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 -
 2327 views
Technical Discussions
Dave Armit
NDT Inspector,
Applus RTD, United Kingdom, Joined Dec 2004, 13

Dave Armit

NDT Inspector,
Applus RTD,
United Kingdom,
Joined Dec 2004
13
17:28 Jan-16-2009
Velocity Measurement.

Can anyone please advise on any practical methods for establishing material velocity ( 316 stainless ) using manual contact ultrasonic methods?

Thanks.

 Reply

Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
17:54 Jan-16-2009
Re: Velocity Measurement.
In Reply to Dave Armit at 17:28 Jan-16-2009 (Opening).

Normally you would just measure the velocity in a reference sample of known thickness. All modern flaw detectors and thickness gages have the capability to calibrate velocity when thickness or sound path length is known. Perhaps there is some special circumstance in this case that prevents that?

 Reply

TJ
TJ
18:07 Jan-16-2009
Re: Velocity Measurement.
In Reply to Dave Armit at 17:28 Jan-16-2009 (Opening).

Be careful as the velocity will be different when changing wave modes. For example longitudinal waves travel around twice as fast as transverse waves in a given material. There are several reference charts floating around for longitudinal and shear velocities in commonly tested materials.

TJ

 Reply

Navita Gupta
Navita Gupta
08:17 Jan-17-2009
Re: Velocity Measurement.
In Reply to Dave Armit at 17:28 Jan-16-2009 (Opening).

Use the formula c1/c2 = d1/d2.
Consider c1 as the velocity of steel= 5920m/s. d1 would be the thickness of the ss 316 sample that you want to test.
d2 would be the thickness you read on the A scan display if equipment is calibrated for 5920m/s velocity.
Now calculate mathematically the value of c2. This would be velocity of ss 316.
regards
Navita

 Reply

Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 889

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
889
21:13 Jan-17-2009
Re: Velocity Measurement.
In Reply to Navita Gupta at 08:17 Jan-17-2009 .

I'm with TJ on this one. I don't know why you want to do that in the first place, because there are many already accessible chartsthat give you those value. The other point I want to make, also along with what TJ said is that velocity will also change with Heat Treatment and material temperature. I've personnally experience this situation. You calibrate in the morning when the temperature inside the shop is 70F and find out on your cal out that you are as much as 2 mm off in the afternoon when the temperature has risen to 95F. If you still want that info, go to the link below. This is another great NDT site.

http://www.ndt-ed.org/index_flash.htm

Cheerio's

 Reply

Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1300

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1300
22:04 Jan-17-2009
Re: Velocity Measurement.
In Reply to Michel Couture at 21:13 Jan-17-2009 .

Michel, the suitability of simple tables to obtain acoustic velocities is not always reliable. There can be large variations, especially in metals where heat treatment and even rolling methods can cause significant differences even in the same alloy! I have seen up to 10% variation in carbon steels of the same alloy. Stainless steel is anisotropic and birerfringent. Therefore getting meaningful velocities will, at least for the shear mode, require you use a good scope (at least 100MHz sampling frequency) and be ready to use it in RF (not rectified) display to make sure you are identifying the correct wave (SH slow or SH fast) and phase. Ensure parallel surfaces of the test piece and use a good vernier caliper so you can get a repeatable thickness within about 10mircons. Since the material is anisotropic you may require mesurements in several directions. Guidance on this can be found in ASTM E-1961 (in the Appendix).
Ed

 Reply

Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 889

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
889
23:14 Jan-17-2009
Re: Velocity Measurement.
In Reply to Ed Ginzel at 22:04 Jan-17-2009 .

Ed,

Totatlly agree with you. But as TJ and I said to Dave, I think really depends on what you are doing in the world of NDT. From is profile, Dave indicated that he is an inspector. From that point, I conclude that by doing a normal calibration on a test piece of a known thickness as Tom has mentionned, he should be all right. You see where I come from we have a saying that goes like this: "Don't try to be more Catholic than the Pope". Yes, we have to be as precise as possible, but 10 microns in a weld repair doesn't matter very much, specially when the welder will arc gouge it with a 5/16 rode.

