where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -

3383 views
Technical Discussions
Dao Huu Xuan
Other,
Vietnam, Joined Feb 2007, 18

Dao Huu Xuan

Other,
Vietnam,
Joined Feb 2007
18
10:17 Jun-13-2009
Able to convert AWS defect rating to DAC

Hi all,

This discussion refers to AWS D1.1, table 6.2 and 6.3 - UT Acceptance-Rejection Criteria.

These Criteria has been established based on the calculation of the attenuation of sound pressure at far field. Thus, the attenuation by 2 decibels for each increased inch in sound path. (This is included beam spread and absorption, where the first factor is decisive)

Today, many type of commerce digital UT-sets have had build-in AWS software. And this software also used a/b/c/d formula with the fixed the attenuation by 2 decibels for each increased inch in sound path.

The section 6.22.7.2 of the Standard is allows angled transducer dimensions as: [15 to 25 mm] in width and [15 to 20 mm] in height and the maximum width to height ratio shall be 1.2 to 1.0, and the minimum width-to-height ratio shall be 1.0 to 1.0.

This means that the formula of attenuation by 2 decibels is applied for probe sizes from 15x15 to 24x20. But, actually the beam spread of these difference size of probes are difference.

By using IOW DAC block (SDH 1.5mm); the probe 15x17 (2.25 MHz) show the attenuation is about 2.8 decibels per each increased inch in sound path. And the probe 22x20 (2 MHz) show the attenuation is about 1.9 decibels per each increased inch in sound path.

All SDH in IOW block should have the same defect rating (d). But probe 15x17 (2.25 MHz) show the defect rating is difference, especially for the SDH with sound path further 75mm. By table 6.2, the defect rating (d) between Discontinuity Classes A, B, C and D are different only 1 dB.

By above reason, I think that DAC is better and more accurate than a/b/c/d formula in determination the defect rating. So, Table 6.2 and 6.3 needs to convert to related DAC. And, an example of conversion corresponding to material thickness 8-20mm as below:
Table 6.2 (8-20mm):
Discontinuity Classes Response Pulse Amplitude
A >= 25% DAC (DAC-12dB)
B >= 22.4% and <25% DAC
C >= 20% and <22.4% DAC
D < 20% DAC (DAC-14dB)

Table 6.3 (8-20mm):
Discontinuity Classes Response Pulse Amplitude
A >= 45% DAC (DAC-7dB)
B >= 40% and <45% DAC
C >= 36% and <40% DAC
D < 36% DAC (DAC-9dB)



Finally, any one who have experience on this please give me an advice.
Thank you,

    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1254

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1254
16:33 Jun-13-2009
Re: Able to convert AWS defect rating to DAC
In Reply to Dao Huu Xuan at 10:17 Jun-13-2009 (Opening).

Huu Xuan
I suspect the origins of why AWS D1.1 decided to use a simple "fudge-factor" instead of actual observed attenuation as on a DAC curve, are now lost in history. Echo-transmittance curves (seen in the Appendices of the old Krautkramer book) show that the returned pressure changes with angle. Your observations show that variations in available pressure vary with probe parameters (frequency and dimensions). Some steels (even plain carbon) have anisotropic characteristics, so properties (including attenuation) vary with the angle as well.
Clearly, the D1.1 method to use a simple fixed value does not consider any of these. D1.1 therefore is only a means of arbitrary assessment. Since it does not even make consideration for probe variations it is not even a useful technique for ensuring consistency from one operator to the next with both using "approved" equipment.
AWS D1.1 makes provision in more recent editions to use a DAC as described in the Appendices. Unfortunately, this requires Engineer Approval and submission of an Acceptance criteria to replace the Discontinuity Class Levels (also requiring Enigineer approval).
The wording in D1.1 was perhaps useful in the 1960s. However, now that the equipment and techniques have advanced in the past 50 years it no longer seems to fit today.

    
 
 
Roger Duwe
NDT Inspector, API-510, 570, 653
MISTRAS, USA, Joined Jan 2009, 148

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
19:09 Jun-13-2009
Re: Able to convert AWS defect rating to DAC
In Reply to Ed Ginzel at 16:33 Jun-13-2009 .

