A Robust Risk Assessment Model for Stress Corrosion Cracking

2018 ◽  
Author(s):  
Mohammad Al-Amin ◽  
Shahani Kariyawasam ◽  
Elvis SanJuan Riverol
Keyword(s):  
Risk Assessment ◽  
Stress Corrosion ◽  
Stress Level ◽  
Stress Corrosion Cracking ◽  
Risk Model ◽  
Corrosion Cracking ◽  
Assessment Model ◽  
Pipe Material ◽  
Risk Assessment Model ◽  
Integrity Assessment

Stress Corrosion Cracking (SCC) is a time dependent mechanism. Three conditions are required at the same location for the formation of SCC namely, susceptible material, susceptible environment and sufficient stress. Pipe age, operating stress level and coating type are significant parameters in determining the susceptibility to near-neutral pH SCC; whereas, additional parameters such as operating temperature and distance from compressor station are considered for high pH SCC. Environmental conditions such as soil type, topography and drainage have also shown correlation to SCC susceptibility. Several integrity assessment methods can be used to identify SCC on pipeline including hydrostatic testing, in-line inspection (ILI), and direct assessment (DA). Because the occurrence of SCC is a complex phenomenon and it depends on many parameters, it is important to develop a risk assessment model that can systematically incorporate all relevant evidences of SCC in a sensible way. This paper presents a robust risk assessment model for SCC, which uses evidence from failure histories, observation from assessments (i.e., digs, pressure tests, and ILIs), and mechanistic understanding of SCC (i.e. susceptible coating, pipe material, stress level, soil properties, etc.). This risk model is transparent and updateable, which allows incorporation of new scientific learnings and findings of SCC.

Influence of Malonic Acid on the Corrosion and SCC Behaviour of Anodic Coated 1050 Al-Alloys

2010 ◽  
Vol 438 ◽  
pp. 155-162 ◽  
Author(s):  
Panayotis Spathis ◽  
Efthimios Papastergiadis ◽  
Georgios Stalidis ◽  
Georgios Papanastasiou
Keyword(s):  
Stress Corrosion ◽  
Acid Concentration ◽  
Malonic Acid ◽  
Stress Level ◽  
Current Density ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Al Alloy ◽  
Applied Potential ◽  
Protective Properties

Aim of the present work is the study of corrosion and stress corrosion cracking behaviour of 1050 Al-Alloy anodised in a 3M H2SO4 anodising bath with the presence in it of malonic acid, in various concentrations and anodising current densities. The investigation was carried out by SCC (Stress Corrosion Cracking) tests and electrochemical measurements. The influence of applied potential on SCC behaviour was also examined. The corrosion and SCC behaviour of anodised 1050 Al-Alloy was found to vary with malonic acid concentration, anodising conditions, applied potential and stress level. In SCC conditions all prepared coatings protected the bare alloy, with better protective properties in the case of 0.015M concentration of malonic acid prepared with a 6 A.dm-2 anodising current density. The coating prepared in these conditions had better mechanical properties as indicated from the increased protection at a high stress level and also the better behaviour in corrosion, without stress, conditions of coatings prepared in different conditions of malonic acid concentration and anodising current density. For the interpretation of the results, properties of the anodic coatings as thickness, packing density, coating ratio, roughness, were also studied. The anodic coating formed in a electrolytic bath of 0.015M concentration of malonic acid and a 6 A.dm-2 anodising current density was found to be less porous, more compact and rough, with better oxide structure. Prepared coatings were found to increase protective properties in an area of applied potentials slightly more anodic than the free corrosion potential values.

Developing Response Functions for Crack Opening Displacement to Calculate Leak-Rates Through Complex Cracks in Pipes With Weld Overlays

2010 ◽  
Author(s):  
Arindam Chakraborty ◽  
Wasimreza Momin ◽  
Angah Miessi ◽  
Peihua Jing ◽  
Haiyang Qian
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Crack Opening ◽  
Corrosion Cracking ◽  
Flaw Size ◽  
Pipe Material ◽  
Response Functions ◽  
Plant Design ◽  
Alloy 690 ◽  
Complex Crack

