In engineering, material efficiency is a key factor in cost reduction, especially in pressure vessel and tank design. Over the years, I’ve been involved in several projects where optimization was essential to reduce material costs while ensuring compliance with design codes.
One such project involved a horizontal pressure vessel, one of the largest in the Southern Hemisphere at that time, with a diameter of 7 meter and a length of more than 70 meters. Given its size, even a small reduction in material thickness led to significant cost savings. This was achieved by carefully selecting the right design code and material, as different codes yield varying minimum allowable thicknesses.
Choice of design code
Different pressure vessel design codes (ASME VIII Div. 1, ASME VIII Div. 2, PD 5500, and EN 13445) result in different material thicknesses. ASME VIII Div. 2, PD 5500, and EN 13445 generally allow for thinner shell plates compared to ASME VIII Div. 1.
Material selection
Comparing P355 GH to SA 516 Gr 70, P355 GH provides a slight reduction in required thickness under certain design codes.
Dished end selection
- Hemispherical heads are the lightest, requiring the least material.
- Ellipsoidal heads are lighter than torispherical (Klopper) heads, making them a preferred choice for weight-sensitive applications.
Heat treatment cost savings
A major cost-saving opportunity comes from avoiding post-weld heat treatment (PWHT).
- Many design codes exempt PWHT if the material thickness remains below a certain threshold.
- By optimizing the design, it is possible to stay below this threshold and eliminate the need for heat treatment, reducing fabrication time and costs.
Final thoughts
Material thickness optimization isn’t just about reducing weight—it directly impacts manufacturing costs, inspection requirements, and long-term durability. A well-optimized design ensures a cost-effective, compliant, and efficient solution.
Photo: Sunrise Energy’s LPG storage terminal at Saldanha Bay