Concur, Ed. Theoretically, doing a 'fudge factor' analysis of the return from a flaw, in your head, would be easier than working to a DAC curve hand-drawn on the face of an analog scope. Didn't work that way for me, DAC is easier [and more accurate].

On a good [Kraut or Panametrics] digital scope, I find that DAC is still easier than using the onboard D1.1 software. And there is the accuracy of flaw evaluation.

The origin of D1.1 UT criteria may have been something that could be performed with only one calibration block. Seems like a poor reason to sacrifice accuracy. Maybe someone on the D1 committee will take notice of these discussions and observations.

    
 
 
Neil Breslow
Teacher, - -
NDT Supply.com. Inc., USA, Joined May 2009, 3

Neil Breslow

Teacher, - -
NDT Supply.com. Inc.,
USA,
Joined May 2009
3
00:41 Jun-20-2009
Re: Able to convert AWS defect rating to DAC
In Reply to Dao Huu Xuan at 10:17 Jun-13-2009 (Opening).

Please let me supply some historic background on the origin of the AWS Code. This code was adapted from the Bureau of Public Roads (USA) specification which as adapted from an in-house procedure of American Bridge and Iron and dates back to the late 1960's. As I understand it the orginal draft used the Krautkramer DGS System which was rejected because of its origin and that the US companies Branson and Automation Industries did not want the German company Krautkramer to become the authority on flaw sizing. So, the writer of the specification attempted to "Americanize" the system by simulating the decay curve for a 2.25 MHz rectagular probes in a size range similar to the Krautkramer WB series (20x22mm). Please note that at that time the concern was only for flat work on structural grade steel.

Much has happened to the development of steels and ultrasonic instruments and testing techniques over the past 40 years. But there has been little to no developments to the Ultrasonic Testing Procedures in the AWS Code over these years.

Also, there was an article puplished in the late 60's or early 70's in Materials Evaluation that compares the the AWS Code to to the ASME Pressure Vessel Code. If anyone is interested let me have your e-mail address and I will find it and send you a scanned copy.

    
 
 

Product Spotlight

GEKKO - Portable Phased Array Testing with TFM in Real-Time

The portable phased array testing system GEKKO provides 64 parallel test channels. On creating testi
...
ng parameters the operator is assisted by the CIVA software. Due to its modular set-up the GEKKO instrument is suitable for operators of all skill levels.
>

Immersion systems

ScanMaster ultrasonic immersion systems are designed for high throughput, multi shift operation in a
...
n industrial or lab environment. These fully integrated systems provide various scanning configurations and incorporate conventional and phased arrays technologies to support diverse applications, such as inspection of disks, bars, shafts, billets and plates. All of ScanMaster immersion systems are built from high accuracy scanning frames allowing for scanning of complex parts and include a multi-channel ultrasonic instrument with exceptional performance. The systems are approved by all major manufacturers for C-scan inspection of jet engine forged discs. Together with a comprehensive set of software modules these flexible series of systems provide the customer with the best price performance solutions.
>

TVC awarded UKAS accreditation

TVC are delighted to finally announce we have been awarded UKAS accreditation for our calibration
...
laboratory. Laboratory accreditation to ISO/IEC 17025:2005 enables us to conduct the Electrical Verification of Ultrasonic Flaw Detection Equipment to BS EN 12668-1:2010. It has taken many months of hard work and we want to thank our staff for all their efforts during this massive undertaking.
>

ISAFE3 Intrinsically Safe Sensor System

ISAFE3 intrinsically safe sensor system of Vallen Systeme is especially targeted at the petrochemica
...
l - as well as oil and gas transportation industry. The sensor system is designed for permanent monitoring or periodic inspection tasks. Sensors are available for different AE-frequency ranges optimized for corrosion and fatigue crack detection and other applications. The ISAFE 3 sensor system consists of an AE-sensor (model ISAS3) certified according to ATEX/IEC for installation in zone 0, gas group IIC, IP68, 20 to +60 °C, and a signal isolator (model SISO3) certified for installation in zone 2. An ISAS3 sensor can be mounted in atmosphere or submerged, e.g. in water or crude oil. It is supported by mounting tools for temporary (magnets) or permanent (welded) installation. ISAFE3 supports automatic sensor coupling test and can be used with any AE signal processor supporting 28V supply at 90 mA peak, e.g. Vallen Systeme ASIP-2/A.
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window