ISO/TC 67/SC 7/WG 3 - Fixed steel structures

This document contains requirements for defining the seismic design procedures and criteria for offshore structures; guidance on the requirements is included in Annex A. The requirements focus on fixed steel offshore structures and fixed concrete offshore structures. The effects of seismic events on floating structures and partially buoyant structures are briefly discussed. The site-specific assessment of jack-ups in elevated condition is only covered in this document to the extent that the requirements are applicable. Only earthquake-induced ground motions are addressed in detail. Other geologically induced hazards such as liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are mentioned and briefly discussed. The requirements are intended to reduce risks to persons, the environment, and assets to the lowest levels that are reasonably practicable. This intent is achieved by using: a) seismic design procedures which are dependent on the exposure level of the offshore structure and the expected intensity of seismic events; b) a two-level seismic design check in which the structure is designed to the ultimate limit state (ULS) for strength and stiffness and then checked to abnormal environmental events or the abnormal limit state (ALS) to ensure that it meets reserve strength and energy dissipation requirements. Procedures and requirements for a site-specific probabilistic seismic hazard analysis (PSHA) are addressed for offshore structures in high seismic areas and/or with high exposure levels. However, a thorough explanation of PSHA procedures is not included. Where a simplified design approach is allowed, worldwide offshore maps, which are included in Annex B, show the intensity of ground shaking corresponding to a return period of 1 000 years. In such cases, these maps can be used with corresponding scale factors to determine appropriate seismic actions for the design of a structure, unless more detailed information is available from local code or site-specific study. NOTE For design of fixed steel offshore structures, further specific requirements and recommended values of design parameters (e.g. partial action and resistance factors) are included in ISO 19902, while those for fixed concrete offshore structures are contained in ISO 19903. Seismic requirements for floating structures are contained in ISO 19904, for site-specific assessment of jack-ups and other MOUs in the ISO 19905 series, for arctic structures in ISO 19906 and for topsides structures in ISO 19901‑3.

This document specifies requirements and provides recommendations applicable to the following types of fixed steel offshore structures for the petroleum and natural gas industries: ? caissons, free-standing and braced; ? jackets; ? monotowers; ? towers. In addition, it is applicable to compliant bottom founded structures, steel gravity structures, jack-ups, other bottom founded structures and other structures related to offshore structures (such as underwater oil storage tanks, bridges and connecting structures). This document contains requirements for planning and engineering of the design, fabrication, transportation and installation of new structures as well as, if relevant, their future removal. NOTE 1 Specific requirements for the design of fixed steel offshore structures in arctic environments are presented in ISO 19906. NOTE 2 Requirements for topsides structures are presented in ISO 19901-3; for marine operations in, ISO 19901‑6; for structural integrity management, in ISO 19901-9 and for the site-specific assessment of jack-ups, in ISO 19905‑1.

This document specifies principles for the structural integrity management (SIM) of offshore structures subjected to known or foreseeable types of actions. This document specifies requirements and provides recommendations applicable to the following types of fixed steel offshore structures for the petroleum and natural gas industries: — caissons, free-standing and braced; — jackets; — monotowers; — towers. This document is applicable to topsides, including but not limited to the main decks, deck legs, topsides modules, crane pedestals, helideck, drilling derrick, skid beams, flare booms, exhaust towers, radio tower, conductor support frames, and lifeboat davits. In addition, it is applicable to compliant bottom founded structures, steel gravity structures, jack-ups, other bottom founded structures and other structures related to offshore structures (e.g. underwater oil storage tanks, bridges and connecting structures), to the extent to which its requirements are relevant. This document contains requirements for planning and engineering of the following tasks: a) integrity management data requirements; b) in-service inspection and integrity management of both new and existing structures; c) assessment of existing structures; d) evaluation of structures for reuse at different locations; e) evaluation of structures for their future removal.

