ISO 19901-2:2022

Overview

ISO 19901-2:2022 - "Petroleum and natural gas industries - Specific requirements for offshore structures - Part 2: Seismic design procedures and criteria" - defines seismic design procedures and acceptance criteria for offshore structures. The standard focuses on fixed steel and fixed concrete offshore structures, addresses earthquake-induced ground motions in detail, and briefly discusses effects on floating and partially buoyant units. It establishes a framework to reduce risks to people, the environment and assets through exposure-dependent seismic design, a two-level design check (ULS and ALS), and guidance on site-specific seismic hazard assessment.

Key topics and technical requirements

• Two-level seismic design: design to the Ultimate Limit State (ULS) for strength and stiffness, then check to the Abnormal Limit State (ALS) for reserve strength and energy dissipation.
• Seismic event definitions: Extreme Level Earthquake (ELE) - reasonable probability during life; Abnormal Level Earthquake (ALE) - very low probability, abnormal severity.
• Seismic action procedures: provides both a simplified seismic action procedure (supported by worldwide offshore spectral acceleration maps in Annex B for a 1 000-year return period) and a detailed procedure involving site-specific assessments.
• Site-specific seismic hazard: addresses Probabilistic Seismic Hazard Analysis (PSHA) and deterministic approaches; PSHA procedures are required for high seismic exposure but not explained in full detail.
• Spectral acceleration & soil effects: spectral acceleration data, soil classification, local site response analyses and attenuation considerations are specified.
• Geological hazards: mentions liquefaction, slope instability, faults, tsunamis, mud volcanoes and shock waves and their relevance to seismic design.
• Site investigation and risk category: requirements for site investigation and defining seismic risk category based on exposure and expected seismic intensity.

Practical applications

• Design and assessment of fixed offshore platforms and jackets to resist earthquake loading.
• Input standard for structural analysis, dynamic response assessment and selection of seismic actions (spectral accelerations).
• Basis for scope of site-specific seismic hazard studies (PSHA/DSHA) and local site-response analyses.
• Use in project specifications, regulatory compliance, and risk-based design decisions for offshore oil & gas facilities.

Who should use this standard

• Offshore structural and seismic engineers
• Geotechnical and seismic hazard analysts
• Offshore asset owners, operators and project managers
• Regulators and certification bodies specifying seismic criteria for offshore installations

Related standards

• ISO 19900 (general offshore requirements)
• ISO 19902 (fixed steel offshore structures)
• ISO 19903 (fixed concrete offshore structures)
• ISO 19904 (floating structures)
• ISO 19905 (jack-ups and MOUs)
• ISO 19906 (arctic structures)
• ISO 19901-3 (topsides)

Keywords: ISO 19901-2:2022, seismic design, offshore structures, PSHA, spectral acceleration, fixed steel platforms, fixed concrete platforms, ALE, ELE, offshore seismic design.