1、 Guidance Notes on Accidental Load Analysis and Design for Offshore Structures GUIDANCE NOTES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES FEBRUARY 2013 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2013 American Bureau of Sh
2、ipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA ii ABSGUIDANCE NOTES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES .2013 Foreword Foreword These Guidance Notes address the process of identifying, and assessing the effects of, structural loads arising from accidental ev
3、ents. An essential element in the determination of accidental loads in these Guidance Notes is the use of risk based assessment techniques. The traditional approach to accident induced structural loads is the use of prescriptive criteria that are said to be primarily derived from experience and stud
4、ies done for similar situations. Prescriptive criteria may be stated in terms of loading scenarios that may give specific load or pressure magnitudes, directions, durations, area of pressure application, etc. Alternatively some prescriptive criteria may be stated in terms of presumed accident conseq
5、uences; such as, the loss of a major bracing member, extents of accidental collision penetration and flooding, missing mooring components, etc. Over at least the last decade, there has been greater recognition of the use of risk based procedures to replace or support the prescriptive criteria. For e
6、xample in ABS Classification criteria for Mobile Offshore Drilling Units and Floating Production Installations see 1-1-3/5 of the Rules for Building and Classing Floating Production Installations (FPI Rules) and 1-1-4/13 of the Rules for Building and Classing Mobile Offshore Drilling Units (MODU Rul
7、es) risk based evaluations are permitted to establish alternatives to the usual criteria given in the Guide and Rules. For new or novel situations, and structural types; the accidental load criteria may state primary reliance on the risk based accidental load determination; for example see the 2-2/3
8、 Guide for Building and Classing Floating Offshore Liquefied Gas Terminals (FLGT Guide). With the use of risk based criteria, these Guidance Notes are meant to provide an overview of the approach that can be used to identify and assess the effects of accidental structural loads arising from four haz
9、ards (i.e., dropped objects, vessel collision, fire and blast). The given methodologies should be adapted to accidental structural loads arising from other hazards as specified in the Classification criteria of a particular type of offshore installation or MODU. Users are cautioned that Regulatory b
10、odies having jurisdiction over the offshore installation or unit may require the use of prescriptive accidental loads criteria. Accordingly, it is the responsibility of the Owner to discuss with the applicable authorities the acceptance of alternatives based on risk evaluations. These Guidance Notes
11、 become effective on the first day of the month of publication. Users are advised to check periodically on the ABS website www.eagle.org to verify that this version of these Guidance Notes is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to r
12、sdeagle.org. ABSGUIDANCE NOTES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES .2013 iii Table of Contents GUIDANCE NOTES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES CONTENTS SECTION 1 Introduction 1 1 General . 1 3 Design Philosophy for Accidental Loading . 1 SECTI
13、ON 2 Accidental Loading Hazard Evaluation Overview 2 1 General . 2 1.1 Existing Standards for Reference 6 3 Hazard Evaluation Process. 6 3.1 Accidental Hazard Risk Assessment Plan . 6 3.3 Preliminary Accidental Hazard Risk Assessment 7 3.5 Detailed Accidental Hazard Risk Assessment . 10 3.7 Document
14、ation 10 TABLE 1 Overview of the Accidental Hazard Identification Methods 9 TABLE 2 Overview of Accidental Hazard Evaluation Documentation Requirements 11 FIGURE 1 Idealization of Three Distinct Activities in the Accidental Hazard Evaluation Process . 3 FIGURE 2 Overview of the Preliminary Accidenta
15、l Hazard Risk Assessment Process 4 FIGURE 3 Overview of the Detailed Accidental Hazard Risk Assessment Process 5 SECTION 3 Ship Collision Hazards 12 1 Introduction . 12 1.1 Existing Standards for Reference 15 3 Ship Collision Evaluation 15 3.1 Acceptance Criteria . 15 3.3 Assessment Inputs 16 3.5 Sh
16、ip Collision Assessment 18 3.7 Mitigation Alternatives . 21 3.9 Documentation 21 iv ABSGUIDANCE NOTES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES .2013 FIGURE 1 Preliminary Ship Collision Risk Assessment Process 13 FIGURE 2 Detailed Ship Collision Risk Assessment Process . 14 FIGU
17、RE 3 Idealization of the Ship Collision Strain Energy Balance 19 FIGURE 4 Three Alternative Approaches to Predicting Facility and Colliding Vessel Strain Energy 20 SECTION 4 Dropped Object Hazards . 22 1 Introduction . 22 1.1 Existing Standards for Reference 25 3 Dropped Object Evaluation . 25 3.1 A
