Dynamic Apparatus for CTOA Measurement in Pipeline Steels

2008 ◽  
Author(s):  
Avigdor Shtechman ◽  
Christopher McCowan ◽  
Rony Reuven ◽  
Elizabeth Drexler ◽  
Philippe Darcis ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Fracture Mode ◽  
High Speed ◽  
Crack Propagation Rate ◽  
Full Scale ◽  
Opening Angle ◽  
Test Machine ◽  
Hydraulic Test ◽  
Pipeline Steels ◽  
Initial Results

When a crack initiates and propagates in a pressurized pipe, the only thing that might stop this high-velocity event is the release of internal pressure (decompression), resulting in a deceleration in the crack-propagation rate. This deceleration can be achieved through the use of crack arrestors, or the ability of the pipeline material to resist ductile fracture. To evaluate the resistance to crack growth, the crack tip opening angle (CTOA) is used. Recent articles on the CTOA of pipeline steels at quasi-static rates with modified double cantilever beam specimens (MDCB), and at dynamic displacements rates by use of drop weight tear testing have provided data to support this need. These laboratory results from the literature, compared with results of full-scale tests, indicate that details of the fracture mode depend on the rate of fracture. To further study the dependence among the rate, fracture mode, and CTOA, a dynamic test apparatus was designed to perform CTOA testing of MDCB specimens, so that comparisons to quasi-static and full-scale results could be made. This new apparatus consists of a 500 kN uniaxial hydraulic test machine capable of stand-alone displacement rates of 300 mm/s, and a disc spring apparatus that is used to further accelerate the testing displacement rate. Initial results of the testing show that full slant fracture mode is observed at the highest rates tested for X65 and X100 steels. Maximum crack velocities approaching 10 m/s were recorded with highspeed photography. CTOA measurements were typically made at a position about 30 mm ahead of the pre-fatigue crack, over a distance of about 15 mm in the steady-state crack propagation regime. In this paper, we describe the high-speed apparatus, discuss the relationship among specimen configuration, crack speed, and CTOA, and present initial results on X65 and X100 pipeline steels.

Corrosion Fatigue Mechanisms and Fracture Mechanics Based Modelling for Subsea Pipeline Steels

2017 ◽  
Author(s):  
Ankang Cheng ◽  
Nian-Zhong Chen
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Corrosion Fatigue ◽  
Fatigue Cracking ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Propagation Time ◽  
Loading Frequency ◽  
Pipeline Steels ◽  
Driving Mechanisms

Subsea structures such as pipelines are vulnerable to environment-assisted crackings (EACs). As a type of EAC, corrosion fatigue (CF) is almost inevitable. For such a process, stress corrosion (SC) and hydrogen-assisted cracking (HAC) are the two mainly driving mechanisms. And it was further pointed out that slip dissolution (SD) and hydrogen embrittlement (HE) should be responsible for SC and HAC respectively. Based on such a fact, a two-component physical model for estimating the CF crack propagation rate was proposed. The proposed model was built in a frame of fracture mechanics integrated with a dissolution model for C-Mn steel and a newly established model by the authors accounting for the influence from HE upon crack propagation. The overall CF crack propagation rate is the aggregate of the two rates predicted by the two sub-individual models, and then the crack propagation time is calculated accordingly. The model has been proven to be capable of capturing the features of HE influenced fatigue cracking behaviour as well as taking mechanical factors such as the loading frequency and stress ratio into account by comparison with the experimental data of X42 and X65 pipeline steels.

scholarly journals Fracture of Titanium Alloys at High Strain Rates and under Stress Triaxiality

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 305 ◽  
Author(s):  
Vladimir V. Skripnyak ◽  
Evgeniya G. Skripnyak ◽  
Vladimir A. Skripnyak
Keyword(s):  
Titanium Alloys ◽  
High Speed ◽  
Stress Triaxiality ◽  
Correlation Method ◽  
Image Correlation ◽  
Shear Stresses ◽  
Test Machine ◽  
Strain Rates ◽  
Hydraulic Test ◽  
Strain Fields

