Mean Load Impact on Mooring Chain Fatigue Capacity: Lessons Learned From Full Scale Fatigue Testing of Used Chains

2019 ◽  
Author(s):  
Øystein Gabrielsen ◽  
Kjell Larsen ◽  
Oddgeir Dalane ◽  
Hans B. Lie ◽  
Svein-Arne Reinholdtsen
Keyword(s):  
Fatigue Test ◽  
Limit State ◽  
Fatigue Tests ◽  
Load Level ◽  
Full Scale ◽  
General Corrosion ◽  
Test Results ◽  
Original Design ◽  
The Mean ◽  
Mooring Chain

Abstract Fatigue of mooring chain is for many floating offshore installations a limiting factor in design. With aging installations and the need for field life extension beyond the original design life, questions on mooring chain endurance are raised. Current SN curves utilized in fatigue limit state (FLS) calculation are based on full scale testing of new chain, performed at a high mean load level (20% of the chains minimum breaking load (MBL)). The high mean load level in the tests do not correspond to the conditions for many chains in operation, as mean load in fatigue relevant seastates are often significantly less than mean load used in the new chain fatigue tests. Mooring chains in operation also experience different degree of corrosion, both general corrosion and pitting. Surface roughness and corrosion pits contribute to crack initiations, and thus reduce fatigue capacity. Fatigue tests with new chain condition cannot be assumed representative for corroded chains. As part of mooring integrity programs, Equinor has been replacing mooring chains since year 2000. To assess actual fatigue capacity, many chain segments have been full scale fatigue tested. First tests started in 2011, and the tests cover different degrees of corrosion. The tests have been performed at typical mean load levels relevant for operation of the installations, which for most cases are less than 20%MBL. From these tests it is observed that fatigue capacity in some cases are better than expected for new chain, even for chain segments with significant corrosion. Fatigue test results show a large effect of the mean load. For test cases with significant corrosion and high mean load (20%MBL), a significant reduction in fatigue capacity compared to new chains is found. This paper presents some of the fatigue test results on used chain, highlighting the effect of the mean load for the given chain conditions. Effect of corrosion at mean load of 20%MBL is also included. The paper discusses some of the underlaying causes for the mean load dependency.

Pipeline Plain Dent Fatigue: A Comparison of Assessment Methodologies

2014 ◽  
Author(s):  
Sérgio B. Cunha ◽  
Ilson P. Pasqualino ◽  
Bianca C. Pinheiro
Keyword(s):  
Fatigue Test ◽  
Fatigue Damage ◽  
Fatigue Tests ◽  
Full Scale ◽  
Assessment Methodology ◽  
Test Results ◽  
Different Shapes ◽  
Cumulative Fatigue Damage ◽  
X80 Steels ◽  
Damage Rule

A collection of results of fatigue tests undertaken on full scale pipeline specimens containing unconstrained plain dents is presented. A total of 61 test results are reported, comprising dents of different shapes and depths, introduced in pipe sections with nominal diameters of 12″ and 24″, D/t ratios varying from 18.6 to 77.2 and made of API 5L X42, X46, X52, X60, X70 and X80 steels. The fatigue test results are used to compare five plain dent fatigue assessment methodologies. The assessment methodologies most widely used in the industry, namely, API 1156 and EPRG, are evaluated; each one of these has two different versions, evaluated independently. A dent assessment methodology previously proposed by the authors is also is included in the study. The classic Palmgren-Miner’s cumulative fatigue damage rule is employed in order to correlate the results, since all tests were carried out with two different pressure cycles. Only two of the evaluated methodologies presented a correlation with the fatigue tests that justifies recommending their application in the industry.

scholarly journals Analysis of the Correlation between the Static and Fatigue Test Results of the Interlayer Bondings of Asphalt Layers

2016 ◽  
Vol 62 (1) ◽  
pp. 83-98 ◽  
Author(s):  
A. Szydło ◽  
K. Malicki
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Asphalt Mixture ◽  
Fatigue Tests ◽  
Test Results ◽  
Static Tests ◽  
Bonding State ◽  
Road Pavement ◽  
The Future ◽  
Pavement Structure

Abstract The bonding state of the asphalt layers in a road pavement structure significantly affects its fatigue life. These bondings, therefore, require detailed tests and optimization. In this paper, the analyses of the correlation between the results of laboratory static tests and the results of fatigue tests of asphalt mixture interlayer bondings were performed. The existence of the relationships between selected parameters was confirmed. In the future, the results of these analyses may allow for assessment of interlayer bondings’ fatigue life based on the results of quick and relatively easy static tests.

