Fatigue of Drill String Connections

1995 ◽  
Vol 117 (2) ◽  
pp. 126-132 ◽  
Author(s):  
F. P. Brennan
Keyword(s):  
Aspect Ratio ◽  
Crack Growth ◽  
Empirical Model ◽  
Drill String ◽  
Full Scale ◽  
Growth Data ◽  
Service Environment ◽  
Threaded Connections ◽  
Bend Tests ◽  
Full Scale Tests

This paper reports full-scale tests on threaded connections used in drill strings. A concise background is given concerning the in-service environment and loading conditions on the connections. This details some of the reasons particular steels are used in preference to others. Crack growth data is given for ten full-scale axial and rotating bend tests. This is compared with predictions from a dedicated weight function fracture mechanics solution designed for threaded connections. Crack aspect ratio is considered with a view to development of an appropriate empirical model.

The Story of the Dent-Gouge Fracture Model

2020 ◽  
Author(s):  
Andrew Cosham ◽  
Phil Hopkins
Keyword(s):  
Empirical Model ◽  
Factor Of Safety ◽  
Original Model ◽  
Full Scale ◽  
Fracture Model ◽  
Burst Pressure ◽  
Two Dimensional ◽  
Dimensional Representation ◽  
Full Scale Tests ◽  
Semi Empirical

Abstract Once upon a time the dent-gouge fracture model was developed by the then British Gas Corporation to estimate the burst pressure of a dent and gouge subject to internal pressure. The dent-gouge fracture model is based on a two-dimensional representation of a dent and gouge; it assumes an infinitely long, longitudinally-orientated gouge (a crack) at the base of infinitely long, longitudinally-orientated dent. The model was calibrated using the results of 109 ring tests and 23 vessel tests conducted by the British Gas Corporation; a dent was introduced and then a slot was machined in the base of the dent (all at zero pressure). It is a semi-empirical model. Part 12 of API 579-1/ASME FFS-1 2016 quotes the original dent-gouge fracture model. A number of variations on the theme of the original dent-gouge fracture model have been developed. The variants have not significantly improved the accuracy of the original model, as is demonstrated by comparing the variants against the results of burst tests on rings and vessels containing a dent and gouge (or notch) reported in the published literature. The dent-gouge fracture model is deconstructed in order to illustrate its component parts. The deconstruction clearly identifies the parts of the model that could be improved. It also highlights where semi-empiricism is embedded in the model. The effect of changes to the original model is illustrated using the results of the full-scale tests. The difficulties introduced by the scatter in the full-scale tests are discussed, noting that a number of different methods have been used to introduce the dent and gouge (or notch) into the ring or vessel. A factor of safety is proposed. Pointers are given to how the dent-gouge fracture model might be improved or replaced. The need for a dent-gouge model is also considered, in the context of the guidance given in API Recommended Practice 1160 and ASME B31.8S.

Development of Fatigue Design Data for the Ormen Lange Offshore Project: An Overview

2006 ◽  
Author(s):  
Hans Olav Knagenhjelm ◽  
Oddvin O̸rjasæter ◽  
Per J. Haagensen
Keyword(s):  
Crack Growth ◽  
Full Scale ◽  
Small Scale ◽  
Formation Water ◽  
Worst Case ◽  
Vortex Induced Vibrations ◽  
Welding Defects ◽  
Condensed Water ◽  
Full Scale Tests ◽  
Full Scale Testing

The Ormen Lange offshore pipelines from shore to the field go through very difficult terrain creating freespans in the range 40–80m for the 30” lines. For the 6” lines long freespans will be present prior to burial and vortex induced vibrations (VIV) will give a contribution during laying due to strong currents. Using existing codes for fatigue calculation was giving too conservative results compared to the welding technology used and experience from SCR work showed that better S-N data should be expected. A dedicated program was started as part of the Ormen Lange (OL) technology verification program overseen by Norwegian Authorities. An overview of the results is presented here. A full evaluation of the data is not yet complete. Papers will be published later presenting the full technical details and dataprocessing. Fatigue test results from the OL pipeline fatigue verification are presented focusing on the following topics: • Defect sizes in pipeline production welds; • Contractor-A: 5G welding position; • Contractor-B: 2G welding position; • 6” pipe full scale testing; • 30” pipe full scale testing; • Residual stresses; • Crack growth tests and sector specimen fatigue tests in production environments. The following are a summary of the main test variables in the program: • Mapping of actual welding defects compared to AUT results. • Welds with varying misalignment (high/low) and lack of penetration (LOP) from installation contractors tested in air. • Welds with natural welding defects in internal environment (Condensed water and formation water). • Welds with notches made by electrical discharge machining (EDM) (2×65mm and 2×15mm) in internal environment (condensed water and formation water). • Crack growth tests using large compact tension (CT) specimens in air, seawater and internal product environments (condensed water and formation water). • Full scale tests including worst case high/low, LOPs, and tests with normal welds including repair welds. The following main conclusions can be drawn from the work: • Small scale testing with representative worst case defects predicts well large scale testing results with the same features when the small scale specimen stresses are corrected for bending moments etc. arising from the cutout of the pipe. • Full scale testing of 30”×35.5mm wall thickness 2G pipes welded continuously (without start/stop) with worst case defects and high/low exceeds the D curve. • Full-scale tests of 30”×35.5mm wall thickness 5G non continuous welds with worst case defects and high/low exceeds the E curve. • Pipe welds showed low or even compressive residual stresses in the root. For continuously welded pipes the stress levels were low but more varying, also on the cap side. This partly explains the good results. • It is verified that the fatigue loads during operation are below the threshold of crack growth, and thus fatigue will not be a probable failure mechanism. This is under the condition that the measurements of vortex induced vibrations (VIV) during operation confirm the engineering calculations.

