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In-Service Corrosion Mapping—Challenges for the Chemical Industry

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This presentation from ECNDT 2018 reviews the following topics:

Corrosion inspection—particularities of the chemical industry
Pitting detection in thin-wall components
Challenges of in-service inspection: high temperature
Results of accuracy tests with temperature variation

Published in: Technology
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In-Service Corrosion Mapping—Challenges for the Chemical Industry

  1. 1. Olympus Europe | Florin Turcu Evonik Technology and Infrastructure Timon Jedamski2, and Dr. Dirk Treppmann2 Gothenburg, 06/12/2018 In-Service Corrosion Mapping—Challenges for the Chemical Industry
  2. 2. Agenda 1 Corrosion inspection—particularities of the chemical industry 2 Pitting detection in thin-wall components 3 Challenges of in-service inspection: high temperature 5 Results of accuracy tests with temperature variation
  3. 3. Agenda 1 Corrosion inspection—particularities of the chemical industry 2 Pitting detection in thin-wall components 3 Challenges of in-service inspection: high temperature 5 Results of accuracy tests with temperature variation
  4. 4. “Inspection during operation reduces downtime and increase safety” ü Thousands of vessels and hundreds of km of process piping; 90% are insulated—hard to access + high temperature (70– 350 oC (158–662 °F)) ü Inspection during downtime every 5 years for 4 weeks ü X-ray can be done in service up to 250 mm (9.8 in.) diameter ü Pressure may be lower than atmospheric pressure—risk is implosion ü Some vessels and pipes are cladded with corrosion-resistant alloys ü Low degree of predictability ü Lack of uniformity ü High and variable evolution ü Speed of corrosion Corrosion Mapping in the Chemical Industry: Challenges and Requirements Evonik plant in Marl, Germany
  5. 5. Aggressive corrosion process, nonuniform, highly unpredictable, low pressure Random pitting in stainless steel (15 days) Unpredictable temperature variations Corrosion Mapping in the Chemical Industry: Challenges and Requirements
  6. 6. Requirements for Corrosion Mapping § Able to detect wall thickness in the range of 2 to 50 mm with maximum accuracy. This requirement is due to the very low predictability and highly aggressive corrosion phenomena that may take place in a typical chemical plant. § Able to detect localized pitting corrosion (resolution in the range of millimeters). § Must be portable for in-service use in chemical plants (in the temperature range between 70 °C to 350 °C (158–662 °F). § Suitable for gas, foam, liquids, and alternating pressures on the opposite side, meaning that the process on the internal surface of the pressure vessel shall not influence the accuracy of the NDT system on the external side. § Able to inspect austenitic and ferritic steels and metallic high-alloy materials (like nickel-based alloys). § Able to measure in welding zones (due to the higher risk of erosion damage or localized corrosion in these areas). § Characterized by good near-surface resolution to get precise information about the remaining wall thickness, even with severe pitting. Decreasing wall thickness means increasing risk. § High probability of detection.
  7. 7. Agenda 1 Corrosion inspection—particularities of the chemical industry 2 Pitting detection in thin-wall components 3 Challenges of in-service inspection: high temperature 5 Results of accuracy tests with temperature variation
  8. 8. Challenge § Detection of isolated pits § Deep pits (close to the surface) must be detected § Pits in thin-wall components must be differentiated from less dangerous indications, like inclusions or delaminations Requirement § Focused beam for a good signal-to-noise ratio § Excellent near-surface resolution § Beam steering and focusing Pitting Detection in Thin-Wall Components
  9. 9. TX RX • Roof angle and V-path focus sound at the base of pits• Much of the sound is scattered away from the transducer Twin crystalSingle crystal Solution—Conventional Ultrasonic Testing
  10. 10. Benefits of Dual Element Transducers True Thickness Sample Angular Sound Path TX RX § Very good near-surface resolution — transmitter/receiver configuration § High precision, good signal-to-noise ratio (SNR)—V- path (roof angle) § Low coverage § Grid-method—low probability of detection 12o
  11. 11. Dual Linear Array™ Probes § Reproduces a twin crystal probe in a phased array version § Pitch-catch technique produces very little interface echo for improved near-surface resolution: 1 mm (0.04 in.) § Beam coverage width up to 32 mm (1.26 in.) § Imaging = higher probability of detection (POD) V-path Immaging (POD) Same benefits as duals + Imaging
