3. Marco teórico
3.1 Migración: un acercamiento al concepto
Submitted to
Materials Technical Committee of the Pipeline Research Council International
Prepared by
Maher A. Nessim, Ph.D., P.Eng.
tel: 780 450 8989 ext 207 email: [email protected]
Copyright © 2002 C-FER Technologies
August 2002 Project L074
C-FER Technologies
NOTICE
Restriction on Disclosure
Information contained in this proposal may not be disclosed, duplicated or used in whole or in part for any purpose other than in evaluation of the Pipeline Research Council International, Inc.
(PRCI). In the event that the proposal is not accepted, this proposal document should be returned to C-FER Technologies. This restriction does not limit the use of information contained in the document if it is obtained from another source without restriction.
C-FER Technologies
ii TABLE OF CONTENTS
Notice i
Table of Contents ii
List of Figures and Tables iii
Executive Summary iv
1. TERMS OF REFERENCE ... 1
2. TECHNICAL BACKGROUND... 2
2.1 General 2
2.2 Previous Work 2
2.3 Proposed Framework 2
2.4 Technical Issues 4
3. PROPOSED PROGRAM... 5
3.1 Objective and Scope 5
3.2 Incentive 5
3.3 Work Plan 6
3.3.1 Task 1: Finalize Project Plan 6
3.3.2 Task 2: Investigate Methodologies for Identifying Likely Damage Sites 6 3.3.3 Task 3: Develop Reliability Evaluation Model 6
3.3.4 Task 4: Develop Decision Models 7
3.3.5 Task 5: Assess Overall Methodology 7
3.3.6 Task 6: Preparation of Deliverables and Reporting 8
3.4 Schedule 8
3.5 Cost 9
4. PROJECT TEAM ORGANIZATION AND QUALIFICATIONS ... 10
5. CORPORATE QUALIFICATIONS ... 11
5.1 Corporate Profile 11
5.2 Qualifications Related to the Proposed Project 11
APPENDICES
Appendix A Resumes of Project Team
C-FER Technologies
LIST OF FIGURES AND TABLES
Figures
Figure 1 Overview of Direct Assessment Methodology
Tables
Table 1 Proposed Schedule
Table 2 Cost Breakdown by Task (US$)
C-FER Technologies
iv EXECUTIVE SUMMARY
TITLE Direct Assessment Approaches to Mechanical
Damage
CONTRACTOR C-FER Technologies
NEW PROJECT
FUNDING REQUESTED PRCI $150,000 2003 - 2004 ESTIMATED COMPLETION DATE December 31, 2004
TOTAL ESTIMATED COST PRCI $150,000 Objective
The objective of the proposed project is to develop a methodology for direct assessment of pipelines with respect to mechanical damage. The project will focus on in-service mechanical damage, which is defined as dent and gouge features that occur due to equipment impact during the service life of the pipeline (other damage such as dents occurring during construction is not included).
Incentive
Mechanical damage is the most common cause of pipeline failures and is responsible for a significant proportion of ruptures and large leaks. Although the majority of mechanical damage failures occur at or immediately after the damage incident, delayed failures can occur due to the fatigue growth of gouge defects. Such damage features can be identified by in-line inspection or eliminated through hydrostatic testing; however, there is no economical way to assess integrity for pipelines that are not amenable to these methods. The development of such a methodology will enable operators to cost-effectively manage the integrity of old pipelines with respect to mechanical damage.
Framework
The proposed basic direct assessment methodology for in-service mechanical damage is demonstrated in Figure 1. The first step is to define likely damage sites based on the best available method and select the most critical damage sites for excavation. These sites are then excavated and any necessary repairs carried out. Based on the information obtained from the damage site identification analysis and the excavations, the integrity of the pipeline can be evaluated. If the integrity is adequate the process is terminated. If the integrity is not adequate, one must determine whether or not the direct assessment method is sufficiently promising to warrant further excavations. If further excavations are to be undertaken, the information from previous excavations is used to update the site selection method before the new excavation site locations are defined. This creates an iterative process that should be continued until sufficient confidence is achieved in the integrity of the line, or the assessment method is shown to be ineffective.