18、cceptance Criteria . 25 3.3 Assessment Inputs 26 3.5 Dropped Object Assessment . 27 3.7 Mitigation Alternatives 29 3.9 Documentation. 29 FIGURE 1 Dropped Object Preliminary Risk Assessment Process . 23 FIGURE 2 Dropped Object Detailed Risk Assessment Process 24 SECTION 5 Fire Hazards 30 1 Introducti
19、on . 30 1.1 Existing Standards for Reference 33 3 Fire Evaluation 33 3.1 Acceptance Criteria . 33 3.3 Fire Assessment Inputs . 35 3.5 Fire Assessment Methods . 36 3.7 Mitigation Alternatives 38 3.9 Documentation. 39 TABLE 1 Example Fire Evaluation Acceptance Criteria 34 TABLE 2 Relationship between
20、Maximum Acceptable Member Utilization at Ambient Temperature at Maximum Observed Member Temperature API RP 2FB 38 FIGURE 1 Fire Hazard Preliminary Risk Assessment Process . 31 FIGURE 2 Fire Hazard Detailed Risk Assessment Process 32 SECTION 6 Blast Hazards 40 1 Introduction . 40 1.1 Existing Standar
21、ds for Reference 43 3 Blast Evaluation 43 3.1 Acceptance Criteria . 43 3.3 Blast Assessment Inputs . 45 3.5 Blast Assessment Methods . 48 3.7 Mitigation Alternatives 49 3.9 Documentation. 49 ABSGUIDANCE NOTES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES .2013 v TABLE 1 Example Blas
22、t Evaluation Acceptance Criteria . 45 FIGURE 1 Blast Hazard Preliminary Risk Assessment Process 41 FIGURE 2 Blast Hazard Detailed Risk Assessment Process 42 FIGURE 3 Generic Pressure Curve Highlighting Key Parameters. 47 APPENDIX 1 Abbreviations . 50 This Page Intentionally Left Blank ABSGUIDANCE NO
23、TES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES .2013 1 Section 1: Introduction SECTION 1 Introduction 1 General These Guidance Notes provide an overview of the process for identifying and assessing a variety of accidental loading scenarios that can be experienced by offshore oil
24、and gas facilities with an emphasis on minimizing health and safety, environment, and facility risks. While a wide range of potential accidents exists, the focus here is on key events that can affect the structural performance of the facility, namely ship collisions, dropped objects, fires, and blas
25、t loadings. The same conceptual process can be used with other accidental loading scenarios, such as the survival of permanent mooring systems under extreme environmental conditions. The guidance highlights activities associated with the assessment including: i) Accidental loading scenario hazard ev
26、aluation overview ii) Ship collision hazards iii) Dropped object hazards iv) Fire hazards v) Blast hazards These Guidance Notes are not intended to serve as a design or assessment standard, but rather to highlight the primary activities relating to accidental loading assessment to promote more effic
27、ient and safer design and operation of the facility. 3 Design Philosophy for Accidental Loading Accidents are defined as unintended events that arise during the course of installing, operating, or decommissioning an offshore oil and gas facility. The purpose of assessing accidental loadings is to un
28、derstand the extent of initial damage and verify that the accident does not escalate in terms of personnel health and safety, environmental concerns, or facility damage (i.e., financial consequences). Escalation of the accident occurs when the local failure causes a chain of additional cascading eve
29、nts. For instance, a fire may impinge on a primary structural member resulting in its failure. While this may prove to be a financial consequence to the facility in terms of the member repair, an escalation of additional members failing may raise the event to include a subsequent global collapse wit
30、h potential loss of life or significant environmental release. Unlike design loadings where elastic behavior is expected, the accidental loading assessments may consider the structure well into the plastic (inelastic) regime. The sheer magnitude of the accident makes requiring an elastic response im
31、practical in most cases given the low likelihood of the event occurring. The acceptance criteria for the events will need to be modified to reflect the acceptability of these high strains and large deflections during the event provided that the damage is such that the event does not escalate. The pr
32、ocess for assessing accidental loadings follows the standard hazard risk assessment method for the oil and gas industry that incorporates traditional hazard identification methods and existing structural assessment methods. First, a preliminary risk assessment examines the potential for accidental l
33、oading based on evaluating the risk exposure that includes both the likelihood of the accident and its consequence. A detailed accidental hazard risk assessment is then performed, if required. The events identified during the preliminary risk assessment are categorized so that low level risk and ext
