Field Instrumentation

Best Practices for Impulse Tubing Installation

  • Impulse tubing is a critical component in process measurement systems, connecting process pipelines to transmitters and instruments to accurately transfer process pressure. 
  • Proper installation of impulse tubing is essential to ensure accurate readings and prevent common issues like blockages, leaks, and measurement errors. 
  • Impulse tubing plays a crucial role in the accurate transmission of pressure, level, and flow measurements from process points to the instrumentation devices. 
  • Proper installation is key to maintaining system integrity and accuracy.

Below, we explore the comprehensive best practices for installing impulse tubing, with detailed elaboration on critical aspects.

Best Practices for Impulse Tubing Installation 1
  • The material of the impulse tubing should be compatible with the process fluid to prevent corrosion or degradation. 
  • Because stainless steel is resistant to a variety of chemicals, it is frequently used. 
  • Other materials like copper or PVC may be used depending on the specific process fluid.

When selecting the material, consider the following factors:

  • Process temperature and pressure
  • Corrosion and erosion resistance
  • Compatibility with the process fluid
  • Strength and durability

Using the appropriate material ensures the integrity and longevity of the impulse tubing installation.

  • Selecting the appropriate material for impulse tubing is important, Stainless steel is the preferred material for most applications due to its resistance to corrosion and high durability. 
  • For environments with low moisture, carbon steel may be used, but it requires vigilant monitoring to prevent scaling. 
  • Scaling can obstruct valve seats and compromise transmitter accuracy​ 
  • The material choice should also consider the environmental conditions, such as exposure to corrosive substances, extreme temperatures, and atmospheric conditions. 
  • For instance, in offshore applications, stainless steel is preferred to prevent saltwater-induced corrosion

Impulse lines should be as short as possible to minimize the potential for error. Long lines can lead to increased pressure drops, slower response times, and a higher risk of blockages.

  • Impulse tubing should be kept as short as possible. 
  • Long runs can delay response times and increase the risk of resonance frequency issues, which are detrimental in vibratory or seismic environments. 
  • The recommended maximum length is 16 meters; beyond this, electrical or pneumatic transmission is advised​.

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  • The routing of impulse tubing should be planned to avoid any obstructions that may hinder personnel movement or impede maintenance activities. 
  • It should also steer clear of hot environments and areas with a potential fire risk. 
  • Proper routing enhances safety and ensures easy access for maintenance​ activities.

Click here to know more about Instrument Hook-Up Diagrams

Best Practices for Impulse Tubing Installation 2
  • Proper support for impulse tubing is essential to maintain its position and prevent sagging, which can cause measurement errors and physical damage. 
  • Supports such as brackets, clips, or hangers should be strategically placed along the entire length of the tubing. 
  • However, these supports should not be used to fasten other equipment like cable trays​
  • Sufficient clearance should be maintained to allow for any thermal expansion or contraction, which can cause sagging if not properly managed. 
  • Regular inspections can help identify and correct any sagging issues before they lead to significant problems​.
  • Impulse tubing must accommodate thermal expansion and contraction to prevent stress and potential failure. 
  • This can be managed by incorporating bends, elbows, and offsets in the tubing design. 
  • Flexible hoses may also be used in certain applications to absorb thermal movements
Best Practices for Impulse Tubing Installation 3
  • Bends should be preferred over fittings to change direction, as this reduces potential leak points and stress concentrations. Sharp bends should be avoided to prevent kinking, flattening, wrinkling and flow obstruction. 
  • The use of a bending tool ensures precise and controlled bends, maintaining the integrity of the tubing​,
Best Practices for Impulse Tubing Installation 4
  • Impulse lines should be insulated to maintain a consistent temperature and prevent measurement errors due to temperature fluctuations. 
  • Heat tracing can be used to maintain the temperature of the process fluid in the impulse line above its freezing point or below its boiling point.
Best Practices for Impulse Tubing Installation 5
  • The positioning and sloping of impulse tubing are crucial for accurate pressure measurements.
  • For flow measurements, the impulse lines should be connected at the same horizontal level to avoid measurement errors due to the head of fluid in the lines. 
  • For level measurements, the impulse lines should be connected at different vertical levels corresponding to the high and low points of the tank.
Best Practices for Impulse Tubing Installation 6
  • The slope of impulse tubing is critical to prevent the accumulation of liquids in gas lines and vice versa. 

The sloping of impulse lines is also important based on the type of fluid being measured:

