Pipefitter Rigging, Hangers, and Supports 2 — Questions and Answers

Question 1: When using a wire rope sling in a choker hitch configuration, the rated capacity is reduced to what percentage of its vertical hitch capacity?

100%
80%
75% (Correct answer)
60%

Correct answer: 75%

A wire rope sling used in a choker hitch has a rated load capacity of 75 percent of its vertical (straight) hitch rating, due to the bend angle and stress concentration at the choker point.

Wire rope sling capacities change with hitch configuration per ASME B30.9 (Slings). Vertical (straight) hitch = 100 percent of rated capacity. Choker hitch = 75 percent (reduced due to the 135-degree bend at the choke point; this can further reduce to 65 percent if the choke angle is below 120 degrees). Basket hitch = 200 percent (two vertical legs sharing the load). Pipefitters using rigging equipment must always refer to the tag capacity, identify the hitch type being used, and apply the appropriate de-rating. Overloading a sling in a choker configuration is a common cause of sling failure and dropped loads.

Question 2: What type of pipe hanger is designed to allow the pipe to move axially (along its centerline) while still providing vertical support?

Rigid hanger
Constant spring hanger
Sliding pipe support or roller support (Correct answer)
Anchor (fixed point)

Correct answer: Sliding pipe support or roller support

A sliding pipe support or roller support allows unrestricted axial movement of the pipe due to thermal expansion and contraction while providing full vertical load support, preventing pipe sag.

Piping expands and contracts thermally during operation. Support systems use anchors (fixed points that resist all movement), guides (allow axial movement only), and sliding/roller supports (allow axial and sometimes lateral movement while providing vertical support) to manage this movement. Sliding supports use a low-friction PTFE or stainless-steel wear pad so the pipe can glide over the support shoe during thermal cycles without binding. If sliding supports are replaced with rigid clamps, pipe stress increases dramatically, potentially causing flange leaks, weld cracking, or equipment nozzle overload.

Question 3: What is the purpose of a spring can (variable spring hanger) in a piping system?

To provide a fixed support point that prevents all pipe movement
To support pipe weight while allowing limited vertical movement due to thermal expansion, maintaining continuous load support (Correct answer)
To anchor the pipe to the structure to absorb anchor forces
To act as a vibration dampener for pump discharge lines

Correct answer: To support pipe weight while allowing limited vertical movement due to thermal expansion, maintaining continuous load support

A variable spring hanger supports the pipe's dead weight load while allowing controlled vertical movement during thermal expansion or contraction, preventing the pipe from going into tension or overloading nozzles as it moves vertically.

In piping systems operating at elevated temperatures, pipes expand vertically as well as horizontally. Variable spring hangers contain a coiled spring sized to support the cold load. As the pipe moves vertically during heat-up, the spring compresses or extends, changing the support load by up to plus or minus 25 percent of the design load. The spring rate and travel are selected by the pipe stress engineer from a stress analysis. They are preset at the shop and field-locked during hydrostatic testing to prevent overload.

Question 4: Per OSHA 1926.1416, before a mobile crane is used for lifting operations, what must the operator do?

Sign a verbal agreement with the rigger confirming the lift
Conduct a pre-shift visual inspection of the crane and all associated rigging equipment (Correct answer)
File a lift permit with OSHA before beginning
Test the crane at 125 percent of rated load before each shift

Correct answer: Conduct a pre-shift visual inspection of the crane and all associated rigging equipment

OSHA 1926.1416 requires a pre-shift visual inspection of the crane by the operator before each shift and after any event that could affect safety (such as an overload or collision), checking wire ropes, hooks, brakes, and outriggers.

OSHA 29 CFR 1926.1416 (Equipment Inspections) requires a visual inspection each shift before work begins. The inspection covers all functional mechanisms for maladjustment, deterioration, or damage; wire rope used that day; hooks with safety latches; rigging hardware; outriggers and stabilizers; load/boom angle indicators; and backup alarms. Any deficiency that could affect safe operation must be corrected before use. The annual comprehensive inspection (per 1926.1412) is separate and performed by a qualified person. Pipefitters acting as signal persons or riggers are affected by this regulation and must not rig loads to a crane that has not been inspected.

Question 5: What does the term 'proof load test' mean in the context of rigging hardware?

Testing the rigging equipment at exactly its rated working load limit (WLL)
Loading the equipment to a multiple (typically 2x) of the WLL to verify structural integrity without permanent deformation (Correct answer)
A field test performed before every lift to verify sling condition
Testing a new crane at 110 percent of its rated load

Correct answer: Loading the equipment to a multiple (typically 2x) of the WLL to verify structural integrity without permanent deformation

A proof load test applies a load of typically 2 times the working load limit (WLL) to rigging hardware such as shackles, hooks, and slings at the factory to verify they can handle overload conditions without permanent deformation, cracking, or failure.

Proof load testing is a manufacturing quality assurance test performed on rigging hardware (shackles, hooks, eyebolts, lifting beams, etc.) before they are placed in service. The test load is typically 2 times the WLL (per ASME B30.10 for hooks, ASME B30.26 for hardware). The item must withstand the proof load without permanent deformation or failure. After the proof test, the item is inspected and marked with its WLL. This test is performed by the manufacturer, not in the field. In the field, rigging hardware should only be visually inspected, not proof-tested, as overloading in the field can create hidden damage.

Question 6: When calculating the load on each leg of a two-leg bridle sling, what is the effect of decreasing the sling angle (angle between the sling leg and horizontal)?

Decreasing the angle reduces the load per leg
Decreasing the angle increases the load per leg, requiring a higher rated sling (Correct answer)
Decreasing the angle has no effect on leg tension
Decreasing the angle only affects the horizontal force, not the vertical

Correct answer: Decreasing the angle increases the load per leg, requiring a higher rated sling

As the bridle sling angle from horizontal decreases (sling legs become more horizontal), the tension in each sling leg increases significantly. At 30 degrees from horizontal, each leg carries twice the load it would at 90 degrees (straight up).

The leg tension in a bridle sling is calculated as: T = (W/2) / sin(angle from horizontal), where W is the total load weight. At 90 degrees (vertical): T = W/2 (each leg carries half the load). At 60 degrees: T = W / (2 x sin 60) = W / 1.732, approximately 0.577W per leg. At 30 degrees: T = W / (2 x sin 30) = W / 1.0 = W per leg (each leg carries the full load). Industry safety guidelines typically require a minimum sling angle of 45 degrees from horizontal, and most rigging tables are based on a 60-degree angle. This is why long slings or spreader bars are used for long loads, to maintain a safe sling angle.

Pipefitter Rigging, Hangers, and Supports 2

When using a wire rope sling in a choker hitch configuration, the rated capacity is reduced to what percentage of its vertical hitch capacity?