Fatigue Assessment of Mooring Chain Considering the Effects Of Mean Load and Corrosion

2021 ◽  
Author(s):  
Erling N. Lone ◽  
Thomas Sauder ◽  
Kjell Larsen ◽  
Bernt J. Leira
Keyword(s):  
Negative Impact ◽  
Fatigue Tests ◽  
Design Practice ◽  
Extended Formulation ◽  
Considerable Influence ◽  
Corrosion Condition ◽  
Capacity Model ◽  
Significant Negative Impact ◽  
The Mean ◽  
Mooring Chain

Abstract Results from full scale fatigue tests of offshore mooring chains performed in recent years have revealed considerable influence of both mean load and corrosion condition on the fatigue capacity. It has been shown that a reduction of the mean load gives an increase in fatigue life, whereas the corrosion experienced by used chains have a significant negative impact. Neither of these effects are properly addressed by current S-N design curves or design practice. This paper suggests an extended S-N curve formulation, that includes the effects of mean load and corrosion condition. The parameters of the extended formulation are estimated empirically from mooring chain test data that includes new and used chains, with various mean loads and with different degrees of corrosion. The fitted capacity model is then used for fatigue calculation for the mooring system of a semi-submersible, showing the importance of using realistic mean loads and mooring chain corrosion in fatigue assessments.

Three Ways of Sampling and Fatigue Test Results of Steel P92

2014 ◽  
Vol 891-892 ◽  
pp. 273-277
Author(s):  
Josef Volák ◽  
Zbynek Bunda
Keyword(s):  
Mechanical Properties ◽  
Power Plant ◽  
Fatigue Test ◽  
Fatigue Tests ◽  
Energy Industry ◽  
Fatigue Properties ◽  
Test Results ◽  
Steam Turbines ◽  
Standard Samples ◽  
Energy Component

This paper describes the fatigue properties of the steel P92. This material is widely used in the energy industry, especially for pipes and pipe bends of supercritical steam turbines. Steel P92 is alloyed with 2 % of tungsten compared to steel P91. This increases a creep strenght of the material. It is possible to reduce wall thickness of the P92 pipe up to about 20%. Fatigue tests were carried out on standard samples and compared with SFT samples (Small Fatigue Test). Using the device SSam 2 made by company Rolce Royce, it is possible to gently remove a samples from energy component without power plant shutdowns. Consider these correlations, i tis possible to determine mechanical properties of the material from small amount of removed experimental material.

Comparison Between ASME Code-Case N-761, NUREG/CR-6909 and Stainless Steel Component Fatigue Test Results

2014 ◽  
Author(s):  
H. T. Harrison ◽  
Robert Gurdal
Keyword(s):  
Stainless Steel ◽  
Fatigue Test ◽  
Fatigue Tests ◽  
Test Series ◽  
Test Results ◽  
Actual Number ◽  
Steel Component ◽  
Class 1 ◽  
Asme Code ◽  
Number Of Cycles

For Class 1 components, the consideration of the environmental effects on fatigue has been suggested to be evaluated through two different methodologies: either NUREG/CR-6909 from March 2007 or ASME-Code Case N-761 from August 2010. The purpose of this technical paper is to compare these two methods. In addition, the equations from Revision 1 of the NUREG/CR-6909 will be evaluated. For these comparisons, two stainless steel component fatigue test series with documented results are considered. These two fatigue test series are completely different from each other (applied cyclic displacements vs. insurge/outsurge types of transients). Therefore, they are producing an appropriate foundation for these comparisons. In general, the severities of the two methods are compared, where the severity is defined as the actual number of cycles from the fatigue tests, including an evaluation of the scatter, divided by the number of design cycles from the two methods. Also, how stable the methods are is being evaluated through the calculation of the coefficient of variation for each method.

scholarly journals Long-Life Fatigue Test Results for Two Nickel-Base Structural Alloys

1981 ◽  
Vol 103 (2) ◽  
pp. 126-132 ◽  
Author(s):  
D. F. Mowbray ◽  
E. V. Giaquinto ◽  
F. J. Mehringer
Keyword(s):  
Fatigue Test ◽  
Closed Loop ◽  
Iron Alloy ◽  
Fatigue Tests ◽  
Alloy 600 ◽  
Test Results ◽  
Loading Mode ◽  
Long Life ◽  
Cold Worked ◽  
Nickel Base

This paper reports the results of fatigue tests on two nickel-base alloys, hot-cold-worked and stress-relieved nickel-chrome-iron Alloy 600 and mill-annealed nickel-chrome-moly-iron Alloy 625 in which S-N data were obtained in the life range of 106 to 1010 cycles. The tests were conducted in air at 600°F, in the reversed membrane loading mode, at a frequency of ~ 1850 Hz. An electromagnetic, closed loop servo-controlled machine was built to perform the tests. A description of the machine is given.