Crack Growth Model of Pipeline Steels in Near-Neutral pH Soil Environments

2008 ◽  
Author(s):  
Weixing Chen ◽  
R. Kania ◽  
R. Worthingham ◽  
S. Kariyawasam
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Model ◽  
Full Scale ◽  
Loading Frequency ◽  
Pipeline Steels ◽  
Neutral Ph ◽  
Full Scale Tests

This paper reports the crack growth behavior of pipeline steels in near-neutral pH environments. Crack growth data both from laboratory tests using compact tension (CT) specimen and from full scale tests of shallow cracks were analyzed using a true corrosion-fatigue model established recently. It has been found that the crack growth rate can be correlated with ΔK2Kmax/fα, where ΔK is the stress intensity factor range; Kmax is the maximum stress intensity factor; f is the loading frequency; and α is a factor related to corrosivity of soil environments. This correlation enables determination of threshold ΔK2Kmax/fα values for long cracks such as in a test using CT specimen. The above growth correlation appears also true for small/shallow cracks in full scale tests except that small/shallow cracks were found to grow at appreciable rates below the threshold of long/deep cracks. Implications of the growth model to crack growth occurring in the field and pipe integrity management were also discussed in the paper.

Investigation of planing craft maneuverability using full-scale tests

2021 ◽  
pp. 147509022110303
Author(s):  
Kazem Sadati ◽  
Hamid Zeraatgar ◽  
Aliasghar Moghaddas
Keyword(s):  
Full Scale ◽  
Performance Characteristics ◽  
Forward Speed ◽  
Speed Reduction ◽  
Planing Craft ◽  
Full Scale Tests ◽  
Turning Maneuver

Maneuverability of planing craft is a complicated hydrodynamic subject that needs more studies to comprehend its characteristics. Planing craft drivers follow a common practice for maneuver of the craft that is fundamentally different from ship’s standards. In situ full-scale tests are normally necessary to understand the maneuverability characteristics of planing craft. In this paper, a study has been conducted to illustrate maneuverability characteristics of planing craft by full-scale tests. Accelerating and turning maneuver tests are conducted on two cases at different forward speeds and rudder angles. In each test, dynamic trim, trajectory, speed, roll of the craft are recorded. The tests are performed in planing mode, semi-planing mode, and transition between planing mode to semi-planing mode to study the effects of the craft forward speed and consequently running attitude on the maneuverability. Analysis of the data reveals that the Steady Turning Diameter (STD) of the planing craft may be as large as 40 L, while it rarely goes beyond 5 L for ships. Results also show that a turning maneuver starting at planing mode might end in semi-planing mode. This transition can remarkably improve the performance characteristics of the planing craft’s maneuverability. Therefore, an alternative practice is proposed instead of the classic turning maneuver. In this practice, the craft traveling in the planing mode is transitioned to the semi-planing mode by forward speed reduction first, and then the turning maneuver is executed.

Full-scale tests of the trash racks of the Kapchagai hydroelectric station

1984 ◽  
Vol 18 (4) ◽  
pp. 166-170
Author(s):  
A. L. Rakhmanova ◽  
I. O. Rybak
Keyword(s):  
Hydroelectric Station ◽  
Full Scale ◽  
Full Scale Tests

Effect of Hardness and Tensile Mean Stress on Fatigue Crack Growth in Beryllium Copper

1969 ◽  
Vol 11 (3) ◽  
pp. 343-349 ◽  
Author(s):  
L. P. Pook
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Residual Stresses ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Mean Stress ◽  
Growth Data ◽  
Beryllium Copper

Some fatigue crack growth data have been obtained for age-hardened beryllium copper. The fatigue crack growth rate was found to be very dependent on the hardness and tensile mean stress. This dependence is believed to be associated with the intense residual stresses surrounding Preston-Guinier zones.

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