Helicopter guidelines for land seismic & helirig operations - OGP

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International Association of Oil & Gas Producers B.1 Design definitions and standards Note: Slings, rigging hardware and other items of lifting equipment, manufactured by recognized and reputable sources, should comply with recognized international or country standards and should meet, as a minimum, the guidance in this publication. B.1.1 Working load limit (WLL): WLL is the maximum working load (or force) a product is authorized to support when the pull is applied in-line, unless noted otherwise, with respect to the centerline of the product. The WLL of a component is specified by the manufacturer. Note: The actual load on a sling will depend on the configuration in which it is used. Only for single (vertical) sling configuration will the load on the sling equal the weight of the load attached. Even then, the effective weight of the load will increase during acceleration and banking. Slings with a diagonal or slant configuration (e.g., a four-point attachment to a basket) will be subject to significantly larger forces than the mere weight of the load. This must be taken into account in the design of multi-point sling configurations. ASME B30.9, Chapter 9-2 has useful tables for calculating loads on slings of different types and in various configurations. B.1.2 B.1.3 B.1.4 Design breaking strength: the design breaking strength (also called minimum breaking strength) is the load at which a new or unused rope, cable or structural strand could be expected to break when loaded to destruction in direct tension. Breaking strength is usually the optimum strength achieved under laboratory conditions, in accordance with prescribed test procedures, on new rope, pulling at a slow, steady rate in a straight line. Field use of lifting equipment normally involves many different types of forces and factors which may cause the lifting equipment to fail at much reduced loads. Accordingly, the working load limit of any rope is much lower than its breaking strength. Design factor: The design factor is the ratio between nominal or minimum breaking strength and the rated capacity (WLL) of a component (sling, rigging hardware, etc.). The design factor is sometimes referred to as the “safety factor”. Simply put, dividing the breaking strength of a rope, cable or sling by the designated design factor results in the WLL. Two important terms from the definition of design factor are “nominal strength” and “minimum breaking strength.” Nominal is a term that relates to breaking strengths published by the Wire Rope Technical Board. This is the minimum breaking strength that a wire rope can have. A wire rope may break at a value greater than nominal, but never less. Design Factors have been established by OSHA, by ASME, by the American National Standards institute (ANSI), and similar government and international industrial organizations. Proof testing: A non-destructive load test made to a specific multiple of the rated load (WLL) of a component. B.2 Practical application B.2.1 Working load limit (WLL): the WLL of any item of external lifting equipment should be equal to or greater than the maximum lifting capacity of the cargo hook. It should be noted that breaking strengths, when published, were obtained under controlled laboratory conditions. Listing of the breaking strength does not mean the WLL should ever be exceeded. 46 © OGP
Helicopter guidelines for land seismic & helirig operations B.2.2 B.2.3 Design breaking strength and design factor: wire rope, straps, slings, shackles, and swivels should have a design breaking strength of five (5) times the rated WLL (a design factor of “5”). Synthetic fiber rope and slings require a higher safety factor and breaking strength as synthetic materials are more vulnerable to the environmental conditions. It is recommended to use a designed breaking strength of at least seven (7) times the rated WLL (a design factor of “7”) for synthetic fiber rope and slings. Proof testing: After manufacture, all items should be proof tested to twice the WLL by the manufacturer or test facility. Test certificates are to be retained until the item is scrapped and should provide the WLL, design factor or design breaking strength, and the proof testing results. Table 1: Example of OGP recommended working loads, and design and initial testing ratings A helicopter will be lifting seismic drills weighing 1,850 pounds. Operator will use a cargo hook rated at 4,000 pounds maximum capacity. Shown are OGP guidelines for any item of lifting equipment. OGP recommended minimum WLL of any lifting equipment item OGP recommended design factor (safety factor) Minimum design breaking strength (by manufacturer) Proof testing load (by manufacturer or test facility) Calculation used Hook capacity Per ASME WLL x design factor 2 x WLL Wire rope/sling 4,000 lbs. 5 20,000 lbs. 8,000 lbs. Synthetic fiber rope 4,000 lbs. 7 28,000 lbs. 8,000 lbs. B.3 Markings and records Note: The manufacturer shall identify slings initially. The user shall maintain the sling identification during the life of the sling. Replacement of the identification shall be considered a repair to be completed by the manufacturer or person/organization approved in accordance with recognized standards. B.3.1 B.3.2 B.3.3 B.3.4 All cables, slings and straps should be tagged or marked to show the name or trademark of manufacturer and the swaging collar embossed with: 1. A reference number. 2. Rated load limit (WLL). Note: Some countries may use SWL or “rated capacity.” 3. Diameter or size, and length of the sling. 4. Date of next formal inspection. All other lifting items should be stamped or marked to show a reference number, and WLL. If it is not practical to mark the required items, a suitable color code should be used. An appropriate maintenance program should be developed for all items, which provides a traceable record of testing and inspections. A useful tool for this is a ‘sling register’ in which a full inventory is kept of all slings and other lifting equipment as well as the type of attachments and shackles etc., in use, documenting age, date put into service, inspection and replacement cycle and dates and, where appropriate, maximum wear allowed. © OGP 47
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Helicopter guidelines for land seismic & helirig operations - OGP

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