API Bull 2HINS-2009 pdf download.Guidance for Post-hurricane Structural Inspection of Offshore Structures.
3 Organization of Document This document is organized in a progressive manner such that the user starts with the early sections to determine the need for post-hurricane inspections. If inspections are required, the later sections provide specific guidance. Section 4 describes the initiators to determine the need for and the general extent of inspections that should be performed. Section 5 provides guidance for safe initial boarding of the structure as well as guidance for the above-water structure inspection. The above-water inspections also assist in establishing the need for below-water inspections. Section 6 provides guidance for below-water inspection of fixed structures. Section 7 provides guidance for below-water inspection of the external and internal structure of floating structures. Section 8 provides guidance for documentation. 4 Inspection Initiators 4.1 General After a hurricane has passed through the Gulf of Mexico, inspection initiators determine if an offshore structure requires a special post-hurricane structural inspection. The inspection initiators are based upon the following: — the structure’s exposure to hurricane conditions; and — indications that the structure has suffered damage, as in the case where large objects may have fallen overboard or the structure is leaning, tilted or listing. For the purposes of this document, a hurricane event is a named tropical cyclone, as defined by the National Hurricane Center (NHC), which enters or generates in the Gulf of Mexico. The NHC is the official U.S. agency for establishing hurricanes. NHC defines a hurricane as a storm with maximum sustained 1-minute surface winds greater than or equal to 74 mph (64 kt). Surface winds are those observed to occur at the standard meteorological height of 10 m (33 ft) in an unobstructed exposure. 4.2 Assessment Process The process for determining if a structure should be inspected following a hurricane is shown in Figure 1.
The process for a particular structure is initiated when the structure has been exposed to wind speeds equal to or greater than hurricane conditions, as defined in 4.1. The wind speed used in this determination, can be based upon any of the following: — measured wind speeds at the structure location, using calibrated monitoring equipment demonstrated to be accurate and operating continuously throughout the duration of the hurricane; — maximum hurricane wind speed based upon hindcast data, using generally accepted meteorological practices. A special above-water inspection should be performed once it is determined the structure has been subjected to hurricane winds or greater. The intent of this inspection is to gain a general understanding of the condition of the structure to determine if it is safe for boarding, if above-water damage is evident and if any large objects have fallen overboard possibly damaging the structure below water. Guidance for the special above-water inspection is provided in Section 5. An engineering check should be performed in those cases when no structural damage is apparent in order to determine whether the hurricane conditions at the site or the structure response exceeded the limits beyond which the structure may have suffered damage. This can be a simple comparison of the hurricane conditions experienced by the structure to the structure’s design environmental conditions, or a more detailed engineering study intended to determine if the hurricane loads or structure motions were sufficient to cause damage.
A special below-water inspection should be performed when the special above-water inspection finds structural damage indicating potential below-water damage, or when the results of the engineering check indicate that the structure could be damaged below-water. The scope and methods of the below-water inspection are dependent upon the findings of the special above-water inspection and/or the results of the engineering check. Guidance for the special below-water inspection for fixed and floating structures is provided in Section 6 and Section 7. 4.3 Engineering Check 4.3.1 General The engineering check is used to determine if the hurricane may have damaged the structure and a special below- water inspection is required. There are various methods to conduct the engineering check with four methods defined in 4.3.2 to 4.3.5. Additional methods may be applicable if they can be demonstrated to accurately determine the hurricane conditions in which structural damage is expected. Typically, the engineering checks are performed in the order shown since they become increasingly more complex.