1. Pressure Vessel Inspection Techniques
Stan Botten

2. Introduction FACTORS TO BE CONSIDERED. MATERIAL SELECTED
DESIGN PRESSURES
MAXIMUM ALLOWABLE DISCONTINIUTY
PRODUCTION
ACCESSABILITY
ENVIRONMENTAL LIMITATIONS
INSPECTABILITY
DAMAGE MECHANISM

3. List of NDE methods LIQUID PENETRANT (PT) MAGNETIC PARTICLE (MT)
RADIOGRAPHY (RT) DIGITAL (DRT)
ULTRASONIC (MUT) AUTOMATED ULTRASONIC (AUT)
EDDY CURRENT (ET)
ACOUSTIC EMISSION TESTING (AET)

4. Liquid Penetrant (PT)
LIMITATIONS : OPENING TO SURFACE MINIMUM 1.9 MICRONS
SURFACE BREAKING DISCONTINIUTIES ONLY.
ADVANTAGE: LOW COST SEMI SKILLED.

5. Magnetic Particle (MT)

6. Limitations & Advantages of MT
Limitation: Surface and near surface only
Indication must exceed 16 microns deep
No permanent record.
Need full access to area to be inspected.
Advantage: Semi skilled labor, Low cost

7. Radiography (RT) Digital (DRT)

8. Digital image Weld flaw

9. Limitations of RT /DRT 2% of material thickness Flaw orientation
Special facilities Radiation Hazard.
Skilled labor required.
Processing time (Film)
Storage if Film used

10. Ultrasonic flaw detection (UT)
There are three major techniques for Ultrasonic flaw detection.
Manual scanning of inspection area (MUT)
Phased Array both automated and manual scanning (MUT & AUT)
All techniques suffer from the same limitations
The major differences being the computerized recording of the results

11. Ultrasonic Inspection (Pulse-Echo)
High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws.
Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features that reflect sound. f 2 4 6 8 10
initial
pulse
back surface
echo
crack
echo
crack
plate
Oscilloscope, or flaw detector screen

12. SOUND TRAVEL GEOMETRY
Discontinuity obliquely oriented to the test surface: angle beam transducer

13. Limitations of UT
Coverage: In order to inspect 100% of the area every square mm of the area of interest must be scanned
The smallest flaw detectable is governed by the transducer frequency and the material being inspected. The laws that govern this is ½ the wave length or 3 times the material grain size which ever is the larger, typical carbon steel with a 4 Mhz transducer would be 1 square mm.
The orientation of the flaw in relation to the UT beam is important for the detection.
At least one clean surface must be accessible
Highly skilled operators are required for good results.

14. COMPUTER CONTROLLED TRANSDUCER
Typical UT Parameters Controlled
Scanning Angle
Focal Distance
Focal Spot Size

15. ADVANTAGES OF PHASED ARRAY UT
Control of Beam Parameters
Multiple Angel Inspection With One Probe
Inspect Complex Geometries Easily
Multiple Configurations P/E, P/R, TOFD
Better S/N Ratio
LIMITATIONS OF PHASED ARRAY UT
Same as Conventional Shear Wave UT
Large transducer size

16. EXAMPLES OF WELD DEFECTS
Presentation of the different types of defects found in welds using X-ray, TOFD and Phased array techniques

17. Root Crack
Radiography
Phased Array technique
TOFD technique

18. Porosity
Radiography
Phased Array technique
TOFD technique

19. Slag inclusion
Radiography
Phased Array technique
TOFD technique

20. Eddy Current Testing Crack Coil's Coil magnetic field Eddy current's
Conductive
material

21. Limitations of Eddy Current (ET)
Surface breaking flaws only
Full area must be scanned
Smallest Flaw is 3 x surface roughness
Skilled operator required
Weld inspection only possible if surface ground flush
Calibration standards with EDM notches required.

22. Definition of Acoustic Emissions
“The class of phenomenon where transient elastic waves are generated by the rapid release of energy from localised sources within a material, or the transient elastic waves so generated.”
SNAPPING OF TWIGS – Tin Cry
Bindschadler, R., W.D. Harrison, C.F. Raymond and R. Crosson. “Geometry and dynamics of a surge-type glacier.” Journal of glaciology. Vol. 18 (1977):

23. Acoustic Emission Detection
Electrical
Signal
Stress Waves
Acoustic Emissions
Sensor
Flaw
LOADING

24. Actual AE signal of crack in carbon steel

25. Lead-Breaks Hso Nealson AE source 0.5mm 2H lead Lead breaks
Material Stressed
Producing AE signal in material

26. Data Analysis (Signal Parameters)
Amplitude
Five Measured Parameters
Counts
threshold
Rise Time
Duration
Relative Energy Signal Strength

27. Data Analysis (Calculated Parameters)
Average Signal Level (ASL)
Burst type activity
Low ASL (Crack Activity)
Continuous noise
High ASL (Leak Activity)

28. Stress strain curve Stress concentration YEILD 60% YEILD
ONSET OF AE ACTIVITY
Stress concentration
CRACK SITE
NORMAL STRESS
5% UY
STRESS CONCENTRATION
> 60% OF UY

29. Location of defect PLANAR LOCATION SENSOR LOCATION SHOCK WAVE SOURCE
LOCATION T1-T2

30. PRESSURE VESSEL REMOVED FOR AE SENSOR PLACEMENT
AE sensor locations

31. 1,000 PSI 15,000 PSI HOLD AT 19,500 HOLD AT 25,500 HOLD AT 30
  1,000 PSI 15,000 PSI HOLD AT 19,500 HOLD AT 25,500 HOLD AT Start to increase to 33,000 Pressure stopped                                                                                      
1,000 PSI
15,000 PSI
HOLD AT 19,500
HOLD AT 25,500
HOLD AT
Start to increase to 33,000
Pressure stopped

32. TEST CORELATION PLOTS

33. Planar location of AE activity
Crack area

34. Linear location on circ. weld

35. Cracks located on jacket to shell weld.

36. Thank You