Dual Linear Array Probe for Corrosion Imaging

Olympus Dual Linear Array™ Probe for Corrosion Imaging

OmniScan Dual Linear Array Corrosion Probe – Overview

The Olympus DLA corrosion probe is a 7.5Mhz 64 element probe optimized for pitch-catch zero degree corrosion scans.

The element configuration is a 1mm pitch in two rows of 32 elements. The DLA corrosion probe has an internal wiring configuration that does not require

the pulser-receiver or “PR” option. Compatible with any 16:64 instruments including the OmniScan SX and MX2. Near surface resolution of up to 1mm depending on surface conditions and a

thickness reading accuracy of +\- .25mm or .010”.

OmniScan Dual Linear Array Corrosion Probe – OmniScan Bootup

Turn on the OmniScan and using the touch screen and upon boot up select the operating system version. (MXU 4.1)

OmniScan Dual Linear Array Corrosion Probe – Preconfigured Files cont.

The Olympus dual linear array corrosion probe is designed to be used with one of the preconfigured files with optimized beam size and focal depth based on thickness.These files are delivered on a USB thumb drive with the DLA corrosion probe from the Olympus factory. The default files provided are designed for carbon steel materials with a default

longitudinal velocity of 5890 meters\sec.Files must be selected based on the following three criteria and moved to the :\User\Setup folder on the SD memory card:1. OmniScan Instrument. (MX, MX2, SX)

2. OmniScan module. (PA1 or PA2)

3. Thickness range.

OmniScan DLA Corrosion Probe – Sensitivity Verification Overview cont.

The total number or A-scans (VPAs) in any DLA corrosion probe configuration will change depending on the number of elements used in each aperture.

For the 5 element aperture default setup file, 28 independent A-scans (VPAs) are generated across the probe. Each A-scan is zero degrees, 5mm long on the active axis of the probe.

3 element aperture (VPA1)



VPA 1 of 28

OmniScan Dual Linear Array Corrosion Probe – Setup Optimization Overview

Configuration of the OmniScan setup file for use with the dual linear array corrosion probe requires the following:

– UT configuration. – Gate configuration.– C-scan configuration.– File save.

These parameters will be adjusted based on the material thickness, surface condition and damage mechanism such as corrosion, pitting, HIC, creep, etc.

Inspection of materials other than carbon steel requires a velocity to be calculated through the OmniScan velocity wizard described in another section.

Select Menu > UT >General and adjust the UT start to 0mm and UT range to cover the inspection area.

In most cases the UT range need only be long enough to cover the first back wall but when using gate B-A functions to remove coatings the range must be long enough to cover at least two back walls.

OmniScan Dual Linear Array Corrosion Probe – UT Configuration cont.

Component back wall

Adjust the UT gain so that the back wall is between 100-200% amplitude. The amplitude of the back wall or general gain used for inspection must be adjusted

based on current conditions and will affect the accuracy of the thickness reading, the detectability of small flaws, and the ability to image the back wall condition.

OmniScan Dual Linear Array Corrosion Probe – UT Configuration cont.

Component back wall

Select > Gate\Alarms > Gates > Parameters: Mode. Select > Peak Selection: First Peak and Measure: Edge. This is the default mode for corrosion and can be changed to first or max peak mode

if necessary. (Not recommended for corrosion readings) This mode will affect where and at what amplitude the thickness reading (T) is

measured.

OmniScan Dual Linear Array Corrosion Probe – Gate Configuration

The minimum and maximum thickness will default to the gate position and can be modified.

This thickness range will set the limit of the T and TminZ readings and can be changed in the data file after inspection.

OmniScan Dual Linear Array Corrosion Probe – Gate Configuration cont.

The minimum and maximum range entered here determines how the color palette is applied to the C-scan based on thickness.

The purple vertical scale on the right side of the C-scan displays the color pixel scaled to each thickness.

OmniScan Dual Linear Array Corrosion Probe – C-scan Configuration cont.

In addition to manipulating the color palette in > Display > Properties, at any time using the touch screen the color palette can be manipulated by dragging the purple bar to the right of the color scale as pictured below.

