An advanced procedure for the quantitative risk assessment of offshore installations in explosions

Hydrocarbon explosion and fire are typical accidents in the offshore oil and gas industry, sometimes with catastrophic consequences such as casualties, property damage and pollution. Successful engineering and design should meet both functional requirements associated with operability in normal conditions and health, safety, environmental and ergonomics (HSE&E) requirements associated with accidental and extreme conditions. A risk-based approach is best for successful design and engineering to meet HSE&E requirements. This study aimed to develop an advanced procedure for assessing the quantitative risk of offshore installations in explosions. Unlike existing industry practices based on prescriptive rules or qualitative approaches, the proposed procedure uses an entirely probabilistic approach. The procedure starts with probabilistic selection of accident scenarios. As the defining components of risk, both the frequency and consequences associated with selected accident scenarios are computed using the most refined technologies. Probabilistic technology is then applied to establish the relationship between the probability of exceedance and the physical values of the accident. Acceptance risk criteria can be applied to define the nominal values of design and/or level of risk. To validate and demonstrate the applicability of the proposed procedure, an example of its application to topside structures of an FPSO unit subjected to hydrocarbon explosions is detailed. The conclusions and insights obtained are documented

Strength assessment of stiffened blast walls in offshore installations under explosions

Offshore installations are exposed to hydrocarbon explosions and/or fire accidents. Especially, explosions lead to serious damages to human, safety, and environment. To minimise and prevent the damage from explosions, blast walls are generally installed in oil and gas production structures. Typical blast walls are classified into flat, corrugated, and stiffened types. Among them, corrugated blast walls are frequently used for reasons such as construction, cost, and energy absorption. However, it has been known that a corrugated type of blast wall buckles between the web and flange under the explosion loads, and loses its stiffness. It means that the buckling phenomenon of a blast wall is closely related to the structural strength. This study investigates on the structural characteristics of a blast wall under quasi-static and dynamic (explosion) loads with or without a flat-plated stiffener. Finally, it can be concluded that the flat type of stiffeners are located at the buckling region to delay the buckling and improve the strength of blast walls

Long-term stochastic heave-induced dynamic buckling of a top-tensioned riser and its influence on the ultimate limit state reliability

A top-tensioned riser is a slender pipe that conveys fluids between a floater and a subsea system. High top-tension keeps its straight configuration and helps to prevent compressive loads. Because of the floater's heave motion, the tension on the riser fluctuates giving rise to dynamic buckling. This paper examines the dynamic buckling characteristics of a top-tensioned riser analyzing the governing equation with nonlinear damping. The equation is discretized in space by the finite difference method and then is numerically integrated by the Runge-Kutta method. As main objective, an ultimate limit state function for risers is used to investigate its reliability during parametric excitation. While the short-term stationary Gaussian random motion of a floater can be described by a response spectrum, the uncertainties of a long-term response are considered by Monte Carlo simulation. In view of an applied example, it is found that the dynamic buckling would occur often, and although the probability of failure is acceptable, it can cause serious failure when axial excitation is of significance in harsher sea states. This study aims to contribute in clarifying the role of parametric vibrations (dynamic buckling) in the reliability of risers for ultimate limit state

A life-cycle cost model for the reliability-based design of disconnectable FPSO mooring lines

Floating production, storage, and offloading units (FPSOs) are widely used to develop offshore oil fields from shallow to ultra-deep waters, and some possess fast disconnection systems to avoid harsh environmental conditions. According to a literature survey, the current industry practice is based on the perceptions and experiences of operators to judge the disconnection of these units during cyclonic storms. However, systematic criteria should be established to judge whether disconnection is needed, and the downtime costs and safety issues associated with life-cycle costs should be considered. In this paper, a life-cycle cost model is proposed to optimize (1) the disconnection criteria of FPSOs and (2) the design of their mooring system. Relevant ultimate limit states and reliabilities are considered in association with hull collapse, mooring system failure, and green water impact failure. Effects of downtime costs (deferred production costs), mobilization, and other failure costs are considered. Disconnection criteria are then formulated in terms of the significant wave height and wind speed limits. Because a permanent mooring system may exhibit excessive resistance, it is possible to further optimize the life-cycle cost by reducing the system’s resistance until an optimum reliability is obtained, minimizing the costs for non-permanent service. An FPSO in the Gulf of Mexico is selected as an example to illustrate the application of the developed model. The results of this study show that important savings for an overall FPSO project can be achieved by implementing the proposed optimizations

On design criteria for a disconnectable FPSO mooring system associated with expected lifecycle cost

Some floating production, storage and offloading units (FPSOs) possess disconnectable systems to avoid harsh environments. According to a literature survey, the practice is based on perceptions and experiences of operators to judge disconnection; however, this paper offers a rational approach. A life-cycle cost model is proposed to optimise (1) the disconnection criteria and (2) the design of mooring lines under reliability format. Relevant ultimate limit states are considered in association with hull, moorings and green water failure. Effects of future failure costs are considered (downtime, environmental damage, reputation, etc.). Disconnection criteria are then formulated in terms of significant wave height and wind speed limits. Because a permanent mooring system may exhibit excessive resistance, it is possible to reduce the lines’ thickness until the cost is optimised for non-permanent service. Results for an example in the Gulf of Mexico show that important savings can be achieved by implementing the proposed optimisations

Benefits of biomarker selection and clinico-pathological covariate inclusion in breast cancer prognostic models

