gas that can be employed as fuel by commercial, residential, and industrial customers.
Gas Distribution - Gathering Systems
Gas from a well is collected using gathering lines, which are like branches on a tree, they get larger as they become closer to the central collection point. The pressure products from Ametek Calibrations are employed to measure and test temperatures and pressures throughout the varying lines.
Gas Distribution - The Transmission System
The transmission system transports large amounts of natural gas thousands of miles from the gathering systems to local distribution companies, in a similar way to the nation's interstate highway system for cars. The pressure of gas in each part of line normally ranges between 200 to 3000 psi / 30 to 200 bar, depending on the type of area in which the pipeline is operating. A number of measurements are carried out on transmission pipelines.
Gas Distribution - Gate Stations
When the natural gas reaches a local gas utility, it typically passes through a gate station, which serves three purposes:
- The pressure in the line from transmission levels is reduced (200 to 3000 psi / 20 to 200 bar) to distribution levels (0.25 to 900 psi / 20 mbar to 60 bar)
- An odorant is added
- The flow rate of the gas is measured to establish the amount being acquired by the utility
Gas Distribution - Reduction Stations
Reduction stations/units exist throughout the network, as the gas distribution system is based on the fundamental principle of gas from high to low pressure sections. The temperature of natural gas decreases by about 65% when the pressure decreases by 88%.
This temperature decrease can cause operational (freezing valves) and quality problems. Measuring temperature and pressure throughout the process is paramount to controlling this.
Gas Distribution - Maintenance of the Distribution Grid and System
A variety of tests are performed before any gas is put into the systems, leak testing is one of the major ones, found throughout the grid with varying pressure ranges. Data logging of these pressure tests is common.
Gas Distribution - Metering Systems
From high-end gas correctors, to simple mechanical domestic types, for custody transfer to other distribution companies, or for larger business customers to calculate the energy supplied instead of the amount of gas. Correctors contain a thermometer, a volume meter, and a pressure meter. Values from each of these are sent to the calculator. Each part can be calibrated individually, and usually pressure and temperature can be calibrated on-site.
Gas Distribution - The Distribution System
Distribution lines, or "mains," are parts of the pipe which operate at different pressures using regulators, some of which are controlled remotely to control the pressure. The gas utility's central control center monitors flow rates continuously to ensure that gas reaches each customer with sufficient pressure and flow rate to fuel appliances and equipment. They also ensure that pressures stay under the maximum for each segment.
Gas Distribution - Service Lines
Using a service line, natural gas from the mains is passed into a business or home. The gas usually flows between 60 and 0.25 psi / 4 bar to 20 mbar. When the gas reaches the meter of a customer, it may pass through another regulator to decrease its pressure to below 0.25 psi / 20 mbar, if needed.
Transmitter/Flow Computer Calibration and Validation
Using transmitters and flow computers, static and differential pressures, along with temperature, are frequently measured to calculate flow. Calibration and validation are required to ensure their accuracy.
The nVision permits a user to complete pressure calibration and validation of a differential transmitter, temperature calibrators from Ametek Calibration calibrate the temperature component, and their ASC-400 and CSC201 simulate the signal to the flow computer.
Tank Level (Storage)
Natural gas producers store their inventory in tank farms, holding tanks, and underground caverns. An accurate temperature and pressure measurement of each storage vessel generate a record of their inventory on-hand. The nVision provides a simple and quick method to record accurate pressure measurements, and the RTC measures and calibrates temperature.
Found both offshore and onshore, wellheads supply the pressure interface for both production and drilling equipment. Ametek Calibration delivers unmatched accuracy to test and record pressures on the wellhead up to 15 000 psi / 1000 bar.
Chart Recorder Replacement
The nVision is an exceptional replacement for aging chart recorders. It provides better accuracy in a lighter, smaller, and more robust package, whilst saving data in an electronic format. It is thought that one 10 000 psi nVision could replace most chart recorders, since chart recorders do not usually have more than 1 psi resolution.
An orifice plate is utilized to decrease pressure, restrict flow, or to measure flow. The nVision can measure and record differential pressure at high static pressure directly across an orifice plate.
To characterize the pump, the nVision monitors inlet and outlet pressures and records from two pressure sensors, up to 15 000 psi, as quick as 10 times per second.
To stimulate production a pressurized fluid or gas is injected into a well. Operators observe injection pressure and wellhead pressure simultaneously to optimize flow. The nVision can record two pressures at the same time at up to 10 times per second, and store 500,000 readings.