A double tap on the same bar returns the color palette to the full range.


OmniScan DLA Corrosion Probe – Sensitivity Verification Overview cont.

Place the DLA corrosion probe on a reference standard or pipe of known thickness and ensure the probe is well coupled to the surface and stable.

Prior to entering the sensitivity wizard the back wall to be used for the verification or calibration should be visible in the S-scan like pictured below.

The A-scan display only shows 1 VPA at a time. To see all VPAs the S-scan must be used.

Reference block back wall at 25mm

OmniScan DLA Corrosion Probe – Sensitivity Calibration Wizard Use cont.

Ensure probe is well coupled and move it back and forth and side to side slightly while applying equal pressure across the probe.

Adjust the dB gain until the green envelope trace of all A-scans (VPAs) is completely contained within the tolerance window between 70-90% amplitude.

Select clear envelope and observe the envelope signal in the calibration window while making any adjustment to the gain.

Select accept when all A-scans (VPAs) are within the 10% tolerance lines.

OmniScan DLA Corrosion Probe – Sensitivity Calibration Wizard Use cont.

A green S is present in the OmniScan header when the calibration sensitivity wizard was used to either accept as-is or modify the probe sensitivity.

If it was not possible to bring all A-scans (VPAs) within the 70-90% tolerance window and a calibration adjustment was required, the gain offset correction that was automatically added to individual A-scans (VPAs) can be seen in UT > Beam > Gain Offset.

OmniScan DLA Corrosion Probe – Wedge Delay Verification Overview

The dual linear array corrosion probe has an integrated rexolite wedge that is permanently coupled to the probe and cannot be removed, repaired, or replaced.

Minor scuffs or scratches are normal and will not affect the delay or reading accuracy.

Care should be taken to ensure that the adjustable probe stabilization system is secured in place for flat or curved surfaces so as not to wear or damage the integrated rexolite wedge.

OmniScan DLA Corrosion Probe – Wedge Delay Wizard Use cont.

Enter the thickness of the step wedge or reference standard. Enter a tolerance of .25mm (.01 inches) Select next.


Ensure the DLA corrosion probe is coupled to the reference standard and apply even pressure across the probe.

Move the probe back and forth or side to side slightly and select clear envelope to refresh the white A-scan envelope trace in the calibration window.

If the white envelope trace for all A-scans (VPAs) is contained within the .25mm tolerance lines select accept. No adjustment is required.

OmniScan DLA Corrosion Probe – Wedge Delay Wizard Use cont. If the white envelope trace for all A-scans (VPAs) is not contained within the .25mm

tolerance lines a wedge delay adjustment is necessary. It is normally not required to make a wedge delay adjustment for carbon steel

inspections unless the DLA corrosion probe is damaged or worn. Prior to selecting calibrate ensure that the thickness input earlier in the wizard was as

intended. Select calibrate and accept.

OmniScan DLA Corrosion Probe – Wedge Delay Wizard Use cont. A dynamic clock scan of the step wedge is also a quick way to validate wedge delay,

velocity, and the thickness reading tolerance in one step using the C-scan with the OmniScan on pause.

Manipulate the color palette in Display > Properties > Category: Color Palette to optimize C-scan for maximum contrast of thickness range.

4 8

10mm

6

4mm 6mm 8mm

10

46

8

2


Pictured below is a standard ASTM FBH (Flat bottomed hole) resolution block. A clock scan of the FBH row of different depths within the range required for

inspection is another fast way to validate wedge delay, velocity, and thickness reading tolerance.

The tolerance of the DLA corrosion probe thickness readings is +\- .25mm. (.010”)

.100 .200 .300 .400 .500 .750

OmniScan DLA Corrosion Probe – Velocity Measurement Overview Question: What is the difference between a modern digital ultrasonic instrument and

an analog solid state instrument with regard to horizontal linearity and velocity tolerance?

The modern digital instrument can achieve precision and repeatability using a recalled file with a velocity that was predetermined and entered into the software.

The analog instrument requires that the velocity be dialed in from a reference standard for each use and it is normal that every instrument is slightly different.

Both require use of a reference standard (Step wedge) prior to inspection.

