Double Service Rig Design API 4F

The American Petroleum Institute (API) is a body which provides standards for the operation, manufacture, and design of drilling and service rigs.  The API 4F standard provides a guideline for the design of drilling and service rigs, both on and offshore, for a range of environments and weather conditions.

Sparta has been using the API 4F Specification as a guideline in the design of service rigs (workover rigs) since 2008.  Today, every service rig Sparta designs has ties back to API 4F, whether it is a monogrammed API rig or not.

Why design to API 4F?

The API 4F Specification gives us a tried and tested guideline for rig design.

The standard “facilitates the broad availability of proven, sound engineering and operating practices.”  The standard itself is reviewed and revised every five years, ensuring a current grasp on design practices.

A major component of any service rig design is the loading on the mast due to wind.  As anyone who has taken a fluid dynamics class can tell you, pressure loading on complex structures can be difficult to calculate. API 4F provides a simple method of calculating wind load on a large steel structure through a wind pressure analysis on individual members.

Steel Mast Analysis API 4FAPI 4F is not without its challenges. With each new edition of 4F, the new wind loading requirements increase the calculated load on the structure.  This leads to more stringent conditions for the stabilizing package to combat overturning and sliding and generally requires a larger rig footprint.  For instance, a rig designed to the 2nd Edition of 4F would likely require some structural reinforcement and increased stability structure to meet the 3rd Edition requirements, and even more structure to meet 4th Edition.

Related Content: API 4F: 3rd Edition Vs 4th Edition

While wind loading is a major component of API 4F, it is not the only one.  API 4F provides a limit on allowable stresses on components, as well as safety factors on all structural components for different environmental conditions.  It also provides information on acceptable materials and quality control methods during the manufacturing of the rig.  These conditions provide a level of confidence that the rig will function safely in its intended environment.

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