C-FER Technologies
Figure 1 Overview of Direct Assessment Methodology
Work Plan
Tasks that will be carried out to achieve the project objectives are as follows:
1. Finalize Project Plan. The project plan will be finalized based on the comments of the project ad hoc committee and the results of a literature review.
2. Investigate Methodologies for Identifying Likely Damage Sites. Produce a listing of possible methods of identifying likely damage sites, a summary of all available information relating to their potential accuracy, and a proposed approach to characterize their accuracy. Approaches that will be considered include coating damage surveys supplemented by other information (such as clock position of the coating damage) and damage susceptibility models (such as the fault tree model developed by C-FER).
3. Develop Reliability Evaluation Model. Develop a model to calculate reliability taking into account the additional uncertainties resulting from the use of indirect information (e.g. from
C-FER Technologies Executive Summary
vi ground surveys) and limited excavation information. Define the reliability levels that must be met to demonstrate adequate integrity.
4. Develop Decision Models. Develop a model that uses accumulated excavation data to determine whether additional excavations should be undertaken for cases that do not meet the target reliability with the amount of data available. Where additional excavations are required, update the model used to select initial damage sites using the information from previous excavations. Demonstrate the model by realistic example cases.
5. Assess Overall Methodology. Use a suitable test case to demonstrate and assess the integrated methodology, and define bounds within which it could be successfully implemented. Use sensitivity analyses to investigate the conditions under which a direct assessment approach can be successfully used. Determine the required accuracy of the damage location method and evaluate the methods proposed in Task 2 against these requirements. Develop project conclusions and recommendations based on the results.
6. Present findings at two committee meetings, deliver quarterly project updates, and prepare a comprehensive final report.
C-FER Technologies
1. TERMS OF REFERENCE
This document contains a proposal submitted by C-FER Technologies in response to a Request For Proposal (RFP) issued by PRCI on the subject of “Direct Assessment Methods for Mechanical Damage”. The objective of the proposed project is to develop methods to assess integrity with respect to in-service mechanical damage for pipelines that are not amenable to in-line inspection or hydrostatic testing.
This proposal describes the approach that will be used for this work. It includes a technical background section (Section 2) that describes previous work on direct assessment and the major technical issues involved in implementing it for in-service mechanical damage. Section 3 deals with the objective, incentive, proposed tasks, schedule and cost. Section 4 outlines the project management structure and team qualifications, while Section 5 summarizes the relevant experience of the proposed team.
C-FER Technologies
2 2. TECHNICAL BACKGROUND
2.1 General
With growing emphasis on pipeline safety over the past few years, there has been an increasing demand for effective ways to demonstrate and maintain pipeline integrity. The main tools used for this purpose are In-Line Inspection (ILI) and hydrostatic testing, but these methods are not always viable. For example, hydrostatic testing is not practical for lines with no supply redundancy. Similarly, some pipelines that are not fitted with launch/receive facilities, or have sharp bends or small diameter valves that cannot be negotiated by an inspection tool. Direct assessment methods, which infer the condition of the pipeline from information that can be obtained from sources other than an in-line inspection, have been developed as an alternative integrity management approach for pipelines that are not amenable to ILI or hydrostatic testing.
2.2 Previous Work
Ongoing work by Battelle on direct assessment is focused on external corrosion. The information used in the assessment is obtained from ground surveys (such as close interval and direct current voltage gradient surveys) and bell hole excavations. Ground surveys detect areas of coating damage and determine the condition of the cathodic protection system. The information from ground surveys typically provides 100% coverage of the pipeline, but is indirect in the sense that it provides the location of potential rather than actual areas of corrosion.
Direct information is then obtained from excavations, in which the defects in the excavated sections are located and accurately measured. Battelle suggests that confidence in the model can be developed by correlating the excavation information to the survey data and repeating the process until the model predictions compare favourably to the excavation findings. This methodology is still under development, requiring further validation with actual pipeline data.
Although not referred to as direct assessment, a similar methodology has been used for some years to manage SCC damage. In this context, potential defect locations are identified using a susceptibility model that is based on coating type, soil type, topography and drainage. The most susceptible locations are excavated to locate and repair any existing defects. Confidence in the susceptibility model improves as more excavations are undertaken, allowing better correlation between reality and model results. The susceptibility models used in this case are largely line-specific and proprietary.