ISO 19901-1:2015 gives general requirements for the determination and use of meteorological and oceanographic (metocean) conditions for the design, construction and operation of offshore structures of all types used in the petroleum and natural gas industries. The requirements are divided into two broad types: - those that relate to the determination of environmental conditions in general, together with the metocean parameters that are required to adequately describe them; - those that relate to the characterization and use of metocean parameters for the design, the construction activities or the operation of offshore structures. The environmental conditions and metocean parameters discussed are: - extreme and abnormal values of metocean parameters that recur with given return periods that are considerably longer than the design service life of the structure, - long-term distributions of metocean parameters, in the form of cumulative, conditional, marginal or joint statistics of metocean parameters, and - normal environmental conditions that are expected to occur frequently during the design service life of the structure. Metocean parameters are applicable to: - the determination of actions for the design of new structures, - the determination of actions for the assessment of existing structures, - the site-specific assessment of mobile offshore units, - the determination of limiting environmental conditions, weather windows, actions and action effects for pre-service and post-service situations (i.e. fabrication, transportation and installation or decommissioning and removal of a structure), and - the operation of the platform, where appropriate. NOTE Specific metocean requirements for site-specific assessment of jack-ups are contained in ISO 19905‑1, for arctic offshore structures in ISO 19906 and for topside structures in ISO 19901‑3.

ISO 19901-3:2014 gives requirements for the design, fabrication, installation, modification and structural integrity management for the topsides structure for an oil and gas platform. It complements ISO 19902, ISO 19903, ISO 19904‑1, ISO 19905‑1 and ISO 19906, which give requirements for various forms of support structure. Requirements in this part of ISO 19901 concerning modifications and maintenance relate only to those aspects that are of direct relevance to the structural integrity of the topsides structure. ISO 19901-3:2014 is applicable to the topsides of offshore structures for the petroleum and natural gas industries, as follows: topsides of fixed offshore structures; discrete structural units placed on the hull structures of floating offshore structures and mobile offshore units; certain aspects of the topsides of arctic structures. ISO 19901-3:2014 contains requirements for, and guidance and information on, the following aspects of topsides structures: design, fabrication, installation and modification; in-service inspection and structural integrity management; assessment of existing topsides structures; reuse; decommissioning, removal and disposal; prevention, control and assessment of fire, explosions and other accidental events. ISO 19901-3:2014 applies to structural components including the following: primary and secondary structure in decks, module support frames and modules; flare structures; crane pedestal and other crane support arrangements; helicopter landing decks (helidecks); permanent bridges between separate offshore structures; masts, towers and booms on offshore structures.

ISO 19901-2:2017 contains requirements for defining the seismic design procedures and criteria for offshore structures; guidance on the requirements is included in Annex A. The requirements focus on fixed steel offshore structures and fixed concrete offshore structures. The effects of seismic events on floating structures and partially buoyant structures are briefly discussed. The site-specific assessment of jack-ups in elevated condition is only covered in ISO 19901-2:2017 to the extent that the requirements are applicable. Only earthquake-induced ground motions are addressed in detail. Other geologically induced hazards such as liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are mentioned and briefly discussed. The requirements are intended to reduce risks to persons, the environment, and assets to the lowest levels that are reasonably practicable. This intent is achieved by using: a) seismic design procedures which are dependent on the exposure level of the offshore structure and the expected intensity of seismic events; b) a two-level seismic design check in which the structure is designed to the ultimate limit state (ULS) for strength and stiffness and then checked to abnormal environmental events or the abnormal limit state (ALS) to ensure that it meets reserve strength and energy dissipation requirements. Procedures and requirements for a site-specific probabilistic seismic hazard analysis (PSHA) are addressed for offshore structures in high seismic areas and/or with high exposure levels. However, a thorough explanation of PSHA procedures is not included. Where a simplified design approach is allowed, worldwide offshore maps, which are included in Annex B, show the intensity of ground shaking corresponding to a return period of 1 000 years. In such cases, these maps may be used with corresponding scale factors to determine appropriate seismic actions for the design of a structure. For design of fixed steel offshore structures, further specific requirements and recommended values of design parameters (e.g. partial action and resistance factors) are included in ISO 19902, while those for fixed concrete offshore structures are contained in ISO 19903. Seismic requirements for floating structures are contained in ISO 19904, for site-specific assessment of jack-ups and other MOUs in ISO 19905 (all parts), for arctic structures in ISO 19906 and for topsides structures in ISO 19901‑3.