  1. For liquid services, the lines should slope downwards from the process connection to the transmitter to allow gas venting. 
  2. For gas/steam services, the lines should slope upwards from the process connection to the transmitter to allow condensate drainage. 
  • The recommended minimum slope is 1:12, which should be adjusted for more viscous liquids.​ 
  • Proper sloping ensures that the impulse lines are self-draining or self-venting, preventing the accumulation of condensate or gasses that can affect the accuracy of the measurements.
  • Maintaining a consistent orientation helps ensure accurate measurements and prevents the formation of air pockets or liquid traps. 
  • This is especially important in applications involving differential pressure (ΔP) measurements, where the impulse lines should be kept close together to avoid temperature-induced pressure differences​.
  • Impulse lines should be installed to avoid trapping gasses in liquid lines or liquids in gas lines. 
  • Trapped gasses can cause measurement errors, while trapped liquids can lead to blockages or freezing issues.
  • Minimizing the number of joints in impulse tubing reduces potential leak points and enhances system reliability. 
  • Where bends are not practical, high-quality fittings should be used. Each fitting introduces a potential failure point, so they should be used sparingly and only where necessary​ 
  • Each joint should be carefully sealed and tested to ensure it does not introduce leaks. 
  • Proper installation techniques and the use of appropriate sealing materials can prevent leaks and maintain system integrity​.
  •  In seismic zones, impulse tubing should be designed to withstand potential movements. 
  • Flexible hoses can be employed to absorb seismic and vibrational movements, provided they meet the design requirements for service life and pressure ratings. 
  • This ensures that the tubing remains intact and functional during and after seismic events​ 
  • To mitigate the effects of vibration, tubing supports should include vibration dampening elements. 
  • Regular inspections can help identify areas where vibrations might cause wear and tear, allowing for timely maintenance and replacements​.
  • Each impulse line and associated valve should be clearly tagged with identification numbers and relevant information. 
  • This facilitates maintenance, troubleshooting, and ensures that each line can be quickly and accurately identified during inspections and repairs​​.
  • Tagging should be consistent and standardized across the installation. Tags should be placed at key points, including the process line root-valve connection, the instrument, and any wall or floor penetrations. 
  • This standardization simplifies maintenance and enhances operational efficiency​
  • Careful handling of tubing is essential to prevent scratches and physical damage, which can lead to corrosion and sealing issues. 
  • Tubing should not be dragged across surfaces that might cause damage. Visual inspections should be conducted to ensure the tubing is free from defects before installation.​ 
  • Cutting and bending tools should be used correctly to avoid introducing imperfections. 
  • For instance, a tube cutter is preferred over a hacksaw to achieve clean cuts without burrs, which can affect the sealing quality​ 
  • Standardizing the design of impulse tubing systems can significantly reduce complexity and maintenance efforts. 
  • A consistent set of design criteria ensures that systems are easier to understand and service, reducing the likelihood of errors during maintenance​
  • Impulse lines should be easy to access for maintenance purposes. 
  • This includes providing adequate space around the lines for technicians to work and using fittings that allow for easy disassembly and reassembly.
  • Separate redundant sensing lines by at least 450mm or use a barrier to prevent single failures from affecting multiple lines. 
  • This redundancy ensures that the system can continue to operate even if one line experiences an issue.
  • Impulse lines should include isolation valves and drains/vents for purging when necessary. 
  • These components allow for the safe isolation of the instrument from the process and the venting of process fluid during maintenance or troubleshooting.
  • Routine inspections and maintenance are crucial for ensuring the longevity and accuracy of impulse tubing systems. 
  • Regular checks for leaks, corrosion, and physical damage can prevent small issues from becoming major problems. 
  • Maintenance schedules should be adhered to, and any issues should be addressed promptly​.

Click here for What are Impulse lines? – Impulse line problems and solutions

  • Standardizing the design and installation of impulse tubing across multiple systems can simplify maintenance and reduce potential issues. 
  • Documenting the installation details, including materials, dimensions, and configuration, helps ensure consistency and facilitates troubleshooting in the event of an issue.
  • Adherence to industry standards and guidelines ensures the installation meets safety, reliability, and performance requirements. 

Some relevant standards include:

  • ASME B31.3: Process Piping
  • ISO 2186: Fluid Flow in Closed Conduits – Connections for Pressure Signal Transmissions between Primary and Secondary Elements
  • ISA 7.4: Instrument Piping Installation
  • API RP 551: Process Measurement Instrumentation

These standards provide detailed requirements for materials, design, fabrication, assembly, and testing of impulse tubing systems.

  • Ensure the installation complies with local regulations and codes, which may vary by region and industry. 
  • This includes environmental, health, and safety regulations that govern the installation and operation of process measurement systems.
  • Confirm that the tubing material matches the specifications for the process fluid and environmental conditions.
  • Check for any visible defects or damage in the tubing and fittings before installation.
  • Ensure the tubing is clean and free from contaminants that could affect the process measurements.
  • Use appropriate tools like tube cutters to ensure clean cuts, and deburr the ends to prevent contamination and ensure proper sealing.
  • Utilize bending tools to create smooth, precise bends, avoiding sharp angles that could cause flow restrictions or stress points.
  • Use high-quality fittings and ensure they are properly tightened to avoid leaks. Follow the manufacturer’s torque specifications for optimal sealing.
  • Conduct pressure tests on the installed tubing to ensure there are no leaks. This can be done using hydrostatic or pneumatic testing methods.
  • Verify that the impulse tubing accurately transmits pressure signals to the instrumentation devices. Check for proper response times and absence of signal damping.
  • Calibrate the connected transmitters and instruments to ensure accurate readings after installation.
  • Maintain detailed records of the installation process, including material specifications, tubing layouts, and testing results. This documentation aids in future maintenance and troubleshooting.
  • Document any changes or modifications made to the impulse tubing system during its lifecycle to keep track of its configuration and history.
  • Ensure that personnel involved in the installation and maintenance of impulse tubing are adequately trained. Training should cover best practices, safety procedures, and troubleshooting techniques.
  • Where applicable, personnel should be certified to industry standards, ensuring they have the necessary skills and knowledge to perform their tasks effectively.
  • Ensure that all personnel wear appropriate PPE, such as gloves, safety glasses, and protective clothing, during installation and maintenance.
  • Follow safety protocols for working in hazardous areas, including the use of explosion-proof tools and equipment when necessary.
  • Establish and communicate clear emergency procedures for dealing with leaks, pressure releases, and other potential hazards.
  • Implement measures to prevent spills and leaks that could harm the environment. Use secondary containment systems where necessary.
  • Properly dispose of any waste materials generated during installation and maintenance, following local environmental regulations.

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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