The Use of ILI In Dent Assessments

Transcription

1 The Use of ILI In Dent Assessments Prepared for: 2014 CRUG Conference Date: 11 September 2014 Prepared by: Rhett Dotson, PE Contributions from Dr. Chris Alexander and Markus Ginten

2 Contents Current Dent Regulations High Resolution Geometry Tool RoGeo XT SCFs and Remaining Life Analysis Case Study Comparison of Depth, Strain and SCF Composite Repair Options Conclusion 2

3 Current Regulations Dent Depth Plain dents with a depth up to 6% are permitted in both gas and liquid lines Most operators target a depth of 2% for evaluation The primary shortcoming in using dent depth is that it does not address the shape of the dent Dent Strain For gas pipelines, plain dents of any depth are acceptable provided the strains do not exceed 6% The primary shortcoming in using strain is that the method is less-straightforward and typically requires some form of smoothing or filtering Neither approach addresses the threat posed by cyclic stresses 3

4 Current Regulations Circumferential Curvature Longitudinal Curvature The Appendix R calculations from B31.8 are shown for well behaved dents The method is difficult to apply for complex shapes and dents interacting with each other 4

5 State of the Art Advances in caliper technology have resulted in strain calculations becoming more common However, the strain calculations are sensitive to tool accuracy sometimes requiring heavy smoothing and/or filtering to accurately determine the radii of curvature More detailed assessments are possible as the accuracy of in-line-inspection tools improve 5

6 Contents Current Dent Regulations High Resolution Geometry Tool RoGeo XT SCFs and Remaining Life Analysis Case Study Comparison of Depth, Strain and SCF Composite Repair Options Conclusion 6

7 High Resolution Geometry Tool RoGeo XT Standard Caliper Tool RoGeo XT Example: 55% circumferential coverage Dent depth = 2% up to 64% under-sizing 7

8 High Resolution Geometry Tool RoGeo XT d Radius Measurement b = d Touchless Proximity Sensor + b Electronic Angle Sensor 8

9 High Resolution Geometry Tool RoGeo XT 100% circumferential coverage Compensation of dynamic effects sensor bouncing Sizing of sharp and narrow dents Sizing of wrinkles and buckles Accurate contour sampling 9

10 Contents Current Dent Regulations High Resolution Geometry Tool RoGeo XT SCFs and Remaining Life Analysis Case Study Comparison of Depth, Strain and SCF Composite Repair Options Conclusion 10

11 SCFs and Remaining Life Analysis Stress Concentration Factors (SCFs) are a widely recognized means for characterizing the severity of discontinuities By definition, an SCF represents the ratio of the peak stress in a body to the calculated nominal stress peak SCF = nom 11

12 SCFs and Remaining Life Analysis Analytical SCFs are available for simple shapes, and are typically shown in graphical form The SCF is useful because it permits the peak stress to be calculated and conveys the severity of a particular discontinuity 12

13 SCFs and Remaining Life Analysis It is straightforward to expand the methodology to dents First, a finite element model of the dent must be constructed, and this requires the geometry to be known Second, an internal pressure can be applied to the model The magnitude of the maximum principal stresses from the analysis will depend on the dent shape, pipe diameter, and wall thickness The nominal stress is calculated according to Barlow s equation (i.e., σ = P*D / 2*t) 13

14 SCFs and Remaining Life Analysis After the analysis is complete the SCF can be computed as the ratio of the maximum principal stress to the nominal stress The SCF can be used to calculate the peak stresses for a given internal pressure The SCF is also directly proportional to the severity of the dent and indirectly proportional to the life of the dent The analysis is not limited by the shape or complexity of the dent If pressure history is provided, then the fatigue life of the dent can be calculated 14

15 SCFs and Remaining Life Analysis The SCF for this particular dent is 3.28 (i.e., 32.8 / 10) This SCF can be used to calculate the peak stress for any pressure condition 15

