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Advances in Phased Array Inspection of API 620 LNG Tanks

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Improvements in PA Inspection of LNG Tanks

Presentation Objectives:

- Overview of the equipment and hardware that make up an LNG phased
array inspection system
- Overview of the unique considerations for inspection of 9% Ni to I-625
dissimilar metal welds typical of LNG tank shell fabrication
- Overview of API 620 and ASME V code requirements and references
relative to LNG tank shell inspection
- Overview of the LNG quad-probe phased array inspection strategy
- Overview of personnel requirements and production expectations

Learn more at: https://www.olympus-ims.com/en/phasedarray/

Published in: Technology
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Advances in Phased Array Inspection of API 620 LNG Tanks

  1. 1. Advances in Phased Array Inspection of API 620 LNG Tanks 0081_0122_000246
  2. 2. Improvements in PA Inspection of LNG Tanks • Overview of the equipment and hardware that make up an LNG phased array inspection system • Overview of the unique considerations for inspection of 9% Ni to I-625 dissimilar metal welds typical of LNG tank shell fabrication • Overview of API 620 and ASME V code requirements and references relative to LNG tank shell inspection • Overview of the LNG quad-probe phased array inspection strategy • Overview of personnel requirements and production expectations Objectives
  3. 3. Improvements in PA Inspection of LNG Tanks • LNG tank requires low-temperature cryogenic storage conditions • 9% Ni inner tank shell to remain ductile at low temperature. (−160 °C) • Concrete outer shell and thermal insulation layer • LNG tank shell wall thickness 7 mm (top rings) to 45 mm (bottom rings) • Typical shell dimensions up to 12 m × 3 m with thickness variation of approx. 3 mm for successive rings • Large LNG tanks can exceed 5000 m (16,000 ft) of total linear welds LNG Tank Construction Overview — Shell Sections
  4. 4. Improvements in PA Inspection of LNG Tanks • LNG shell welds are made with high-alloy consumables, typically I-625 • I-625 welds have an anisotropic, coarse-grained structure that results in the high attenuation of ultrasound typical of other austenitic welds • I-625 requires highly skilled welders (more expensive, higher rejection rate) • I-625 welding is slower due to the size of passes and WP LNG Tank Construction Overview — Weld Bevels 9% Ni I-625
  5. 5. Improvements in PA Inspection of LNG Tanks • LNG shell welds include vertical, horizontal, and annular at tank bottom • Vertical welds are symmetrical and often start out as a V weld, are back- gouged on the outside, and rewelded to form an X-weld bevel LNG Tank Construction Overview — Weld Bevels Horizonal Girth Weld Vertical Seam Weld
  6. 6. Improvements in PA Inspection of LNG Tanks • The inspection system software includes an integrated module for creation of the LNG tank shell weld bevels • All weld bevels for the entire LNG tank are configured in the inspection software before starting and are typically part of the new system training • Weld bevels can be imported quickly and easily for the current production LNG Tank Construction Overview — Weld Bevels
  7. 7. Improvements in PA Inspection of LNG Tanks • Phased array instrumentation • Phased array probes and wedges (LNG quad probe) • Phased array acquisition and analysis software • Mechanical encoded scanner (manual or mechanized) • Water supply (probe coupling) • Inspection personnel Phased Array LNG System Overview
  8. 8. Improvements in PA Inspection of LNG Tanks • Phased array instrument pulser configuration of 32:128 minimum • 30 MBsec 12-bit digitizing capability • AC power or battery operated for up to 5 hours of continuous scan time • IP rating, industrial casing with bumper protection, no cooling fan inputs Phased Array System Overview — Instrumentation
  9. 9. Improvements in PA Inspection of LNG Tanks • >50 mmsecond acquisition speed • Typical file size of an LNG shell weld is 1–3 GB • Compact job site for fast setup time and mobilization Phased Array System Overview — Instrumentation
