Development of a Novel Test Method to Characterize Material Properties in Corrosive Environments for Subsea HPHT Design

2017 ◽  
Author(s):  
Ramgopal Thodla ◽  
Colum Holtam ◽  
Rajil Saraswat
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Cathodic Protection ◽  
Material Properties ◽  
Test Method ◽  
Corrosive Environments

High pressure high temperature (HPHT) design is a significant new challenge facing the subsea sector, particularly in the Gulf of Mexico. API 17TR8 provides HPHT Design Guidelines, specifically for subsea applications. Fatigue endurance (i.e. S-N) and fracture mechanics design are both permitted, depending on the criticality of the component. Both design approaches require material properties generated in corrosive environments, such as seawater with cathodic protection and/or sour production fluids. In particular, it is necessary to understand sensitivity to cyclic loading frequency (for both design approaches), crack growth rates (for fracture mechanics approach) as well as fracture toughness performance. For many subsea components, the primary source of fatigue loading is associated with the start-up and subsequent shutdown operation of the well, with long hold periods in-between, during which static crack growth could occur. These are the two damage modes of most interest when performing a fracture mechanics based analysis. This paper presents the preliminary results of a novel single specimen test method that was developed to provide fatigue crack growth rate and fracture toughness data in corrosive environments, in a timeframe that is compatible with subsea HPHT development projects. Test data generated on alloy 625+ in seawater with cathodic protection is presented along with a description of how the test method was developed. A crack tip strain rate based formulation was applied to the data to rationalize the effect of frequency, stress intensity factor range (ΔK) and maximum stress intensity factor (Kmax).

Development of a Novel Test Method to Characterize Material Properties in Corrosive Environments for Subsea HPHT Design

2019 ◽  
Vol 142 (3) ◽  
Author(s):  
Ramgopal Thodla ◽  
Colum Holtam ◽  
Rajil Saraswat
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Cathodic Protection ◽  
Material Properties ◽  
Test Method ◽  
Corrosive Environments

Abstract High pressure high temperature (HPHT) design is a significant new challenge facing the subsea sector, particularly in the Gulf of Mexico. API 17TR8 provides HPHT Design Guidelines, specifically for subsea applications. Fatigue endurance (i.e., S–N) and fracture mechanics design are both permitted, depending on the criticality of the component. Both design approaches require material properties generated in corrosive environments, such as seawater with cathodic protection and/or sour production fluids. In particular, it is necessary to understand sensitivity to cyclic loading frequency (for both design approaches), crack growth rates (CGR) (for fracture mechanics approach) as well as fracture toughness performance. For many subsea components, the primary source of fatigue loading is associated with the start-up and subsequent shutdown operation of the well, with long hold periods in-between, during which static crack growth (CG) could occur. These are the two damage modes of most interest when performing a fracture mechanics based analysis. This paper presents the preliminary results of a novel single specimen test method that was developed to provide fatigue crack growth rate (FCGR) and fracture toughness data in corrosive environments, in a timeframe that is compatible with subsea HPHT development projects. Test data generated on alloy 625+ in seawater with cathodic protection are presented along with a description of how the test method was developed. A crack tip strain rate based formulation was applied to the data to rationalize the effect of frequency, stress intensity factor range (ΔK), and maximum stress intensity factor (Kmax).

scholarly journals CIRCUMFERENTIAL INHOMOGENITY ANALYSIS IN G.A. SIWABESSY REACTOR’S PRIMARY COOLING PIPE

2016 ◽  
Vol 18 (3) ◽  
pp. 155
Author(s):  
Roziq Himawan ◽  
Mike Susmikanti
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Elliptic Crack ◽  
Crack Model ◽  
Welding Part ◽  
Service Inspection

