Pipe Support Design Flashcards

Which load category per ASME B31.3 is used to evaluate sustained (primary) stresses in a piping system?

Answer: Pressure, weight, and other sustained mechanical loads combined

ASME B31.3 sustained load cases combine internal pressure, deadweight (pipe, fluid, insulation), and other continuously acting mechanical loads to check primary stress limits.

What is 'cold spring' in pipe support and piping design?

Answer: An intentional cut-short or offset during installation to pre-compensate for thermal growth

Cold spring pre-stresses the system by installing the pipe in a slightly compressed or offset state so that thermal growth moves it toward its stress-free position, reducing hot loads on supports and equipment nozzles.

When calculating allowable pipe support span, which single geometric factor most increases the permissible span length?

Answer: Larger pipe diameter and schedule (greater section modulus)

A larger pipe cross-section increases the moment of inertia and section modulus, directly raising the bending stiffness and allowable span before stress or deflection limits are reached.

A constant-effort (constant load) hanger is preferred over a variable spring hanger when:

Answer: Thermal movement is so large that a variable spring would have unacceptable load variation (>25%)

When vertical thermal displacement is large, a variable spring's load change (from cold to hot travel) can exceed 25%, making a constant-effort hanger necessary to maintain nearly uniform support load.

What maximum mid-span deflection is most commonly specified in piping project standards to avoid flow and stress problems?

Answer: 1/2 inch (12.7 mm) or as defined by the applicable code and project specification

A 1/2-inch sag limit is the widely accepted industry default, preventing ponding in liquid lines, vapor locking, and appearance issues while keeping stresses within acceptable ranges.

How are 'occasional loads' such as wind and seismic treated differently from sustained loads in ASME B31.3?

Answer: They are combined with sustained loads but checked against higher allowable stress limits

ASME B31.3 allows a higher allowable stress (typically 1.33× the basic allowable) for occasional load combinations because such events occur infrequently and for short durations.

What is the function of a 'limit stop' (travel stop) in a pipe support system?

Answer: It restricts pipe displacement to a defined range, allowing normal thermal movement but preventing excessive travel

A limit stop acts as a mechanical boundary that permits controlled thermal displacement within a preset range while blocking abnormal or emergency movements beyond that range.