ASME Code — CAE Glossary

In short, it's a rulebook for safely designing and fabricating pressure vessels and boilers. The ASME BPVC is divided into 13 Sections. The ones CAE engineers deal with most are Section VIII (pressure vessels) and Section III (nuclear equipment).

Division 1 is "Design by Rule"—you simply plug numbers into formulas. For example, the minimum wall thickness for a cylindrical shell under internal pressure is $t = \dfrac{PR}{SE - 0.6P}$. Division 2, on the other hand, is "Design by Analysis," where you use FEA for detailed stress evaluation. Division 2 allows higher stresses, but requires more analysis work.

Great question. Division 1 formulas are conservative, so they often result in thicker walls than necessary. In large industrial reactors, reducing wall thickness by just 5 mm can save millions in material costs. Division 2 using FEA lets you evaluate stresses in detail and eliminate unnecessary thickness. However, you must properly perform stress linearization and follow all evaluation procedures correctly.

When you run FEA on a pressure vessel, you get a non-linear stress distribution through the wall thickness. Stress linearization involves drawing a Stress Classification Line (SCL) at the section you want to evaluate and separating the stress distribution through integration. The uniform component becomes membrane stress $\sigma_m$, the linear component becomes bending stress $\sigma_b$, and the remainder becomes peak stress $\sigma_F$. The equations are:

That's actually a pain point in practice. The basic rule is to draw it where stress is likely to peak and perpendicular to the wall thickness. Typical locations are nozzle-to-shell junctions, flange roots, and dome-to-shell connections. However, you must avoid singular points (sharp corners without fillets), and the SCL must be perpendicular to the neutral axis or your separation will be incorrect. In ANSYS you can use Path operations, in Abaqus there's a free body cut function.

ASME Section VIII stress classification changes allowable values based on failure mode. Here's how they break down:

Good catch. Secondary stress has "self-limiting" properties. For example, thermal stress, once the material yields slightly, redistributes and stops growing. The condition $P_L + P_b + Q \leq 3S_m$ is called the shakedown condition, which guarantees that after cyclic loading, the material returns to elastic behavior—no ratcheting. However, if $3S_m$ is exceeded, cyclic plastic strain accumulates (ratcheting), eventually leading to failure.

Here are some common pitfalls. First, **incorrect SCL placement**—drawing it at singular points (sharp corners without fillets) causes infinite stress spikes. Second, **confusing stress types**—FEA outputs von Mises stress, but ASME uses stress intensity (Stress Intensity = Tresca equivalent = $\sigma_1 - \sigma_3$), which gives different values. Third, **missing load combinations**—you need to check not just internal pressure, but combined cases with weight, thermal, seismic, and wind loads, evaluated in both Design and Operating conditions.

Japan uses JIS B 8265 (general structural standards for pressure vessels) and JIS B 8266 (pressure vessel design), which largely follow ASME Section VIII Division 1. The main difference is in allowable stress—ASME uses 1/3.5 of tensile strength, JIS sometimes uses 1/4. Recently, API 579-1/ASME FFS-1 (Fitness-for-Service) has become important for remaining life assessment of aging equipment.