Guidance on the Use, Specification, and Anomaly Assessment of Modern Linepipes

Transcription

1 Guidance on the Use, Specification, and Anomaly Assessment of Modern Linepipes Yong-Yi Wang Center for Reliable Energy Systems 5858 Innovation Dr. Dublin, OH May 16, /16/2018 CRES

2 Issues Being Targeted Low strain tolerance of girth welds Anomaly assessment Potentially reduced tolerance of anomalies in new linepipes reduced safety margin when the current assessment methods are used Anomalies Corrosion (deferred to Corrosion Committee project, EC-2-8) mechanical damage New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 2

3 Failure Path with HAZ Softening of a Manual Weld Weld HAZ Weld Root Pipe/Base Metal Representative hardness values Pipe: 235 Hv Root pass: 165 Hv (70% of pipe) Fill pass: 205 Hv (87% of pipe) HAZ: 185 Hv (79% of pipe) Contour of plastic strain. Note that the plastic strain in the HAZ is much higher than that in the pipe and upper fill passes. Low Strain Tolerance in Some Newly Constructed Pipelines 05/16/2018 CRES 3

4 Role of Pipe Specifications and Weld Qualification Requirements Pipe strength can be significantly higher than the specified minimum strength Girth welds qualification requires welds meeting the minimum strength. For instance, for welds on X70 pipes Pipe yield strength can be as high as 90 ksi Welds can be qualified if it breaks at a stress level 82 ksi or higher. Weld strength can be significantly lower than the strength of the pipe, yet pass qualification. In an event of settlement, strains are concentrated in the weld. Low Strain Tolerance in Some Newly Constructed Pipelines 05/16/2018 CRES 4

5 Contributors Contributors to low strain tolerance of girth weld (low strain capacity) Weld strength undermatching the actual strength of the pipe HAZ softening Soft root Weld bevel (manual SMAW/FCAW) Contributors to girth weld failures, in addition to low strain capacity (strain demand) Bending loads from nominal ground settlement and other sources Large-scale ground movement (not subject of the current work) Contributors to potentially reduced tolerance of anomalies Low strain hardening New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 5

6 There could be multiple causes. General facts Why Is It Happening Now? Manual girth welding of X70 pipes has largely unchanged since the use of X70. More spiral pipes are being used in cross-country pipelines in last two decades. All incidents so far are on spiral or ERW pipes. Steelmaking continues to evolve. Lean chemistry, contributing to (1) reduced propensity of HAZ hydrogen cracking and (2) higher levels of HAZ softening Increase in pipe strength, at least evident from pipes involved in the incidents Very large increase, in some cases, in pipe yield strength, although the increase in UTS is less. Low Strain Tolerance in Some Newly Constructed Pipelines 05/16/2018 CRES 6

7 Weld Strength Mismatch - Impact of Changing Pipe Strength Two girth welds Same weld metal strength 2002 SAWL pipe low strength, weld strength overmatching 2013 ERW pipe high strength, weld strength undermatching The strength of pipes and welds has distributions, not a single value. The example may or may not represent a broad industry trend. All Weld Metal Native Strength: strength as measured by all weld metal tensile test All Weld Metal Apparent Strength: estimated weld strength in a girth weld, incorporating the apparent strength increase due to weld cap reinforcement and the constraint of the weld bevel Low Strain Tolerance in Some Newly Constructed Pipelines 05/16/2018 CRES 7

8 Enhance Girth Weld Strain Capacity - Pipe Limit pipe strength for a given grade Can we reduce longitudinal strength more than hoop strength, reduce YS more than UTS, while meeting the strength requirement in hoop direction? Reduce HAZ softening Greater hardenability from chemical composition Limit welding heat input New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 8

9 Enhance Girth Weld Strain Capacity - Welding Change bevel geometry Not in the current scope (There is an interest in double-joints.) Wider weld cap, i.e., cap reinforcement Stronger deposited weld metal Stronger root pass Stronger fill and cap passes Low hydrogen processes FCAW-G or FCAW-S Reduce HAZ softening Lower heat input New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 9

10 Reduce Strain Demand Guidelines for construction (a 2019 project idea) Make sure the profile of the pipe string fits the profile of the ditch Don t force pipe ends together at tie-in locations Backfill procedures to reduce differential settlement New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 10

11 Material Characteristics Change of grade and strain hardening characteristics New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 11

12 Material Characteristics Change in the characteristics of tensile properties of the same grade (X52) New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 12

13 Engineering Stress (MPa) X70 SAWH ~2016 Engineering Stress (ksi) Engineering Stress (MPa) Engineering Stress (ksi) The lowest reported YS (0.2% offset) in hoop direction = 73.8 ksi The highest reported YS (0.2% offset) in longitudinal direction = 84.9 ksi, 11.1 ksi higher than hoop. However, the overall strength in both directions are almost identical. The yield strength happens to capture the knee area where large difference in strength exist. The difference in strength becomes minimal when the strain is greater than 1.0% % offset 0.5% total Longitudinal: T1 Longitudinal: T2 Hoop: T3 Hoop: T Engineering Strain (%) Longitudinal 1 Longitudinal 2 Hoop 1 Hoop Engineering Strain (%) Guidance on the Use, Specification, and Anomaly Assessment of Modern Linepipes 05/16/2018 CRES 13

14 Material Characteristics EPRG work New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 14

15 Material Characteristics Longitudinal vs. hoop properties New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 15

16 Welding Matrix Change three parameters Weld cap size Consumable for the root pass Heat input Weld No. Priority Consumables Cap Reinforcement Heat Input Purpose 1 High Group B, E6010/E8010 Regular cap, no extra reinforcement Mid-range, or nominal Baseline, established practice 2 High Group B, E6010/E8010 Regular cap, no extra reinforcement High end 3 High Group B, E6010/E8010 Regular cap, no extra reinforcement Low end Baseline, established practice, high heat input to see to the impact on HAZ softening, to a lesser extent, any impact on weld metal strength Baseline, established practice, low heat input to see to impact on HAZ softening, to a lesser extent, any impact on weld metal strength 4 High Group B, E6010/E8010 Larger cap, with extra reinforcement Mid-range, or nominal Impact of larger cap than Weld No. 1, nominal heat input 5 High Group B, E6010/E8010 Larger cap, with extra reinforcement High end Impact of larger cap than Weld No. 2, high heat input to generate the maximum amount of HAZ softening 6 High Group C, E8010/E8010 Regular cap, no extra reinforcement Mid-range, or nominal Baseline, stronger root than Weld No. 1 7 Medium Group C, E8010/E8010 Larger cap, with extra reinforcement Mid-range, or nominal Impact of larger cap, nominal heat input, stronger root than Weld No. 4 8 Medium Group C, E8010/E8010 Larger cap, with extra reinforcement High end Impact of larger cap, high heat input to generate the maximum amount of HAZ softening, stronger root than Weld No. 5 New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 16

17 Regular vs. Wider Cap Change three parameters Weld cap size Consumable for root pass Heat input New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 17

18 Tensile Test - PRCI Non-flattened near full-thickness hoop specimen JIP - Enhanced Girth Weld Performance for Newly Constructed Grade X70 Pipelines 05/16/2018 CRES 18

19 Industry Awareness and Long-Term Solutions Reaching out API 1104 and 5L IPC paper AIST paper New Linepipes and Related Girth Welds and Other Issues 05/16/2018 CRES 19

20 Q&A Thank you! Guidance on the Use, Specification, and Anomaly Assessment of Modern Linepipes 05/16/2018 CRES 20