Phased Array Inspection BY API

--------------------------------------------------------------------------------------------------------------------------------- Page 1

Manual Multi-Channel Omniscan MX Phased Array Inspection of Ferritic

Piping and Plate Welds IAW API-UT-2

Chris Magruder Technical Support R/D Tech Tel: 281 922 9300 12559 Gulf Fwy [email protected] Houston, TX 77034 www.rd-tech.com

Technical Support - Olympus NDT

Page 2

Overview The objective of this project is to demonstrate the ability of the Omniscan MX Phased Array Instrument to detect, characterize, length size and plot defects as per API procedure API-UT-2 used in the API certification examination for manual ultrasonic inspection of Ferritic welds. Although these inspections have been performed for years using conventional single channel UT, the results and accuracy are extremely dependent on the skill and experience level of the inspector. The advantage of the phased array technique is that it allows an inspector to perform API inspections to a much higher level of accuracy with much greater speed than with single channel conventional UT methods. The Phased Array instrumentation, probes, calibration, and technique meet all of the requirements of the conventional UT inspection procedure API UT-2 (API Defined Procedure for the Examination of Ferritic Welds). No exceptions or exemptions are required for the phased array technique. This report is limited to manual inspection only. No encoders or automation were used during the collection of data samples for this report. A similar report to this one has been prepared for the automated and semi-automated phased array inspection on the same weld samples. The weld samples used for this project were provided from the Davis NDE Advanced UT Detection and Flaw Characterization Training Program and of similar design as those specified in the API QUTE Test Protocol. Special Thanks to Mark Davis for his assistance and support on this project.


Page 3

Equipment Used

• Olympus Omniscan PA MX 16/128 phased array acquisition system • Olympus Omniscan Software version 1.4 (Multi-channel option enabled) • Olympus 5L64 phased array probe (5 MHz, .6mm element pitch, 64 elements) • Olympus SA2N55S phased array wedges (Flat for the plate samples and contoured for 8 and

12 inch pipe samples)


Page 4

Inspection Requirements All samples inspected are plate to plate and pipe to pipe single Vee and double Vee with two sided access. All welds are in the “As welded” condition with possible mismatch and representative field conditions such as excessive weld reinforcement, root concavity and minor undercut. The material samples were 12.7mm plate V welds, 25.4mm plate X welds, 12.7mm X 8 inch pipe V welds, and 15mm X 12 inch pipe V weld samples.

Taken from the API UTCE candidate orientation package and test protocol The required inspection area includes the entire weld volume and base material for a distance of 8mm from each weld toe. All relevant flaws are characterized as one of the following:

• Inside surface connected crack • Outside surface connected crack • Embedded slag • Embedded porosity • Embedded centerline crack • Side wall lack of fusion • Inadequate penetration

Flaw depth and height sizing is only required to determine inside surface connected, outside surface connected, or embedded. Additionally, the location of the flaw in relation of the weld centerline is required for upstream or downstream placement. No specific through wall dimensioning for depth and height is required.


Page 5

Omniscan Phased Array Channel Set Up The Omniscan set up file used for this inspection requires 4 independent channels to be configured and calibrated. The calibration requires all focal laws on all channels to be calibrated for sensitivity, time of flight (wedge delay or zero offset), and a TCG/DAC to cover the range required for the inspection. (1/2, 1 or 1 1/2 skips) Essentially, every focal law on every channel must meet the same requirements as an A-scan on a single channel conventional flaw detector. This means linearity, sensitivity, time of flight (sound path or wedge delay), and TCG/DAC to cover the inspection range. This configuration is suitable for single V or double V bevel plate to plate or pipe to pipe butt welds in the thickness range of 7mm to 25mm. After completion of the calibration, the inspector need only enter the part thickness into the Omniscan, adjust the range and gates for the area of interest, and adjust the sensitivity on the ID and/or OD notch based on the specimen thickness. Only the sensitivity changes for different thickness or weld bevels. Group 1 Sector Scan 45-70 degree shear wave (Full volume) Group 2 Linear Scan 70 degree shear wave (Lower ½ of weld) Group 3 Linear Scan 60 degree shear wave (Full volume) Group 4 Linear Scan 52 degree shear wave (Upper ½ of weld) Up to 8 channels can be programmed on an Omniscan MX PA and three channels can be displayed simultaneously. The preferred inspection method is to display only the sector scan for detection and switch between linear scan channels to optimized and characterize defects.


Page 6

Verification of Beam Exit Point and Beam Angle using an IIW Block API-UT-2 requires that the exit point and beam angle be verified on an IIW block and recorded on the inspection data sheet. This is done in the same way as with a single channel conventional flaw detector on a standard IIW block. The difference for the phased array check is that instead of physically marking the one exit point of the beam on the wedge for conventional UT, the phased array focal laws checked and the exit position is verified in the software. Every focal law or A-scan will have a different exit point in the wedge. The exit point is calculated by the focal law calculator in the software and is available in the UT-Beam-Beam Index Offset field on the Omniscan. It is a distance that is calculated by the software using the focal law beam information and parameters of the probe and wedge. Beam index offset = -25mm (distance between the face of the wedge and the exit point). This will be a slightly different reading for every focal law.