2.3 Proposed Framework
The proposed basic direct assessment methodology for in-service mechanical damage is demonstrated in Figure 1. The first step is to define likely damage sites based on the best available method and select the most critical damage sites for excavation. These sites would then be excavated and any necessary repairs carried out. Based on the information obtained from the
C-FER Technologies Technical Background
damage site identification analysis and the excavations, the integrity of the pipeline can be evaluated. If the integrity is adequate the process is terminated. If the integrity is not adequate, one must determine whether or not the direct assessment method is sufficiently promising to warrant further excavations. If further excavations are to be undertaken, the information from previous excavations is used to update the site selection method before the new excavation site locations are defined. This creates an iterative process that should be continued until sufficient confidence is achieved in the integrity of the line, or the assessment method shown to be ineffective.
Figure 1 Overview of Direct Assessment Methodology
It is noted that an in-line inspection can be represented by a single pass through the steps shown in Figure 1. Only one pass is required for an accurate ILI tool, because the results of the first excavation are likely to match the tool data. This suggests that the efficiency of direct assessment depends largely on the ability of the initial damage site definition method to identify critical defect locations. If the method is perfect, critical defects will be identified in the first pass, leading to complete confidence in the integrity of the pipeline. In the other extreme, if a method of identifying defect locations is not available, the initial excavation sites will be selected
C-FER Technologies Technical Background
4 randomly and a significant pipeline length may need to be excavated in order to demonstrate integrity with sufficient confidence. In general, the number of iterations required and the length of pipeline excavated is a function of the accuracy of the defect identification method.
2.4 Technical Issues
Based on the discussion in Section 2.3, the technical issues involved in developing a direct assessment method for mechanical damage are as follows:
1. Identification of likely damage sites. As argued earlier, the effectiveness of direct assessment is highly dependent on the accuracy of the method used to identify likely damage sites.
There are currently no recognized methods to locate mechanical damage features, and therefore a methodology needs to be developed for this purpose.
2. Characterizing integrity based on incomplete information. In a direct assessment situation integrity assessment is affected by two sources of uncertainty. The first source is the basic uncertainty resulting from variability in material properties, dimensions and loading. This uncertainty affects all pipelines regardless of the assessment methodology. The second source is the incompleteness of available information (referred to here as measurement uncertainty). This relates to the fact that the assessment is being made using a combination of indirect information (e.g. CIS data for external corrosion) and incomplete direct information (i.e. from selected excavations). While basic uncertainty cannot be reduced because it relates to intrinsic variability in loading and manufacturing processes, measurement uncertainty can be reduced by carrying out more excavations and improving the methods used to predict damage locations. The integrity measure used should be capable of incorporating the impact of these two sources of uncertainty.
3. Measuring the effectiveness of direct assessment. The RFP states that direct assessment methods should be as effective as in-line inspection and hydrostatic testing. The effectiveness of direct assessment can be measured by the level of confidence in the reliability estimates obtained using the information available for the assessment. If an adequate reliability estimate is demonstrated with a high level of confidence, the assessment is successful. On the other hand, if it is demonstrated that there is a low chance of achieving the desired level of confidence with a reasonable amount of further excavations, then the direct assessment approach may be deemed unsuccessful. To make these determinations, a methodology is required to estimate the level of confidence in calculated reliability as a function of the accuracy of the method used to identify initial damage sites and the total length of pipeline excavated.
While the first issue mentioned above is unique to mechanical damage, the other two relate to direct assessment methodology in general. Therefore, some of the project results will be applicable to direct assessments related to other failure causes such as corrosion and SCC.
C-FER Technologies
3. PROPOSED PROGRAM
3.1 Objective and Scope
The objective of the proposed project is to develop a methodology for direct assessment of pipelines with respect to mechanical damage. The project will focus on in-service mechanical damage, which is defined as dent and gouge features that occur due to equipment impact during the service life of the pipeline (other damage such as dents occurring during construction is not included).
The focus areas of the project will be as follows:
1. Develop a direct assessment framework for mechanical damage (see Section 2.3).
2. Develop models to address the individual components of the framework (Section 2.4).
3. Use the models in 2, to assess the feasibility of the framework and define the bounds within which the methodology is likely to be successful (e.g. What is the required accuracy of the method used to identify damage locations for a specific pipeline?).
