Fatigue Life Assessment of a Drilling Riser Containing Corrosion Pits

Abstract

Fatigue Life Assessment of a Drilling Riser Containing Corrosion Pits Adilson Carvalho Benjamin; Adilson Carvalho Benjamin Petrobras Search for other works by this author on: This Site Google Scholar Divino Silveira Cunha; Divino Silveira Cunha Petrobras Search for other works by this author on: This Site Google Scholar George Carneiro Campello; George Carneiro Campello Petrobras Search for other works by this author on: This Site Google Scholar Francisco Edward Roveri; Francisco Edward Roveri Search for other works by this author on: This Site Google Scholar Rita Carvalho Silva; Rita Carvalho Silva LNCC Search for other works by this author on: This Site Google Scholar Joao Nisan Guerreiro Joao Nisan Guerreiro LNCC Search for other works by this author on: This Site Google Scholar Paper presented at the Offshore Technology Conference, Houston, Texas, USA, May 2008. Paper Number: OTC-19251-MS https://doi.org/10.4043/19251-MS Published: May 05 2008 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Benjamin, Adilson Carvalho, Cunha, Divino Silveira, Campello, George Carneiro, Roveri, Francisco Edward, Silva, Rita Carvalho, and Joao Nisan Guerreiro. "Fatigue Life Assessment of a Drilling Riser Containing Corrosion Pits." Paper presented at the Offshore Technology Conference, Houston, Texas, USA, May 2008. doi: https://doi.org/10.4043/19251-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsOffshore Technology ConferenceOTC Offshore Technology Conference Search Advanced Search AbstractThe residual fatigue life of a corroded riser joint can be evaluated by means of a fatigue analysis based on S-N data. In this case nominal stresses are determined through a global riser analysis in which the drilling riser is modeled as a tensioned beam subjected to loads throughout its length and with boundary conditions at each end. The effect of the corrosion defects is taken into account multiplying the nominal stresses by stress concentration factors derived by local Finite Element analyses of the riser joints containing corrosion defects.In this paper the fatigue life assessment of a drilling riser containing corrosion pits is presented. These pits are situated on the external surface of the riser joints. Five depths of corrosion pits are considered: 12.6%, 20.1%, 30.2%, 40.3% and 50.3% of the riser wall thickness. Stress concentration factors are calculated using solid Finite Element models and the fatigue analyses are performed considering the wave loads and the vortex induced vibrations. The results show the possibility of operational life extension of riser joints that would have to be replaced according to the usual acceptance criterion.IntroductionIn order to assure the integrity of a drilling riser, inspection is required at various times during its life span [1]. After each retrieval, the drilling riser joints should be inspected for fatigue cracks and wall thickness reduction due to corrosion (or wear).According to the API RP 16Q [1], the acceptance criterion to be applied to wall thickness reduction should be agreed upon between operator and drilling contractor. The usual acceptance criterion dictates the substitution of the riser joints with wall thickness reduction above 12.5% of the nominal thickness. This criterion, called herein the maximum defect depth criterion, is excessively conservative because it applies to a corroded riser joint in operation the same wall thickness tolerance that is applied to a new pipe, manufactured in accordance with the API Specification 5L [2].Areas of high wall thickness reduction form potential fatigue hotspots. In this context, the authors have been studying the fatigue of drilling risers with defects caused by corrosion in the base metal [3,4]. This paper presents the fatigue life assessment of a drilling riser containing corrosion pits. Stress concentration factors are calculated using solid Finite Element models and the fatigue analyses are performed considering the wave loads and the vortex induced vibrations.Study AssumptionsThe following assumptions were adopted:There is corrosion on the external surface of the riser joints;The internal surface of the riser joints, the connectors and the welds are free of corrosion;The internal surface of the riser joints is free of wear from the drill string rotation;The riser joints are free of dents and cracks;The drilling mud is not contaminated with corrosive gases such as carbon dioxide and hydrogen sulfide;The internal pressure is higher than the external pressure. Keywords: defect, fatigue damage, criterion, corrosion pit, acceptance criterion, riser joint, stress concentration factor, fatigue life assessment, upstream oil & gas, fatigue damage acceptance criterion Subjects: Pipelines, Flowlines and Risers, Risers This content is only available via PDF. 2008. 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