2.1 Types of Slings: Synthetic, Wire Rope, Alloy Chain & Metal Mesh

Types of Slings: Synthetic, Wire Rope, Alloy Chain & Metal Mesh

In industrial rigging, slings serve as the critical mechanical connection between the crane hook and the load. Choosing the correct sling material and construction is fundamental to ensuring safety, load stability, and regulatory compliance. Under ASME B30.9 (Slings) and OSHA 29 CFR 1926.251 (Rigging Equipment for Material Handling), slings are categorized into five distinct classifications based on their mechanical properties, load-bearing architecture, and environmental resistance.

Selecting the improper sling type can lead to sudden catastrophic failure from chemical degradation, thermal damage, cutting on sharp corners, or structural unlaying. This section provides a thorough technical breakdown of each sling type, establishing the operational criteria required for NCCER Basic and Advanced Rigger certification.

---

1. Synthetic Web Slings

Synthetic web slings are manufactured from woven synthetic yarns—predominantly nylon (polyamide) or polyester (polyethylene terephthalate). They are highly flexible, lightweight, non-conductive, and non-marring, making them ideal for handling delicate machinery, polished shafts, finished architectural components, and fragile assemblies.

Web Sling Configurations (Types I through VI)

Chemical Vulnerabilities & Temperature Thresholds

The fundamental exam distinction between nylon and polyester lies in their chemical resistance:

• Nylon: Severely degraded and dissolved by acids (hydrochloric, sulfuric, nitric). However, nylon is highly resistant to alkalis (caustics, ammonia, lime, sodium hydroxide), hydrocarbons, and dry-cleaning solvents.
• Polyester: Severely degraded by alkalis / caustics (hot sodium hydroxide, concentrated ammonium compounds). However, polyester is highly resistant to acids and bleaching agents.
• Polypropylene: Highly resistant to both acids and alkalis, but possesses very low mechanical strength and a low melting point; rarely used except in specialized marine/plating environments.
• Operating Temperature Limits: Standard nylon and polyester web slings have an operating temperature range of -40°F to 194°F (-40°C to 90°C). Exposure to temperatures exceeding 194°F permanently breaks down synthetic polymers.
• UV & Core Inspection: Exposure to direct sunlight causes ultraviolet (UV) degradation, resulting in color fading and brittleness. Web slings are manufactured with internal red core warning yarns; when surface yarns wear through and expose red warning yarns, the sling must be removed from service immediately.

---

2. Polyester Roundslings

Polyester roundslings consist of a continuous, endless loop of high-tenacity polyester core yarns enclosed within a double-wall seamless woven tubular polyester jacket.

+-------------------------------------------------------------------------+
|      Outer Woven Polyester Jacket (Carries 0% Load / Protects Core)     |
|  +-------------------------------------------------------------------+  |
|  |   Inner Core Yarns (Continuous Polyester Loop: Carries 100% Load)  |  |
|  +-------------------------------------------------------------------+  |
+-------------------------------------------------------------------------+

Structural Mechanics

1. Core Load Sharing: The inner polyester yarn core carries 100% of the suspended load weight.
2. Jacket Protection: The outer tubular jacket carries zero load. Its sole function is to protect the internal load-bearing core from UV rays, abrasion, dirt, and mechanical cutting.
3. Flexibility & Pliability: Roundslings mold tightly to irregular contours, providing exceptional contact surface area and preventing load slippage.

Standardized WIC/WSTDA Color Coding

While the manufacturer's identification tag is the only legal authority for working load limits, industry standards (Web Sling & Tie Down Association) establish universal color coding for polyester roundslings:

---

3. Wire Rope Slings

Wire rope slings provide high tensile strength, moderate flexibility, and excellent resistance to abrasion and fatigue. Standard rigging slings are constructed from 6x19 or 6x36 classification wire ropes fabricated from Extra Improved Plow Steel (EIPS) or Extra Extra Improved Plow Steel (EEIPS) with an Independent Wire Rope Core (IWRC).