OmniScan DLA Corrosion Probe – Velocity Measurement Overview cont.

True\False? Because the OmniScan or any phased array instrument has more A-scans, better software and imaging capability, use of reference standards such as FBH resolution blocks and step wedges are no longer necessary prior to inspection.

False. It is normal procedure and practice to validate readings on a step wedge or reference standard prior to inspection and under normal circumstances the default files provided with the DLA corrosion probe will be in tolerance without modification.

OmniScan DLA Corrosion Probe – Velocity Measurement Overview cont.

Question: Is it possible that velocity can be out of tolerance if two or more thickness readings on a standard step wedge are within the precision specified for the DLA corrosion probe of +\- .25mm or .010 inches?

No. Validation of two or more thicknesses on step wedge using the default setup files provided with the DLA corrosion probe is validation of both wedge delay and velocity and they need not be modified if already within tolerance.

OmniScan DLA Corrosion Probe – Velocity Wizard Use cont.

Select > Echo Type: Thickness and enter the thickness of target 1 and target 2 that will be used for the velocity measurement. (12mm and 24mm below)

Select next.

Back wall 1

Back wall 2

Back wall 1

Back wall 2

OmniScan Dual Linear Array Corrosion Probe – Inspect. Preparation Overview

Configuration of the OmniScan for inspection with the dual linear array corrosion probe requires the following:

– Enter part thickness.– Configure encoder.– Change screen mode to full screen.– Adjust UT gain (Inspection sensitivity)– Start inspection and clear C-scan.– Scan, pause and save data.

These parameters will be adjusted based on the material thickness, surface condition and damage mechanism such as corrosion, pitting, HIC, creep, etc.

Inspection of materials other than carbon steel requires a velocity to be calculated through the OmniScan velocity wizard described in another section.

OmniScan Dual Linear Array Corrosion Probe – Enter Part Thickness

Select the > Group\Probe & Part menu and enter the nominal part thickness if known. If unknown at time of inspection, couple the probe to the part and measure the back wall

reading. (T reading) The part thickness entered here will determine the % material loss during the inspection using

the T reading and is explained in detail in the analysis section.

OmniScan Dual Linear Array Corrosion Probe – Configure Encoder

Select > Scan > Inspection and change the scan to encoder 1. This will synchronize the pulser to the encoder for data recording.

By default the C-scan is configured for a clock inspection and will record data at the speed of the PRF visible in the header. (60mm\sec below)

Configuration of the encoder for data recording is explained in its own section.


C-scan

A-scan S-scan

Select > Scan > Area and adjust the length of the C-scan as needed. Modifying these parameters will change the length of scan recorded in the data file

and the length of the data visible on the C-scan whether the data is recorded or not. The OmniScan has a 300 meg file size limit that is dependent on these settings and

the software will not allow a C-scan to be defined larger than this limit.


OmniScan Dual Linear Array Corrosion Probe – Scan and Save Data File Select the save data button on the OmniScan to create the data file on the SD memory card. A file name was entered prior to inspection start and a warning is given to prevent accidental

overwriting of any data file on the SD memory card using the same name. The size of the data file, the length of the acquisition visible on the C-scan, and the number of

data points in the C-scan are a function of the settings in the > Scan > Area sub menu. Deselect pause to activate C-scan and continue inspecting.

OmniScan Dual Linear Array Corrosion Probe – Analysis Overview

Real time analysis on the OmniScan or analysis of a recorded data file is performed using the following steps:

1. C-scan optimization by use of color palette scale and reposition gate A if needed for general screening.

2. Use of S-scan and A-scan displays from individual low data points in C-scan for back wall thickness monitoring to include general corrosion, isolated pitting, creep damage, HIC, MIC, or other failure mechanisms.

3. Use of data cursor for individual data point thickness and material loss readings.

4. Use of measure cursors for zone min thickness and location.

OmniScan Dual Linear Array Corrosion Probe – C-scan Optimization cont.

The blue horizontal ruler at the bottom of the C-scan represents the scan axis of the wheel encoder attached to the probe and is recorded at a 1mm default resolution. (Scan>Area>Scan Resolution)

The green vertical ruler represents the probe aperture that is built from the individual A-scans in the dual linear array probe and the resolution is a function of the element size also called element pitch.

