Creating a tube system is complicated. In many systems, fluid conveyance and the actual plumbing or ‘pathways’ that tubes provide need to be bent, twisted, and formed to fit inside the housing of the system being designed. The fittings must accommodate a tight seal around the tube and therefore are carefully selected for appropriate parameters of the design at-hand including operating pressure and temperature cycles. These factors of aerospace tubing design present a unique convergence of engineering disciplines, where structural integrity, fluid dynamics, thermal management, and manufacturability must be precisely balanced under some of the most demanding conditions imaginable.
The challenges of tubing design present big issues to the aerospace industry. Large original equipment manufacturers (OEMs) like Boeing invented many of the tube design standards that guide the aerospace industry today. But with technology advancing at current rates, many companies are embracing a startup style strategy—a more “on the fly” style of engineering. As L&E is a contract manufacturer rather than an engineering hub, we’ve worked with many different companies and individual engineers, seeing designs that range from 3D models to paper drawings. So, we know a thing or two about what works, and what doesn’t.
But before we dive into those specifics, let’s look at the overall concerns of tubing systems in the industry:
Weight Constraints and Material Selection
Weight is a dominant design constraint in aerospace. Tubing must be lightweight yet capable of withstanding high pressures, temperature extremes, and vibrational loads. Materials such as titanium and Inconel are often selected for their high strength-to-weight ratios, corrosion resistance, and thermal performance. However, these materials pose machining and forming challenges, often requiring specialized equipment and processes like precision bending and orbital welding.
High Pressure and Temperature Demands
Fluid and gas systems in aerospace applications routinely operate at pressures exceeding 3,000 psi and at temperatures ranging from cryogenic (e.g., liquid hydrogen) to combustion-zone heat. Designers must consider not only burst strength but also fatigue life, creep, and thermal expansion.
Complex Routing and Integration
Tubes are often routed through tight and irregular spaces. Minimizing bend radii while avoiding flow restrictions and maintaining accessibility for maintenance requires sophisticated 3D computed-aided design (CAD) tools and often, physical prototyping. In many cases, flexible sections or custom-formed components are integrated to accommodate movement and vibration, introducing additional design variables.
Leak Prevention and Joining Techniques
Leak-proof joining is critical, especially for fuel, oxidizer, or pressurized cabin systems. Technologies such as orbital welding, swaged fittings, or brazed joints are common, but each comes with trade-offs in terms of inspection complexity, reparability, and weight. Non-destructive testing (NDT) techniques, including dye penetrant, radiography, or ultrasonic inspection, are standard in quality assurance but add to cost and lead time.
Regulatory and Lifecycle Considerations
Compliance with aerospace standards such as AS9100 adds layers of documentation, traceability, and testing. Moreover, systems must be designed for maintainability and longevity, often spanning decades, with resistance to corrosion, wear, and fatigue.
Sharing Knowledge is Pivotal
Aerospace tubing design, though often behind the scenes, is a cornerstone of system reliability and performance. Its challenges demand a rigorous, multidisciplinary approach—where every bend and weld is a critical decision point. At Lafarge & Egge, we have 60+ years’ experience in the tube business, positioning us as a wealth of information for many smaller and newer manufactures.
Our Tips:
- Watch out for sole sources and/or high lead-time fluid fittings. Many lead times for high performing fluid fittings have expanded to 52-80 weeks. Alloy availability, such as titanium, is also a concern for lead-time. Make sure to design in as many options as possible and in some cases. Aerospace credentials will certainly limit the options available, due to critical performance needs, tight tolerances, and high mix.
- Share expertise: If you’re like us, receiving many tube system drawings, it can be easy to place a no-bid on a design that’s overly complicated or expensive. But this industry—besides valuing experience—values connections and partnerships. Giving feedback is a means to help a new engineer, kindle a working relationship, and lead to improvements in future drawings.
- Listen to feedback: As contract manufacturers, we are responsible for the designs we accept. But, to accept designs, we sometimes need to alter plans. Whether reducing the complexity of the geometry or suggesting a different joining technique, working together often leads to a better end product.
- Keep it simple! Tubing is not straightforward, but simplicity is a golden rule that we’ve learned over the years. Simplicity means (if applicable) fewer parts, fewer connections, slower lead times, and lower cost. There’s no reason to add a special bend with a different radius for no reason—sometimes the simplest plan is often the best one.
Interested in learning more about tubing design, or have a design for a tubing system you want to manufacture? Contact L&E via our website or by email and see how we can help you with your tubing needs.
