Guidelines for Engineering Critical Assessments for Pipeline Installation Methods Introducing Cyclic Plastic Strain

2004 ◽  
Author(s):  
Stig Wa¨stberg ◽  
Henryk Pisarski ◽  
Ba˚rd Nyhus
Keyword(s):  
Plastic Strain ◽  
Materials Testing ◽  
Plastic Strains ◽  
Strain Development ◽  
Cyclic Plastic ◽  
Guideline Document ◽  
Fracture Control ◽  
Cyclic Plastic Strain ◽  
Assessment Procedures ◽  
Validation Testing

Conventional flaw assessment procedures are not explicitly developed for situations with large cyclic plastic strains, e.g. for pipelines installed by the Reeling method, and if used indiscriminately may give un-reliable results. In order to resolve this dilemma DNV, TWI and Sintef conducted a Joint Industry Project (Fracture Control for Installation Methods Introducing Cyclic Plastic Strain – Development of Guidelines for Reeling of Pipelines) to provide guidelines on testing and assessment procedures that can be employed by the industry. The project included Materials Testing, FEM Analyses and Validation Testing of Pipe Segments as well as Full Scale Pipes. This paper summarizes the Guideline document that was developed in the project.

Testing of Segment Specimens and Full Scale Pipes for the Assessment of Fracture During Reeling Installation

2004 ◽  
Author(s):  
Stig Wa¨stberg
Keyword(s):  
Stable Crack Growth ◽  
Full Scale ◽  
Fusion Line ◽  
Materials Testing ◽  
Strain Development ◽  
Guideline Document ◽  
Fracture Control ◽  
Cyclic Plastic Strain ◽  
Bending Loading ◽  
Good Agreement

This Paper describes the testing of Segment Specimens and Full Scale Pipes carried out at DNV within the Joint Industry Project “Fracture Control for Installation Methods Introducing Cyclic Plastic Strain – Development of Guidelines for Reeling of Pipelines”. The JIP was a cooperation between DNV, TWI and Sintef. A total of 24 full thickness Segment Specimens, with cracks/notches introduced in the Base Metal, Fusion Line Root and Fusion Line Cap, were tested. The specimens were loaded both monotonically and cyclically, simulating reeling installation. Two Full Scale Pipes were subjected to a bending loading program simulating a reeling installation. Each pipe contained three test welds and cracks/notches were introduced both at the 6 o’clock and the 12 o’clock positions, i.e. six cracks/notches in each pipe. In one pipe the cracks/notches were introduced in the Weld Metal and in the other in the Fusion Line from the Cap side. After the loading program all the cracks/notches were broken open and the stable crack growth were measured and compared to predictions based on fracture mechanics principals (essentially following BS 7910-1999). A method for adjusting the analysis procedure, in order to obtain good agreement between the predictions and the experimental observations, is suggested. The JIP also included Materials Testing and FEM Analyses. A Guideline Document was developed which is currently being used by the project participants and it is the intention to issue a DNV Recommended Practice in support of the DNV Offshore Standard OS-F101 “Submarine Pipeline Systems – 2000” based on the experience gained and feed back received from the participants. The Guideline document is described in another paper (OMAE2004-51061) at the conference.

Background and New Revision of DNVGL-RP-F108

2018 ◽  
Author(s):  
Steinar Lindberg Bjerke ◽  
Jens P. Tronskar ◽  
Steven Chong ◽  
Asle Venås
Keyword(s):  
Fracture Mechanics ◽  
Extensive Experience ◽  
Cyclic Plastic ◽  
Service Testing ◽  
Fracture Control ◽  
Cyclic Plastic Strain ◽  
Girth Welds ◽  
Assessment Procedures ◽  
Cyclic Plastic Deformation ◽  
Sour Service

DNV-RP-F108 [1] was first issued in 2006. The Recommended Practice was developed to provide guidance on testing and analyses for fracture control of pipeline girth welds subjected to cyclic plastic deformation, e.g. during installation by the reeling method, but also for other situations where pipelines may be subjected to large plastic strains. The Recommended Practice was based upon a Project Guideline developed within the Joint Industry Project “Fracture Control for Installation Methods Introducing Cyclic Plastic Strain - Development of Guidelines for Reeling of Pipelines”. The new revision is based on the extensive experience and knowledge gained over the years use of the previous versions, as well as new knowledge from recent R&D projects. The main content of Appendix A of DNV-OS-F101 (now DNVGL-ST-F101) [2] have been transferred to DNVGL-RP-F108. Only the requirements relative to ECA and testing have been retained in DNVGL-ST-F101 [2]. The new revision has got a new number and new title, i.e. DNVGL-RP-F108, “Assessment of Flaws in Pipeline and Riser Girth Welds”. This paper lists the fundamental changes made in the new RP from the old Appendix A of the previous DNV-OS-F101 and discusses some of the changes, although within this paper it is not possible to cover all changes. The focus is on clarification of use of S-N versus the fracture mechanics approach for fatigue life computation, classification of fatigue sensitive welds, calculations of more accurate crack driving force by re-introduction of the plate solution, for which a new Lr,max (plastic collapse) calculation and a modified way to account for residual stresses have been specified. The RP presents new assessment procedures pertaining to use of finite element analyses for fracture mechanics assessments. A unique feature of the new RP is the guidance on sour service testing and assessments included in the Appendix C of the document to support pipeline/riser ECAs to develop flaw acceptance criteria for NDT.

Elastic-Plastic Finite Element Simulation and Fatigue Life Prediction for Beam and Elbow Under Cyclic Loading

2007 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Cyclic Loading ◽  
Plastic Strain ◽  
Kinematic Hardening ◽  
Kinematic Model ◽  
Cyclic Plastic ◽  
Hardening Models ◽  
Critical Location ◽  
Cyclic Plastic Strain

Work hardening and Bauschinger effects on plastic deformation and fatigue life for a beam and an elbow under cyclic loading are examined using finite element analysis (FEA). Three typical material plastic hardening models, i.e. isotropic, kinematic and combined isotropic/kinematic hardening models are adopted in the FEA calculations. Based on the FEA results of cyclic stress and strain at a critical location and using an energy-based fatigue damage parameter, the fatigue lives are predicted for the beam and elbow. The results show that (1) the three material hardening models determine similar stress at the critical location with small differences during the cyclic loading, (2) the isotropic model underestimates the cyclic plastic strain and overestimates the fatigue life, (3) the kinematic model overestimates the cyclic plastic strain and underestimates the fatigue life, and (4) the combined model predicts the intermediate cyclic plastic strain and reasonable fatigue life.

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