Page 7

Multi-channel Phased Array Calibration In order for the phased array technique to be used with standard codes and accepted conventional UT procedures, all focal laws or A-scans must meet the same criteria as conventional UT for linearity, sensitivity, wedge delay or time of flight, and be capable of an independent DAC/TCG to cover the inspection range. The use of software wizards allow these functions to be performed simultaneously on all the focal laws within a channel or group. The same calibration procedure must be repeated for all 4 channels. Wedge Delay (Zero offset) Calibration Wedge delay or zero offset is calibrated using the Omniscan calibration wizard and an IIW block or side drilled hole at a known depth. The 15mm side drilled hole on an IIW block is used for calibrated wedge delay on all focal laws simultaneously. As the probe is moved over the 15mm hole, the 45-70 degree beams are exposed to the hole and an independent beam offset is calculated for each focal law. As the A-scan tracks the hole in the gated area, the depth of each focal law is available in the DA reading window. In other words, every angle from 45-70 degrees in one degree increments is calibrated on a 15mm side drilled hole and an independent wedge lay in usec is saved in the software.


Page 8

Sensitivity (ACG) Calibration Sensitivity or ACG (Angle Corrected Gain) is calibrated using the Omniscan calibration wizard and a side drilled hole at a known depth. Typical ACG calibration is done using 1.5 or 2mm side drilled holes such as the 15mm hole in the IIW block or a standard ASME Sec V or VIII calibration block. As the probe is moved over the side drilled hole, the 45-70 degree beams (at one degree increments) are exposed to the hole and a curve is created that displays the amplitude of the hole on each focal law. An independent gain offset is calculated and added to the hardware gain. The end result of this calibration is that focal laws 45-70 will detect the hole with an amplitude of 80%. Without an independent focal law gain it would be impossible to set the correct sensitivity for each angle of inspection. One side of the array would be too sensitive and the other side not sensitive enough. Sector scan curve prior to calibration.

Sector scan curve equalized after calibration. An independent gain offset is calculated and added to the UT gain so that all focal laws detect the side drilled hole at 80% amplitude.


Page 9

TCG Calibration Continuing the same process over a series of side drilled holes or ID/OD notches will create a DAC/TCG (Distance amplitude correction and time corrected gain). This corrects the same calibration reflectors at different depths or metal paths so they are all detected at 80% amplitude. As the probe is moved exposing all focal laws to the calibration reflectors, the calibration wizard in the Omniscan stores an independent gain offset for every A-scan at every TCG/DAC point. The end result of the sensitivity, wedge delay, and TCG calibrations is that the side drilled holes or notches at different metal paths can be detected at the same amplitude and correct time of flight. Every A-scan on every channel has to be the equivalent of a single channel conventional flaw detector for time of flight, sensitivity, velocity, and linearity. To do this quickly and accurately requires using the software tools and a familiarity with the Omniscan user interface.


Page 10

Flaw Detection The inspection is performed +6 dB over the reference sensitivity IAW API-UT-2. Regardless of amplitude, all suspected flaw indications are investigated to the extent necessary to provide accurate characterization, identity and location in the weld volume. As the probe is moved forward, backward and parallel to the weld, the sector scan consisting of 45-70 degree shear wave focal laws will cover 100% of the weld volume and required base material. This only requires about a 1 inch manual raster in and out from the welds. The primary inspection display for initial detection is the sector scan channel. This is an end view that visualizes the 45-70 degree focal laws at the same time.

Sufficient screen range is required to ensure the 45 degree focal law has at least 1.5 skips and the 70 degree focal law has at least .75 skips. All geometric reflectors should be considered non-relevant, regardless of amplitude. All flaws can be detected with the probe perpendicular to the weld. Although skewing the probe is not required for detection, it is useful for optimizing flaw signals to more accurately characterize and plot defects. Once a flaw is detected on the sector scan, the inspector switches between the linear scan channels to optimize the flaw indications. The flaw is also plotted using the Reading on the Omniscan on the sector scan and linear scan channels. In general, with the probe butted up against the weld toe, an ID connected flaw is best detected on the Linear 70, OD connected flaws are detected on the Linear 52, and embedded flaws are best detected on the Linear 60. The absence of a flaw on a channel is also useful in characterizing and locating a flaw. Example: An ID connected crack or Inadequate Penetration will be detected best by the Linear 70 channel, and probably will not be detected by the Linear 52 channel without repositioning the probe further back from the weld. All flaws will be detected on the sector scan but not all flaws will not be detected on the linear channels. The linear scans are best used for characterization and plotting.


Page 11

Flaw Characterization As mentioned previously, the primary inspection display while scanning the weld is the 45-70 degree sector scan channel. This channel will detect all the flaws. Once the flaw is detected, switching between the sector scan and linear scans to optimize the signal aids the operator in determining the flaw type. Below are examples of typical flaws using samples from Mark Davis NDE training samples and guidelines for determining flaw type. Inner Diameter Connected Crack Sector scan characterization of ID connected crack

Linear 70 degree characterization of ID connected crack

• Multiple facets and edges visible in the A-scan and sector scan. Distinct start and stop on A-scan.