ABSTRACT In the in-service inspection conducted to G.A. Siwabessy reactor’s primary cooling system pipe, it was found the presence of inhomogenity inside of welding part. To verify whether the inhomogenity could be tolerated or not, comparative data from welding pre-service inspection is needed. Unfortunately, this weld wasn’t covered in pre-service inspection. Therefore, this inhomogenity needs to be analyzed. The purpose of this study is to evaluate the stress intensity factor of the inhomogenity, whether it is within a limit value or not and to predict the crack growth. Analysis were performed based on fracture mechanics theory using parameter of stress intensity factor. Two models were used for calculation approach that are plane crack model and semi-elliptic crack model. Hence, in order to predict the length of inhomogenity in the future, crack growth calculations were performed. The results showed that stress intensity values from both two models are remain below fracture toughness value of pipe’s material. Besides that, stress intensity factor from plane crack model is higher than those from semi-elliptic crack model. Under consideration that inhomogenity has an arc shape in actual, thus, stress intensity factor from this inhomogenity still low enough compare to the fracture toughness. Crack growth calculation’s results showed that after 300th cycle of loading, the length of inhomogenity reaches approximately 2 mm. Based on operation data of G.A. Siwabessy reactor, 300 cycle number is corresponds to 30 years operation. Based on these results it could be concluded that the presence of inhomogenity in the welding part does not affect the structure’s integrity of piping system. Keywords : Inhomogenity, fracture mechanics, fracture toughness, stress intensity factor, crack growth   ABSTRAK Pada pelaksanaan in-service inspection terhadap perpipaan sistem pendingin primer reaktor G.A. Siwabessy diketahui adanya inhomogenitas pada salah satu sambungan lasan pipa. Untuk memverifikasi apakah inhomogenitas ini dapat ditoleransi atau tidak, diperlukan data pembanding hasil pemeriksaan lasan pada saat fabrikasi. Namun, ternyata pada saat fabrikasi, sambungan lasan ini tidak mengalami pemeriksaan. Oleh karena itu, dalam rangka menetapkan apakah keberadaan inhomogentitas ini dapat ditoleransi atau tidak perlu dilakukan analisis terhadap inhomogenitas tersebut. Tujuan penelitian ini adalah untuk melakukan evaluasi stress intensity factor inhomogenitas di dalam pipa apakah masih berada di dalam batas nilai dan untuk memprediksi perambatan retak. Analisis dilakukan berdasarkan teori fracture mechanics dengan menghitung stress intensity factor inhomogenitas. Dalam perhitungan ini digunakan dua model untuk pendekatan, yaitu model retak planar dan model retak semi-ellips. Selanjutnya, untuk memprediksi panjang inhomogenitas di masa yang akan datang, dilakukan juga simulasi perambatan retak. Hasil-hasil analisis memperlihatkan bahwa nilai stress intensity factor berdasarkan model retak bentuk planar dan retak bentuk semi ellips masih jauh di bawah nilai fracture toughness material pipa. Selain itu, nilai yang dihasilkan berdasarkan model retak bentuk planar lebih besar dibandingkan dengan model retak bentuk semi ellips. Mengingat bentuk inhomogenitas yang berupa busur lingkaran, maka nilai stress intensity factor yang sesungguhnya dari inhomogenitas tersebut jauh lebih kecil dibandingkan dengan nilai fracture toughness. Sementara itu, untuk hasil simulasi perambatan retak menunjukkan bahwa pada siklus pembebanan ke-300 memberikan panjang sekitar 2 mm. Berdasarkan data operasi reaktor G.A. Siwabessy, jumlah siklus sebanyak 300 kali setara dengan pengoperasian reaktor selama 30 tahun. Berdasarkan dua hasil tersebut dapat disimpulkan bahwa keberadaan inhomogenitas pada sambungan lasan tidak berpengaruh terhadap integritas struktur sistem perpipaan. Kata kunci : Inhomogenitas, fracture mechanincs, fracture toughness, stress intensity factor, pertumbuhan retak 

Review of Technical Basis for ASME Code Section XI Appendix L

2020 ◽  
Author(s):  
Deepak S. Somasundaram ◽  
Dilip Dedhia ◽  
Do Jun Shim ◽  
Gary L. Stevens ◽  
Steven X. Xu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Multiple Cracks ◽  
Single Crack ◽  
Flaw Tolerance ◽  
Asme Code ◽  
The Impact

Abstract Equivalent Single Crack (ESC) sizes are provided in ASME Code, Section XI, Nonmandatory Appendix L, Tables L-3210-1 (for ferritic piping) and L-3210-2 (for austenitic piping). These two tables define initial flaw aspect ratios for use in fatigue flaw tolerance evaluations. These ESC sizes were based on the results of probabilistic fracture mechanics (PFM) evaluations that determined the equivalent single crack size that resulted in the same probability of through-wall leakage as the case when multiple cracks are initiated and grown around the inner circumference of a pipe. The PFM software, pc-PRAISE, used for the evaluation of ESC sizes had fracture mechanics models based on available data and models in the early 2000s. The stress intensity factor solutions used in pc-PRAISE were generated for a pipe radius-to-thickness ratio, Ri/t, of 5, and used a root-mean-square (RMS) averaged methodology. And the crack growth model was based on NUREG/CR-2189, Volume 5. This paper presents the results of evaluations to calculate a limited number of ESC sizes using updated fracture mechanics models for stress intensity factor and fatigue crack growth rates. The effect of crack growth due to stress corrosion cracking (SCC) in determining the ESCs is also discussed. The impact of the revised ESCs by performing two sample fatigue flaw tolerance problems and the associated results are also presented and discussed in this paper.