To develop a fully functional methodology, a specific method to identify damage locations must be selected and its accuracy characterized and validated using excavation data. This activity cannot be undertaken under the current project, as it requires a significant level of effort. The project will identify promising methods and make recommendations on how to characterize, quantify and validate their accuracy.
3.2 Incentive
Mechanical damage is the most common cause of pipeline failures and is responsible for a significant proportion of ruptures and large leaks. Although the majority of mechanical damage failures occur at or immediately after the damage incident, delayed failures can occur due to the fatigue growth of gouge defects. Such damage features can be identified by in-line inspection or eliminated through hydrostatic testing; however, there is no economical way to assess integrity for pipelines that are not amenable to these methods. The development of such a methodology will enable operators to cost-effectively manage the integrity of old pipelines with respect to mechanical damage.
C-FER Technologies Proposed Program
6 3.3 Work Plan
3.3.1 Task 1: Finalize Project Plan
The project ad hoc committee will be contacted to obtain comments on the project scope and approach. A literature search will also be carried out to ensure that all published relevant information is obtained. Any required adjustments to the project plan will be made at this stage.
3.3.2 Task 2: Investigate Methodologies for Identifying Likely Damage Sites
This task will produce a listing of possible methods of identifying likely damage sites, a summary of all available information relating to their potential accuracy, and a proposed approach to characterize their accuracy. Approaches that will be considered include:
• Modified coating damage surveys. Since most mechanical damage events result in a coating holiday, coating damage surveys are likely to identify in-service mechanical damage sites.
This method however, cannot directly distinguish between coating holidays resulting from mechanical damage and those resulting from other causes. Methods that could be considered to make this distinction include the clock position (mechanical damage is likely to occur near he top of the pipe) and the characteristics of the signal obtained.
• Damage susceptibility model. Damage susceptibility is dependent on the hit rate and the potential for damage given a hit. The hit rate is a function of such pipeline attributes as land use, burial depth, one-call system, surveillance interval, right-of-way condition, and excavation procedures. The potential for damage given a hit is a function of the pipe wall thickness, grade and pressure. Excavations could be initially directed to sections with the highest damage potential. Damage susceptibility characterization will utilize a fault tree model previously developed and calibrated by C-FER for PRCI. The model calculates the likelihood of an impact in a specific location, allowing initial excavations to be targeted to more susceptible locations.
Information for this task will be collected from the literature and from informal discussions with member companies. Information on mechanical damage features found during excavations aimed to corrosion or SCC repair will be especially valuable.
3.3.3 Task 3: Develop Reliability Evaluation Model
This task will develop the measures that will be used to characterize pipeline integrity based on the information obtained from a direct assessment, and the criteria that must be met to demonstrate adequate integrity.
To address the second issue discussed in Section 2.4, integrity of a given pipeline will be characterized by its reliability, defined as the probability that it will not fail for a period of one
C-FER Technologies Proposed Program
year (reliability = 1 – annual failure rate). Bayesian methods will be used to estimate reliability, because they combine the effect of basic uncertainty and measurement uncertainty into the reliability estimate. The resulting estimate incorporates a degree of conservatism commensurate with the level of measurement uncertainty associated with the information used in the assessment. In addition, the model will update the reliability based on new information obtained from subsequent excavations.
A reliability-based criterion will be defined, against which the calculated reliability can be evaluated. Confidence in the calculated reliability level (as determined by the quality of the damage site selection model and the total length of pipeline excavated) will be considered in the criteria. The model will be tested and demonstrated by realistic example cases that will be included in the project report.
The basic reliability calculation will utilize the PRISM software, which has been developed by C-FER to calculate the reliability of pipelines with respect to a number of failure modes including mechanical damage. Adjustments to the model will be made to account for measurement uncertainty.
3.3.4 Task 4: Develop Decision Models
This task will develop a model that uses accumulated excavation data to determine whether additional excavations should be undertaken for cases that do not meet the target reliability with the amount of data available. This choice will be based on the probability that additional
This task will develop a model that uses accumulated excavation data to determine whether additional excavations should be undertaken for cases that do not meet the target reliability with the amount of data available. This choice will be based on the probability that additional