This article was originally published on December 12, 2022, and updated on June 2, 2025.
Depending on the industry and application, your choice of pressure gauge construction can significantly affect the performance and lifespan of your instrument and your operation. Bourdon tube pressure gauges are known for their reliability and accuracy, making them a common choice for use across process, industrial and OEM markets.
Ashcroft is a pioneer in pressure measurement instrumentation and holds the distinction of acquiring the U.S. patent rights for the Bourdon tube from its inventor, Eugène Bourdon, in 1852. This led to the widespread adoption of the "Ashcroft Gauge" in American industry, including railroads, steam locomotives, maritime vessels, factories and industrial plants. Over the years, Ashcroft has continued to innovate, developing various Bourdon tube constructions to meet the evolving needs of different applications.
Read on to learn about Bourdon tube construction types, how they operate and where they work best. You will find links to additional articles and resources related to pressure gauges with guidance on selecting the most suitable one for your particular requirements.
Bourdon tube requirements and industry standards
Industries such as oil and gas, petrochemical processing and power generation all rely on pressure instruments to provide accurate readings while also withstanding the demanding pulsating pressure and harsh environments. To ensure safety and performance, Bourdon tubes are held to stringent standards outlined in ASME B40.1 for pressure indicating dial-type gauges with elastic elements. These standards focus on:
Bourdon tube fatigue resistance
Fatigue testing, especially under high-pressure pulsation conditions, is one of the most important requirements of ASME B40.1 standards. The testing simulates real-world dynamic pressure conditions in systems such as compressors, hydraulic machinery, and chemical processing lines, which typically range from 20% to 80% of the full-scale range. The minimum standard for a high-quality Bourdon tube should endure at least 1 million pressure cycles without structural failure.
Bourdon tube design requirements
To meet ASME B40.1 standards and ensure a long pressure gauge lifespan, Bourdon tubes must be engineered with:
- Low-stress design: Reducing stress concentrations helps mitigate metal fatigue over time.
- Smooth forming: The tube should have even curves and be free of scratches, notches, or sharp corners, as these can cause stress and lead to early failure.
- Quality materials: High-grade metals such as 316 Stainless steel, Monel® or phosphor bronze are often chosen for their corrosion resistance and mechanical stability under cyclic loads.
Types of Bourdon tube construction
The construction method of a Bourdon tube influences its mechanical properties, fatigue resistance, and overall performance. Understanding the differences between construction types is essential for selecting the appropriate gauge for your application.
1. Seamless Construction
Seamless Bourdon tubes are manufactured by extruding or piercing a white-hot billet into a 2- to 3-inch diameter tube shell, followed by a series of drawing and annealing operations to achieve the desired dimensions and metallurgical properties. While this method can produce high-quality tubes, each processing step introduces a potential for defects.
For instance, the casting and extrusion operations are the most common sources of defects, and drawing and annealing steps can lead to oxidation or excessive grain growth if not conducted under tightly controlled conditions. These metallurgical issues can compromise the mechanical integrity of the tube over time. Some specifications mandate the use of seamless tubing. However, this requirement alone does not guarantee a satisfactory service life. Pressure gauge performance ultimately depends on the manufacturing process and the quality control measures in place.
Common applications: Seamless construction Bourdon tubes are often specified in applications requiring high purity and corrosion resistance, such as in the chemical and pharmaceutical industries.
2. Welded and Drawn Construction
This construction method begins with a metal strip formed into a tubular shape, then welded under inert gas shielding to ensure a clean, strong seam. The tube is then cold drawn, which helps restore strength and refine dimensions that may have been compromised during welding.
Since the tube starts with a strip of consistent thickness, the resulting tube is more uniform than a seamless tube. This enhances the mechanical balance and pressure deflection response. In addition, strip material is inherently less prone to internal defects compared to cast or extruded tubing. A major advantage is that both surfaces of the strip can be visually inspected before forming, allowing for tighter quality control before fabrication even begins.
Although this method yields high-quality tubing, it does not compare to properly made seamless tubing in terms of inherent structural uniformity. The drawing step is essential to restore mechanical properties lost during the welding process.
Common applications: Welded and drawn Bourdon tubes are an excellent choice for general industrial applications where cost, consistency, and moderate-to-high performance are important. These are common in equipment monitoring, plant utilities, and OEM systems.
3. As-Welded Construction
The majority of Ashcroft's pressure gauge Bourdon tubes are manufactured with our patented as-welded construction technique. With this method, the tube is formed from annealed strip material and welded directly into the final shape without additional drawing. The weld is strategically placed in the tube's lowest stress region of the Bourdon tube cross-section on the flat, instead of on the edges to enhance durability and performance. (See Figure 1 below.) This method allows for precise control over wall thickness and stress distribution, resulting in consistent and extended gauge life.
Common applications: Ideal for applications with dynamic pressure conditions, such as in oil and gas, power generation, and water treatment industries.
Figure 1: Ashcroft® Bourdon Tube Construction
4. C-Tubes
Shaped like the letter "C," these tubes flex when pressure is applied, causing the tube to straighten slightly. This motion is translated into a dial reading. C-type tubes are commonly used for pressure ranges between 15 psi and 1,000 psi.
Common applications: C-Tube Bourdon tubes are suitable for general-purpose pressure measurement in HVAC systems, water supply networks, and other low to moderate pressure applications.
Figure 2: Ashcroft® C-Tube Construction
5. Helical and Spiral Bourdon Tubes
Helical and spiral tubes are designed for higher pressure ranges, with helical tubes handling pressures from 1,000 psi up to 30,000 psi, and spiral tubes accommodating even higher pressures. The extended length of these tubes allows for greater deflection and sensitivity.
Common applications: Helical and Spiral construction tubes are used in high-pressure environments such as hydraulic systems, process industries, and research laboratories requiring precise pressure monitoring.
Figure 3: Ashcroft® Helical Tube Construction
Ready to learn more?
Now that you have a better understanding of Bourdon tubes and the applications best suited for each construction type, you can make informed decisions that enhance the reliability and efficiency of your pressure monitoring systems. Regardless of which manufacturing method is used, it is important that the tubing be dimensionally consistent and free of defects. One of the basic requirements for good gauge performance is a Bourdon tube with long life.
For your reference, we have included links to additional articles and resources to help address other questions you may have:
- 10 Steps to Selecting Your Pressure Gauge
- Advantages of Ashcroft Pressure Gauges
- Choosing the Right Pressure Gauge Dial Size
- How To Identify Your Pressure Gauge and Get the Proper Replacement
- How Does Temperature Affect Pressure Gauge Performance?
- How Often Should I Check the Calibration of My Pressure Gauge?
Contact us any time to get your questions addressed by one of our industry experts. In the meantime, download our guide to learn how to avoid common mistakes when choosing a pressure gauge.