Application of 3D Fracture Mechanics for Improved Crack Growth Predictions of Gas Turbine Components

2017 ◽  
Author(s):  
Kanwardeep S. Bhachu ◽  
Santosh B. Narasimhachary ◽  
Sachin R. Shinde ◽  
Phillip W. Gravett
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Gas Turbine ◽  
Crack Growth ◽  
Structural Integrity ◽  
Crack Arrest ◽  
3D Crack Growth ◽  
Mechanics Analysis

Fracture mechanics analysis is essential for demonstrating structural integrity of gas turbine components. Usually, analyses based on simpler 2D stress intensity solutions provide reasonable approximations of crack growth. However, in some cases, simpler 2D solutions are too-conservative and does not provide realistic crack growth predictions; often due to its inability to account for actual 3D geometry, and complex thermal-mechanical stress fields. In such cases, 3D fracture mechanics analysis provides extra fidelity to crack growth predictions due to increased accuracy of the stress intensity factor calculations. Improved fidelity often leads to benefits for gas turbine components by reducing design margins, improving engine efficiency, and decreasing life cycle costs. In this paper, the application of 3D fracture mechanics analysis on a gas turbine blade for predicting crack arrest is presented. A comparison of stress intensity factor values from 3D and 2D analysis is also shown. The 3D crack growth analysis was performed by using FRANC3D in conjunction with ANSYS.

scholarly journals Application of a New, Energy-Based ΔS* Crack Driving Force for Fatigue Crack Growth Rate Description

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 518 ◽  
Author(s):  
Grzegorz Lesiuk
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Engineering Practice ◽  
Stress Effect ◽  
New Energy

This paper presents the problem of the description of fatigue cracking development in metallic constructional materials. Fatigue crack growth models (mostly empirical) are usually constructed using a stress intensity factor ΔK in linear-elastic fracture mechanics. Contrary to the kinetic fatigue fracture diagrams (KFFDs) based on stress intensity factor K, new energy KFFDs show no sensitivity to mean stress effect expressed by the stress ratio R. However, in the literature there is a lack of analytical description and interpretation of this parameter in order to promote this approach in engineering practice. Therefore, based on a dimensional analysis approach, ΔH is replaced by elastic-plastic fracture mechanics parameter—the ΔJ-integral range. In this case, the invariance from stress is not clear. Hence, the main goal of this paper is the application of the new averaged (geometrically) strain energy density parameter ΔS* based on the relationship of the maximal value of J integral and its range ΔJ. The usefulness and invariance of this parameter have been confirmed for three different metallic materials, 10HNAP, 18G2A, and 19th century puddle iron from the Eiffel bridge.

Fracture Mechanics Analysis of Aero-Engine Compressor Disc

2013 ◽  
Author(s):  
K. M. Sathish Kumar ◽  
G. V. Naveen Prakash ◽  
K. K. Pavan Kumar ◽  
H. V. Lakshminarayana
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Growth ◽  
Stable Crack Growth

Fracture is a natural reaction of solids to relieve stress and shed excess energy. The design philosophy envisions sufficient strength and structural integrity of the aircraft to sustain major damage and to avoid catastrophic failure. However there are inherent limitations in the methodology, resulting in significant under utilization of component lives and an inability to account for non-representative factors. Ductile materials used in aircraft engine are likely to experience fatigue and stable crack growth before the occurrence of fast fracture and final failure. Fatigue crack propagation can be characterized by a crack growth-rate model that predicts the number of loading cycles required to propagate a fatigue crack to a critical size. Stress Intensity Factors under fatigue loading are below the critical value for quasi-static or unstable crack propagation. Under these circumstances, Linear Elastic Fracture Mechanics helps to characterize the crack growth-rate model. Stable crack growth and final failure generally occur at the very last loading cycle of the life of aircraft. Crack propagation at this stage involves elastic-plastic stable tearing followed by fast-fracture. Since crack growth is no longer under small-scale yielding conditions, Elastic-Plastic Fracture Mechanics is needed to characterize the fracture behavior and to predict the residual strength. The most likely places for crack initiating and development are bolt holes in a compressor disk. Such cracks may grow in time leading to a loss of strength and reduction of the life time of the disc. The objective of this work is to determine Stress Intensity Factor for a crack emanating from a bolt hole in a disk and approaching shaft hole. The objective is achieved by developing a 2D finite element model of a disk with bolt holes subjected to a centrifugal loading. It was observed that stress concentration at the holes has a strong influence on the value of Stress Intensity Factor. Also, fatigue life prediction was carried out using AFGROW software. Different fatigue crack growth laws were compared. This provides necessary information for subsequent studies, especially for fatigue loads, where stress intensity factor is necessary for the crack growth rate determination and prediction of residual strength.

scholarly journals Analisis Probabilistic Fracture Mechanics Pada Evaluasi Keandalan Bejana Tekan Reaktor Secara 3-D