• Significant walk to the signal as the probe is moved in and out from the weld. (See echo dynamic envelope on A-scan in 70 degree linear channel)

• Detection and correct plot from both sides of the weld. • Best detection on the sector scan and linear 70 degree channels. • Plots to the ID (B0) skip line.


Page 12

Lack of Side Wall Fusion Sector scan characterization of lack of side wall fusion

Linear 52 degree characterization of lack of side wall

• Plots correctly on weld fusion line. • Significantly different response from each side of the weld. Near side is typical >6 dB above

reference sensitivity. • Detected by 75% of focal laws in sector scan from the same position. • A-scan fast rise and fall time with short pulse duration indicative of planar flaw. • No multiple facets or tips. • Detected with high amplitude on all 4 channels from near side, and one or more from far side. • Skewing the probe slightly does not produce multiple peaks or jagged facets as in a crack. • Mode converted multiple signals that rise and fall together and maintain equal separation.


Page 13

Porosity Sector scan characterization of porosity

Linear 52 degree characterization of porosity

Linear 60 degree characterization of porosity

• Multiple signal responses varying in amplitude and position. • Plots correctly to weld volume. • Start and stop positions blend with background at low amplitude. • May not be detected from both sides of the weld. • Best characterized by sector scan and/or linear 52 and 60 channels. • Typically not greater then reference sensitivity and difficult to distinguish from slag. • A-scan low rise and fall time with long pulse duration indicative of non-planar flaw. • Best characterization is achieved on full V-path skip (Between B0 and T1)


Page 14

Outside Diameter Toe Crack Sector scan characterization of OD toe crack

Linear 52 degree characterization of OD toe crack

• Multiple facets and edges visible in the A-scan and sector scan. • Significant walk to the signal as the probe is moved in and out from the weld. (See echo

dynamic envelope on A-scan in 70 degree linear channel) • Detection and plot from both sides of the weld. • Best characterized on the sector scan and linear 52 degree channels. • Plots to the OD (T1) skip line.


Page 15

Inadequate Penetration Sector scan characterization of inadequate penetration

Linear 70 degree characterization of inadequate penetration

• High amplitude signal with significant walk or travel over the ID (B0) skip line. (See envelope on A-scan)

• Similar response and plot from both sides of the weld. Plots right at weld centerline at ID (B0). • Do not confuse with excessive root reinforcement (convexity) or ID centerline crack. • Detected on all channels with highest amplitude on 70 degree linear scan. • A-scan fast rise and fall time with short pulse duration indicative of a planar flaw.


Page 16

Slag Sector scan characterization of slag

Linear 60 degree characterization of slag

• Multiple facets and edges visible in the A-scan and sector scan. • A-scan slow rise and fall time with long pulse duration indicative of non-planar flaw. • Typically lower amplitude than planer flaws. • Similar response and plot from both sides of the weld. Plots to weld volume. • Difficult to distinguish from porosity. • Best characterized with sector scan.


Page 17

Determining Flaw Location - Upstream or Downstream Position Once a flaw is detected the signal is optimized and evaluated on all four phased array channels. The distance from the face of the wedge to the weld centerline is measured and entered into the Probe/Part – Part – Position – Index Offset. This will place the weld centerline correctly on the sector scan display. (Green scale and green vertical CL line).

Once the index position is entered into the Omniscan the VIA reading is then available. This gives the volumetric position of the flaw in relation to the weld centerline. Negative value would plot on the upstream (near) side of the weld, and a positive value would plot on the downstream (far) side of the weld. In the example below, the face of the wedge is -28mm from the weld CL; the defect is -16.72mm from the weld centerline on the upstream or near side, and the flaw’s surface distance is 11.28mm from the face of the wedge. (PA = 11.28)

Flaw located -16mm from weld centerline on upstream side


Page 18

Length Sizing Length sizing is preformed similarly to conventional single channel UT. The start and stop position of the flaw should be evaluated on all channels that detect the flaw. Identify the area of the flaw that is detected at the highest amplitude. (Lmax) Move the probe along the weld line from Lmax until the relevant A-scan drops in amplitude by 6 dB. Repeat this for each side of the flaw and identify these two positions as L1 and L2.

L1 ��

Lmax��

L2 ��


Page 19

Conclusions Using standard calibration blocks typical for conventional UT, Omniscan MX PA is capable of complying with all aspects of the API-UT-2 test procedure. No exceptions are required. The benefits of the phased array are enormous for reducing the dependency on the skill of the inspector and increasing the accuracy and speed of manual UT inspections in the API environment. Training for this application is available through the Davis NDE Advanced UT Detection and Flaw Characterization Training Course. Information for this course and other phased array training courses is available at: www.rd-tech.com/training.html Please forward questions and comments regarding this inspection technique to [email protected] or [email protected]

Date post:	26-Dec-2015
Category:	Documents
Upload:	shahid-nisar-bangash
View:	164 times
Download:	4 times

Phased Array Inspection BY API

Documents