Selecting the right tube wall thickness and pressure rating is one of the most consequential decisions in any industrial piping or tubing project. An undersized wall leads to premature failure; an oversized one wastes material, adds weight, and increases cost. Between those extremes sits a precise engineering sweet spot that depends on operating pressure, temperature, material properties, the corrosion environment, and the applicable design code. This guide walks through the key factors, formulas, and practical considerations that engineers and procurement professionals need to specify industrial tubing correctly. Whether the application involves pneumatic systems, fluid transfer, or chemical processing, the principles covered here apply across materials and industries. If you are already looking for specific tube products, explore the full range of industrial tubes to see what is available in different materials and dimensions.
Key Factors That Determine Wall Thickness Requirements
Wall thickness is not a single number pulled from a catalog. It is the result of balancing several interacting variables: internal pressure, external loads, operating temperature, corrosion environment, dimensional tolerances, and the design code governing the application. Getting any one of these wrong can compromise the entire system.
The starting point is always the tube’s outer diameter (OD) and the internal pressure it must contain. A larger OD at the same pressure demands a thicker wall. But pressure is only part of the picture. External forces such as bending loads, vibration, vacuum conditions, and mechanical impact all add to the required thickness. Temperature matters too, because elevated temperatures reduce the yield and tensile strength of most materials, meaning the wall must be thicker to maintain the same pressure capability.
Corrosion Allowance
In environments where the tube contacts corrosive fluids, gases, or abrasive media, the design must include a corrosion allowance. This is additional wall material beyond what the pressure calculation requires, sized to compensate for metal loss over the tube’s intended service life. The allowance is calculated by multiplying the expected corrosion rate by the design life. In chemical plants and refineries, carbon steel components commonly carry a corrosion allowance of around 3 mm.
For plastic tubing, corrosion in the traditional metallic sense does not apply, but chemical compatibility and UV degradation play an analogous role. The tube material must resist the specific chemicals it contacts, and wall thickness may need to account for gradual material softening or swelling over time.
Tolerance and Minimum Wall Considerations
Manufacturing tolerances directly affect how much wall thickness is actually present in a delivered tube. Seamless metal tubes typically carry a wall thickness tolerance of plus or minus 10%, while seamless pipe can have an under-tolerance as large as 12.5%. This means a tube specified at 2.0 mm wall could measure as thin as 1.75 mm at any given point. Calculations should always account for this by using the minimum expected wall, not the nominal value.
Plastic extrusion tubing generally achieves tighter tolerances than metal pipe, but the same principle applies: always verify the manufacturer’s stated tolerance range and design to the minimum wall that could be delivered.
How Pressure Ratings Relate to Material Properties
A tube’s pressure rating is fundamentally a function of its material strength, its dimensions, and the temperature at which it operates. Two tubes with identical OD and wall thickness will have very different pressure ratings if one is made from polyamide and the other from cross-linked polyethylene, because their yield and tensile strengths differ.
For metallic tubing, standards like ASME B16.5 pressure-temperature tables organize materials into groups and publish allowable pressures at specific temperatures. As temperature rises, tensile strength falls, and the allowable working pressure drops accordingly. A conservative rule of thumb for metal pressure vessels is to apply a 15 to 25 percent derating when operating temperatures climb well above ambient.
For plastic tubing, the relationship between temperature and pressure capability is even more pronounced. Thermoplastics soften progressively with heat, so a tube rated for 10 bar at 20°C may only handle 4 or 5 bar at 60°C. Material datasheets from the resin manufacturer are the authoritative source for these derating curves, and they should always be consulted rather than relying on generic assumptions.
The key takeaway is that a pressure rating is never a fixed number. It is always conditional on temperature, and specifying one without the other is incomplete. Every tube specification should state both the maximum working pressure and the temperature at which that rating applies.