The present study investigates the effect of stress triaxiality on mechanical behavior and fracture of Ti-5Al-2.5Sn alloy in a practical relevant strain rate range from 0.1 to 1000 s−1. Tensile tests were carried out on flat smoothed and notched specimens using an Instron VHS 40/50-20 servo-hydraulic test machine. High-speed video registration was conducted by Phantom 711 Camera. Strain fields on the specimen gauge area were investigated by the digital image correlation method (DIC). The fracture surface relief was studied using digital microscope Keyence VHX-600D. Stress and strain fields during testing of the Ti-5Al-2.5Sn alloy were analyzed by the numerical simulation method. The evolution of strain fields at the investigated loading condition indicates that large plastic deformation occurs in localization bands. The alloy undergoes fracture governing by damage nucleation, growth, and coalescence in the localized plastic strain bands oriented along the maximum shear stresses. Results confirm that the fracture of near alpha titanium alloys has ductile behavior at strain rates from 0.1 to 1000 s−1, stress triaxiality parameter 0.33 < η < 0.6, and temperature close to 295 K.

scholarly journals Introduction of Fatigue Markers in Full Scale Fatigue Test of an Aircraft Structure

2012 ◽  
Vol 2012 (4) ◽  
pp. 29-37 ◽  
Author(s):  
Andrzej Leski ◽  
Sylwester Kłysz ◽  
Janusz Lisiecki ◽  
Gabriel Gmurczyk ◽  
Piotr Reymer ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Test ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Full Scale ◽  
Life Assessment ◽  
Load Spectrum ◽  
Preliminary Load ◽  
Different Levels

Abstract Air Force Institute of Technology participates in the service life assessment programme SEWST. The aim of this programme, funded by the Polish Ministry of Defense, is to modify the operation system of PZL-130 "Orlik" TC-II turbo propelled trainer aircraft. The structural part of the programme is focused on the Full Scale Fatigue Test of the whole airframe to be conducted at the VZLU in the Czech Republic. The load spectrum for the test was developed by the AFIT based on the flight test results. The basic load block represents 200 simulated flight hours and consists of 194 flights showing different levels of severity. At the end of the Full Scale Fatigue Test a teardown inspection is planned during which it would be most beneficial to be able to determine crack propagation rate by means of a crack surface inspection. Markers are usually visible on most fatigue crack surfaces, however they occur randomly therefore it is almost impossible to conclude anything about the crack history. Since the preliminary load block consisted of separate flights (flight loads together with landing and taxing loads) showing significantly different levels of severity, the easiest way to modify the load block was to change the order of flights within the block. Hence a pilot programme was started at the AFIT which was focused on the determination of the influence of flight sequence on crack appearance. Several load blocks were determined using various techniques of rearranging the order of flights within the preliminary load spectrum. This approach ensured the preservation of the initial severity of the load block and simultaneously enabled a significant increase in the probability of the markers occurrence introducing neither artificial underloads nor overloads that would most probably affect the crack propagation rate. Fatigue crack surfaces were inspected using Scanning Electron Microscope. As a result of the investigations a series of images were obtained showing the specimen microstructure with visible markers arranged in the desired sequences. Based on the obtained pictures the most promising load block arrangements were chosen for the Full Scale Fatigue Test.

