API Bull 2TD pdf download Guidelines for Tie-downs on Offshore Production Facilities for Hurricane Season
1Drilling and Workover Drilling Units1.1BACKGROUND
The oil and gas industry has experienced rig failures and movement of rig components during recent hurricanes in the Gulf ofMexico. Some, if not all, of the failures are attributable to the tie-down components. Occurrences on both fixed and floating plat-forms have resulted in significant platform damage as well as lost andor deferred production.Recent experience shows thatenhancements to current industry practice can improve tie-down performance during hurricanes.
This document addresses situations where failure of a drilling or workover rig would result in significant damage to the platformor adjacent infrastructure. Generally, this would include any facility designated as having a high or medium consequence of fail-ure as defined by API RP2A. In other situations, a risk-based operational decision process should be followed.Situations thatmight allow deviation from the recommendations below include drilling operations in the non-hurricane season or the use oflight-weight workover masts on shallow water platforms.
Drilling rig tie-downs to the platform and between drilling components are critical structural components and should have thesame, or higher,level of design, material traceability, quality assurance, maintenance, and documentation as other critical struc-tural components.
Primary rig and substructure tie-downs should be designed or assessed for location-specific loading conditions (environmentaland dynamic) consistent with those utilized in the facility structural design and should be approved by an engineer experiencedand qualified in offshore structural engineering.
For the same design environment, wind gust and height factors appropriate for the derrick and substructure may be higher thanthose used for designing the topside as a whole, and the short-term extremes will be much higher than the average loadings usedin combination with wave forces for jacket or mooring design.Guidance in wind codes supports the use of 5-to 15-second gustfactors for the design of such components.
Dynamic accelerations and tilting of the platform topside should also be considered, again at the extreme (not RMS) level.Rigidbody (quasi-static) analysis of the rig packages themselves may be used as a first approximation.
The following items should be considered for implementation as appropriate by the platform operator andor rig owner in theshort-term timeframe:
Visually inspect all tic-downs to confirm that they are in good condition and are constructed per the design drawings.
.Verify that all tie-downs can be properly installed and that no obstructions exist that might prevent installation (e.g. stiffen-
ers on plate girders).
For bolted tie-downs:
– Verify by visual inspection that the bolts are in good physical condition.
– Verify that bolts meet the required material specifications and the specifications are suitable for this application.
Note:ASTM 325 or 490 high strength bolts are not recommended, since retorquing of these bolts is not permited per AISC specifica-tions.
– Verify that the number of bolt torquing cycles does not exceed the design allowable.
– Verify required bolt torque is defined and required equipmenttools are available to achieve the required torque.- New bolts should be installed if the above items cannot be verified.
For mechanical/hydraulic tie-downs:
– verify that the tie-down system is in good working condition.
– Verify that operating personnel are familiar with the operating procedures of the equipment.