Industrial Thermowells: Sometimes Taken for Granted, but Critically Important

Thermowells come in a wide variety
of shapes, materials, and sizes.
(Courtesy of Ashcroft)

One of the most important accessories for any temperature-sensing element is a pressure-tight sheath known as a thermowell. This may be thought of as a thermally conductive protrusion into a process vessel or pipe allowing a temperature-sensitive instrument to detect process temperature without opening a hole in the vessel or pipe.

Thermowells are critically important for installations where the temperature element (RTD, thermocouple, etc.) must be replaceable without de-pressurizing the process.

Thermowells may be made out of any material that is thermally conductive, pressure-tight, and not chemically reactive with the process. Most thermowells are formed out of either metal (stainless steel or other alloy) or ceramic materials.

A simple diagram showing a thermowell in use with a temperature sensor (RTD) is shown here:

Typical RTD thermowell installation.

As useful as thermowells are, they are not without their caveats. All thermowells, no matter how well they may be installed, increase the first-order time lag of the temperature sensor by virtue of their mass and specific heat value. It should be intuitively obvious that a few pounds of metal will not heat up and cool down as fast as a few ounces’ worth of RTD or thermocouple, and therefore the addition of a thermowell to the sensing element will decrease the responsiveness of any temperature- sensing element. What is not so obvious is that such time lags, if severe enough, may compromise the stability of feedback control. A control system receiving a “delayed” temperature measurement will not see the live temperature of the process in real time due to this lag.

For more information on thermowells, contact Mead O'Brien by visiting https://meadobrien.com or by calling (800) 892-2769.

Five Important Criteria in Applying Pressure Gauges

Process pressure gauge.
(Ashcroft)

Pressure gauges are installed in countless industrial and commercial applications around the world. From hygienic pharmaceutical process lines, to the most unpleasant and hostile areas in chemical, power, and food processing plants.

While there are millions of possible combinations of shapes, sizes, options and materials, pressure gauges all share the five  following application criteria, required for safe use and long product life.

Diaphragm seal.
(Ashcroft)

1 - Process Media Properties: Media that is corrosive, sludgy, or that can solidify is a potential problem for pressure gauges. In non-corrosive, non-clogging media applications, a direct connection without intermediate protection can be applied. For process media that could potentially clog or chemically affect the gauge's wetted parts, a diaphragm seal should be used.

2 - Process Media Temperature: Very hot media, such as steam or hot water, can elevate the gauge's internal temperature leading to failure or an unsafe condition. For high temperature applications, the use of a "pigtail siphon" or diaphragm seal is recommended. Siphons act as a heat sink and lower the exposure temperature. Diaphragm seals isolate the gauge from the higher temperatures.

Pigtail siphon.

3 - Ambient Operating Temperature and Environment: It is important to know the ambient environmental rating for any process instrument. Elevated ambient temperatures, moisture, vibration, and corrosive atmospheres can all affect accuracy, calibration, and safety. Choose the proper housing and mechanism materials if oxidizing or reducing atmospheres exist, and consider the addition of ancillary devices, such as remote diaphragm seals to physically relocate the gauge away from the hostile area.

Snubber

4 - Severe Pressure Fluctuations: In applications where dramatic line pulsations or strong over-pressure conditions are a possibility, the use of pressure restrictors, snubbers, or liquid-filled gauges will extend the service life of the pressure gauge.

5 - Mounting: Pressure gauges are standardly available with bottom (radial) and back connections. NPT (National Pipe Thread Taper) threaded connections are generally the standard. Many other process connections are available though, such as straight threads, metric threads, and specialized fittings. Make sure you know how the gauge is being connected. When mounting, pressure gauges should be almost always be mounted upright.

For more information about pressure gauges, contact Mead O'Brien by visiting https://meadobrien.com or by calling (800) 892-2769.

Limitorque Fluid Power Systems (LFPS)

Limitorque Fluid Power Systems is a group of modular scotch yoke fluid power actuators designed to deliver maximum torque with the lowest possible displacement and overall size. These heavy-duty, fluid-powered valve actuators and control systems are design primarily for the oil and gas industry. The group is categorized into three major sub-groups:

• Gas Powered Actuators - The Limitorque LDG direct gas actuator is designed to operate on high pressure pneumatic supply, including pipeline gases, nitrogen and any other equivalent high pressure source.
• Hydraulic Actuators - LHS and LHH are Limitorque’s range of hydraulic, quarter-turn, scotch yoke actuators. Designed to meet or exceed the most current and stringent safety and reliability standards for application in the oil and gas industry LHS and LHH are suitable for on/off and modulating control of all quarter-turn valves. 
• Pneumatic Actuators - Limitorque’s LPS and LPC are pneumatic quarter turn scotch yoke actuators, featuring a robust design suitable for heavy duty services, and among the longest design lifespans and maintenance intervals in the industry.

Download the Limitorque Fluid Power Systems PDF here.

Mead O'Brien
www.meadobrien.com
(800) 892-2769

Industrial Boiler and Burner Limit Control Switches

Ashcroft Limit Control Switch

Designers and manufacturers of industrial boilers are focused on meeting regulatory and safety requirements when developing highly efficient burner management systems (BMS). BMS are responsible for startup, operation and shutdown of a burner boiler systems. BMS monitor temperature, pressure and flow and employs safety shutoffs to shut down the burner boiler if an unsafe condition occurs.

The following white paper describes safety standards for boilers and burners relating to pressure switches and controls.

