How to Design and Use Below-the-Hook Lifting Devices According to ASME Standards 

Below-the-hook lifting devices are tools that attach a load to a hoist, crane, or other lifting equipment. They can come in various forms, such as hooks, clamps, magnets, slings, and beams, and they are used for lifting, moving, and positioning loads of different shapes, sizes, and weights. 

However, designing and using below-the-hook lifting devices is not a simple task. There are many factors to consider, such as the load characteristics, the lifting device components, the environmental conditions, and the safety requirements. That’s why it is important to follow the ASME standards that provide guidance and best practices for below-the-hook lifting devices. 

In this article, we will introduce two ASME standards that are relevant for below-the-hook lifting devices: ASME BTH-1 and ASME B30.20. We will explain what they are, what they cover, and how they can help you design and use below-the-hook lifting devices more efficiently and safely. 

What is ASME BTH-1? 

ASME BTH-1 is a standard that provides minimum structural, mechanical, and electrical design criteria for below-the-hook lifting devices. It applies to the design or modification of any device that is used for attaching a load to a hoist, such as structural and mechanical lifting devices, vacuum lifting devices, operated close proximity lifting magnets, remotely operated lifting magnets, or scrap and material handling grapples. 

ASME BTH-1 does not replace ASME B30.20, which is another standard that addresses the safety requirements for below-the-hook lifting devices. ASME BTH-1 only covers the design aspects, while ASME B30.20 covers the marking, construction, installation, inspection, testing, maintenance, and operation of below-the-hook lifting devices. 

ASME BTH-1 requires that lifting devices be designed by, or under the direct supervision of, a qualified person. It also specifies the rated load, load geometry, design category, and service class that must be considered during the design process. It provides formulas and methods for calculating the allowable stresses, materials, welding designs and procedures, and other design criteria. 

The latest edition of ASME BTH-1 was published in 2023 and it includes some changes from the previous edition, such as: 

• Clarification of requirements to establish the rated load of a lifting device by calculation 
• Incorporation of ASME B30.30-2019 into rope requirements 
• Additional requirements for the design and application of vacuum lifting devices 
• Incorporation of ASME B30.1-2020 into the fluid power requirements 
• Additional requirements added to address lifting attachments and load blocks 
• Updated fatigue design parameters 

Design Categories in Lifting Device Design 

Design Categories determine the level of risk associated with the lifter’s operating environment and loading conditions. These categories are also tied to specific Nominal Design Factors N_d, which ensure the structural integrity of the device under varying conditions. 

Design Category	Description	Nominal Design Factor (Nd)
A	Designated when the magnitude and variation of loads applied to the lifter are predictable, where the loading and environmental conditions are accurately defined or not severe.	2.00
B	Designated when the magnitude and variation of loads applied to the lifter are not predictable, where the loading and environmental conditions are severe or not accurately defined.	3.00
C	Designated for the design of special-application lifting devices for which the specified design factor is required.	6.00

Why Design Categories Matter: 
Each category is tailored to specific conditions: 

• Category A applies to controlled environments with well-defined loads but is restricted to Service Class 0. 
• Category B accommodates more severe or undefined conditions, providing a higher safety margin with an increased N_d
• Category C is reserved for unique, critical applications where an even greater design factor is essential. 

Service Classes 

Service Classes classify lifting devices based on the expected number of load cycles during their operational life. They primarily address fatigue life criteria, ensuring the lifter can withstand repeated loading and unloading over time. The five Service Classes are outlined below: 

Service Class	Load Cycles	Description
0	0–20,000	For applications with minimal usage and a very low number of load cycles over the device’s lifespan.
1	20,001–100,000	For moderate usage where the device experiences a limited number of repetitive loads.
2	100,001–500,000	For regular usage in applications with a higher number of repeated loads.
3	500,001–2,000,000	For heavy-duty applications where the device is subjected to frequent loading and unloading cycles.
4	Over 2,000,000	For extremely demanding applications with continuous use and a very high number of load cycles.

Why Service Classes Matter 
Service Classes focus on fatigue life, which is distinct from static strength. They establish: 

• Allowable stress ranges for structural members (Section 3-4). 
• Design parameters for mechanical components (Sections 4-6 and 4-7). 

While Service Classes do not directly impact the Nominal Design Factor (N_d), they ensure the lifter is durable enough for its intended usage over time. 

How Design Categories and Service Classes Work Together 

Although Design Categories and Service Classes address different aspects of lifting device design, they are used together to tailor a lifter to its specific application: 

• Design Categories determine the static strength and safety margins (N_d). 
• Service Classes establish durability based on expected load cycles and fatigue life. 