Crack Propagation Modeling and Crack Arrestor Design for X120

2006 ◽  
Author(s):  
Andrea Fonzo ◽  
Andrea Meleddu ◽  
Massimo Di Biagio ◽  
Gianluca Mannucci ◽  
Giuseppe Demofonti ◽  
...  
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Wall Thickness ◽  
Full Scale ◽  
Operating Conditions ◽  
Experimental Results ◽  
Finite Element Code ◽  
Pipeline Steels ◽  
Propagation Modeling

The new, higher grade pipeline steels provide an opportunity to reduce pipeline costs by enabling a shift to higher pressure at reasonable wall thickness. However, these higher operating stresses place greater demands on the pipeline, particularly when a running fracture is considered. Several studies have shown that intrinsic arrest cannot be counted on for these grades under all operating conditions. In such cases, crack arrestors will be needed. This paper presents results obtained using CSM’s proprietary PICPRO® finite element code to predict the performance of crack arresters on X120 pipes, and shows that the predictions agree well with full-scale experimental results obtained in arrestor trials.

CTOA Results for X65 and X100 Pipeline Steels: Influence of Displacement Rate

2008 ◽  
Author(s):  
R. Reuven ◽  
C. McCowan ◽  
E. Drexler ◽  
A. Shtechman ◽  
Ph. Darcis ◽  
...  
Keyword(s):  
Opening Angle ◽  
Dynamic Mode ◽  
Test Machine ◽  
Pipeline Steels ◽  
Static Mode ◽  
Static Tests ◽  
Uniaxial Test ◽  
Dynamic Experiments ◽  
X65 Steel ◽  
Crack Tip Opening

The toughness and plasticity of steel generally decreases with increasing testing rate. The crack tip opening angle (CTOA) was measured on two types of commercial pipeline steels API-X65 and API-X100, at a range of displacement rates to characterize rate effects. The testing was conducted at quasi-static and dynamic rates. The crosshead displacements in our test matrix ranged from 0.002 mm/s in the quasi-static mode to approximately 8000 mm/s in the dynamic mode. The quasi-static tests were conducted in a servo-hydraulic uniaxial test machine using Modified Double Cantilever Beam (MDCB) specimens. The dynamic experiments were made on a similar servo-hydraulic uniaxial test machine using the same type of specimen and with the addition of a disc spring setup for the fastest rate. The results of these tests indicate that the rate effect has negligible influence on the CTOA values measured for these materials for the reported rates. The CTOA values measured for the two materials show a small but convincing difference. The resistance to fracture was found to be higher for the X65 steel, as indicated by a higher CTOA and lower crack growth velocity. This paper presents results on the influence of displacement rates from quasi-static to dynamic for the X65 and X100 grade pipeline steels, and discusses a method for optimizing the reduction of the CTOA data.

Corrosion–fatigue crack propagation of aluminum alloys for high-speed trains

2017 ◽  
Vol 31 (16-19) ◽  
pp. 1744009 ◽  
Author(s):  
Lin Shen ◽  
Hui Chen ◽  
Xiaoli Che ◽  
Lidong Xu
Keyword(s):  
Fatigue Crack ◽  
Aluminum Alloys ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Corrosion Fatigue ◽  
High Speed ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Crack Propagation Rate ◽  
Corrosion Fatigue Crack

A modified single-edge notch tension (SENT) specimen exposed to saline environment was utilized to investigate the corrosion–fatigue crack growth behaviors of 5083, 6005 and 7N01 aluminum alloys. The fatigue crack propagation life, corrosion–fatigue crack rate ([Formula: see text]) were tested. The microstructures and fracture surfaces of specimens were examined by optical microscopy and scanning electron microscopy (SEM). The results showed that fatigue crack propagation rate of 7N01 in 3.5% NaCl was significantly higher than 6005 and 5083 alloys. The mechanisms of anodic dissolution and hydrogen embrittlement are used to explain the results.