ISO 19901-3:2010 gives requirements for the design, fabrication, installation, modification and structural integrity management for the topsides structure for an oil and gas platform. It complements ISO 19902, ISO 19903, ISO 19904‑1, ISO 19905‑1 and ISO 19906, which give requirements for various forms of support structure. Requirements in ISO 19901-3:2010 concerning modifications and maintenance relate only to those aspects that are of direct relevance to the structural integrity of the topsides structure. The actions on (structural components of) the topsides structure are derived from ISO 19901-3:2010, where necessary in combination with other International Standards in the ISO 19901 series. The resistances of structural components of the topsides structure can be determined by the use of international or national building codes, as specified in ISO 19901-3:2010. If any part of the topsides structure forms a primary structural component of the overall structural system of the whole platform, the requirements of ISO 19901-3:2010 are supplemented with applicable requirements in ISO 19902, ISO 19903, ISO 19904‑1, ISO 19905‑1 and ISO 19906. ISO 19901-3:2010 is applicable to the topsides of offshore structures for the petroleum and natural gas industries, as follows: topsides of fixed offshore structures; discrete structural units placed on the hull structures of floating offshore structures and mobile offshore units; certain aspects of the topsides of arctic structures. ISO 19901-3:2010 is not applicable to those parts of the superstructure of floating structures that form part of the overall structural system of the floating structure; these parts come under the provisions of ISO 19904‑1. ISO 19901-3:2010 only applies to the structure of modules on a floating structure that do not contribute to the overall integrity of the floating structural system. ISO 19901-3:2010 is not applicable to the structure of hulls of mobile offshore units. ISO 19901-3:2010 does not apply to those parts of floating offshore structures and mobile offshore units that are governed by the rules of a recognized certifying authority and which are wholly within the class rules. Some aspects of ISO 19901-3:2010 are also applicable to those parts of the hulls of floating offshore structures and mobile offshore units that contain hydrocarbon processing, piping or storage. ISO 19901-3:2010 contains requirements for, and guidance and information on, the following aspects of topsides structures: design, fabrication, installation and modification; in-service inspection and structural integrity management; assessment of existing topsides structures; reuse; decommissioning, removal and disposal; prevention, control and assessment of fire, explosions and other accidental events. ISO 19901-3:2010 applies to structural components including the following: primary and secondary structure in decks, module support frames and modules; flare structures; crane pedestal and other crane support arrangements; helicopter landing decks (helidecks); permanent bridges between separate offshore structures; masts, towers and booms on offshore structures.

ISO 19901-1:2005 gives general requirements for the determination and use of meteorological and oceanographic (metocean) conditions for the design, construction and operation of offshore structures of all types used in the petroleum and natural gas industries.

ISO 19901-2:2004 contains requirements for defining the seismic design procedures and criteria for offshore structures; guidance on the requirements is included. The requirements are applicable to fixed steel structures and fixed concrete structures. The effects of seismic events on floating structures and partially buoyant structures are also briefly discussed. The site-specific assessment of jack-ups in elevated condition is only covered in ISO 19901-2:2004 to the extent that the requirements are applicable. Only earthquake-induced ground motions are addressed in detail. Other geologically-induced hazards such as liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves are mentioned and briefly discussed. The requirements are intended to reduce risks to persons, the environment, and assets to the lowest levels that are reasonably practicable. This intent is achieved by using seismic design procedures which are dependent on the platform's exposure level and the expected intensity of seismic events and a two-level seismic design check in which the structure is designed to the ultimate limit state (ULS) for strength and stiffness and then checked to abnormal environmental events or the accidental limit state (ALS) to ensure that it meets reserve strength and energy dissipation requirements. For high seismic areas and/or high exposure level fixed structures, a site-specific seismic hazard assessment is required; for such cases, the procedures and requirements for a site-specific probabilistic seismic hazard analysis (PSHA) are addressed. However, a thorough explanation of PSHA procedures is not included. Where a simplified design approach is allowed, worldwide offshore maps are included that show the intensity of ground shaking corresponding to a return period of 1 000 years. In such cases, these maps may be used with corresponding scale factors to determine appropriate seismic actions for the design of a structure.

Contains guidelines for the design of steel, fixed offshore platforms and contains provisions for specific regional areas. Applicable to the design of complete platform structures including substructures, topside structures and foundations. Specifies design principles that are also applicable to the successive stages in construction (fabrication, transportation and installation).