Calculating Safe Working Pressure From Tube Dimensions
The most widely used formula for calculating the burst or working pressure of a tube from its dimensions is Barlow’s formula: P = (2 × S × t) / (D × SF), where P is the maximum allowable pressure, S is the material’s yield strength, t is the wall thickness, D is the outside diameter, and SF is the safety factor. Safety factors typically range from 1.5 to 10, depending on the application and governing code.
This formula provides a useful starting estimate, but it assumes ideal conditions: room temperature, no corrosion, no external loads, and a perfectly uniform wall. In practice, several adjustments are necessary:
- Subtract corrosion allowance from the wall thickness before entering it into the formula
- Apply temperature derating if operating above ambient conditions
- Account for manufacturing tolerance by using the minimum expected wall thickness
- Include weld joint factors for welded tubes, which reduce the effective strength of the wall at the seam
For applications governed by ASME B31.3 (process piping), the pressure design thickness formula is more detailed: t = PD / [2(SEW + PY)], where E is the quality factor, W is the weld joint strength reduction factor, and Y is a coefficient that varies by material and temperature. The minimum required thickness then adds the corrosion, erosion, and mechanical allowances on top of this calculated value.
For plastic tubing, Barlow’s formula still applies conceptually, but the material strength values used must reflect the long-term hydrostatic strength (often called the Minimum Required Strength, or MRS) rather than the short-term tensile strength. Plastics creep under sustained load, so a tube that withstands a given pressure for one minute may fail at the same pressure after thousands of hours. Design standards for plastic pressure tubing account for this by building the long-term creep behavior into the rated strength.
Matching Specifications to Real-World Application Demands
Correct tube specification goes beyond calculating a wall thickness and pressure rating on paper. The specification must match the full range of conditions the tube will encounter in service, including chemical exposure, temperature cycling, mechanical handling, and regulatory requirements.
Application-Specific Considerations
Different industries impose very different demands on tubing. Consider these examples:
- Pneumatic systems: Require tubing with consistent OD for reliable fitting connections, good flexibility for routing, and pressure ratings that include a safety margin above the system’s maximum operating pressure
- Chemical transfer: Material compatibility with the transported fluid is the primary concern, followed by temperature resistance and pressure capability
- Food and pharmaceutical: Regulatory compliance (FDA, EU 10/2011) and cleanability often dictate material choice, with wall thickness selected to meet pressure needs while maintaining flexibility
- Hydraulic systems: High working pressures demand thick walls and high-strength materials, and the tube must resist fatigue from pressure cycling
For gas service, a thicker wall is generally required compared to liquid service at the same pressure, because gas stores significantly more energy and a failure releases it far more violently. Many tubing manufacturers publish separate pressure ratings for liquid and gas service for exactly this reason.
Product Comparison: Three Common Industrial Tube Materials
The following comparison illustrates how material choice affects the key specification parameters for industrial tubing:
- ToppTube™ PA12P40 (Polyamide 12, plasticized): Offers excellent chemical resistance, good flexibility at low temperatures, and strong resistance to stress cracking. Suited for pneumatic lines, fuel systems, and environments where the tube must flex repeatedly without fatigue. Polyamide 12 maintains its mechanical properties across a wide temperature range.
- ToppTube™ PE-HD (High-Density Polyethylene): Lightweight, chemically inert to a broad range of acids and bases, and cost-effective for large-diameter or high-volume applications. PE-HD has lower pressure capability than PA12 at elevated temperatures but excels in water transport, irrigation, and general industrial fluid handling.
- ToppTube™ PEX (Cross-Linked Polyethylene): The cross-linking process gives PEX significantly higher temperature and pressure resistance than standard PE-HD. PEX tubing maintains its strength at elevated temperatures and resists creep, making it well suited for hot water systems, radiant heating, and applications where sustained pressure at higher temperatures is required.
Choosing among these materials requires weighing the operating temperature range, chemical environment, required flexibility, and pressure demands of the specific application. A tube that performs well in one context may be entirely wrong for another.