  12. 12. Beam Steering and Focusing for Corrosion Mapping Multigroup and angle beams Merged data Pitting 12o -12o0o 12o12o Active aperture elevation
  13. 13. Defining Pitting Areas § 12o V-path mechanically with dual array probes = pseudo focusing § 12o V-path electronically = electronic focusing DLA 3 groups Merged – C and D-Scans 12o12o Active aperture elevation Scanning direction
  14. 14. 8/2/18 Olympus Insert Header and Footer here14 Benefits § Discriminate easier between delamination (or pseudo planar defects) and severe loss of thickness § Hydrogen-induced cracking (HIC) vs pitting § No need to saturate the signal for high POD; higher precision of measurement § Better near-surface resolution 1. Need a multigroup instrument 2. Need C-scan merging 3. A bit slower Reconstructed 3d image of a corroded plate § Processing in MS Excel®
  15. 15. Agenda 1 Corrosion inspection—particularities of the chemical industry 2 Pitting detection in thin-wall components 3 Challenges of in-service inspection: high temperature 5 Results of accuracy tests with temperature variation
  16. 16. Phased Array at High Temperature In-Service High-Temperature Corrosion Mapping Specialized replaceable wedges enable slow heat transmission What are the challenges?
  17. 17. 1. Operator Safety and Comfort • Safety first—wear protective equipment; probe casing might heat up • Protect from hot liquid couplant • Explosion risks due to pipe wall loss (implosion is less dangerous) • Physical comfort of operator: lack of comfort due to high temperatures from the surrounding environment affects inspection quality and POD
  18. 18. 2. Couplant • Water-based couplants will evaporate quickly • Ethylene glycol, glycerine, ceramic paste, and oil could stand up to 150 °C (302 °F) • Needs to be environmentally friendly • Couplant must not contaminate the surrounding areas • Contact with operator must be avoided since the couplant may be hot
  19. 19. 3. Inspection Methodology § Calibration: velocity and wedge delay − Velocity of sound in steel changes by about 1% every 55 °C (131 °F) − Velocity in the delay line changes about 10 times faster § Calibration must be done on a block at the same temperature § Wedge delay is more difficult: the wedge heats up continuously during scanning − Repeat the wedge delay calibration more often − Reduce the duty cycle
  20. 20. Agenda 1 Corrosion inspection—particularities of the chemical industry 2 Pitting detection in thin-wall components 3 Challenges of in-service inspection: high temperature 5 Results of accuracy tests with temperature variation
  21. 21. Accuracy Tests with Temperature Variation § Different defect sizes: 5, 3, 2, and 1 mm flat-bottom hole (FBH) § Depths: 1.1, 2.4, 3.6, and 4.2 mm § Temperatures 20, 50, 100, and 150 °C (68, 122, 212, 302 °F) § Calibration: ‒ Sensitivity calibration was performed at the lowest temperature (room temperature) so that the largest defect echo does not saturate (amplitude remains below 250% full-screen height FSH) ‒ Velocity and wedge delay calibrations must be performed after any change in the sample temperature
  22. 22. Results
  23. 23. Results The study considered a number of 320 tests for each temperature value. The results and conclusions are: § Good POD and repeatability across the temperature range for flat-bottom hole (FBH) defects as small as 2 mm and 1 mm at depths starting at 1.1 mm. Detection of small, near-surface defects at high temperatures is more difficult due to sound beam attenuation and loss of intensity at the near-surface area. § Accuracy of measurement maintains between ±0.03 mm and ±0.1 mm. The lowest accuracy (±0.3 mm) found the smallest FBH (1 mm) near the surface (1.1 mm). Accuracy does not seem to depend on the temperature as long as the scanning times are reduced and wedge heating is limited as much as possible. § A decrease in SNR with an increase in temperature above 100–150 ºC (212–302 °F) results in lower signal amplitude from 1 mm and sometimes 2 mm FBH at a depth of 1.1 mm, illustrating the need for a separate sensitivity calibration for higher temperature ranges. § Choice of couplant: glycerine and thermal (ceramic) grease perform well up to 150 °C (302 °F). Silicone-based lubricants should not be used as they are not chemically compatible and may damage the wedge material. § Scanning time must be limited at higher temperatures to avoid erroneous measurements due to sound velocity variation within the wedge. If necessary, calibration for wedge delay should be performed at regular intervals.
  24. 24. Thank you for your attention Olympus is a registered trademark, and Dual Linear Array is a trademark of Olympus Corporation. Excel is a registered trademark of Microsoft Corporation in the United States and/or other countries.

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