Test Analysis on Crack Propagation Rate of Axle Pipe Steel

2010 ◽  
Vol 146-147 ◽  
pp. 1-4 ◽  
Author(s):  
Zhong Guo Huang ◽  
Hong Lei Dong ◽  
Qing Hua Yuan ◽  
Jia Fan
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Crack Propagation ◽  
Pipe Steel ◽  
Reference Value ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Test Machine ◽  
Test Analysis ◽  
Rate Test

The crack growth rate test of XCQ16 and XCQ16-1 axle steels were introduced using MTS material test machine. The test data of the crack propagation rate of axle steels has been analyzed by Paris formula. The results showed the crack propagation rate test of XCQ16 was faster than XCQ16-1, and the fatigue residual of XCQ16-1 life is longer. The correlated coefficient of the experimental data indicates that the result of this paper is comparatively ideal and has reference value to appraising the life span.

Experimental Measurement of CTOA During Ductile Crack Propagation in Pipeline Burst Tests

2018 ◽  
Author(s):  
Kazuki Shibanuma ◽  
Hikaru Yamaguchi ◽  
Takahiro Hosoe ◽  
Katsuyuki Suzuki ◽  
Shuji Aihara
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Crack Velocity ◽  
High Speed ◽  
Crack Arrest ◽  
Opening Angle ◽  
Small Scale ◽  
Outer Diameter ◽  
Burst Test ◽  
Pipe Burst

Dynamic measurement of drop-weight tear test (DWTT) and pipe burst test for 356 mm outer diameter and 9.5 mm wall thickness steel pipe were conducted using high-speed camera. Crack velocity in the DWTT were 10 m/s during the steady state. Crack Tip Opening Angle (CTOA) values measured in the DWTT showed the constant value of about 20.1° during steady state propagation. On the other hand, crack velocity in the burst test showed monotonically decreasing during crack propagation from 200 m/s but it was found that CTOA value kept constant value of about 13.2° until crack arrest irrespective of the crack velocity. These results showed the validation of the CTOA criterion for the high-pressure gas pipelines. The results also showed that CTOA in a burst test is generally different from that in a test using small-scale specimen. Future developments of the experimental procedure using a small-scale specimen to provide CTOA value corresponding with that in a burst test would be effective.

Investigation of Crack Propagation Characteristics Using Instrumented Charpy and DWT Tests for Full-Scale Burst Tested 1219 mm OD Grade 550 (X80) Linepipe

2016 ◽  
Author(s):  
Satoshi Igi ◽  
Cindy Guan ◽  
Brian Rothwell ◽  
Takashi Hiraide
Keyword(s):  
Crack Propagation ◽  
High Speed ◽  
Large Diameter ◽  
Propagation Speed ◽  
Test Site ◽  
Management Program ◽  
Full Scale ◽  
In Situ Observation ◽  
Separation Index ◽  
Crack Propagation Speed

TransCanada, on behalf of the Coastal GasLink (CGL) project, has carried out two full-scale burst tests [1, 2] at the Spadeadam test site of DNV GL, to validate the effectiveness of crack arrestors and refine the propagation control design for the large-diameter, X80 linepipe required for this project. The tests were supported by LNG Canada and TransCanada Technology Management Program. For these full-scale burst tests, Grade 550linepipe having Charpy energies from 125 to over 450 J were produced using thermomechanical controlled processing (TMCP) technology. This paper describes propagation and arrest properties of the X80 linepipe materials having various Charpy energy values from the aspect of crack propagation energy and crack propagation speed relationships from instrumented Charpy and press-notched (PN) and static pre-cracked drop-weight tear (SPC-DWT) tests, together with in-situ observation of crack propagation by high-speed video camera. It was found that crack propagation speed is greatly affected by crack propagation energy measured by both Charpy and instrumented DWT tests. The crack propagation energy is lower in DWTT specimens with a higher separation index. It is not clear whether the crack propagation energy is only affected by the separations. However, the crack velocity is higher in DWTT specimens with a higher separation index. It is assumed that the crack propagation speed might be not only affected by separation but also low propagation energy. The testing data obtained from Charpy and instrumented DWT tests are compared with the fracture speed data measured from the full-scale burst test. The correlation between Charpy energy and crack propagation energy in DWTT is also compared with the predictions of an empirical equation.

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