Revisiting the FPSO São Mateus Accident From a Human Reliability Perspective Using Phoenix HRA Methodology

Several incidents in the offshore oil and gas industry have human errors among core events in incident sequence. Nonetheless, human error probabilities are frequently neglected by offshore risk estimation. Human Reliability Analysis (HRA) allows human failures to be assessed both qualitatively and quantitatively. In the petroleum industry, HRA is usually applied using generic methods developed for other types of operation. Yet, those may not sufficiently represent the particularities of the oil and gas industry. Phoenix is a model-based HRA method, designed to address limitations of other HRA methods. Its qualitative framework consists of three layers of analysis composed by a Crew Response Tree, a human response model, and a causal model. This paper applies a version of Phoenix, the Phoenix for Petroleum Refining Operations (Phoenix-PRO), to perform a qualitative assessment of human errors in the CDSM explosion. The CDSM was a FPSO designed to produce natural gas and oil to Petrobras in Brazil. On 2015 an explosion occurred leading to nine fatalities. Analyses of this accident have indicated a strong contribution of human errors. In addition to the application of the method, this paper discusses its suitability for offshore operations HRA analyses.

Sensitivity Analysis in Parametric Rolling of a Modern Cruise Ship Using Numerical Simulations in 6-DOF

Parametric roll is a nonlinear phenomenon that can result in large roll angles coupled with significant pitch motions. These motions might induce large loads on the ship structure, and compromise the safety of the crew and the cargo. The severity of the motions might reach to such levels that capsizing might occur. In this study sensitivity analysis in parametric rolling of a modern cruise ship is investigated using numerical simulations. Several parameters were considered as sources of uncertainty such as the combined effect of GM and roll radius of gyration, roll damping, ship speed, and fin characteristics. In terms of fin characteristics, fin angle rate and maximum angle, fin area and aspect ratio, and fin gains were investigated. Additionally, the non-ergodicity of parametric roll was studied as well as the effect of simulation duration on the statistics of parametric roll. The simulations were carried out with a hybrid time-domain seakeeping and manoeuvring code. The time-domain code was used in combination with a strip-theory based frequency-domain program in order to calculate diffraction and radiation forces as well as added-mass. The time-domain code was able simulate the dynamic behavior of a steered ship in 6-DOF, where the motions can be large up to the moment of capsize.

Fracture Toughness Characterization of LSAW UOE Pipes in Sour Media and Implications on Burst Pressure

Large diameter Sour Service Pipelines are designed for the safe and efficient transportation of production fluids containing H2S. This service condition exposes the pipe to hydrogen embrittlement mechanisms and demands a material with high Sulfide Stress Cracking (SSC) resistance, and thus, a high fracture toughness in a representative sour environment. Engineering Critical Assessment (ECA) procedures are usually employed to determine the suitability of a pipeline design, These procedures require the correct determination of the material fracture mechanical properties. Although Method D of NACE TM0177_16 [1] using DCB specimens is the currently recognized testing methodology to evaluate SSC pipe performance, other type of tests could be employed for the purpose of an ECA. In the present paper, a fracture mechanics experimental program in sour environment is presented. Parent Pipe and Weld Material of Longitudinal Submerged Arc Welded (LSAW) large diameter pipes in H2S were studied. Fracture Toughness Parameters, such K-limit from standard DCB tests and K-threshold from Single Edge Notch Tension (SENT) specimens under constant loading, are compared and discussed. Furthermore, the fracture toughness values obtained from SENT specimens in sour environment are used to estimate the burst pressure using an ECA procedure.

Fatigue Analysis for Mooring System of a Spar-Type Floating Offshore Wind Turbine

This paper aims to perform a time-domain mooring fatigue analysis for a Spar-type floating offshore wind turbine operated in the South China Sea. Tension ranges of mooring lines are achieved from a hydrodynamic analysis where the effects of wind, wave and current are considered. A rainflow counting method is used to calculate the number of mooring tension cycles with corresponding ranges. The fatigue lives of mooring lines are then predicted by Palmgren-Miner’s rule according to T-N & S-N curves. A comparison of fatigue lives predicted by T-N & S-N curves-based approaches with/without considering safety factors is made. The results show that the T-N curves-based approach is more conservative than the S-N curves-based approach if safety factors are not considered in the two approaches, while the fatigue lives predicted by both approaches are in general comparable when the safety factors suggested by API and DNVGL are applied in the two approaches. A comparative study of three kinds of R4 grade studless mooring chains with different diameters (2.5-inch, 4-inch, 5-inch) is also conducted and the results show that the design with the 2.5-inch chain does not meet the fatigue requirements.

Floating Hose Behavior During Different Scenarios of an Offloading Operation

Considering the deep water oil exploitation in remote fields far away from the coast, the use of shuttle tankers connected to FPSOs (Floating, Production, Storage and Offloading) for offloading and oil transporting shows to be a preferred alternative compared to constructing oil pipelines considering technic and economic matters, even if offshore offloading operation is still considered one of the riskiest operations in the offshore environment. From the concerns about hazards of an offloading operation, one is related to hose failure during oil transferring and the consequences on the environment. Different aspects of FPSO and shuttle tanker influence floating hose behavior during offloading operation as environmental condition, ships loading conditions, ships distance, heading, FPSO offloading station position and number of hose sections. The different aspects may be combined in several scenarios, in which integrity of floating hoses in terms of tension and bending strength shall be guaranteed. In the present paper, global numerical analyses of offloading operation considering a spread moored FPSO and a typical dynamic positioning shuttle tanker (DPST) moored in tandem are carried out. The analyses are based on a coupled numerical model of FPSO, DPST and floating hose [2]. Covering a wide combination of the scenarios considering the aspects listed above, full time domain simulation is used to estimate hose sections force and moments during the operation. Numerical model results are validated for a couple of scenarios against field data. With focus on floating hose integrity, the main objective is to define minimum requirements for a safe offloading operation, as environmental criteria, maximum and minimum distances between FPSO and DPST, limit operating sectors and minimum number of hose sections. The results can be used as reference to offloading procedures and manuals of owners and operators in combination with recommendations of international organizations.

