Fatigue performance of pre-strained pipes with girth weld defects: Full-scale experiments and analyses

Technip began qualification of reeled Steel Catenary Risers (SCR) back in 1997. Industry had raised concerns at that time over the plastic straining cycles that are intrinsic to the reel lay method and the impact these could have upon the service fatigue life of the girth welds. The qualification programme, therefore, included comparison of reeled welds against virgin welds for a suite of fatigue and mechanical testing including full scale fatigue and fatigue crack growth tests. Reeling was shown to have no discernable impact for the fatigue performance level sought when a controlled SCR fabrication process was adhered to. This provided sufficient confidence that the technology was fit for purpose and led to successful fabrication and installation of the first reeled SCR in 2001. Since then more than 25 have been installed in the Gulf of Mexico, with most projects including full scale weld fatigue test qualification following reeling simulations. This paper includes the following: (a) a summary of the philosophy adopted for qualification, fabrication and installation of a reeled SCR, (b) presentation of the reeled SCR track record and evolution of the technology to include mechanized welding processes (c) a look at ongoing developments targeting even higher fatigue performance, and (d) discussion on the development of fracture mechanics techniques that provide further confidence in the concept and can be used to derive appropriate weld acceptance criteria.

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Fatigue performance monitoring of full-scale PPC beams by using the FBG sensors

Smart Structures and Systems ◽

10.12989/sss.2014.13.6.943 ◽

2014 ◽

Vol 13 (6) ◽

pp. 943-957 ◽

Cited By ~ 1

Author(s):

Licheng Wang ◽

Jigang Han ◽

Yupu Song

Keyword(s):

Performance Monitoring ◽

Full Scale ◽

Fatigue Performance ◽

Fbg Sensors

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Fatigue Performance of Grade R4 and R5 Mooring Chains in Seawater

Volume 1A: Offshore Technology ◽

10.1115/omae2014-23491 ◽

2014 ◽

Cited By ~ 3

Author(s):

Jonathan Fernández ◽

Walther Storesund ◽

Jesús Navas

Keyword(s):

Fatigue Test ◽

Fatigue Damage ◽

Fatigue Tests ◽

Design Methods ◽

Full Scale ◽

Fatigue Performance ◽

Test Program ◽

Gas Industry ◽

Fatigue Design ◽

Cumulative Fatigue Damage

With more than 50.000 tons in service to date, the Oil&Gas Industry has the need to understand the tension fatigue performance of grade R5 chains in straight tension, and corroborate the validity of the existing design methods. The chain fatigue design curves in API and DNV are based on fatigue tests obtained in the nineties and early two thousands. However the tests were performed on lower grades such as ORQ, R3 and R4, and small chains, 76 mm diameter being the largest studless chain tested. The industry has moved towards the use of large studless chains, especially in permanent units, where chain diameters above 150 mm are not unusual. This paper gathers information from a full scale fatigue test program on grade R4 and R5 studless chains, performed in seawater and with diameters between 70 mm and 171 mm. The chains being tested are actual production chains supplied for different drilling units and large permanently moored production floating units. The paper analyses the data and determines tension-tension fatigue curves based on API and DNV methods for computation of cumulative fatigue damage, regardless of other damaging mechanisms. Improved fatigue capacity is obtained with respect to the above recommended design methods.

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Research on Full-Scale Hydrostatic Burst Testing of Different Pipeline Girth Weld Defects

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.853.351 ◽

2016 ◽

Vol 853 ◽

pp. 351-355

Author(s):

Wen Bo Xuan ◽

Fu Xiang Wang ◽

Li Jian Zhou ◽

Ting Wang ◽

Jian Chen ◽

...

