Hill Engineering

Evaluating Cracks and Dents with Damage in Pipelines

The course content as outlined below is being offered through Clarion Technical. Follow this link to the Clarion website for information on the next scheduled upcoming dates and locations and to register http://www.clarion.org/conferencesDate.php 

Various forms of cracks, crack-like indications and long seam weld anomalies are
known to be present in pipelines, which can become a safety concern over the
operational life of the pipeline. The most typical forms of cracking are Manufacturing
Related (such as lack of fusion, cold welds and hook crack-like), Operational Driven
(fatigue cracks initiating at imperfections or dents) and Environmentally Assisted
(stress corrosion cracking, hydrogen-induced cracking and corrosion fatigue
cracking).

This course will cover in greater depth the formation and conditions that drive crack
growth until they become unstable, leading to leaks or ruptures. The appropriate
assessment methods such as ILI tools, pressure testing and direct assessments will be
reviewed as well as traditional and current engineering methods for determining
crack severity for response and remediation. Each attendee will receive a
complimentary Excel based crack assessment calculator which will be demonstrated in
class using practical case studies. It will be necessary to bring a laptop to this course.

1. Characteristics and Behavior of Cracks in Pipelines

• A review of line pipe making, with emphasis on vintage ERW, Flash and
  Direct Current Welded pipelines
• A description of factors that formation and growth of
  • Environmentally Assisted Cracking (SCC, corrosion fatigue, hydrogen
    induced, sulfide stress cracking, selective seam corrosion) and
  • Manufacturing Related Anomalies (lack of fusion, cold welds, stitching,
    and hook crack-like features)
  • Operational Driven (fatigue cracks)
• Review of current industry standards and recommended practices related to
  addressing cracking and seam weld integrity: ASME, API, CSA, and NACE
• An approach for addressing cracks: Measure + Analyze + Predict + Verify

2. Foundations of Engineering Fracture Mechanics

•  The concept of Stress Intensity Factor-K describing the relationship of failure
  stress as a function of crack size and material properties
• The influence of cracks on the fracture behavior of pipelines: brittle and
  ductile
• Fracture Toughness testing: Impact Charpy V-Notch and Drop Weight and
  their relation to Ductile-to-Brittle transition curve
  • Stress Intensity Factor resulting in K MAT & J MAT

3. Performing Engineering Analyses of Cracks

• What to look for in any engineering method for determining the failure
  pressure of pipelines in the presence of cracks or seam weld anomalies
  • Review of NG-18 Equation, Newman-Raju Equation, API-579, and CorLAS and in class demonstration with case studies
  • Predicting the fracture stress of pipeline with cracks while accounting for the expected fracture behavior (brittle or ductile or mix-mode)
• Pressure cycle fatigue crack growth analysis and remaining safe life assessments
  • The total fatigue life of crack concept
  • Setting initial cracks sizes, choosing material properties, applicability of fatigue crack growth relation and fatigue as a function of toughness
  • Fatigue life S-N (stress) and ε -N (strain) curves and their application to pipeline fatigue analysis
  • In-class demonstration of case studies and the analysis of cyclic pressure spectra

4. Evaluating Dent Fatigue Behavior

• The capacity of pipelines to allow plastic deformation
• Dent strain analyses using ILI data or in-field measurements
• Plain dents and dents with damage
• Crack formation in dents
• Fatigue growth behavior of cracks in and around dents
  • Restrained and unrestrained
• Review of full-scale fatigue testing of pipeline samples with dents and dents with damage completed throughout the years
  • Design of experiments and scope of applicability
  • What we have learned from full scale dent fatigue testing so far
    • DOT and PRCI- MD 4 programs –modern and vintage pipelines
  • Dent fatigue life assessment models
    • Fowler, Alexander & Kiefner, Rosenfeld and EPRG
    • Petrobras, API 579/ASME FFS-1 and PRCI
• Managing the threat of dent fatigue failures

5. Integrity Assessments for Addressing Cracks and Dents

• Factors to consider when evaluating and deciding on assessment methods
• Hydrostatic Testing: setting up appropriate pressure test targets, hold times, the role of spike testing and determination of appropriate re-test intervals
• In-line Inspection: description of the UT, EMAT and C-MFL technologies, their performance, industry experience, and development of response criteria
• Direct Assessment methods: review and applicability of NACE SP0204 for SCCDA and CSA Z662 & CEPA Condition Monitoring for SCC

6. In-Ditch Non-Destructive Evaluation (NDE) and Repair Methods

• Review of current NDE methods and technologies
• In-class demonstration of NDE technologies and techniques
• Review of repairs options in the industry: ASME B31.4 & B31.8 and PCC-2, API, PRCI Repair Manual, and applicable US and Canadian regulations
  • The basis for sleeve repairs, Type A and B sleeve repair systems
  • o Guidelines for buffing out cracks and linear indications
• Review repair case studies: what would you recommend for repair?

