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

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. 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. 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. “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. 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. 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. 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. 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. 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. 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. 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. Beam Steering and Focusing for Corrosion Mapping
Multigroup and angle beams
Merged data
Pitting
12o -12o0o 12o12o
Active aperture
elevation

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. 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. 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. Phased Array at High Temperature
In-Service High-Temperature Corrosion Mapping
Specialized replaceable wedges enable slow heat transmission
What are the challenges?

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. 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. 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. 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. 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. Results

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. Thank you for
your attention
Olympus is a registered trademark, and Dual Linear Array is a trademark of Olympus Corporation.
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