Keyword(s):

Bearing Capacity ◽

Oil And Gas ◽

Full Scale ◽

Experimental Results ◽

Fitness For Purpose ◽

Technical Challenge ◽

Weld Defects ◽

Oil And Gas Pipelines ◽

Girth Welds ◽

Pipeline Safety

Recently incidents related to cracking of girth welds in oil and gas pipelines occurred frequently. With highly concentrated stresses, girth weld defects may significantly reduce bearing capacity of pipelines. Many girth weld defects were detected in the in-line inspection and excavated verification. How to assess the severity of these defects to avoid the excessive and unnecessary repair was a technical challenge. Four different kinds of girth weld defects were manufactured in the 32-inch pipeline and full-scale hydrostatic burst testing were carried out to assess the pressure performance of these defects. Many fitness-for-purpose assessment methods were applied to verify the accuracy of experimental results. After the testing, pipelines with failure defects were cut out to carry out the microanalysis. The research results make us understanding the severity of these defects and avoid the excessive and unnecessary repair of these defects to ensure the pipeline safety.

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Fatigue Testing of Out-of-Plane Bending Mechanism of Chain Links

Volume 3: Safety and Reliability; Materials Technology; Douglas Faulkner Symposium on Reliability and Ultimate Strength of Marine Structures ◽

10.1115/omae2006-92488 ◽

2006 ◽

Cited By ~ 2

Author(s):

Lucile Rampi ◽

Pedro Vargas

Keyword(s):

Fatigue Testing ◽

Empirical Relationship ◽

Fatigue Tests ◽

Full Scale ◽

Fatigue Performance ◽

Special Focus ◽

Out Of Plane ◽

Plane Bending ◽

Chain Links ◽

Mooring Chain

Three years ago, several mooring chains of an off-loading buoy failed after only 8 months of service. These chains were designed according to conventional fatigue assessment using API RP 2SK T-N curves to a fatigue life or 20 years with a factor of safety equal to 3 on life. Of particular interest is that the mooring chain failure underwent significant mooring chain motions that caused interlink rotations. Although traditionally neglected, these interlink rotations, when combined with significant chain tensions can cause bending stresses in the chain links (See Figure 1). This recently identified phenomena, Out-of-Plane Bending (OPB), explains the extensive fatigue damage causing the mooring chains of the off-loading buoy to fail [3][4][5]. References [3] and [4] document full scale tests of the OPB mechanism using a full scale test frame with the ability of applying inter-link rotation to a pre-tensioned chain. This testing confirmed that interlink rotations with a constant tension load can result in significantly high stresses. OPB stresses were measured on four different chain sizes of various grades: 1) 81 mm Studded Grade R3S, 2) 107 mm Stud-less Grade RQ3, 3) 124 mm Stud-less Grade R4, and 4) 146 mm Stud-less Grade RQ4, Grade R3 in [3] and [4], but no actual fatigue tests were performed. References [3] and [5] document analytical and computational efforts to explain and quantify the OPB stresses. In this paper, special focus is placed on obtaining actual fatigue failures of chains from OPB loading. Smaller chain sizes (40 mm) are used to accommodate the load limits of the testing frame. To mimic the actual loading as close as possible, sub size models of actual chainhawses were used in the testing. Two chainhawses were used: 1) the chainhawse has internal curvature where a link rests on the intrados, similar to offloading buoy that failed in eight months, and 2) a straight chainhase, a design that is in use today with demonstrated improved fatigue performance over the curved chainhawse. OPB stresses are measured and reported. Fatigue loading in the OPB mode was applied for several configurations. The two chainhawse exhibit very different stress levels and fatigue performance. An empirical relationship previously reported in [3][4][5] is compared to the measured OPB stresses with mixed results. Although limited in number, the fatigue tests indicate that overall the chain fatigue performance is at or above the B1 DnV curve. The BS B1 curve is also compared.

