Ellipsoidal heads are standard for moderate pressure. Torispherical heads (Dished) are cheaper but suitable for lower pressures. Hemispherical heads are used for very high pressures but are expensive to fabricate. What is the purpose of a "Corrosion Allowance" (CA)?
The Expectation: Fitness-for-Service (FFS) – API 579. Model Answer: "First, I would measure the actual depth of the gouge with a pit gauge or UT (Ultrasonic Testing). Then, I would classify it. If it's in a low-stress area, the remaining thickness might still exceed the required thickness from the original calculations. If it is critical, I would perform a Level 1 or Level 2 FFS assessment per API 579 . I would calculate the remaining ligament efficiency and compare MAWP to the operating pressure. Often, grinding the gouge smooth to remove stress risers (sharp corners) and running a calculation is acceptable without welding."
The Expectation: Understanding of pressure thresholds (often 15 psi) and design standards. Model Answer: "The general rule of thumb is that a 'vessel' operates above 15 psig (internal or external), while a 'tank' operates at atmospheric pressure or slightly above (typically less than 2.5 psig). Vessels are designed to ASME Section VIII, while tanks are designed to API 650 (large welded storage) or API 620 (low-pressure)."
Static equipment forms the backbone of the oil and gas, petrochemical, and power generation industries. Unlike rotary equipment, these components do not have moving parts, but they operate under extreme pressures, temperatures, and corrosive environments.
12. Explain Hydrogen Induced Cracking (HIC) and Sulfide Stress Cracking (SSC). static equipment interview questions
Be prepared to discuss how specific chemicals ( H2Scap H sub 2 cap S
What is the requirement for inspection openings according to code?
: Where do you see your career in five years regarding specialization in static equipment design or maintenance?
The Expectation: Residual stress relief. Model Answer: "PWHT, or Stress Relieving, involves heating the welded vessel to a specific temperature (typically 1150°F – 1200°F / 620°C – 650°C) for a specific soak time (usually 1 hour per inch of thickness). It is required for carbon steel when thickness exceeds a Code threshold (e.g., ~1.5 inches for Group 1 materials) or for service conditions like Lethal Service or Sour Service. It is not always required for thin P-No. 1 materials in non-corrosive service, but the WPS (Welding Procedure Specification) dictates it." Ellipsoidal heads are standard for moderate pressure
: Roles and responsibilities for inspectors, including non-destructive testing (NDT) like Ultrasonic or Radiographic testing. 3. Essential Professional Skills
Test Pressure=1.3×MAWP×(Allowable Stress at Test TemperatureAllowable Stress at Design Temperature)Test Pressure equals 1.3 cross MAWP cross open paren the fraction with numerator Allowable Stress at Test Temperature and denominator Allowable Stress at Design Temperature end-fraction close paren Interview Success Tips for Static Equipment Engineers
The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) is the global standard. The most critical sections include:
If both fluids are corrosive, you might use a shell lining or exotic material on tubes only. What is the purpose of a "Corrosion Allowance" (CA)
This reveals your knowledge of pressure vessel geometry. A 2:1 Ellipsoidal head is deeper and has a smooth transition from the shell, creating better stress distribution. It is standard for high-pressure vessels. A Torispherical head (often called a "dished head") has a crown radius and a knuckle radius. It is shallower, easier to manufacture, and cheaper, but the knuckle area experiences higher stress. Therefore, torispherical heads are used for lower pressures or storage tanks.
Interviews will heavily test your knowledge on verifying the structural integrity of static assets using code-compliant NDT methods.
: Which specific paragraphs of the ASME codes govern the calculation of shell thickness?