SPED Stress Analysis & Mechanical Integrity 2 — Questions and Answers
Question 1: In ASME B31.3 piping stress analysis, what does the sustained stress range include?
- Thermal expansion stresses only
- Pressure, weight, and other sustained mechanical loads (Correct answer)
- Occasional loads such as wind and seismic
- Displacement stresses from anchor movements
Correct answer: Pressure, weight, and other sustained mechanical loads
Sustained stresses in ASME B31.3 encompass pressure, weight, and other continuously applied mechanical loads.
Question 2: Which flexibility analysis method is considered the most rigorous for complex piping systems?
- Guided cantilever method
- Chart-based Spielvogel method
- Finite element analysis (FEA) (Correct answer)
- Approximate expansion loop sizing
Correct answer: Finite element analysis (FEA)
Finite element analysis provides the most accurate and rigorous stress results for complex piping geometries.
Question 3: What is the primary purpose of an expansion loop in a piping system?
- Reduce pipe wall thickness requirements
- Provide flexibility to absorb thermal growth (Correct answer)
- Increase flow velocity through the loop
- Separate high-pressure and low-pressure sections
Correct answer: Provide flexibility to absorb thermal growth
Expansion loops add piping flexibility that allows the system to absorb thermal expansion without overstressing equipment nozzles or supports.
Question 4: A piping system experiences a thermal anchor force of 50,000 lb. This force is most critical for which component evaluation?
- Pipe wall hoop stress check
- Equipment nozzle load evaluation (Correct answer)
- Pipe insulation thickness selection
- Flange bolt torque specification
Correct answer: Equipment nozzle load evaluation
Anchor forces from thermal expansion are transmitted directly into connected equipment nozzles, which must be evaluated against manufacturer allowable loads.
Question 5: Under ASME B31.3, the allowable displacement stress range (SA) increases when which condition applies?
- Operating temperature exceeds 750°F
- The system operates at cryogenic temperatures
- Unused sustained stress allowance is available (Correct answer)
- The pipe material has high yield strength
Correct answer: Unused sustained stress allowance is available
ASME B31.3 allows the unused portion of the sustained stress allowance (Sh) to be added to SA, increasing the permissible displacement stress range.
Question 6: What distinguishes a rigid support from a spring support in piping design?
- Rigid supports allow axial pipe movement; spring supports do not
- Rigid supports restrain all movement; spring supports permit controlled vertical movement (Correct answer)
- Spring supports are used only for small-bore piping
- Rigid supports are only used at pipe elbows
Correct answer: Rigid supports restrain all movement; spring supports permit controlled vertical movement
Rigid supports resist pipe displacement in all constrained directions, while spring supports allow vertical thermal movement while still carrying the pipe load.
Question 7: In piping stress analysis, a 'cold spring' is applied to:
- Reduce operating stresses by pre-stressing the piping in the cold condition (Correct answer)
- Increase the spring rate of variable spring hangers
- Lower the design temperature rating of the pipe
- Prevent condensation on cryogenic piping
Correct answer: Reduce operating stresses by pre-stressing the piping in the cold condition
Cold spring involves cutting the pipe short (or long) so installation pre-stresses it, reducing stresses during thermal expansion in service.
SPED Stress Analysis & Mechanical Integrity 2
In ASME B31.3 piping stress analysis, what does the sustained stress range include?