Barrier Analysis of Emergency Disconnect on DP Mobile Offshore Drilling Units

Technical, operational and organization barrier elements related to the emergency disconnect on dynamically positioned mobile offshore drilling units on the Norwegian Continental Shelf are identified. Position loss scenarios are analyzed based on the published station-keeping incidents by IMCA (International Marine Contractors Association). How these barrier elements may fail in different types of position loss scenarios are addressed qualitatively and quantitatively in an event tree model. A case study is provided in the paper and notational probability of failure to disconnect given position loss is calculated. Risk reduction effect of various barrier elements are investigated by sensitivity studies. The paper provides insights into risk given position loss and failure of emergency disconnect on DP MODUs. It offers decision support for risk management of DP drilling and well operations in shallow water and harsh environment.

Development of Accidental Scenarios Involving Human Errors for Risk Assessment in Restricted Waters

The navigation in restricted waters imposes several challenges when compared to open sea navigation. Smaller dimensions, higher traffic density and the dynamics of obstacles such as sandbanks are examples of contributors to the difficulty. Due to these aspects, local experienced maritime pilots go onboard in order to support the ship’s crew with their skills and specific regional knowledge. Despite these efforts, several accidents still occur around the world. In order to contribute to a better understanding of the events composing accidental sequences, this paper presents a hybrid modelling specific for restricted waters. The main techniques used are the fault tree analysis and event tree analysis. The former provides a framework to investigate the causes, while the latter allows modelling the sequence of actions necessary to avoid an accident. The models are quantified using statistical data available in the literature and a prospective human performance model developed by the Technique for Early Consideration of Human Reliability (TECHR). The results include combined estimates of human error probabilities and technical failure probabilities, which can be used to inform the causation factor for a waterway risk analysis model. In other words, given that the ship encounters a potential accidental scenario while navigating, the proposed models allow computing the failure probability that of the evasive actions sequence. The novelty of this work resides on the possibility of explicitly considering dynamicity and recovery actions when computing the causation factor, what is not a typical feature of similar works. The results obtained were compared with several results available in the literature and have been shown to be compatible.

Assessing Climate Change in the North Atlantic Wave Regimes

An improved understanding of the present and future marine climatology is necessary for numerous activities, such as operation of offshore structures, optimization of ship routes and the evaluation of wave energy resources. To produce global wave information, the WW3 wave model was forced with wind and ice-cover data from an RCP8.5 EC-Earth system integration for two 30-year time slices. The first covering the periods from 1980 to 2009 represents the present climate and the second, covering the periods from 2070–2099, represents the climate in the end of the 21st century. Descriptive statistics of wind and wave parameters are obtained for different 30-year time slices. Regarding wind, magnitude and direction will be used. For wave, significant wave height (of total sea and swell), mean wave period, peak period, mean wave direction and energy will be investigated. Changes from present to future climate are evaluated, regarding both mean and extreme events. Maps of the theses statistics are presented. The long-term monthly joint distribution of significant wave heights and peak periods is generated. Changes from present to future climate are assessed, comparing the statistics between time slices.

Treatment of Bending Deformations in Maritime Crash Analyses

This paper focuses on the bending deformation experienced by metallic materials and its characterization during the crash analysis of ship structures. These analyses are conducted with plane stress shell elements for computational reasons. The inherent nature of through thickness plane stress poses restrictions on how the bending associated stress and strain distribution are resolved. Namely, fracture criteria used in crash analysis account bending damage accumulation differently. Most criteria do not specifically address the issue as element erosion is activated once all through thickness integration points have reached the predefined failure condition. However, when elements are bent, material layers (top and bottom) display strong variations in mechanical field variables that are commonly used to control element deletion. Therefore, the focus of current analyses is to show how different fracture criteria account bending deformation and how sensitive are the results depending on the chosen element size.

Simplified Analytical Calculation and Modification of the Crushing Forces of Intersection Units in Vessel-Bridge Collisions

Because of the increasingly busy maritime trade, the number of bridges damaged by ship-bridge collision also increases. In order to reduce the serious losses caused by ship-bridge collision incidents, it is necessary to make a rapid estimation of ship collision forces. The simplified analytical formulas can be used to rapidly evaluate the collision force in ship collision accidents, but it is found that the existing simplified formulas are only applicable to bulb structures including small-angle inclined elements and not suitable for large-angle inclined elements which exist in ship-bridge collision. In this paper, the quasi-static crushing simulation of the bulbous structure with small-angle inclined angle elements is carried out, and the applicability of the simplified analytical formula of the intersection unit to the typical structure is verified. By comparing the simplified analytical results of the bow with the quasi-static simulation results and the ratio of the strength reduction factor to the effective crushing distance, it is found that the inclined angle of the inclined element will affect the impact force of the simplified analytical calculation. Then, finite element analysis of the truncated-type intersection structure with different element inclination angles are carried out, and the results show that the existing simplified analytical formula is no longer suitable for the calculation of collision force when the inclined angle is greater than 40°. For this reason, the existing simplified analytical formulas are modified for the large-angle inclined elements, and it can provide a certain reference calculation value for the collision force of vessel-bridge collision which includes large-angle inclined elements.