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Full Scale Sour Fatigue Testing With Dense Phase Gases

Volume 6: Materials Technology; Polar and Arctic Sciences and Technology; Petroleum Technology Symposium ◽

10.1115/omae2012-83898 ◽

2012 ◽

Author(s):

Pedro M. Vargas ◽

Ben Crowder ◽

Weiwei Yu ◽

Sam Mishael ◽

Keith Armstrong

Keyword(s):

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Research Work ◽

Full Scale ◽

Acceleration Factor ◽

Fatigue Performance ◽

Small Scale ◽

Dense Phase ◽

Sour Service

The petrochemical industry is very interested in the sour service fatigue performance of girth welded steel pipes. As a result several papers are published every year addressing this issue, and several Joint Industry Projects (JIP) are currently underway addressing different aspects of sour service performance of steel pipelines. To date research work has focused on quantifying the fatigue performance via small scale specimens due to the difficult and danger in dealing with H2S. Currently a JIP is underway that promises to provide full scale fatigue performance of pipeline welds under sour service. This paper documents the knockdown-factor-on-life (KD) determination for full scale sour service testing. In an industry first, a very difficult full scale sour service test was performed: 1) High Pressure, 2) High content of H2S, 3) Dense phase gases with ultra low water content (less than 400 ppm), and 4) Loading rate of 0.01 Hz. The loading was applied in full longitudinal tension. The full scale sour tests are compared with full scale in-air tests to obtain the knockdown factor. Resource constraint limited the number of full scale tests to 3. The main objective of the tests for the practical application was to ensure that the usage of crack growth based knock-down factors, i.e. the use of Fatigue-Crack-Growth-Acceleration-Factor (FCGAR) from small scale fracture mechanics specimens, was reasonable and conservative. Some additional comparisons are done with crack-growth based knockdown factors that may help explain the effect of the ultra-low water concentration. Knockdown factors from small scale crack growth specimens, Fatigue-Crack-Growth-Acceleration-Factor = 60 (FCGAR), are significantly higher than the full scale results, KD = 7. The ultra-low-water dense phase gases do not pit the surface, thus leaving the initiation life relatively intact. The knockdown factor for the full scale test is then mostly the result of the accelerated crack growth that occurs once a macro-crack nucleates.

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The Rationale for Update of S-N Curves for Single Sided Girth Welds for Risers and Pipelines in DNV GL RP C-203 Based on Fatigue Performance of More Than 1700 Full Scale Fatigue Test Results

Volume 4: Materials Technology ◽

10.1115/omae2018-78408 ◽

2018 ◽

Cited By ~ 1

Author(s):

Agnes Marie Horn ◽

Inge Lotsberg ◽

Oddvin Orjaseater

Keyword(s):

Deep Water ◽

Fatigue Testing ◽

Fatigue Loading ◽

Full Scale ◽

Fatigue Performance ◽

Test Results ◽

Severe Fatigue ◽

Adequate Quality ◽

Two Phases ◽

Girth Welds

Deep-water tendon and riser systems are often subjected to severe fatigue loading from waves, currents and vessel movements. The girth welds between successive lengths of pipe or at pipe terminations represent fatigue-critical features where failure would be catastrophic. Hence, validation fatigue testing by full scale pipes of the most critical welds are often performed to ensure adequate quality and/or to document a better S-N curves than those available in standards today like DNVGL-RP-C203 [1] and BS7608 [2]. To better understand the fatigue performance with respect to identify trends, dependencies and critical features that influence the fatigue performance, a JIP on Fatigue of Girth Welds were initiated in 2011. Two phases have been conducted and a total of 1700 full scale one sided girth welds, mostly run by Stress Engineering, have been statistically analyzed. The test data has been interrogated to investigate the effect of as-welded condition, OD ground, OD/ID ground, un-reeled pipe, reeled pipe, thickness and effect of misalignment. Based on these analyses, new S-N curves for risers and pipelines have been included in DNVGL-RP-C203 for non-reeled girth welds. This paper presents the findings and trends from the JIP work which has been the rationale for the updates of girth welds in section 2.10 in DNVGL-RP-C203 2016 edition.

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