Mechanical Factors Affecting Stress Corrosion Crack Growth Rates in Buried Pipelines

2000 ◽  
Author(s):  
S. B. Lambert ◽  
J. A. Beavers ◽  
B. Delanty ◽  
R. Sutherby ◽  
A. Plumtree
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Electrical Potential ◽  
Potential Drop ◽  
Maximum Load ◽  
Load Test ◽  
Factors Affecting ◽  
Transgranular Crack ◽  
Groundwater Environment ◽  
Crack Growth Rates

Over the past several years, investigations have been carried out into the rate of crack growth in pipeline steels in simulated, near-neutral pH, groundwater environment (NS4 solution). Pre-cracked specimens were subject to constant amplitude loading under various frequencies, maximum loads and R-ratios (minimum/maximum load). Test times varied from about 20 to 400 days. Transgranular crack features, similar to those found in service, have been observed. The extent of crack growth was monitored using either electrical potential drop or detailed metallographic examinations at two laboratories. The resulting crack growth rates from both labs are consistent with a superposition model based on a summation of fatigue (Paris Law) and static (SCC) crack growth rates. Differences between the results at the two laboratories are discussed.

scholarly journals Crack Growth of a Polycrystalline Nickel Alloy under TMF Loading

2014 ◽  
Vol 891-892 ◽  
pp. 1302-1307 ◽  
Author(s):  
Christopher J. Pretty ◽  
Mark T. Whittaker ◽  
Steve J. Williams
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Peak Stress ◽  
Potential Drop ◽  
Polycrystalline Nickel ◽  
Testing Method ◽  
Transgranular Crack ◽  
Engine Components ◽  
Crack Growth Rates ◽  
Time Dependent Crack Growth

Thermo-mechanical fatigue (TMF) is an important factor for consideration when designing aero engine components due to recent gas turbine development, thus understanding failure mechanisms through crack growth testing is imperative. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180°OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.

Fracture and Fatigue Tolerant Steel Pressure Vessels for Gaseous Hydrogen

2010 ◽  
Author(s):  
Kevin A. Nibur ◽  
Chris San Marchi ◽  
Brian P. Somerday
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Maximum Load ◽  
Pressure Vessels ◽  
Hydrogen Gas ◽  
R Ratio ◽  
History Of ◽  
Crack Growth Rates

Fatigue crack growth rates and rising displacement fracture thresholds have been measured for a 4130X steel in 45 MPa hydrogen gas. The ratio of minimum to maximum load (R-ratio) and cyclic frequency was varied to assess the effects of these variables on fatigue crack growth rates. Decreasing frequency and increasing R were both found to increase crack growth rate, however, these variables are not independent of each other. Changing frequency from 0.1 Hz to 1 Hz reduced crack growth rates at R = 0.5, but had no effect at R = 0.1. When applied to a design life calculation for a steel pressure vessel consistent with a typical hydrogen trailer tube, the measured fatigue and fracture data predicted a re-inspection interval of nearly 29 years, consistent with the excellent service history of such vessels which have been in use for many years.

Influence of Environment and Creep on Fatigue Crack Growth in a High Temperature Aluminum Alloy 8009

1994 ◽  
Vol 116 (1) ◽  
pp. 45-53 ◽  
Author(s):  
K. V. Jata ◽  
D. Maxwell ◽  
T. Nicholas
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Hold Time ◽  
Maximum Load ◽  
Frequency Effects ◽  
Crack Growth Rates

Frequency effects on fatigue crack growth rates are examined in aluminum alloy 8009 in sheet and extruded product forms. The investigations show that frequency effects on the fatigue crack growth rates are pronounced in the sheet but minimal in the extrusion. The influence of creep cracking on fatigue crack growth rate is studied through tests with a 60 s hold-time at maximum load at several stress intensity ranges. A 60 s hold-time at maximum load at 315°C tends to retard fatigue crack growth in both the sheet and the extrusion. The mechanism by which this retardation occurs is attributed to stress relaxation at the crack tip. At 204°C a 60 s hold at Pmax accelerates crack growth rate in the sheet but not in the extrusion. Vacuum and laboratory air tests show that fatigue crack growth rates in vacuum are lower than in air by about a factor of four. A 60 s hold-time at minimum load has only a minor effect on the fatigue crack growth rates at 315°C and no effect at 204°C, confirming the absence of any strong environmental contribution to crack growth rate. Fracture modes in fatigue, creep crack growth and hold-time at Pmax are significantly different. The fractographic results are discussed in relation to the mechanical property data.

scholarly journals Advantageous Description of Short Fatigue Crack Growth Rates in Austenitic Stainless Steels with Distinct Properties

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 475
Author(s):  
Lukáš Trávníček ◽  
Ivo Kuběna ◽  
Veronika Mazánová ◽  
Tomáš Vojtek ◽  
Jaroslav Polák ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Growth Rates ◽  
Large Scale ◽  
J Integral ◽  
Scale Yielding ◽  
Residual Fatigue ◽  
Crack Growth Rates

In this work two approaches to the description of short fatigue crack growth rate under large-scale yielding condition were comprehensively tested: (i) plastic component of the J-integral and (ii) Polák model of crack propagation. The ability to predict residual fatigue life of bodies with short initial cracks was studied for stainless steels Sanicro 25 and 304L. Despite their coarse microstructure and very different cyclic stress–strain response, the employed continuum mechanics models were found to give satisfactory results. Finite element modeling was used to determine the J-integrals and to simulate the evolution of crack front shapes, which corresponded to the real cracks observed on the fracture surfaces of the specimens. Residual fatigue lives estimated by these models were in good agreement with the number of cycles to failure of individual test specimens strained at various total strain amplitudes. Moreover, the crack growth rates of both investigated materials fell onto the same curve that was previously obtained for other steels with different properties. Such a “master curve” was achieved using the plastic part of J-integral and it has the potential of being an advantageous tool to model the fatigue crack propagation under large-scale yielding regime without a need of any additional experimental data.

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