Leak-Before-Break (LBB) is employed in design of nuclear power reactor piping to eliminate consideration of the dynamic effects of pipe rupture from the plant design basis for the affected piping system. LBB cannot be applied if environmental conditions that could lead to degradation by stress corrosion cracking exists. For Alloy 600/82/182 dissimilar metal welds (DMW) in pressurized water reactor plants, primary water stress corrosion cracking (PWSCC) is found to be active. Application of weld overlay (WOL) of non-susceptible Alloy 690/52/152 material has been shown to mitigate PWSCC growth in DMW. Therefore, LBB can be considered for a DMW with Alloy 690/52/152 overlay. However, WOL sizing design postulates a complex crack which is through wall in the overlay material and part through or full circumferential in the DMW base material. This significantly reduces the critical flaw size and in turn the maximum allowable flaw size for leak rate. The current industry practice conservatively ignores the full circumferential crack in the original pipe material and assumes a through wall crack along the entire pipe thickness. This assumptions leads to significantly reduced leakage due to smaller crack opening. The problem becomes more critical with small diameter pipes. The current work calculates the crack opening displacements (CODs) for a pipe with complex crack. Since it is a function of several geometry and materials parameters, response functions are generated to calculate CODs.

Threshold for Stress Corrosion Cracking Initiation of Alloy X750 under Long-Term Uniaxial Constant Load Test in High-Temperature Water

CORROSION ◽  
2004 ◽  
Vol 60 (3) ◽  
pp. 229-236 ◽  
Author(s):  
M. Yamamoto ◽  
J. Kuniya ◽  
S. Uchida
Keyword(s):  
High Temperature ◽  
Crack Initiation ◽  
Stress Corrosion ◽  
Applied Stress ◽  
Stress Level ◽  
Stress Corrosion Cracking ◽  
Pure Water ◽  
Constant Load ◽  
Corrosion Cracking ◽  
Load Test

Abstract Uniaxial constant load (UCL) tests of the nickel-based alloy X750 (UNS N07550) were performed in high-temperature pure water (288°C, 8 ppm dissolved oxygen [DO]) to investigate stress corrosion cracking (SCC) fracture time and the crack initiation process. The SCC fracture was initiated at a stress level below the 0.2% offset yield stress and many small cracks were observed in the middle of the nonfractured test specimens. The distribution of the crack length for each observation time is shown by Weibull probability distributions. Crack initiation and propagation process had different behavior depending on the applied stress level and the stress intensity factor at the crack tip. SCC initiation at the minimum applied stress is discussed with respect to the grain size, which depended on the size of an initial crack.

Spent Fuel Canister Probabilistic Confinement Integrity Assessment

2017 ◽  
Author(s):  
John E. Broussard ◽  
Shannon Chu ◽  
Kevin Fuhr
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Probabilistic Model ◽  
Population Based ◽  
Corrosion Cracking ◽  
Spent Fuel ◽  
Integrity Assessment ◽  
Induced Stress

A probabilistic model was developed that considers the likelihood of through-wall penetration of chloride-induced stress corrosion cracking (CISCC) in austenitic stainless steel canisters and compares different population-based sample inspection regimes. This paper describes the inputs and methods used to simulate multiple canisters with a range of susceptibilities. This paper also summarizes results of key illustrative cases.

Development of the Dundee Caries Risk Assessment Model (DCRAM) - risk model development using a novel application of CHAID analysis

2011 ◽  
Vol 40 (1) ◽  
pp. 37-45 ◽  
Author(s):  
Heather M. B. MacRitchie ◽  
Christopher Longbottom ◽  
Margaret Robertson ◽  
Zoann Nugent ◽  
Karen Chan ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Risk Model ◽  
Model Development ◽  
Assessment Model ◽  
Risk Assessment Model ◽  
Caries Risk ◽  
Caries Risk Assessment ◽  
Chaid Analysis

A Validated Risk Model for Prediction of Early Readmission in Patients with Hepatic Encephalopathy

2018 ◽  
Vol 17 (5) ◽  
pp. 0-10
Author(s):  
Andrew J. Kruger ◽  
Fasika Aberra ◽  
Sylvester M. Black ◽  
Alice Hinton ◽  
James Hanje ◽  
...  
Keyword(s):  
Risk Assessment ◽  
Hepatic Encephalopathy ◽  
High Risk ◽  
Risk Model ◽  
Cox Regression ◽  
Low Risk ◽  
Assessment Model ◽  
Risk Assessment Model ◽  
Early Readmission ◽  
The Impact

