Joint Technical Meeting Development in the Assessment and Management of Pipeline Dents and Mechanical Damage: Putting Research into Practice By: SC Rapp and GT Vervake (Presenter) Spectra Energy AD Batte Macaw Engineering 1
Spectra Energy Transmission System Storage Capacity Transmission Pipe System Compression Natural Gas Throughput Canadian Processing Capacity Distribution Main Lines Distribution Service Lines Retail Customers 250 Bcf 17,500 mi 3,000,000 HP 3.2 Tcf 5.3 Bcf/day 22,000 mi 13,000 mi 1.3 MM 2
Current Situation U.S. gas pipeline operators follow prescriptive code requirements for mechanical damage in HCA s. Integrity management procedures are also required outside of HCA s. Basis and schedule for excavation decisions - foundation of the mechanical damage management plan. Spectra Energy 2005 and 2006 approx. 2700 miles of large diameter, high-pressure pipelines were inspected using HR MFL and HR Caliper ILI. Over 5000 dents discovered, approx. 5% were dents with metal loss. Majority of metal loss dents were bottom-side. Issues indicate need for further research to improve the effectiveness of the dent management process. 3
Damage Criteria Damage was prioritized based on risk, taking into account the following features: Damage located at the top of the pipe with metal loss or containing abrupt or multiple indications. Damage located at the bottom of the pipe with metal loss or containing abrupt or multiple indications. Damage at girth or seam welds with depths exceeding 2%, and with calculated strains exceeding 4%. Damage with depths exceeding 6%, and with calculated strains exceeding 6%. 4
ILI Inspection Findings ILI inspections were performed in 2005 and 2006. The table summarizes the defects that exceeded the reported thresholds: Calendar Year 2005 2006 Miles inspected (approx) 1100 1600 Topside dents with metal loss 16 26 Bottom-side dents with metal loss 70 159 Topside dents without metal loss 172 345 Bottom-side dents without metal loss 1450 2923 Dents associated with welds 28 74 Total 1700 3496 The majority of the defects marginally exceeded reporting thresholds for each category. Of the 33 defects that exceeded 6% depth, the deepest bottom-side defect was approx. 8.3% deep, and the deepest top-side defect was approx. 6.6% deep. 5
Excavation Findings Bottom-side-dents were typically due to impingement between the pipe and a rock, resulting in a restrained dent. As a result, bottom-side dents were consistently found to be due to original construction damage. 6
Excavation Findings Top-side-dents with metal loss were primarily due to third party damage contact with the pipelines. Since no restraint is typically present for top-side-dents, ILI measured length and depth are typically in close agreement with excavation measurements. 7
Excavation Findings Review of excavation results with respect to location and position: Location: The majority (98%) of the dents with metal loss were concentrated on lines in rocky regions. Circumferential Distribution Approx. 84% of dents with metal loss were located at the bottom of the pipe (5 to 7 o clock position). Approx. 97% of dents without metal loss and greater than 2% deep were located between 5 and 7 o clock position. Approx. 97% of dents greater than 6% deep were located between 5 and 7 o clock position. 8
Excavation Findings Damage Shapes Most dents were uniform depressions. Uniform shapes allowed for accurate depth, length and contour data. For bottom-side dents, the removal of restraint and elastic response resulted in significant difference between ILI and excavation depth measurements. Bell-hole strain measurements had reasonably good correlation to calculated strains from ILI data. Generally strains were between 1% and 4%, with a maximum strain of 10% measured in the bellhole. Only a few dents with multiple signature peaks were detected. 9
Comparison ILI and Bell-Hole Results HRMFL reliably found metal loss within a dent. HRMFL was not able to distinguish metal loss as either a gouge or corrosion. Bell-hole measurements of metal loss were generally in agreement with MFL data. Accurate depth and strain estimates from high resolution multi-channel caliper ILI tools was difficult to verify. Restrained bottom-side dents re-rounded upon removal cover and restraint. Important depth and profile information of interest - mechanical damage prior to excavation. Defines the structural significance of the damage. Determines the excavation decisions (immediate, scheduled, or monitored). 10
Mitigation Decision flow chart for assessment of excavated dents and applicable mitigation options. Strain criteria Interactive threats (corrosion, SCC, gouges, internal cracking) and interaction with welds are addressed. Repair of SCC, corrosion, and gouges are included. Final repair options for dents based on the presence of any remaining SCC, cracks, internal wall loss, or gouges present. 11
Mitigation Response is determined by character and location of the discovered damage. Critical considerations that determine the type of repair is whether the dent includes any gouges, SCC, crack like features, or internal metal loss. The results of 122 field excavations are shown below: Cut-out, replacement* Welded sleeve repair Composite sleeve repair Recoat and backfill Topside damage 8 0 6 22 Bottomside damage 7 0 9 68 Damage at welds 0 1 1 0 12
Mitigation 74% of excavated bottom side dents were found to be acceptable and recoated and backfilled. Approximately 7% required response within 5 10 days. Bottom side dents with metal loss were consistently found to be due to original construction damage. Response change for locations outside HCA/s from 30 days to 1 year. 13
Implications and Issues Current ILI technologies are adequate to meet the applicable US regulations for integrity management. It was confirmed that HRMFL reliably finds very small dent features and metal loss within dents. The sizing capability for HR Caliper ILI tools to accurately estimate depth, strain and geometry was also confirmed. 14