28mm

28mm


The data was acquired with the color palette range of the C-scan set to 1mm for minimum and the nominal part thickness of 12mm for the maximum.

Display > Properties > Category: Color Palette > Min – Max. The purple vertical ruler on the C-scan displays 1-12mm representing this range and

next to each thickness is the associated pixel color. With this color palette configuration, a red pixel would only be generated for a signal

detected in gate A at 1.25mm or thinner.

1.25mm


The data point displayed below at the cursor crosshairs in the C-scan is at 80mm on the scan axis and VPA 18. (Virtual probe aperture 18)

The data point is on the nominal back wall with only .2% material loss and a thickness measurement of 11.97mm.

11.97mm


Increase the minimum thickness until an individual data point turns red and notice the vertical color palette scale on the C-scan.

Although the A-scan readings and S-scan imaging have not been evaluated yet, the color palette was used to determine the thickness of the low area is between 2-3mm.

OmniScan Dual Linear Array Corrosion Probe – C-scan Optimization cont. Continue to increase the minimum thickness until a general area of corrosion turns

red and notice the vertical color palette scale on the C-scan. Although the A-scan readings and S-scan imaging have not been evaluated yet, the

area boxed below with red pixels represents some readings at least 6mm or thinner . After the color palette has been adjusted for maximum contrast and color

representing the low areas, the next step is S-Scan and A-scan analysis.

If a C-scan is created that contains more data points than the number of pixels available on the current C-scan display, a red C appears in the header indicating that compression is present.

The OmniScan compression will ensure that the thinnest or most relevant color pixel is displayed when one pixel represents more than one data point.

OmniScan Dual Linear Array Corrosion Probe – C-scan Compression

OmniScan Dual Linear Array Corrosion Probe – S-Scan\A-scan Analysis cont.

Another useful view is the A-B-C-S layout that displays the side, top, and end views simultaneously with the A-scan for fast data cursor interaction.

The views with the mechanical resolution from the probe movement have a blue scan axis ruler (C-scan and B-scan) and the views with the electronic probe aperture resolution have a green index ruler (C-scan and S-scan).

B-Scan

S-Scan

OmniScan Dual Linear Array Corrosion Probe – S-Scan\A-scan Analysis cont.

Look closely at the S-scan image at and above the horizontal B0 line that represents the nominal part thickness, and to the left and right of the vertical data cursor.

Although this is an area of no detection on the C-scan the low amplitude in the A-scan still generates a light blue color in the S-scan allowing visualization of the back wall conditions.

It is the S-scan characterization that will enable users to identify and size other failure mechanisms such as pitting, HIC, and creep damage that must be distinguished from normal back wall geometry, laminations, or other adverse conditions.

OmniScan DLA Corrosion Probe – Corrosion Readings – Thickness (T)

The T reading is the thickness of the current A-scan (VPA) at the cursor crosshair. The T reading is affected by the gate selection mode for either first peak or max

peak, and measure mode for edge or peak. Additionally the source of the T reading can be configured for use with more than one

gate such as gate B\-A\ to eliminate a coating from the reading. (Gate\Alarm > Thickness > Source)

The default setting for the DLA corrosion probe setup files is first peak edge mode using gate A.

OmniScan DLA Corrosion Probe – Corrosion Readings – Material Loss (ML%)

For the current data point and T reading, the ML% readings displays the percentage of material loss based on the nominal thickness entered in Group\Probe > Part > Thickness.

(Nominal thickness – T reading) ÷ nominal thickness = % material loss. (12mm – 2.70mm)÷12mm = 77.5% material loss.

OmniScan DLA Corrosion Probe – Corrosion Readings – Zone Readings

Select full screen then select the A-C layout and tap the readings area on the touch screen or click with mouse to toggle to the second group of 4 readings.

These 4 readings are associated with the zone box that is created using the cross hairs of the red and green cursors on the C-scan.

Measure cursor

Reference cursor

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Dual Linear Array Probe for Corrosion Imaging