  10. 10. Improvements in PA Inspection of LNG Tanks • 4 MHz quad probe designed for austenitic (I-625) dissimilar welds • Combines two shear-wave PA probes and two dual linear array PA probes into a single connector; 6 probe housings, 4 S-scans, 128 total elements • No splitter box required, significantly reducing the probe costs • Optimized wedges with wear plates, water ports, and minimized echoes • 5 m umbilical that includes the probe cables, encoder, and water supply Phased Array System Overview — LNG Quad Probe Set
  11. 11. Improvements in PA Inspection of LNG Tanks • DLA probes at 4 MHz optimized for the I-625 dissimilar metal weld • Phased array equivalent of conventional UT TRL probes • Combines the surface “creeper” inspection with volumetric RL Phased Array System Overview — LNG Quad Probe Set
  12. 12. Improvements in PA Inspection of LNG Tanks • LNG 9% Ni shells are ferrous and compatible with magnetic scanners • Encoder mounted on scanner for encoding position in data • Integrated water manifold for supply to all four probes • Cable management accessories, offset scales, and push handles Phased Array System Overview — Mechanical Encoded Scanner
  13. 13. Improvements in PA Inspection of LNG Tanks Phased Array System Overview — Play Movie Demo
  14. 14. Improvements in PA Inspection of LNG Tanks • API 620 and ASME V allow use of manual encoded push scanners; however, some LNG fabricators insist on a fully mechanized AUT scanner for acquisition • Steerable in two axes • Small, easy-to-use handheld LED controller • More expensive than manual-push encoded scanner Phased Array System Overview — Mechanized Encoded Scanner
  15. 15. Improvements in PA Inspection of LNG Tanks • Water is required to couple the ultrasound from the wedges to the shells • On most LNG job sites, water flow from the PA is not an issue • Most crews prewet the welds before and during the inspection with a manual pump (bug sprayer) water supply using <1 liter per 12 m weld • Scanner and probes are compatible with an electric water pump • Water supply tank or hose somewhere near the job site required Phased Array System Overview — Water Supply
  16. 16. Improvements in PA Inspection of LNG Tanks • DLA 30–89 degree S-scan • DLA uses a pitch-catch technique with an acoustically insulated receiver • Only refracted longitudinal beams can penetrate the I-625 weld • Typical flaws are incomplete penetration in weld root, lack of fusion in weld volume, and centerline vertical cracking • Shear-wave beams cannot penetrate the weld, and successful qualification of LNG shell welds without use of conventional or PA refracted longitudinal (RL) is not possible PA Setup and Configuration — DLA (Dual Linear Array)
  17. 17. Improvements in PA Inspection of LNG Tanks • Expert use of DLA includes understanding mode converted beam dynamics related to conventional UT TRL techniques: – Direct L-wave – RTT (round trip tandem) – Primary and secondary surface creeping wave – TLL and 30-70-70 • Phased array DLA or dual matrix array (DMA) probes combine all these techniques into a single S-scan beam set PA Setup and Configuration — DLA (Dual Linear Array) 1 4 3
  18. 18. Improvements in PA Inspection of LNG Tanks • In this example, embedded lack of fusion is detected, and the length is sized from the 270° skew of the DLA probe, using RTT detection. • Inspection below is at reference sensitivity IAW API 620 (3 mm SDH) • Flaw length is sized on the C-scan or B-scan PA Setup and Configuration — DLA (Dual Linear Array) 4 S-scan C-scan A-scan
  19. 19. Improvements in PA Inspection of LNG Tanks • Reference gain is increased 6 dB and the direct L is visible in the weld • A precision depth and height measurement is made for the API 620 acceptance decision and excavation for repair PA Setup and Configuration — DLA (Dual Linear Array) 4 1
  20. 20. Improvements in PA Inspection of LNG Tanks • In the fusion flaw example below, an upper and lower tip diffracted signal is visible for a precision depth and height measurement • The flaw is at a depth of 10 mm to 13 mm for a through-wall dimension of 3 mm for the acceptance decision • Direct correlation between size of weld pass and maximum size of flaw PA Setup and Configuration — DLA (Dual Linear Array) 3.0mm