2018 ◽  
Vol 24 (1) ◽  
Author(s):  
Entin Hartini ◽  
Roziq Himawan ◽  
Mike Susmikanti
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Probability Density Function ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Pressure Vessel ◽  
J Integral ◽  
Probabilistic Fracture Mechanics ◽  
Reactor Pressure

Analisis integritas material sangat diperlukan pada Reactor Pressure Vessel (RPV). Komponen tersebut merupakan pressure boundary yang berfungsi untuk mengungkung material radioaktif. Adanya retak pada dinding dapat mempengaruhi integritas RPV tersebut. Penelitian ini bertujuan melakukan analisis fracture mechanics menggunakan model probabilistik untuk evaluasi keandalan RPV. Model probabilistik digunakan untuk pendekatan karakter random dari kuantitas input seperti sifat mekanik material dan lingkungan fisik. Karakter random dari kuantitas input menggunakan teknik sampling berdasarkan probability density function.  Material yang digunakan pada RPV adalah baja feritik (SA 533). Analisis fracture mechanics dilakukan berdasarkan metode elemen hingga (FEM) menggunakan perangkat lunak MSC MARC. Output dari MSC MARC adalah nilai J integral untuk mendapatkan nilai stress intensity factor (SIF) pada evaluasi keandalan bejana tekan reaktor 3D. Hasil perhitungan menunjukan bahwa SIF probabilistik lebih dulu mencapai nilai batas fracture toughness  dibanding  SIF deterministik. Nilai SIF yang dihasilkan dengan metode probabilistik adalah 95,8  MPa m0,5, sedangkan dengan metode deterministik adalah 91,8 MPa m0,5, rasio crack (a/c) semakin kecil akan dihasilkan nilai SIF yang semakin besar.Kata kunci: Probabilistic fracture mechanics, bejana tekan, 3-D.

scholarly journals Formation Criterion of Hydrogen-Induced Cracking in Steel Based on Fracture Mechanics

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 940 ◽  
Author(s):  
Lei Fu ◽  
Hongyuan Fang
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Hydrogen Pressure ◽  
Hydrogen Atoms ◽  
Loading Effect ◽  
Hydrogen Molecules ◽  
Hydrogen Induced Cracking

A new criterion for hydrogen-induced cracking (HIC) that includes both the embrittlement effect and the loading effect of hydrogen was obtained theoretically. The surface cohesive energy and plastic deformation energy are reduced by hydrogen atoms at the interface; thus, the fracture toughness is reduced according to fracture mechanics theory. Both the pressure effect and the embrittlement effect mitigate the critical condition required for crack instability extension. During the crack instability expansion, the hydrogen in the material can be divided into two categories: hydrogen atoms surrounding the crack and hydrogen molecules in the crack cavity. The loading effect of hydrogen was verified by experiments, and the characterization methods for the stress intensity factor under hydrogen pressure in a linear elastic model and an elastoplastic model were analyzed using the finite-element simulation method. The hydrogen pressure due to the aggregation of hydrogen molecules inside the crack cavity regularly contributed to the stress intensity factor. The embrittlement of hydrogen was verified by electrolytic charging hydrogen experiments. According to the change in the atomic distribution during crack propagation in a molecular dynamics simulation, the transition from ductile to brittle fracture and the reduction in the fracture toughness were due to the formation of crack tip dislocation regions suppressed by hydrogen. The HIC formation mechanism is both the driving force of crack propagation due to the hydrogen gas pressure and the resisting force reduced by hydrogen atoms.

The Robustness of a Simple Expression for Quantifying Fracture Initiation at a Blunt Flaw

2006 ◽  
Author(s):  
E. Smith
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Peak Stress ◽  
Critical Value ◽  
Simple Expression ◽  
Wide Range ◽  
Fracture Processes

Linear elastic fracture mechanics of cracks is well established, and is based on the stress field near a crack tip being described by the stress intensity factor, with crack extension occurring when the stress intensity factor is equal to a critical value, which is referred to as the fracture toughness of the material. This methodology has been applied to a wide range of materials and structures, with the fracture toughness being related to the micro-mechanistic fracture processes, often via the cohesive-process zone representation of these fracture processes. The author is involved in a wide-ranging research programme whose objective is to extend the fracture mechanics methodology to blunt flaws, so as to take credit for the blunt flaw geometry, the strategy being to parallel, as far as possible, the methods that have been developed for cracks. Earlier work has shown that an appropriate characterizing parameter, analogous to the stress intensity factor for a crack, is the elastic peak flaw tip stress, with fracture initiating when the peak stress attains a critical value, which is related to the flaw geometry, in particular the flaw root radius, and material parameters. A simple expression has been derived for the critical peak stress and, in this paper, we provide support for its robustness.

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