Read the embedded document below, or you can download your own PDF copy of "Industrial Boiler and Burner Limit Control Switches"  from the Mead O'Brien website here.

Industrial Boiler and Burner Limit Control Switches from Mead O'Brien, Inc.

Measuring the Flow of Vaporized Liquid Natural Gas

Veris Accelabar installed on vaporized liquid natural gas line.

Application

A liquid natural gas plant in the Midwest needed to measure gas flow to heaters that vaporize LNG to gaseous natural gas for use during peak periods in the winter season. The company stores LNG in two 12,000,000-gallon tanks and uses gas-fired heaters to vaporize it as required to meet customer demand. For most of the year demand is low (1,000 SCFH); however, during the coldest winter months gas consumption jumps to 60,000 standard cubic feet per hour (SCFH) in a 3” sch 40 line at 80 psig/70° F.




Problem

The plant must account for the gas usage over the entire range as it is part of the operating cost during LNG vaporization, as well as when it is used for plant heating. The customer could not find one meter to accommodate the entire range accurately. The plant had attempted to measure the flow rate with a Roots turbine meter sized for the maximum flow rate, but could not get accurate flow readings at the low end of the measurement range, making it impossible to determine actual usage during the off-peak periods. In addition to accuracy limitations, turbine meters have moving parts that wear and require expensive maintenance. The customer’s operating cost was estimated and charged against the bottom line. In addition, as you can see from the photo, there was no straight run available which hindered a conventional meter’s ability to perform accurately.

Accelabar

Solution

A Model AF 3” 150-H-M Accelabar was installed immediately downstream of a pipe reduction, control valve and pressure regulator. The Accelabar had two Foxboro IDP50 high accuracy DP transmitters directly mounted to the top of the Accelabar sensor. Stacked outputs were required to accommodate the wide turndown in DP of 308.2” w.c. at max and 0.08” w.c. at min.

Results

The Accelabar performed as advertised with ±0.75% accuracy over the entire range of 1,000 to 60,000 SCFH—a flow turndown of 60:1. Because the Accelabar and transmitters have no moving parts to wear or seize, maintenance is minimal. The LNG supplier has found that the flow metering system is user friendly and easy to operate, especially since DP flow measurement is one of the most easily understood of any flow measurement technology available. To the LNG provider, this translates into improved material accountability and lower operating costs to increase profitability.

Reprinted with permission by Veris, a division of Armstrong International.

Configuration and Setting the Schneider Electric / Foxboro IMT30A Magnetic Flow Signal Converter

This video below provides instruction on setting the Schneider Electric / Foxboro Model IMT30A.

The electromagnetic signal converter IMT30A is a used for measuring volumetric flow in various kinds of applications that can be found in the water industry and food and beverage processing. The IMT30A can be used together with Foxboro flow sensors 8400A, 8500A, 9500A, 9600A and 9700A with outputs representing measured values for flow, mass and conductivity.

Industries

• Water & Wastewater
• Food & Beverage
• Heating, Ventilation & Air Conditioning (HVAC)
• Agriculture
• Steel

Applications

• Water and wastewater treatment Water distribution network Irrigation installation
• Water abstraction
• CIP cleaning stations

https://meadobrien.com
(800) 892-2769

Limitorque Fluid Power Systems (LFPS)

Limitorque Fluid Power Systems (LFPS) is the Flowserve Limitorque division that builds fluid power actuators, specifically pneumatic, gas, and hydraulic scotch yoke design cylinder valve actuators. These are used on larger, higher torque requirement valves primarily applied in the oil and gas industries.

GAS POWERED ACTUATORS

The Limitorque LDG direct gas actuator is designed to operate on high pressure pneumatic supply, including pipeline gases, nitrogen and any other equivalent high pressure source. Based on Limitorque’s high efficiency scotch-yoke modules, the self-contained system includes both the gas powered actuation unit and the high pressure gas control circuit. This makes it a robust and efficient way of providing reliable pipeline valve automation, even when no external motive power supplies are present. Limitorque’s advanced design criteria together with the full pressure rated controls allow higher torque output within a smaller dimensional envelope, thus reducing gas use and exhaust, and limiting pipeline product waste and environmental impact.

HYDRAULIC ACTUATORS

LHS and LHH are Limitorque’s range of hydraulic, quarter-turn, scotch yoke actuators. Designed to meet or exceed the most current and stringent safety and reliability standards for application in the oil and gas industry LHS and LHH are suitable for on/off and modulating control of all quarter-turn valves. Limitorque scotch yoke actuators deliver reliable torque ranges up to 300 kNm (221 268 ft-lb) in a low displacement, compact dimensional envelope with a maximum allowable working pressure (MAWP) of 207 barg (3000 psig) for the LHS series and 345 barg (5000 psig) for the LHH series.

PNEUMATIC ACTUATORS

Limitorque’s LPS and LPC are pneumatic quarter turn scotch yoke actuators, featuring a robust design suitable for heavy duty services, and among the longest design lifespans and maintenance intervals in the industry. Limitorque’s high torque LPS (up to 500000 Nm / 369,000 ft-lbs) and compact LPC (up to 5500 Nm / 4056 ft-lb) are the actuators of choice for effective on/off, modulating and control applications of quarter-turn valves in all general and protective services, in the most severe environments.

For more information on Limitorque Fluid Power Systems, contact Mead O'Brien by visiting https://meadobrien.com or calling (800) 892-2769