6 IN-SERVICE INSPECTION AND MAINTENANCE
6.2 ISO 19902 and 19904-
As discussed below, the ISO approach to in-service inspection requirements adopts the Structural Integrity Management (SIM) methodology and also applies RBI procedures.
The main focus of Clause 23 of the ISO 19902 is on the detailed guidance and the requirements for the SIM system for fixed offshore structures. The standards specify that they apply to “fixed steel offshore structures located anywhere in the world, built to any design and fabrication standards, and of any age”, highlighting inherently that the degradation mechanisms and failure modes of structures installed in the marine environment are similar, regardless of the basis for design. However, consideration needs to be given to the specifics of the installation degradation rates, resulting from the design and site environmental factors, the loading and operating history, and the effectiveness of the preventive measures (i.e. coating or cathodic protection system). The high-level schematic of the SIM cycle is shown in Figure 6-1. The four stages of the SIM are shown to involve data collection and evaluation and development of inspection strategy and a detailed inspection program.
The ISO 19902 also provides detailed description of each these four activities within the SIM programme. The standard states that the inspection strategy should contain scheduled and unscheduled inspections. The scheduled inspections are divided into the following sub-categories:
• Baseline inspection – inspection conducted as soon as practical after installation and commissioning (if possible, within first year of operation) to establish the as-installed condition
• Periodic inspection – regular in-service inspection, with timing and scope of work determined based on the inspection strategy and inspection programme
• Special inspection- to monitor known defects, damage, scour, etc. and to assess the performance of repairs undertaken to assure fitness-for-purpose of the structure (conducted approximately 1 year after completion of the repair)
Similar to API RP 2A, the unscheduled inspections are required to evaluate a structure’s condition following an environmental event (i.e. hurricane) or incident (i.e. boat collision).
As an alternative to the SIM, the ISO 19902 presents the requirements for the default periodical inspection requirements. As shown in Table 6-2, the ISO standard follows the API RP-2A philosophy (API requirements were directly adopted, with some minor changes for inspection intervals where ISO requires the lower bounds of the API allowable timeframe for corresponding inspection levels).
The philosophy of the in-service inspections and maintenance of the floating installations presented in the ISO 19904-1 (Clause 18 of the standard), follows the above discussed philosophy of the ISO 19902. The default inspection intervals and scope are also presented. However, similar to ISO 19902, the ISO 19904 focuses on the requirements for the SIM program. It is also stated that the requirements of the RCS which classified the unit should be implemented in the inspection program. A separate issue of the inspection planning related to confined spaces and usually closed areas is also addressed.
6.3 NORSOK N-005
The N-005 standard /27/ presents only high level requirements regarding in-service inspection program. The platform operator is responsible for preparing this program based on the characteristic of the structure, loading history, and inspection findings. No specific requirements regarding the inspection intervals are presented. However the document includes details regarding preparations for inspection and underwater inspection methods (see Table 6-1). More detailed guidelines regarding the in-service inspection of various types of structures (jackets, column stabilized units, ship-shaped vessels and concrete structures) are presented in the normative Annexes C through F, of the standard, respectively.
BOEMRETA&RNO.677
FINAL REPORT ON COMPARISON OF API,ISO, AND NORSOKOFFSHORE STRUCTURAL STANDARDS
Table 6-1 Underwater Inspection Methods
6.4 Summary
All standards emphasize the importance of keeping records of performed in-service inspections, maintenance and structural modifications of the platform. The synergy between different phases of the structural integrity management is highlighted as one of the most important factors extending the lifetime of the structure and increasing the safety of operations.
The standards also define Owner’s responsibility for preparation and proper execution of the inspection program, which may result in decreased (or increased, depending on an outcome of the evaluation and findings of the historical surveys) pre-defined frequencies for different levels of in- service inspections. It is also highlighted that analyzing the inspection findings and implementing a SIM program can reduce costs related to maintenance.
In the ISO and NORSOK standards more significant attention is given to the risk assessment and probability based inspection methods. This approach often requires using of advanced analysis methods and is aligned with current trends and developments in the field of structure integrity management. The API current standard, representing more traditional approach, allows for the
SIM. Detailed guidance for SIM and the Risk Based Inspection (RBI) planning will be implemented into the API system in the planned API RP-2SIM for publication in 2011 or 2012. All standards also include list of preselected areas and minimum inspection requirements for periodical inspections. These minimum requirements for floating installations should also be reviewed and updated based on the requirements of the RCS classifying the vessel, if they are found to be more conservative.
BOEMRETA&RNO.677
FINAL REPORT ON COMPARISON OF API,ISO, AND NORSOKOFFSHORE STRUCTURAL STANDARDS
BOEMRETA&RNO.677
FINAL REPORT ON COMPARISON OF API,ISO, AND NORSOKOFFSHORE STRUCTURAL STANDARDS