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.

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.

Consistent Endurance Fatigue Knockdown Factors for Sour Service From Industry-Wide Database

2011 ◽  
Author(s):  
Weiwei Yu ◽  
Pedro M. Vargas ◽  
Jonathan Bowman
Keyword(s):  
Ph Value ◽  
Fatigue Performance ◽  
Small Scale ◽  
Loading Frequency ◽  
Solution Ph ◽  
Knock Down ◽  
Service Testing ◽  
Highly Correlated ◽  
Girth Welds ◽  
Sour Service

The embrittlement of steel in the presence of water and hydrogen sulfide is a well known phenomenon. For the resulting degradation in fatigue performance, the industry today applies a knock-down factor onto in-air S-N endurance curve that relates the sour-service life to the in-air performance. Several published results are available, and most of these, although rigorous in test approach, report knock-down factors that include unspecified levels of conservatism, consistent with that particular author’s engineering intuition. (For example, typically a lower bound S-N curve in sour-service testing is related to a mean S-N curve in-air). This paper summarizes all of the published small scale sour service testing results, and applies a consistent knock-down factor calculation. Analyses of the data show that sour degradation is highly correlated to H2S concentration and solution pH value. In practice frequency scanning test is highly recommended since sour fatigue test results are highly dependent on loading frequency. Although the database is small, some trends are discernable. In particular, observations indicate that sour service exposure may act as an equalizer, removing the initiation life associated with the time for initial micro-defects at the weld toes to become macro-cracks and leaving only aggravated propagation due to sour service. In this paper, we use initiation life (for welds) to describe the life for the micro-defects (∼0.1mm height) to become macro-cracks (∼1.0 mm height), and a postulation is made that associates the fatigue performance of girth welds (F2, E, D, etc.) with the size and magnitude presence of these micro-defects. The metal surface attack of the sour environment is postulated to provide pitting-like initiation sites for the macro-crack for fatigue propagation. As a base we can use the F2 level performance as the performance due to presence of macro-cracks, and any margin for the D and E level fatigue performances then is associated with more benign initial micro-defects. Once we remove the differences in initiation life; all of the sour performance converges on a single lower performance curve. In this scenario, the knockdown factor is more consistently computed from a standard performance S-N curve rather than the same girth weld’s in-air performance since the in-air data may include significant initiation life. Furthermore, if project sour condition is less severe than NACE TM0177, Solution B with pH = 3.5 and H2S partial pressure = 70mbar, a knock down factor of 45 indexed to BS7608 E design curve is supported from the current database. This provides a design recommendation which can be used for preliminary design in sour environments.

Technical Specification for Subsea Pipelines Alternative Criteria Based in Fracture Mechanics

2008 ◽  
Author(s):  
Petroˆnio Zumpano Ju´nior ◽  
Guilherme Victor Peixoto Donato ◽  
Eduardo Hippert Ju´nior ◽  
Tiago Bohn Kaspary
Keyword(s):  
Fracture Mechanics ◽  
Technical Specification ◽  
Crack Size ◽  
Paris Law ◽  
Offshore Pipeline ◽  
Pipe Segment ◽  
Service Conditions ◽  
Girth Welds ◽  
Subsea Pipelines ◽  
Sour Service

Offshore pipeline laying significant high costs are strongly related to the duration of vessel operations. Even though DNV-OS-F-101 requires an Engineering Critical Assessment (ECA) only when expected total longitudinal strain is above 0.4%, contractors usually prefer to launch lines by using alternative defect acceptance criteria for mechanized girth welds based on fracture mechanics approach in order to save time. BS-7910 standard is worldwide acknowledged for fracture and fatigue analysis, but it requires operators to specify additional criteria in the overall ECA methodology for submarine pipelines. In 2006 DNV-RP-F108 was issued establishing new testing methods based in SE (T) and pipe segment specimens as a way of achieving a more realistic estimation of pipeline toughness. Nowadays, a lot of research has been carried out on testing methodology that will likely lead to a SE (T) testing standard. However, many aspects of pipeline launching and operation must be defined for ECA analysis: operators should establish all the cyclic loads to be considered both for installation and operation period assessment; the approach of in-service fatigue may be determinant for the final allowable crack size; sour service conditions may imply that Paris law constants are not valid for in-service VIV and hydrogen charged SE (B) specimens will give fracture toughness results representative of the material in sour conditions. This paper addresses the premises, based in Petrobras previous experience, for establishing a technical specification in order to carry out an ECA with alternative criteria for subsea pipeline or riser girth welds, based in fracture mechanics approach.

Evaluation of Weld Metal Strength Mismatch in X100 Pipeline Girth Welds

2004 ◽  
Author(s):  
Henryk G. Pisarski ◽  
Yuri Tkach ◽  
Marie Quintana
Keyword(s):  
Fracture Toughness ◽  
Adverse Effects ◽  
Weld Metal ◽  
Axial Stress ◽  
Limit Load ◽  
Allowable Stress ◽  
Simple Method ◽  
Weld Width ◽  
Girth Welds ◽  
Assessment Procedures

A relatively simple method based on standard fracture mechanics flaw assessment procedures, such as BS 7910, but modified using published mismatch limit load solutions is described. It is used to illustrate the effects of weld width and strength mismatch on CTOD requirements for girth welds in Grade X100 strength pipeline material subjected to axial stress. It is shown that fracture toughness requirements based on standard analyses not allowing for mismatch effects can be unnecessarily conservative when either undermatched or overmatched welds are present. Adverse effects of undermatching, in reducing the allowable stress, can be mitigated by reducing weld width. It is shown that even small amounts of overmatching (e.g. 10%) can be beneficial by allowing axial stress to exceed the SMYS of the parent pipe and reducing CTOD requirements.

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