API Bull 2TD-2006 pdf download.Guidelines for Tie-downs on Offshore Production Facilities for Hurricane Season.
1 Drilling and Workover Drilling Units 1.1 BACKGROUND The oil and gas industry has experienced rig failures and movement of rig components during recent hurricanes in the Gulf of Mexico. 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 and/or deferred production. Recent experience shows that enhancements to current industry practice can improve tie-down performance during hurricanes. 1.2 PHILOSOPHY 1.2.1 Applicability This document addresses situations where failure of a drilling or workover rig would result in significant damage to the platform or 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 that might allow deviation from the recommendations below include drilling operations in the non-hurricane season or the use of light-weight workover masts on shallow water platforms. 1.2.2 Design Conditions Drilling rig tie-downs to the platform and between drilling components are critical structural components and should have the same, 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 (environmental and dynamic) consistent with those utilized in the facility structural design and should be approved by an engineer experienced and qualified in offshore structural engineering.
Dynamic accelerations and tilting of the platform topside should also be considered, again at the extreme (not RMS) level. Rigid body (quasi-static) analysis of the rig packages themselves may be used as a first approximation. 1.3 SHORT-TERM RECOMMENDATIONS The following items should be considered for implementation as appropriate by the platform operator and/or rig owner in the short-term timeframe: • Visually inspect all tie-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 permitted 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 equipment/tools 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.
1.4 INTERMEDIATE-TERM RECOMMENDATIONS The following items should be considered for implementation by the platform operator and/or rig owner in the intermediate-term timeframe: • Review design calculations of all tie-downs with updated site-specific environmental and dynamic loads and document results. Analysis and results should be approved by an engineer experienced and qualified in offshore structures. Clamps should be assessed for all appropriate well positions. Special care should be given to calculations that show either no pre- dicted uplift or only a small uplift when compared to the gravity reaction. In such cases, there may effectively be no reserve against slightly higher wind forces. • Review fabrication and material records to assure that all tie-down systems are properly documented. Consider replacement of tie-downs if proper documentation is not available. Otherwise, make an assessment based on conservative assumptions of material and weld properties. • Review derrick or mast and substructure design based on site-specific environmental and dynamic loads and document results. Analysis and results should be approved by an engineer experienced and qualified in this area. 2 Permanent Equipment and Facilities 2.1 BACKGROUND Permanent equipment, quarters, and helidecks also suffered severe damage due to tie-down failure during the recent Gulf of Mex- ico hurricanes. This resulted in a significant amount of damage as well as lost and/or deferred production. Recent experience shows that enhancements to current industry practice can improve tie-down performance during hurricanes.