  21. 21. Improvements in PA Inspection of LNG Tanks • Is the flaw surface connected? No, flaw is subsurface • What is the length of the flaw? 12 mm using −3 dB drop sizing method • What is the height of the flaw? 3 mm using tip diffraction sizing method • Flaw is rejectable: 3 mm subsurface flaw can be up to 8 mm long PA Analysis — API 620 Acceptance Criteria
  22. 22. Improvements in PA Inspection of LNG Tanks • Production example of a good weld with no rejectable flaws or relevant detections above amplitude threshold requiring evaluation PA Analysis — API 620 Acceptance Criteria
  23. 23. Improvements in PA Inspection of LNG Tanks • Shear-wave P/E phased array probes are used for detection and sizing of the bevel’s fusion flaws and HAZ flaws • In qualification and production, failure to supplement the DLA S-scans with shear-wave P/E S-scans results in a higher rejection rate because of oversizing of bevel defects related to the orientation of the RL beam PA Setup and Configuration — Shear-Wave P/E PA Probes
  24. 24. Improvements in PA Inspection of LNG Tanks • The 9% Ni material at 4 MHz is unique from carbon steel in that the weld bevel interface for the dissimilar material is clearly visible in the data PA Setup and Configuration — Shear-Wave P/E PA Probes
  25. 25. Improvements in PA Inspection of LNG Tanks • Scan reference sensitivity is set on static or dynamic weld sample plates with a 3 mm SDH referenced from API • System calibration at shift start or on bevel change takes approx. 15 minutes • Entire thickness range of LNG tank uses same 3 mm SDH sensitivity PA Setup and Configuration — Scan Sensitivity Calibration
  26. 26. Improvements in PA Inspection of LNG Tanks • TCG table files for both the shear-wave P/E and DLA probes are created in advance and imported to expedite daily setup and bevel change time • Sensitivity check on weld plates of production thickness is done at the start of each shift or on bevel change PA Setup and Configuration — Sensitivity Calibration
  27. 27. Improvements in PA Inspection of LNG Tanks • Improved software for more efficient workflow with emphasis on modularity for fast setup and simplicity for production • Setup, calibration, acquisition, analysis, and workflow optimization through the use of module files (weld bevels, probewedge configurations, scan plans, TCG tables, and LNG inspection display layouts) PA Setup and Configuration — Acquisition Software
  28. 28. Improvements in PA Inspection of LNG Tanks • Two-man inspection crew can keep pace with the production of 8–10 welders working the same shift • In some cases, 3 days of inspection for 5 days of welding • The weld quality and rejection rate are factor #1 in production • Manual probe-in-hand prove-up for height sizing is eliminated • PA certified inspectors require 1–2 days training on the unique aspects of LNG quad probe usage to include DLA training PA Setup and Configuration — Personnel and Production
  29. 29. Improvements in PA Inspection of LNG Tanks • All weld bevels, inspection scan plans, configuration files, pre-engineered TCG tables, etc. are created in advance • Inspectors’ day-to-day business is to load weld bevel, load configuration file, position probe offsets in scanner, check calibration, and acquire data • Analysis performed in real time during acquisition, and flaws are marked and graded when detected; data review and reporting are done offline • Level III data review and support can be done remotely via the cloud PA Setup and Configuration — Personnel and Production
  30. 30. Improvements in PA Inspection of LNG Tanks • Availability of off-the-shelf LNG inspection solutions for compliance with API 620 enables more inspection companies and fabricators to bid with confidence on these projects • Improved equipment, software, and procedures enable faster operator training, confident qualifications, and improved production • Strong financial incentive to replace RT and AUT zone systems Conclusions
  31. 31. Questions? Thank You! Dual Linear Array is a trademark and Olympus is a registered trademark of Olympus Corporation.

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