Fatigue Performance of Grade R4 and R5 Mooring Chains in Seawater

2014 ◽  
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.

The Fatigue Behavior of Steel Structures under Random Loading

2008 ◽  
Vol 378-379 ◽  
pp. 3-16
Author(s):  
Henning Agerskov
Keyword(s):  
Fracture Mechanics ◽  
Fatigue Test ◽  
Steel Structures ◽  
Fatigue Tests ◽  
Test Series ◽  
Test Results ◽  
Random Loading ◽  
Mechanics Analysis ◽  
Miner’S Rule ◽  
Miner's Rule

Fatigue damage accumulation in steel structures under random loading has been studied in a number of investigations at the Technical University of Denmark. The fatigue life of welded joints has been determined both experimentally and from a fracture mechanics analysis. In the experimental part of the investigation, fatigue test series with a total of 540 fatigue tests have been carried through on various types of welded plate test specimens and full-scale offshore tubular joints. The materials that have been used are either conventional structural steel or high-strength steel. The fatigue tests and the fracture mechanics analyses have been carried out using load histories, which are realistic in relation to the types of structures studied, i.e. primarily bridges, offshore structures and chimneys. In general, the test series carried through show a significant difference between constant amplitude and variable amplitude fatigue test results. Both the fracture mechanics analysis and the fatigue test results indicate that Miner’s rule, which is normally used in the design against fatigue in steel structures, may give results, which are unconservative, and that the validity of the results obtained from Miner’s rule will depend on the distribution of the load history in tension and compression.

Concepts and Techniques for Helicopter Airframe Fatigue Tests

1966 ◽  
Vol 11 (3) ◽  
pp. 45-57 ◽  
Author(s):  
Walter A. Lane
Keyword(s):  
Experimental Design ◽  
Fatigue Test ◽  
Structural Integrity ◽  
Fatigue Cracking ◽  
Fatigue Tests ◽  
Test Facility ◽  
Test Results ◽  
Fail Safe ◽  
Inspection Techniques ◽  
Automatic Simulation

Between February 1961 and June 1963, Sikorsky Aircraft, under the sponsorship of the U. S. Navy Bureau of Naval Weapons, performed the first laboratory fatigue test of a full scale helicopter airframe. This paper presents the concepts and techniques developed by Sikorsky for such tests. Airframe fatigue test concepts are directed toward defining modes of fatigue cracking, measuring rates of crack propagation, and demonstrating the adequacy of recommended inspection techniques and intervals to provide “fail safe” structural integrity. The experimental design includes consideration of the test article configuration, acceleration of test loads, loading spectra, and evaluation of test fractures. The design of the SH‐3A airframe fatigue test facility to provide automatic simulation of flight and landing loads, and the development problems encountered in achieving this capability are described. The facility and techniques to be used for CH‐53A airframe fatigue tests reflect improvements resulting from SH‐3A test experience. Correlation of airframe fatigue test results and service experience demonstrates the validity of the test concepts and techniques as well as the “fail safe” characteristics of the SH‐3A airframe.

High-Cycle Fatigue Behavior of Type 4340 Steel Pressurized Blocks Including Mean Stress Effect

2019 ◽  
Author(s):  
Elie A. Badr ◽  
Joanne Ishak
Keyword(s):  
Stress Ratio ◽  
Fatigue Behavior ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Ultimate Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Test Results ◽  
Linear Correction ◽  
The Mean

Abstract Mean stress effects in pressurized steel blocks were examined under constant amplitude fatigue loading. The tests were performed to provide experimental data needed to study the effect of mean stress on fatigue lives of subject specimen, and to substantiate the use of analytical expressions to account for the mean stress. The mean stress was the result of subjecting the specimens to an autofrettage pressure which induced compressive residual stresses at the crossbore intersection of the specimens. Fatigue tests were carried out under both tensile and compressive mean stress levels. Test results were compared to several mean stress accounting relationships such as the Smith-Watson Topper, Bergmann and Seeger, modified Goodman, Gerber and Soderberg. Test results indicated that the modified Goodman equation is favorable in accounting for the effect of both tensile and compressive mean stresses on fatigue life (up to a compressive mean stress to ultimate stress ratio of −0.2). The behavior under compressive mean stress to ultimate stress ratio of less than −0.2 indicated that a linear correction relationship was required.

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