Lower Strength Steel Brittle Fracture Assessment

1974 ◽  
Vol 100 (5) ◽  
pp. 983-999
Author(s):  
Mohammed H. Magued ◽  
D. J. Laurie Kennedy
Keyword(s):  
Brittle Fracture ◽  
Lower Strength ◽  
Fracture Assessment

Computational Methods to Support Brittle Fracture Assessment of PSVs Involving Autorefrigeration

2015 ◽  
Author(s):  
Kannan Subramanian ◽  
Jorge Penso ◽  
Harbi Pordal
Keyword(s):  
Brittle Fracture ◽  
Computational Methods ◽  
Cost Effective ◽  
Liquid Hydrocarbon ◽  
Computational Method ◽  
Metal Temperature ◽  
Relief Valve ◽  
Sensitivity Studies ◽  
Fracture Assessment ◽  
Cfd Method

Pressure safety relief valve (PSV) operation generally leads to cooling of the valve itself and the piping connected to the PSV. The temperatures may reach values below the minimum design metal temperature (MDMT) of the valve, and therefore the valve needs to be assessed for brittle fracture susceptibility. Simplistic determination of the minimum metal temperature in the valve may disqualify these valves during the brittle fracture assessments (BFA). Replacement may be time consuming and may not be cost effective. In such circumstances, a sophisticated and more representative BFA approach involving the use of computational fluid dynamics (CFD) followed by finite element method (FEM) based stress analysis which may be further followed by fracture mechanics can be adopted based on the concepts defined in ASME/API 579. The accuracy of the BFA depends on the accuracy of each of the computational method involved in the assessment. Among all the computational methods, CFD poses significant challenge. The low temperature may have been caused due to Joule-Thompson effect or auto-refrigeration. While Joule-Thompson effect can be best captured with easy to implement and robust CFD methods, auto-refrigeration involving adiabatic flashing which causes additional complexity and requires multiple sensitivity studies performed to determine the accuracy of the CFD approach. In this paper, an overview of the computational methods used in the brittle fracture assessment of PSVs is presented. Specific CFD method details are provided for PSV involving the flashing of liquid hydrocarbon to vapor is presented in the form of a case study derived from downstream industry application.

Effects of Specimen Size and Notch Acuity on the Brittle Fracture Strength of a Heat-Treated Steel

1961 ◽  
Vol 83 (4) ◽  
pp. 541-544 ◽  
Author(s):  
S. Yukawa ◽  
J. G. McMullin
Keyword(s):  
Brittle Fracture ◽  
Alloy Steel ◽  
Fracture Strength ◽  
Specimen Size ◽  
Root Radius ◽  
Lower Strength ◽  
Large Size ◽  
Treated Steel ◽  
Heat Treated ◽  
Heat Treated Steel

Effects of various methods of notch preparation on the notched slow bend fracture strengths of heat-treated alloy steel specimens were studied. The results indicate that several kinds of cracks result in about 35 per cent lower strength than a machined 0.005 in. root radius notch. The importance of testing sufficiently large size specimens to reveal this difference is shown.

Brittle Fracture Assessment and Failure Assessment Diagrams

2021 ◽  
pp. 1-8
Author(s):  
Brian Macejko
Keyword(s):  
Fracture Mechanics ◽  
Brittle Fracture ◽  
Flaw Size ◽  
Process Equipment ◽  
Reliable Prediction ◽  
Fracture Failure ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
Assessment Procedures

Abstract A detailed fracture mechanics evaluation is the most accurate and reliable prediction of process equipment susceptibility to brittle fracture. This article provides an overview and discussion on brittle fracture. The discussion covers the purpose for evaluating, provides a brief summary of historical failures that were found to be a result of brittle fracture, and describes key components that drive susceptibility to a brittle fracture failure, namely stress, toughness/temperature, and flaw size. It also presents industry codes and standards that assess susceptibility to brittle fracture. Additionally, a series of case study examples are presented that demonstrate assessment procedures used to mitigate the risk of brittle fracture in process equipment.