Introduction: Multi-marker molecular assays have impacted management of early stage breast cancer, facilitating adjuvant chemotherapy decisions. We generated prognostic models that incorporate protein-based molecular markers and clinico-pathological variables to improve survival prediction. Methods: We used a quantitative immunofluorescence method to study protein expression of 14 markers included in the Oncotype DX™ assay on a 638 breast cancer patient cohort with 15-year follow-up. We performed cross-validation analyses to assess performance of multivariate Cox models consisting of these markers and standard clinico-pathological covariates, using an average time-dependent Area Under the Receiver Operating Characteristic curves and compared it to nested Cox models obtained by robust backward selection procedures. Results: A prognostic index derived from of a multivariate Cox regression model incorporating molecular and clinico-pathological covariates (nodal status, tumor size, nuclear grade, and age) is superior to models based on molecular studies alone or clinico-pathological covariates alone. Performance of this composite model can be further improved using feature selection techniques to prune variables. When stratifying patients by Nottingham Prognostic Index (NPI), the most prognostic markers in high and low NPI groups differed. Similarly, for the node-negative, hormone receptor-positive sub-population, we derived a compact model with three clinico-pathological variables and two protein markers that was superior to the full model. Conclusions: Prognostic models that include both molecular and clinico-pathological covariates can be more accurate than models based on either set of features alone. Furthermore, feature selection can decrease the number of molecular variables needed to predict outcome, potentially resulting in less expensive assays.This work was supported by a grant from the Susan G Komen Foundation (to YK)

Immunohistochemical evaluation of human epidermal growth factor receptor 2 and estrogen and progesterone receptors in breast carcinoma in Jordan

INTRODUCTION: Although breast carcinoma (BC) is the most common malignancy affecting Jordanian females and the affected population in Jordan is younger than that in the West, no information is available on its biological characteristics. Our aims in this study are to evaluate the expression of estrogen receptor (ER) and progesterone receptor (PR) and Her-2/neu overexpression in BC in Jordan, and to compare the expression of these with other prognostic parameters for BC such as histological type, histological grade, tumor size, patients' age, and number of lymph node metastases. METHOD: This is a retrospective study conducted in the Department of Pathology at Jordan University of Science and Technology. A confirmed 91 cases of BC diagnosed in the period 1995 to 1998 were reviewed and graded. We used immunohistochemistry to evaluate the expression of ER, PR, and Her-2. Immunohistochemical findings were correlated with age, tumor size, grade and axillary lymph node status. RESULTS: Her-2 was overexpressed in 24% of the cases. The mean age of Her-2 positive cases was 42 years as opposed to 53 years among Her-2 negative cases (p = 0.0001). Her-2 expression was inversely related to ER and PR expression. Her-2 positive tumors tended to be larger than Her-2 negative tumors with 35% overexpression among T3 tumors as opposed to 22% among T2 tumors (p = 0.13). Her-2 positive cases tended to have higher rates of axillary metastases, but this did not reach statistical significance. ER and PR positive cases were seen in older patients with smaller tumor sizes. CONCLUSION: Her-2 overexpression was seen in 24% of BC affecting Jordanian females. Her-2 overexpression was associated with young age at presentation, larger tumor size, and was inversely related to ER and PR expression. One-fifth of the carcinomas were Her-2 positive and ER negative. This group appears to represent an aggressive form of BC presenting at a young age with large primary tumors and a high rate of four or more axillary lymph node metastases

Association of oestrogen receptor beta 2 (ERβ2/ERβcx) with outcome of adjuvant endocrine treatment for primary breast cancer – a retrospective study

<p>Abstract</p> <p>Background</p> <p>Oestrogen receptor beta (ERβ) modulates ERα activity; wild type ERβ (ERβ1) and its splice variants may therefore impact on hormone responsiveness of breast cancer. ERβ2/ERβcx acts as a dominant negative inhibitor of ERα and expression of ERβ2 mRNA has been proposed as a candidate marker for outcome in primary breast cancer following adjuvant endocrine therapy. We therefore now assess ERβ2 protein by immunostaining and mRNA by quantitative RT-PCR in relation to treatment outcome.</p> <p>Methods</p> <p>ERβ2-specific immunostaining was quantified in 141 primary breast cancer cases receiving adjuvant endocrine therapy, but no neoadjuvant therapy or adjuvant chemotherapy. The expression of mRNA for ERβ2/ERβcx was measured in 100 cases by quantitative RT-PCR. Statistical analysis of breast cancer relapse and breast cancer survival was performed using Kaplan Meier log-rank tests and Cox's univariate and multivariate survival analysis.</p> <p>Results</p> <p>High ERβ2 immunostaining (Allred score >5) and high ERβ2 mRNA levels were independently associated with significantly better outcome across the whole cohort, including both ERα positive and negative cases (Log-Rank P < 0.05). However, only ERβ2 mRNA levels were significantly associated with better outcome in the ERα + subgroup (Log-Rank P = 0.01) and this was independent of grade, size, nodal status and progesterone receptor status (Cox hazard ratio 0.31 P = 0.02 for relapse; 0.17 P = 0.01 for survival). High ERβ2 mRNA was also associated with better outcome in node negative cases (Log Rank P < 0.001).</p> <p>ERβ2 protein levels were greater in ERα positive cases (T-test P = 0.00001), possibly explaining the association with better outcome. Levels of ERβ2 protein did not correlate ERβ2 mRNA levels, but 34% of cases had both high mRNA and protein and had a significantly better outcome (Log-Rank relapse P < 0.005).</p> <p>Conclusion</p> <p>High ERβ2 protein levels were associated with ERα expression. Although most cases with high ERβ2 mRNA had strong ERβ2 immunostaining, mRNA levels but not protein levels were independently predictive of outcome in tamoxifen-treated ERα + tumours. Post-transcriptional control needs to be considered when assessing the biological or clinical importance of ERβ proteins.</p