16 SCFs and Remaining Life Analysis Pressure Range (psi) # Cycles Per Year Nominal Hoop Stress (psi) Stess * SCF (ksi) AWS C-Curve Parameters # Cycles C-Curve Damage Per Year C Curve E E E E E E+00 TOTAL DAMAGE Life Design Life

17 Contents Current Dent Regulations High Resolution Geometry Tool RoGeo XT SCFs and Remaining Life Analysis Case Study Comparison of Depth, Strain and SCF Composite Repair Options Conclusion 17

18 Case Study A case study was performed using a 24-inch OD, inch wall thickness, Grade X52 pipe The dent was generated by pressing a 2-inch indenter into the pipe to a depth of 3.6-inches in an unpressurized condition The indenter was removed and the pipe was subjected to pressure cycles of 0-100% and 10%-80% SMYS nominal hoop stress After denting, the dent depth was characterized using a 3rd party optical scanner and the RoGeo XT tool. The dent was subjected to pressure cycles ranging from 9-72% SMYS until failure occurred after 39,800 cycles. 18

19 Case Study Pipe Prior to Dent Creation Failure after 39,800 cycles 19

20 Case Study Test Data Optical Scan FE-DAT with RoGeo XT Depth (in) Nominal Stress (psi) 33,120 10,000 10,000 Peak Stress (psi) 104,731 38,014 32,784 SCF The RoGEO XT Tool and the test data matched very well The optical scan showed a slightly higher depth and SCF Predicted number of cycles using the SCF would be 3,674. The actual cycles were 39,800 20

21 Contents Current Dent Regulations High Resolution Geometry Tool RoGeo XT SCFs and Remaining Life Analysis Case Study Comparison of Depth, Strain and SCF Composite Repair Options Conclusion 21

22 Comparison of Depth, Strain, and SCF Comparison of: Dent depth Curvature strain (B31.8) SCF (FE-DAT) Based on: RoGeo XT ILI data 14 diameter pipeline wall thickness 113 dents Depths, strain and stress as per table: Dent Depth Strain SCF Statistic inch mm % OD External Internal External Internal Min % 1.3% Max % 5.3% Mean % 2.6% Stdv % 0.8%

23 Results: Comparison of Depth, Strain, and SCF Correlation coefficients: OD Strain ID Strain OD SCF ID SCF Depth OD Strain ID Strain OD SCF 0.73 Depth & OD strain 0.84 Depth & ID strain 0.58 High correlation between depth and SCF However, dents of same depth may have significantly different SCFs / remaining lives Strain has only slight influence on SCF Neither depth nor curvature strain are appropriate basis for remaining dent life prediction 23

24 Contents Current Dent Regulations High Resolution Geometry Tool RoGeo XT SCFs and Remaining Life Analysis Case Study Comparison of Depth, Strain and SCF Composite Repair Options Conclusion 24

25 Repair Options Composite Repairs offer a viable solution for repairing dents and increasing fatigue lives Consider the following preliminary data, courtesy of the DV-CIP Unrepaired Sample: SCF: 3.72 with 23,512 cycles to failure Carbon Epoxy Repair: SCF: 1.31 with over 100,000 cycles to failure E-glass Epoxy Repair: SCF: 1.32 with over 100,000 cycles to failure E-glass Urethane Repair: SCF: 1.35 with over 100,000 cycles to failure 25

26 Contents Current Dent Regulations High Resolution Geometry Tool RoGeo XT SCFs and Remaining Life Analysis Case Study Comparison of Depth, Strain and SCF Composite Repair Options Conclusion 26

27 Conclusions The typical failure mode of dents in pipelines is fatigue. The stress concentration factor is indirectly proportional to the remaining life of the dent. RoGeo XT can provide data suitable for accurate FEA and remaining life analysis. Dent depth and curvature strain indicate dent severity, however they cannot be used for remaining life prediction. For immediate repair decisions curvature strain and SCF are both suitable (complement each other). Composite repairs provide an effective means of reducing the SCF and extending the fatigue lives of dents 27

28 Thank You! 28