Structured wall pipes, including types with deep profiles like Double Wall Corrugated (DWC) pipe, are widely used for non-pressure applications such as drain, waste, venting (DWV), and sewers. While offering lightweight solutions compared to solid wall pipes, their design can introduce specific challenges.
Stiffness and Deformation Risks
The theoretical stiffness of a deep-profile structured wall pipe is calculated based on the moment of inertia of its cross-section. However, in practice, the measured stiffness can be lower than theoretical values. This reduction is attributed to reduced plate stiffness due to the susceptibility of the deep profile to deformation. Under load, the outer fibre distance can shorten, effectively lowering the moment of inertia. This phenomenon is a key reason why sewer standards include a requirement for pipes to withstand a 30% deformation limit without buckling. Buckling can happen under external load.
Joint Tightness and Production Efficiency
Another challenge with deep-profile designs relates to the long-term performance of rubber ring joints. The thin side walls of the deep profile are prone to creep over time. Creep is the tendency of plastics to deform under constant load. In the case of pipe joints, this creep can lower the contact pressure with the elastomeric seal, making it harder to meet the 50-year tightness requirement often needed for sewer applications. Furthermore, the production of deep-profile pipes like DWC requires dedicated equipment (corrugators with mold blocks) which often exhibit a lower Overall Equipment Effectiveness (OEE) for larger sizes compared to the standard downstream equipment used for smooth-outside pipes like foam core.
Technical Considerations
Stiffness Deviation: Actual stiffness can be lower than theoretical due to profile deformation and plate stiffness.
Deformation Limit: Sewer standards often require no buckling up to 30% deflection.
Creep Risk: Thin walls are susceptible to creep, potentially reducing rubber ring joint contact pressure over time.
Production Equipment: Dedicated corrugators may have lower OEE for larger sizes.
FAQ Section
Why might deep profile pipes have lower stiffness than calculated?
Deep profiles are susceptible to deformation under load, which reduces the effective moment of inertia and plate stiffness, resulting in a measured stiffness lower than the theoretical calculation.
How does creep affect joints in deep profile pipes?
The thin walls of deep profiles can creep over the long term, which may reduce the contact pressure on rubber ring seals and make it challenging to meet requirements for joint tightness, such as the 50-year standard for sewers.
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Saurabh Pawar