Common Specification Mistakes and How to Avoid Them
Specification errors are among the most frequent root causes of tubing failures in industrial installations. Most of these mistakes happen before a single tube is cut or installed. Catching them early saves time, money, and risk.
Dimensional and Tolerance Errors
One of the most common mistakes is confusing pipe dimensions with tube dimensions. Pipe is ordered by nominal pipe size (NPS) and schedule, while tube is ordered by exact outside diameter and wall thickness. Mixing them up results in wrong flow areas, incompatible fittings, and incorrect pressure calculations. Always confirm whether the component is pipe or tube before specifying dimensions.
Another frequent error is assuming that a given schedule number always corresponds to the same wall thickness regardless of size. In reality, Schedule 40 for a 2-inch pipe means a wall of about 3.91 mm, while Schedule 40 for an 8-inch pipe means 8.18 mm. The schedule number is a pressure class indicator, not a fixed wall dimension.
Omitting Critical Allowances
Selecting wall thickness based solely on the pressure calculation, without adding corrosion allowance, manufacturing tolerance, or erosion allowance, is a recipe for premature failure. The minimum required thickness must include all of these additions. Similarly, failing to account for thermal expansion in long tube runs can generate stresses that exceed the tube’s capability, even if the pressure rating is adequate.
Material and Code Mismatches
Specifying a material that is not suited to the service conditions is a costly mistake. Carbon steel in an acid environment, standard polyethylene in a high-temperature application, or a welded tube in a high-pressure cyclic service can all lead to rapid failure. The checklist below helps avoid the most common specification errors:
- Confirm whether the component is pipe or tube, and use the correct dimensional standard
- Look up the actual wall thickness for the specific size and schedule or gauge
- Add corrosion, erosion, and mechanical allowances to the calculated pressure design thickness
- Use minimum expected wall (accounting for manufacturing tolerance) in all pressure calculations
- Verify material compatibility with the fluid, temperature range, and external environment
- Apply the correct design code for the application (ASME B31.1, B31.3, or the relevant plastic pipe standard)
- Specify both working pressure and the temperature at which that rating applies
Over-specifying is also a trap. Tighter tolerances or thicker walls than the application requires can increase costs substantially without adding real safety. The goal is to match the specification precisely to the application demands.
How Toppi Helps Buyers Specify the Right Tube Dimensions and Pressure Class
Toppi Oy is a Finnish manufacturer of plastic tubes, hoses, profiles, and cables, founded in 1953 and operating from its production facility in Espoo. With over 70 years of extrusion expertise, Toppi manufactures a broad range of standard and custom-tailored tubing products for industrial applications across multiple sectors, including energy, marine, medical, and general manufacturing.
When specifying tube wall thickness and pressure rating for plastic tubing, Toppi supports buyers through every stage of the process:
- Material selection guidance: Toppi’s engineers help match the right polymer (PA12, PE-HD, PEX, PVC, TPU, and others) to the application’s chemical, thermal, and mechanical requirements
- Custom dimensioning: Using in-house CAD design and an on-site tool shop, Toppi manufactures tubes to specific OD, wall thickness, and tolerance requirements
- Prototyping before production: 3D-printed prototypes allow buyers to validate dimensions and fit before committing to extrusion tooling
- Co-extrusion capability: For applications requiring multiple materials or color coding in a single tube, co-extrusion combines different layers into one product
- Compliance and documentation: Toppi holds ISO 14001 certification, runs production on 100% fossil-free electricity, and provides material and compliance documentation for regulated industries
Products like ToppTube™ PA12P40, ToppTube™ PE-HD, and ToppTube™ PEX are available in standard dimensions or manufactured to customer specifications. Browse the complete tube product range to find the right starting point for your application, or contact Toppi’s design team to discuss your specific wall thickness, pressure, and material requirements. Tell us your needs, and let us make it.