Flemish Eye vs. Hand-Tucked Splice

End terminations dictate the ultimate strength efficiency of a wire rope sling:

• Mechanical Flemish Eye (Swaged Sleeve): The wire rope strands are split into two groups, looped back in opposite directions to re-form the eye naturally (the Flemish loop), and secured with a swaged steel or aluminum mechanical sleeve pressed under high hydraulic pressure.
  • Efficiency: Achieves 90% to 95% of the nominal catalog strength of the wire rope.
  • Safety Advantage: If the swaged sleeve fails under load, the intertwined Flemish eye still retains up to 70% of its ultimate strength, preventing immediate dropped loads.
• Hand-Tucked (Hand-Spliced) Eye: Strands are unlaid and manually tucked back into the main body of the wire rope without a metal sleeve.
  • Efficiency: Achieves only 70% to 80% efficiency.
  • Critical Prohibition: Hand-tucked splices can easily untuck and pull apart if the load is allowed to rotate during hoisting. They are strictly prohibited in single-point picks where rotation is possible.

Multi-Part and Braided Wire Rope Slings

• Multi-Part / Braided Slings: Fabricated by braiding 3, 6, 8, or 9 smaller wire ropes together. This delivers ultra-high flexibility, resists kinking, minimizes rotation, and conforms tightly around cylindrical vessels.
• Thermal Limits: Wire rope slings with an IWRC can operate up to 400°F (204°C) without capacity reduction. Wire ropes with a fiber core (FC) or synthetic internal components are limited to 180°F (82°C).

---

4. Alloy Steel Chain Slings

Alloy steel chain slings are the most durable, rugged, and heat-resistant slings available. Under ASME B30.9 and OSHA 1926.251(b)(1), only alloy steel chains are certified for overhead lifting.

Certified Chain Grades vs. Prohibited Chains

| Chain Grade | Overhead Lifting Permitted? | Identification Markings | Mechanical Properties | |:---|:---:|:---:|:---|| | Grade 30 (Proof Coil) | NO (STRICTLY PROHIBITED) | 3, 30, PC | Low-carbon steel; elongates and snaps under shock loading. | | Grade 43 (High Test) | NO (STRICTLY PROHIBITED) | 4, 43, HT | Carbon steel for binding and tie-downs; brittle under impact. | | Grade 70 (Transport) | NO (STRICTLY PROHIBITED) | 7, 70, G7 | Heat-treated carbon steel for trucking/cargo securement; lacks elongation properties required for overhead lifting. | | Grade 80 (Alloy Steel)| YES (APPROVED) | 8, 80, 800, G8 | Alloy steel with minimum 20% elongation before fracture; standard overhead lifting grade. | | Grade 100 (Premium Alloy)| YES (APPROVED) | 10, 100, G10 | Approx. 25% higher WLL than Grade 80 for identical link size; excellent strength-to-weight ratio. | | Grade 120 (Ultra Alloy) | YES (APPROVED) | 12, 120 | High-performance square/profile links with superior fatigue and bending resistance. |

Thermal Derating for Alloy Chain Slings

Alloy chain slings excel in foundries, steel fabrication, and extreme heat environments, but must be derated when exposed to high temperatures:

• Up to 400°F (204°C): 100% capacity (no reduction).
• 400°F to 500°F: 10% capacity reduction (90% WLL).
• 500°F to 600°F: 20% capacity reduction (80% WLL).
• 600°F to 700°F: 30% capacity reduction (70% WLL).
• 700°F to 800°F: 40% capacity reduction (60% WLL).
• 800°F to 900°F: 50% capacity reduction (50% WLL).
• Above 1,000°F (538°C): PERMANENT REMOVAL FROM SERVICE. The chain link heat treatment is permanently destroyed.

---

5. Metal Mesh Slings

Metal mesh slings (also known as wire mesh slings) are constructed from high-tensile carbon steel or stainless steel wire mesh fabric joined to heavy-duty steel end handles (triangle and choker fittings).

Key Characteristics

• Abrasive & Hot Loads: Ideal for handling hot steel coils, raw billets, rough castings, and sharp-edged structural plates.
• Thermal Range: Standard carbon steel mesh slings operate safely up to 550°F (288°C) without derating. Stainless steel mesh can operate up to 1,000°F under manufacturer guidance.
• Load Conformation: The wide bearing surface (up to 12 inches or more) distributes weight evenly across soft or polished metal surfaces without gouging, while resisting edge cuts that would instantly sever synthetic webbing.

---

Comprehensive Sling Selection Matrix