Pressure Vessel Design Essentials Part 2: Design by Analysis Vs. Design by Rule

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In this edition of the Mechanical, we explore the role of the ASME Boiler and Pressure Vessel Code (BPVC) – particularly Section VII I– in the design and manufacturing of boilers and pressure vessels. We’ll discuss the key considerations of pressure vessel design and the two essential design methods specified in the BPVC standards.

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SPOTLIGHT

The ASME Boiler and Pressure Vessel Code (BPVC) Section VIII is a set of rules that manufacturers can use to design, fabricate, inspect, and test pressure vessels and boilers. The section is structured into three divisions.

• Division 1 offers guidelines for standard pressure vessels, covering mandatory requirements for selecting the materials, design, and fabrication processes​​ for pressure vessels.

• Division 2 includes more rigorous standards for high-pressure applications. It outlines requirements for materials, design, and nondestructive examination​​.

• Division 3 focuses on the needs of extremely high-pressure vessels, generally above 10,000 psi, covering rules for their design, fabrication, inspection, testing, and certification​​.

Designing Safe and Compliant Pressure Vessels with ASME BPVC Section VIII

ASME BPVC Code Section VIII standards have been instrumental in pressure vessel longevity and safety, reducing incidents of failures and leaks. This standard framework employs two primary design methodologies: Design by Rule (DBR) and Design by Analysis (DBA).

DBR, as outlined in Division 1 of ASME Section VIII, is a standard method that relies on empirical relationships and design criteria. Engineers use this conservative approach to size pressure vessels with simple geometries. However, its conservative nature only considers common failure modes and often leads to bulkier and more expensive designs.

On the contrary, the DBA approach in Division 2 involves more detailed calculations using numerical analysis (finite element analysis). This method addresses various failure modes and is ideal for vessels operating in high-stress environments or specialized applications.

Therefore, choosing between the two design methods depends on the intended application of the pressure vessel, operational stresses, and cost considerations. Engineers must clearly understand the differences between these approaches to design safe and ASME BPVC-compliant pressure vessels.

While we wrap up our discussion on DBR and DBA here, let’s not forget that continuous learning is key in the ever-evolving engineering field. To further expand your knowledge and perspectives, explore our curated list of must-read books for mechanical engineers.

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