34、remely low likelihood events are removed from further consideration based on the Owners risk tolerance. A refined assessment is then performed on the remaining accidents with the intention to either conclude sufficient structural capacity or operational constraints exist to reduce the risk (i.e., ad
35、vanced analysis reduces the level of conservatism present in the initial risk assessment), or highlight mitigation activities that can successfully mitigate the risk exposure. 2 ABSGUIDANCE NOTES ON ACCIDENTAL LOAD ANALYSIS AND DESIGN FOR OFFSHORE STRUCTURES .2013 Section 2: Accidental Loading Hazar
36、d Evaluation Overview SECTION 2 Accidental Loading Hazard Evaluation Overview 1 General The accidental loading scenario hazard evaluation defines potential accidents that may occur to the facility during its life from installation to decommissioning and assesses the corresponding risk exposure. For
37、the purposes of these Guidance Notes, an accident is defined as a scenario involving a ship collision, dropped object, fire, or blast that introduces risk to personnel, the environment, or the facility. Fundamentally, there are two basic approaches to addressing the hazards faced by an offshore faci
38、lity: hazard control and predictive hazard evaluation (API RP 14J). Hazard control requires that the facility is designed and operated in a manner consistent with Industry standard practices. While not explicitly stating as such, this approach has a built-in hazard analysis component as industry sta
39、ndard practices evolve to promote the safe operations of many facilities and reflect prior hazard analyses and incident investigations. Typically, a simple checklist approach is utilized to verify standard practices are maintained from design and throughout the service life of the facility. Predicti
40、ve hazard evaluation provides a method to address asset-specific hazards that may be outside of the coverage of hazard control via standards compliance. The steps involved in a predictive hazard analysis are: identify pertinent hazards, evaluate the risk exposure for each hazard, and mitigate the li
41、kelihood and/or consequences associated with each event. These Guidance Notes do not address the hazard control by utilizing industry standard practices. It is assumed that standard practices are adhered to at all phases of the facilitys design and operation. The focus on the accidental loading scen
42、ario identification study is in the execution of a predictive hazard evaluation of the proposed accidents. The proposed accidental loading scenario evaluation process is structured in accordance with a traditional risk assessment where an initial hazard identification defines potential accidents tha
43、t may occur to the facility during its life from installation to decommissioning and then the corresponding risk exposure is developed based on likelihood and consequence for each event. The process is idealized as three distinct activities: develop an accidental hazard risk assessment plan, perform
44、 a preliminary risk assessment, and perform a detailed risk assessment as warranted, as shown in Section 2, Figure 1. The process begins with the definition of the hazard risk assessment method, which focuses on defining the types of accidents considered (in this case, ship collisions, dropped objec
45、ts, fire, and blast), definition of the governing standards driving the evaluation, and the risk assessment guidance (including the risk matrix definition common for all hazards). Once the method is defined, the second step involves the preliminary risk assessment for specific accidents as shown in
46、Section 2, Figure 2. Accidental hazard identification defines the events including a detailed description (accident type, loading characteristics, and safeguards present) after which an assessment is performed to determine the associated likelihood and consequence from which a preliminary risk chara
47、cterization can be determined. The detailed accidental hazard risk assessment presented in Section 2, Figure 3 utilizes information from the preliminary risk assessment to determine if the risk exposure is acceptable or if additional assessment or accident mitigations are required. When identifying
48、potential accidental hazards, these Guidance Notes neglect joint events where one accident type escalates into another. For instance, a dropped object evaluation only considers the structural damage associated with the impact event and will not address the potential escalation into a fire or blast e
49、vent. It is assumed that the initial hazard identification effort will highlight potential joint events for further highly specialized study where loading and structural damage reflect the joint event. The remainder of this Section presents a high-level process for identifying and characterizing accidents and the assessment approach. Details pertaining to the execution of the hazard identification and assessment activities for a given type of accident are given in Sections 3 through 6. Section 2 Accidental Loading Hazard Evaluation Overview ABSGUIDANCE NOTES ON ACCIDENTAL LOAD ANAL