Tubing and Casing Pressure Graphing
Operators must record the tubing and casing pressure of a well simultaneously to perform the correct adjustments to wells. Using Ametek Calibration’s reference recorder, these tests can be completed on the surface, to save both money and time.
Hydrostatic Testing/Leak Testing
By pressurizing a liquid and observing if there is a pressure loss, pipelines and tanks are tested for their strength and leaks. Both the nVision and XP2i record the pressure test and generate a digital record. Using the nVision, pressure and temperature can be recorded simultaneously.
Accuracy is extremely important when transferring oil and gas from one company to another. The high accuracy PKII is the de-facto standard employed in gas measurement. The nVision also meets the custody transfer required accuracy of ± 0.025%. Temperature is also a crucial factor in precise oil flow calculations. The RTC-157, with its active dual zone heating technology, together with a reference probe is capable of accuracy to ± 0.07 °F (0.04 °C).
Using the special custom engineering unit, Ametek Calibration’s equipment can be employed to directly read in ft/lbs, N m, or any other customized unit.
Use the nVision to record pressure, current, temperature, and voltage at up to 10 readings per second. The battery-optimizing, Ultra Low Power (ULP) mode, permits an entire year of continuous recordings on one set of batteries.
General Calibration and Maintenance
Pressure gauges, transducers, electronic sensors, pressure and temperature transmitters, regulators, valves, and pressure and temperature switches must be checked and calibrated periodically. The nVision provides numerous modules and special test modes for fast, easy verification.
The nVision can measure and record differential pressure at high static pressure directly across a filter. A customer can save money by only replacing filters when needed by estimating a filter's relative age and wear using this method.
Direct Pressure Measurement
Numerous places throughout oil and gas facilities need direct measurement of pressure. This could involve permanently mounting an instrument or completed periodic checks. Ametek Calibration provides intrinsically safe instrumentation which supplies the accuracy and flexibility to measure pressure confidently.
Barometric Pressure Measurement
Applications such as calibrating absolute pressure gauges, will require the reference gauge to read directly in barometric pressure. The nVision, with the optional barometric reference will indicate pressure in the absolute scale. You can even toggle between absolute pressure and gauge using the same device.
Rotary Gas Meters
In order to monitor their accuracy, rotary gas meters need periodic differential pressure testing. The nVision records low differentials, at any static pressure. nVision is the only cost effective option at high static pressure. The dampening function in DP mode stabilizes the pulsating output from a rotary meter.
Deadweight Tester Replacement-Augment
The nVision provides the accuracy of a deadweight tester in a much lighter and more portable package. It also requires no special training, is unaffected by temperature or gravity, and is less expensive to calibrate.
Relief Valve and Rupture Disc Testing
Pressure safety valves and rupture discs shield pressure vessels and piping systems from excessive internal pressure. Periodic testing and adjustment of this equipment is crucial to maintain overall safety. Ametek Calibration equipment catches the maximum pressure at high speeds (up to 10 readings per second) to complete and document the tests.
Modernization in plants has resulted in thermocouple and RTD sensors being employed throughout in a variety of sizes and lengths. It wouldn’t be unusual to see over 1000 in a single plant. Depending on accuracy class all of these sensors need to be calibrated one or twice a year.
In the past sensors were calibrated in oil baths, but due to limited temperature ranges, complicated and slow testing procedures, and hazardous liquids, dry block calibrators are replacing them with quick, clean, accurate instruments. Ametek Calibrations line of dry block calibrators provides a wide scope of temperature calibration equipment to calibrate these sensors.
Maintenance of Calibration Standards and Test Equipment
Test equipment and portable calibrators require periodic checks and calibration. Having local standards on site for calibration of these instruments provides savings in cost and downtime of instruments: calibrate the field instruments locally and then only send the standard in for regular calibration. The HPC40 Series and nVision are light-weight, small, instruments that have the accuracy needed to calibrate pressure in the field or in a lab.
The RTC and PTC series are excellent standards for the verification and calibration of handheld thermometers. The DTI Series with an STS may be used as high accuracy temperature references. The AMC-910 offers capabilities for local calibration of electrical signals and with the APM CPF and an STS probe may be used for pressure and temperature calibration.
There is no better pressure standard than a deadweight tester for calibrating pressure instruments and the deadweight testers from Ametek Calibration are designed to be highly accurate but durable.
This information has been sourced, reviewed and adapted from materials provided by AMETEK Sensors, Test & Calibration.
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