Fracture Assessment of Welded Joint With Geometrical Discontinuity Using the Weibull Stress

2006 ◽  
Author(s):  
Satoshi Igi ◽  
Takahiro Kubo ◽  
Masayoshi Kurihara ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Welded Joint ◽  
Fracture Toughness Test ◽  
Geometrical Condition ◽  
Stress Criterion ◽  
Toughness Test ◽  
Fracture Assessment ◽  
Geometrical Discontinuity ◽  
Weibull Stress

Recently the Weibull stress is used as a fracture driving force parameter in fracture assessment. The Weibull stress is derived from a statistical analysis of local instability of micro cracks leading to brittle fracture initiation. The critical Weibull stress is expected to be a critical parameter independent of the geometrical condition of specimens. Fracture toughness test using 3-point bending and tensile tests of welded joint specimens with geometrical discontinuity were conducted in order to study the applicability of fracture assessment procedure based on Weibull stress criterion. Steel plates prepared for this study had tensile strength of 490 MPa for structural use. Two kinds of welded joint specimens, “one-bead welded joint” and “multi-pass welded joint” were prepared for fracture toughness test by using gas metal are welding. In tensile test specimen, corner flaws were introduced at the geometrical discontinuity part at where stress concentration is existed. Three dimensional elastoplastic finite element analyses were also carried out using the welded joint specimen models in order to calculate the Weibull stress. The critical loads for brittle fracture predicted by the Weibull stress criterion from CTOD test results of one-bead and multi-pass welded joint specimens show fairly good agreement with experimental results of welded joint specimens with geometrical discontinuity.

Mode II Brittle Fracture Assessment of Key-Hole Notches by Means of the Local Energy

2014 ◽  
Vol 44 (3) ◽  
pp. 20140295 ◽  
Author(s):  
A. R. Torabi ◽  
A. Campagnolo ◽  
F. Berto
Keyword(s):  
Brittle Fracture ◽  
Mode Ii ◽  
Local Energy ◽  
Fracture Assessment

Brittle Fracture Assessments of Offshore PSVs

2014 ◽  
Author(s):  
Kannan Subramanian ◽  
Jorge Penso ◽  
Harbi Pordal ◽  
Graham McVinnie ◽  
Greg Garic
Keyword(s):  
Brittle Fracture ◽  
Stress Analysis ◽  
Stress Ratio ◽  
Operating Conditions ◽  
Ratio Method ◽  
Conservative Approach ◽  
Relief Valve ◽  
Valve Body ◽  
Fracture Assessment ◽  
Brittle Fractures

Pressure safety relief valve needs to be designed and operated to assure metal temperatures are not lower than the Minimum Allowable Temperature (MAT) to prevent brittle fractures. Design and fitness for service codes include general procedures to prevent brittle fractures. Design procedures in the codes are very conservative whereas fitness for service codes in some cases lack details. In the absence of a detailed brittle fracture assessment procedure for valves subject to significant low temperatures as a result of either Joule-Thompson effect or auto-refrigeration, an approach involving pressure based stress ratio method of ASME/API 579, Part 3 has been adopted and implemented. The initial and very conservative approach involved a worst case combination of the upstream pressure while calculating the stress ratio and a comparison of the newly established MAT with the downstream temperature. This conservative approach resulted in the disqualification of numerous PSVs studied in this work. Valve replacement and associated lost production time leads to high costs. A sophisticated and appropriately conservative brittle fracture assessment approach involving the use of computational fluid dynamics (CFD) followed by finite element method analysis (FEA) based stress analysis was adopted based on the concepts defined in ASME/API 579 and is presented in this paper. Predictive CFD analysis establishes more realistic temperatures and pressures in relation to the actual operating conditions. The CFD predicted pressure and temperature field is used to determine the stresses in the valve body using FEA methods. The stress analysis is followed by an intermediate brittle fracture assessment based on the procedures described in API 579 Part 3 using the actual PSV body metal temperatures and stresses established using the stress analysis. A discussion on the allowable stresses and stress components to be used in this intermediate assessment is also presented. If the PSVs cannot be qualified with this intermediate brittle fracture assessment, fracture mechanics evaluations are carried out to establish the limiting flaw sizes for the valves. In addition, the flaw tolerances of the valves are also established using reference flaw approach described in API 579, Part 9.

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