API Bull 2HINS:2009 pdf download

API Bull 2HINS:2009 pdf download.Guidance for Post-hurricane Structural Inspection of Offshore Structures.
4.3.5 Structural Natural Frequency Measurement (Applicable to Fixed Structures)
This check compares measured pre-hurricane natural frequencies of the structure with measured post-hurricane natural frequencies. The ability of this method to predict damage on a specific structure shall be established using a combination of engineering study and field measurements prior to the hurncane. If the pre-humcane and the post- hurricane frequencies are the same, and structure mass changes have been propeily accounted for, the structure passes the engineering check. If the frequencies are different, there is possible damage to the primary structure. This check is applicable to certain types of fixed structures, typically those with non-redundant framing.
4.3.6 Other Considerations
The observed maximum hurricane wind, wave, and currents at the site should be based on measured or site-specific hindcast hurricane conditions. The calculated hurricane loads should be based on actual loading measurements at the structure or calculated loads using measured or hindcast hurricane conditions.
The engineering check shall account for the configuration and condition of the structure at the time of the hurricane. The configuration accounts for the number of risers. topsides weight, presence of drilling rig, etc. at the time of the hurricane. The condition accounts for knowi corrosion, damage, repairs, etc. of the platform based upon the most recent inspection of the structure,
The engineering check can be performed in advance of hurricanes for some structures to determine the specific hurricane conditions expected to damage the stwcture. If a hurricane occurs, the owner/operator should compare the observed hurricane conditions at the structure site to the results of the engineering check to determine if a below- water inspection is required. This type of pre-planning can assist in rapid identification of the structures where below- water inspections are not necessary.
In lieu of an engineering check, the owner/operator may conduct the special below-water inspection.
4.4 Prioritizing Structures for Inspection
In the case where an owner/operator has multiple structures that have been exposed to hurricane conditions, consideration should be given to prioritizing the structures to be inspected. Candidate structures for priority treatment include:
a) structures located in an area of close proximity to the identified path of the hurricane eye wall and the peak environmental loading due to wind, wave and/or currents:
b) structures where structural problems are identified from the post-hurricane initial aircraft flyovers:
c) structures in areas prone to hurricane induced soil disturbances such as mudslides:
d) structures necessary for housing personnel needed to perform post-hurricane inspections or related repairs:
e) structures identified as possible bases for establishing aircraft logistics, including transfer points and re-fueling:
f) structures important to the restoration of oil and gas production to the field or region;
Safety and environmental concerns should be addressed prior to any structural inspection and are discussed in this section.
It is recommended that owner/operators preplan these inspections for their structures and have specific procedures developed prior to hurricane season.
5.2 Initial Evaluation for Boarding
Post-hurricane flyovers or close approach by boat should be used to establish the general condition of the structure and to determine if the structure has obvious damage. Access to the structure by normal means may be unsafe and may require special planning for the initial boarding party. Examples of potentially unsafe conditions include a leaning structure, structural damage to the helideck, damaged or missing boat landings, walkways and stairways, etc.
Initial boarding personnel should evaluate the life/safety hardware, egress and access features and the general conditions for access including grating, handrails. walkways, stairs, safety nets, etc. Measures should be taken to mark and isolate areas that are unsafe to enable subsequent personnel to board the facility and perform tasks in a safe manner.