Cheerio's

 Reply

Dave Armit
NDT Inspector,
Applus RTD, United Kingdom, Joined Dec 2004, 13

Dave Armit

NDT Inspector,
Applus RTD,
United Kingdom,
Joined Dec 2004
13
22:00 Jan-18-2009
Re: Velocity Measurement.
In Reply to Ed Ginzel at 22:04 Jan-17-2009 .

Thanks very much for your help guys.
The Project I have is to measure the depth of a 4mm dia pore in a weld of 20mm thickness.
The cap has been removed to accomodate scanning.
Scanning has to be carried out with a Twin 2.5MHZ Compression Probe only.
Velocity measurements have to be made of the parent materials and weld to confirm accuracy as the depth of the pore is critcal.
The method I am using is the method which Tom mentioned.
I was keen to find out if anyone had other proven ideas as I dont have a great deal of experience with Ultrasonic Inspection of Stainless Steel Weldments.

Thanks Again To All.
Dave

 Reply

Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 889

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
889
22:38 Jan-18-2009
Re: Velocity Measurement.
In Reply to Dave Armit at 22:00 Jan-18-2009 .

Dave,
You are right in following Tom's advice for this job. Many times even after meticulously calibrating my instrument I have found that my velocity was a little off compare to all the reference materials and charts I've read. And very seldom an inspector do really bother with velocity. What is important is that when using a specific calibration block, the signal amplitude of the backwall is at the proper place on your screen. Like TJ, Ed and myself said before, many factors will affect your velocity and in your case, since you are measuring a pore in a weld, the velocity of the base metal is differnet from the weld and the HAZ as well.

Cheerio's

 Reply

TJ
TJ
00:23 Jan-19-2009
Re: Velocity Measurement.
In Reply to Dave Armit at 22:00 Jan-18-2009 .

Of course my favorite way of determining velocity of a material which has a visible and measurable flaw (with calipers for instance) is to set your screen range then dial in your velocity until the signal reaches the known depth. Voila! Read your velocity.

TJ

 Reply

Product Spotlight

#### NDTkit RT

NDTkit RT, TESTIA's Digital Radiography software The NDTkit product line software for X-ray analysi
...
s. NDTkit RT is a software benefiting from the Ultis kernel which is dedicated to radiographic image analysis. It offers a set of tools and filtering processes to assist RT operators in finding relevant flaws.
>

#### On-Demand Webinar: Advanced Ultrasonic Techniques for HTHA Detection & Assessment

In the Oil and Gas industry, High Temperature Hydrogen Attack (HTHA) can occur in steels operating a
...
t high temperature, usually above 205°C (400°F). Early stages of HTHA are very difficult to detect. Join us for a webinar presented by Guy Maes, Zetec Sales Engineer Director. The webinar will demonstrate how advanced ultrasonic techniques are deployed for efficient and reliable HTHA inspections.
>

#### Varex Imaging Large Field of View (FOV) Digital Detector Arrays (DDAs)

A larger FOV DDA can reduce the space and volume of the X-ray inspection system on the factory floor
...
, enable faster scanning times, better throughput and better resolution images at a lower dose. Customers can also save time and money. With these benefits in mind, Varex Imaging has designed a family of large FOV detectors (4343HE, XRD 1611, 4343DX-I, 4343CT) for our industrial imaging customers.
>

#### IntraPhase Athena Phased Array System

The Athena Phased Array system, manufactured by WesDyne NDE Products & Technology, consists of a pha
...
sed array acquisition system and PC running IntraSpect software. A PC is used to perform acquisition, analysis and storage of the data. System hardware is capable of operating up to four data sets with any combination of phased array or conventional UT probes. NOW AVAILABLE IN 64-64 CONFIGURATION.
>

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