For instance: 

• A lifting device intended for occasional, low-risk use might fall under Design Category A and Service Class 0. 
• In contrast, a device for continuous, demanding applications might require Design Category B or C, with a Service Class 3 or 4. 

What is ASME B30.20? 

ASME B30.20 is a standard that provides safety requirements for below-the-hook lifting devices. It applies to the marking, construction, installation, inspection, testing, maintenance, and operation of any device that is used for attaching a load to a hoist, such as structural and mechanical lifting devices, vacuum lifting devices, operated close proximity lifting magnets, remotely operated lifting magnets, or scrap and material handling grapples. It also applies to clamps used for positioning and anchoring. 

ASME B30.20 is part of the ASME B30 series, which is a collection of standards that cover various aspects of cableways, cranes, derricks, hoists, hooks, jacks, and slings. ASME B30.20 is intended to complement ASME BTH-1, which is another standard that covers the design criteria for below-the-hook lifting devices. ASME B30.20 focuses on the safety aspects, while ASME BTH-1 focuses on the design aspects. 

ASME B30.20 requires that lifting devices be operated by a qualified person. 

It also specifies the marking, inspection, testing, and maintenance procedures that must be followed to ensure the safe performance of the lifting devices. It provides guidelines and precautions for the proper use and handling of the lifting devices, such as the load rating, the load balance, the load control, and the environmental factors. 

The latest edition of ASME B30.20 was published in 2021 and it includes some changes from the previous edition, such as: 

• Revisions to load test requirements 
• Clarification of frequent and periodic inspection requirements 
• Criteria for the removal of a lifting device from service if certain conditions that could result in unsafe performance are present, such as loose or missing guards or fasteners, indications of heat damage, excessive corrosion, or deformation, cracks, or wear 

Safety Requirements of ASME B30.20 

One of the important aspects of ASME B30.20 is the safety requirements, which are used to ensure the safe performance and operation of the lifting devices. ASME B30.20 defines four types of safety requirements: marking, inspection, testing, and maintenance. 

• Marking is the process of applying identification and information labels to the lifting device and its components. The marking must include the name and trademark of the manufacturer, the rated load, the serial number, the weight of the device, and any other relevant data or warnings. The marking must be legible, durable, and visible to the operator and the inspector. 
• Inspection is the process of examining the lifting device and its components for any defects, damage, or wear that could affect its performance or safety. The inspection must be performed by a qualified person at regular intervals, depending on the frequency and severity of use. The inspection must follow the procedures and criteria specified by the manufacturer and the standard. The inspection results must be recorded and reported to the responsible authority. 
• Testing is the process of verifying the capacity and functionality of the lifting device and its components. The testing must be performed by a qualified person before the initial use, after any repair or modification, and whenever deemed necessary by the inspector. The testing must follow the procedures and criteria specified by the manufacturer and the standard. The testing results must be recorded and reported to the responsible authority. 
• Maintenance is the process of repairing, adjusting, cleaning, lubricating, and replacing the lifting device and its components. The maintenance must be performed by a qualified person as required by the inspection and testing results, the manufacturer’s recommendations, and the standard. The maintenance must follow the procedures and criteria specified by the manufacturer and the standard. The maintenance records must be kept and updated. 

How Can SDC Verifier Help You Comply with ASME Standards? 

SDC Verifier is a software and consultancy firm that provides advanced simulation and standard verification solutions for structural engineering. Our software, SDC Verifier, is a powerful tool that can help you design and verify according to various standards. 

Currently, in SDC Verifier, it is possible to perform code checking according to five ASME standards:

• ASME Section VIII, Division 2, 2010 – Design for longitudinal stress check. Section 8 is dedicated to pressure vessels.
• ASME B31.8-2018 (Gas Transmission and Distribution Piping Systems)
• ASME BTH-1 – Below-the-Hook Lifting Devices (2017, 2020, 2023)

SDC Verifier can help you save time and money by automating and streamlining the design and verification process. You can also benefit from our expertise and experience in structural engineering and standard verification. 

Conclusion 

Below-the-hook lifting devices are essential tools for lifting, moving, and positioning loads of different shapes, sizes, and weights. However, they also pose significant challenges and risks for the designers and users of these devices. That’s why it is important to follow the ASME standards that provide guidance and best practices for below-the-hook lifting devices. 

ASME BTH-1 and ASME B30.20 are two standards that cover the design and safety requirements for below-the-hook lifting devices. They provide minimum criteria and recommendations for the structural, mechanical, and electrical design, as well as the marking, construction, installation, inspection, testing, maintenance, and operation of below-the-hook lifting devices.