Implications and Issues Unresolved practical issues Bottom Side Dents: Majority of bottom side dents can reliably be characterized as resident damage. Excavation of these dents can be considered of little value with respect to pipeline integrity, and should ideally be scheduled on a timely but not urgent basis. Bottom side dents with high strain values, or complex geometries should still be considered structurally significant damage and excavated and assessed on an immediate basis. Unresolved practical issues Top Side Dents: Topside dents requires extra consideration - time frame for the damage can not be established, and degree of damage can not be reliably determined by ILI. Evidence of deformation on the top of the pipe should be considered structurally significant. Evidence of metal loss in any measurable topside dent should be excavated and assessed in a timely manner. 15
Implications and Issues Unresolved practical issues Regulatory Requirements: US regulations require urgent response to all dents with metal loss. Integrity management regulations in US have frequently necessitated disruptive, immediate responses to rapidly mobilize excavation work crews for resident bottom quadrant damage from original construction. For non-leaking dents, Spectra requires a safe digging pressure to less than 80% MOP at the damage location. For bottom side restrained dents, Spectra requires a maximum pressure of 40% SMYS. 16
Recent Experience/Current Capabilities HRMFL is capable of reliably detecting a dent, and distinguishing between dents and metal loss. HRMFL is not capable of sizing dents. HRMFL is capable of reliably detecting metal loss associated with dents, however there is no reliable detection of crack features. HR Caliper tools provide dent profile data may be used to calculate dent strains. Damage management strategies using HRMFL and HR Caliper tools meet requirements of CFR 192 and ASME B31.8S. The number of excavations for mechanical damage has increased considerably. CRF 192 requirements for an immediate response has resulted in many urgent calls to mobilize field crews with 5-10 days. Significant unscheduled pressure reductions have been necessary. Safety concerns - removal of constraining rock. 17
Implications for Future Research Reliability and accuracy of feature identification and discrimination Transverse and triaxial MFL signal interrogation may provide better discrimination between features - technology is still under development. Need for improved accuracy and resolution for HR caliper tools, particularly for sharp profile dents and dents with complex shapes. Improvements in MFL and Geometry tool technology requires data from a substantial number of excavations. An ongoing PRCI project collating information to improve understanding of metallurgical, topographic and fractographic features. Understanding structural significance of damage features MFL - Complex issue to separate the signal that is due to stress from the signal that is due to the dent profile. Ongoing project by PRCI and US DOT PHMSA. Concerns that current assessment technology adequately addresses prior bending strain due to denting and re-rounding. Research needed to clarify the relationship between dent strain and damage significance. 18
Implications for Future Research Validity of Predicated Failure Pressures and Remaining Lives Need to develop improved models to determine significance of damage linked to improved understanding and more accurate measurement of key features. Initial screening and ranking of damage severity, based on damage features, to support integrity inspections and determine need for excavation. Accurate determination of failure pressures and remaining lives. Based on comprehensive characterization of damage Provide basis for screening-level assessments Characterize damage severity Set appropriate response times and pressure reductions for excavation and repair. 19
Implications for Future Research Coordination of Ongoing Research PRCI Roadmap for Mechanical Damage Improved understanding of damage severity and reduction in remaining life, and to enable safe and effective repair of damaged regions. Improved inspection tools for locating, characterizing and sizing features that discriminate damage severity, forming basis for quantitative and reliable assessment of severity and structural significance. Effective suite of assessment methods to quantify the severity of damage, and enable sound decisions for scheduling excavation and repairs. New recommendations for determination of safe pressure reductions and working practices during repair. 20
Concluding Remarks Approximately 2700 miles of high-pressure gas transmission pipeline were inspected using HRMFL and HR geometry ILI. The results provided substantial insight into the characteristic features of mechanical damage. Damage assessment algorithms designed for implementation of US CFR 192 and ASME B31.8S has proved successful. Issues were highlighted: Operational difficulties associated with responding within the prescribed 5-day period for significant damage. Apparent benign nature of significant bottom side damage occurrences excavated. Operator s need for improved tools: Discrimination of key features determining severity (failure pressure, remaining life). Improved methods for ranking and screening of damage upon discovery, and determination of the need for excavation and repair. 21
Concluding Remarks Operator s need for improved tools (cont.): More accurate methods for predicting failure pressure and remaining life, quantify damage severity, and enable sound decisions for safe and timely excavations and repairs. Coordinated program of research currently underway by PRCI to deliver many technical components to address these needs. 22