This paper describes the application of solid finite element models in the analysis of five tubular specimens containing interacting corrosion defects. Each of these specimens has been submitted to hydrotest up to failure as part of a previous research project. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The analyses accounted for large strains and displacements, stress-stiffening and material nonlinearity. The failure pressures predicted by the solid finite element models are compared with the failure pressures of these specimens measured in the laboratory burst tests carried out previously. Also the failure behavior of each specimen is described and illustrated by contour plots of stresses.

This paper presents hydrate design premises established to reach the finaldesign and operational philosophy for the 3 phase subsea separation system, also known as Marlim SSAO. The main purpose of this pilot station is toseparate the produced water and reinject it into reservoir for pressure supportwhile routing the oil and gas to topside. Since the subsea process station handles multiphase flow where gas and freewater are present, and the system is exposed to low temperatures by the ambientcold sea water, a good strategy to avoid hydrate formation is necessary. Thehydrate strategy must be incorporated as a part of the total system design andshall handle all critical operational scenarios as shut-down and start-ups. Thehydrate strategy is closely linked to the temperature control and theevaluation of need for thermal insulation of the system. Temperature control isalso important in the system because of high sensitivity in fluid properties. General thermal insulation verification analysis and detailed studies of coldspots are required. Real fluid testing was included in order to better evaluatethe hydrate potential. The Marlim SSAO, as an integrated part of a field system from subsea wells totopside, is divided into several parts for the facilitation of the flowassurance and the hydrate prevention strategy: Multiphase lines, water linesand water injection system. The hydrate prevention is very challenging becauseof several open connections between the multiphase lines and the water lines. Hence, usual means as MEG inhibition and thermal insulation have not beenenough to ensure the hydrate prevention strategy and new strategies have beendeveloped. It has been necessary to challenge the strategies in every part ofthe system. The results of the work methodology and the analysis executed indicated thatMarlim SSAO is a safe system to operate from a flow assurance and hydrateprevention point of view. The material presented in here intends to establish akey reference for preservation design of 3 phase subsea separation systems. Itapplies for future generations of these kinds of equipments. Introduction The Marlim SSAO is a subsea processing pilot station which has been installedin the Campos Basin off the coast of Brazil. The objective is to separate mostof the water from the production stream and re-inject it into the reservoir forpressure support while transporting the oil and gas to topside. The SSAO isinstalled at a water depth of 876 m, 341 m from the production wellhead and2100 m from the injection wellhead. The hydrocarbons will be sent to thetopside facilities 2400 m (riser and flowline length) from the SSAO. This paper describes the challenges and innovative solutions on flow assuranceand hydrate prevention strategy for the Marlim SSAO. This includes the mainphilosophy, the preservation of the station in different operational modes, evaluations of identified risks, and calculations and analysis performed tosupport the strategy.

This paper presents a case study on the failure behavior of four colonies of corrosion defects using solid Finite Element models. These analyses accounted for large strains and displacements, stress-stiffening and material nonlinearity. Colonies 1 and 2 are each composed of two longitudinally aligned defects. Colonies 3 and 4 are each composed of four defects (two longitudinally aligned defects and two circumferentially aligned defects) arranged in a rhombus shape. For each of the four colonies a parametric study is performed in which the longitudinal spacing sL between the two defects longitudinally aligned is varied from a small value (sL)min to a large value (sL)max. Based on the results obtained the failure behavior of each colony is described and illustrated by contour plots of stresses. The failure pressures predicted by the Finite Element analyses are compared with those predicted by six assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects (Part B), the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for interacting defects (Part B).