FATIGUE AND FRACTURE PERFORMANCE OF PIPELINES 

Fatigue analysis and fracture behavior evaluations are important considerations for predicting and demonstrating the future structural integrity of pipelines. Fatigue failures of energy pipelines are governed mainly by the magnitude and frequency of the operational cyclic pressures, fracture behavior (brittle or ductile), initial crack shape and size, fracture toughness and residual deformation stresses. In fatigue analysis, any deficiency in considering the interrelationship of these factors can result in unreliable predictions or overly conservative results.

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Chapter 1: Common Definitions and Concepts in Fatigue Analysis 

• Pressure cycle, maximum and minimum stress, pressure range, amplitude 
• Mean stress, stress ratio-R and frequency 
• The total fatigue life cycle of crack 
• The cumulative effects of cyclic loading on the performance of pipeline with cracks 
• Fatigue life S-N (stress) and ε -N (strain) curves 

 Chapter 2: Pipeline Fracture Behavior 

• Brittle and ductile fracture behaviors 
• The capacity of pipelines to allow plastic deformation 
• True stress-true strain and strain hardening exponent 
• Fracture behavior of vintage long seam welds 
• Fracture toughness testing 
• Foundational principles of engineering Fracture Mechanics  
• The concept of Stress Intensity Factor-K 
• Fatigue crack growth testing 
• Typical fatigue crack growth data behavior 

 Chapter 3: Characterization of Variable Cyclic Pressure Data 

• Review of methods for analyzing and simplifying variable cyclic pressure data sets 
• Rainflow Counting  
• Level-Crossing Counting 
• Peaking Counting 
• Simple-Range Counting 
• Palmgren-Miner’s rule of cumulative damage 
• Demonstration of an Excel based calculator for simplifying cyclic pressure spectra 

Chapter 4: Performing Pressure Cycle Fatigue Crack Growth Analysis 

• Type of cracks, crack-like features and long seam weld defects susceptible to fatigue growth 
• SCC, hydrogen induced cracking, linear indications 
• Hook crack-like, lack of fusion, cold welds, selective seam corrosion 
• Setting the initial crack size 
• From ILI reported or NDE confirmed cracks and crack-like features 
• Cracks that survived a pressure test 
• Choosing material properties 
• Fracture toughness 
• Flow stress properties (yield and tensile) and strain hardening exponent 
• Applicable fatigue crack growth relations 
• Paris-Erdogan 
• Walker  
• Forman 
• NASGRO  
• Determination and use of fitting parameters  
• Fatigue as a function of fracture toughness 
• Determination of next assessment interval 
• Demonstration of an Excel based fatigue crack growth calculator 
• Case studies: 
• Fatigue life analysis of cracks in the base of the pipe and the long seam weld 

Chapter 5: Evaluating Dent Fatigue Performance  

• Crack formation in dents 
• Fatigue growth behavior of cracks in and around dents: restrained and unrestrained 
• Review of full-scale fatigue testing of pipeline samples with dents and dents with damage completed throughout the years 
• Design of experiments and scope of applicability 
• What we have learned from full scale dent fatigue testing so far 
• DOT test program – modern and vintage pipelines 
• PRCI- MD 4 program – modern and vintage pipelines 
• Dent fatigue life prediction models 
• Fowler (1994) 
• Alexander & Kiefner (1997) 
• Rosenfeld (1999) 
• EPRG (1999) 
• PRCI (2016) 
• Finite Element Analysis (FEA) fatigue modeling of dents 
• What to look for when setting up a FEA dent fatigue modeling 
• An integrated dent fatigue management approach 

Chapter 6: Validating Fatigue Crack Growth Life Predictions 

• Measure + Analyze + Predict + Verify model 
• With emphasis on validation 
• The relationship between analytical and experimental evaluations 
• The importance of a physics based analytical foundation and derivation  
• Appropriate design of fatigue experiments and treatment of data scatter 
• Transfer function between actual fatigue crack growth and experimental testing and analytical modeling