Pressure Vessel Inspection Techniques Stan Botten

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

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)

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

Magnetic Particle (MT)

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

Radiography (RT) Digital (DRT)

Digital image Weld flaw

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

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

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

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

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.

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

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

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

Root Crack Radiography Phased Array technique TOFD technique

Porosity Radiography Phased Array technique TOFD technique

Slag inclusion Radiography Phased Array technique TOFD technique

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

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.

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):

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

Actual AE signal of crack in carbon steel

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

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

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

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

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

PRESSURE VESSEL REMOVED FOR AE SENSOR PLACEMENT AE sensor locations

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 30.000 Start to increase to 33,000 Pressure stopped                                                                                       1,000 PSI 15,000 PSI HOLD AT 19,500 HOLD AT 25,500 HOLD AT 30.000 Start to increase to 33,000 Pressure stopped

TEST CORELATION PLOTS

Planar location of AE activity Crack area

Linear location on circ. weld

Cracks located on jacket to shell weld.

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