Introduction and aim. Hepatic encephalopathy (HE) is a common complication in cirrhotics and is associated with an increased healthcare burden. Our aim was to study independent predictors of 30-day readmission and develop a readmission risk model in patients with HE. Secondary aims included studying readmission rates, cost, and the impact of readmission on mortality. Material and methods. We utilized the 2013 Nationwide Readmission Database (NRD) for hospitalized patients with HE. A risk assessment model based on index hospitalization variables for predicting 30-day readmission was developed using multivariate logistic regression and validated with the 2014 NRD. Patients were stratified into Low Risk and High Risk groups. Cox regression models were fit to identify predictors of calendar-year mortality. Results. Of 24,473 cirrhosis patients hospitalized with HE, 32.4% were readmitted within 30-days. Predictors of readmission included presence of ascites (OR: 1.19; 95% CI: 1.06-1.33), receiving paracentesis (OR: 1.43; 95% CI: 1.26-1.62) and acute kidney injury (OR: 1.11; 95% CI: 1.00-1.22). Our validated model stratified patients into Low Risk and High Risk of 30-day readmissions (29% and 40%, respectively). The cost of the first readmission was higher than index admission in the 30-day readmission cohort ($14,198 vs. $10,386; p-value < 0.001). Thirty-day readmission was the strongest predictor of calendar-year mortality (HR: 4.03; 95% CI: 3.49-4.65). Conclusions. Nearly one-third of patients with HE were readmitted within 30-days, and early readmission adversely impacted healthcare utilization and calendar-year mortality. With our proposed simple risk assessment model, patients at high risk for early readmissions can be identified to potentially avert poor outcomes.

Structural Integrity Assessment of WWER Internals on Stress Corrosion Cracking Criterion

2009 ◽  
Author(s):  
Valentina Fedorova ◽  
Boris Margolin
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Structural Integrity ◽  
Corrosion Cracking ◽  
Intergranular Stress Corrosion ◽  
Integrity Assessment ◽  
Dose Curve ◽  
Stress Damage ◽  
Intergranular Stress Corrosion Cracking

Stress-damage dose curve (SDDC) is introduced on the basis of the analysis of experimental data on susceptibility to intergranular stress corrosion cracking (IGSCC) of irradiated stainless steels (SS). Approaches to determination of the SDDC parameters are considered. Based on SDDC calculative procedure for estimation of reactor vessel internals (RVI) lifetime by criterion of initiation crack due to IGSCC is proposed.

Getting to Know Your Bends to Support SCC Management

2020 ◽  
Author(s):  
Chris Wood ◽  
Fernando Merotto ◽  
Brian Kerrigan ◽  
Ramon Loback ◽  
Pedro Gea
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Crack Detection ◽  
Axial Stress ◽  
Corrosion Cracking ◽  
Inspection System ◽  
Pipe Material ◽  
Baseline Assessment ◽  
Limited Information ◽  
Metallographic Examination

Abstract Nova Transportadora do Sudeste (NTS) own and operate a gas transmission system in Brazil constructed in 1996. One of the confirmed primary integrity threats to this system is axial stress corrosion cracking. The pipelines vary in diameter, weld type, manufacturer and age. One of the pipelines failed in 2015 due to an axial stress corrosion crack. Since the failure, NTS have executed an intense inspection campaign to detect and size axial cracking within their network. The 2015 failure occurred on a field bend. The inspection campaign and following dig campaign has confirmed that cracking (both axial and circumferential) within field bends is the primary integrity threat. Brazil has a challenging terrain and approximately 40% of joints within the network were subject to cold field bending. The influences of the pipeline geometry within these areas have resulted in localised elevated stresses where the axial stress corrosion cracking colonies are initiating and growing. To date, no cracking (axial or circumferential) has been verified within their straight pipe joints. NTS initially took a conservative baseline assessment approach using API 579 Part 9, due to the limited information regarding the pipe material and complex stress state. In addition to the hoop stress from internal pressure, the baseline assessment also considered weld residual stress and bending stress due to ovalization to determine immediate and future integrity. An intensive dig campaign is underway following a crack detection in-line inspection campaign using electromagnetic acoustic transducer technology. A large number of deep cracks were reported by the in-line inspection system, these were verified to be deep and repaired with a type B sleeve. However, at one site an entire joint was removed for further analysis, to investigate the crack morphology, confirm material properties and refine the predictive failure pressure modelling. This paper outlines how NTS have combined a burst test, mechanical testing, FEA modelling, fractography and metallographic examination to further understand the feature morphology and stresses within these areas and how they have been able to reduce conservatism from their baseline assessment with confidence and adopt a plastic collapse approach to accurately predict failure.

Sign in / Sign up

Export Citation Format

Share Document