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Technical Discussions
Carl Olson Jr.
Carl Olson Jr.
06:58 Jan-14-2002
Pipe Scale and NDT Readings

I am a consulting engineer with over 20 years experience in steam piping engineering, design, and maintenance. Is it possible to have a UT reading for a steam line show a larger-than-installed wall thicknes due to internal scale build up or does the UT process/quipment eliminate this scale due to it's dissimilar density than the original pipeline? Thanks...

Carl Olson Jr.
Cubex, Inc.
colson@cubexcontrols.com



    
 
 Reply 
 
Ted Ballenger
Consultant
Krautkramer, USA, Joined Jan 2002, 3

Ted Ballenger

Consultant
Krautkramer,
USA,
Joined Jan 2002
3
07:03 Jan-14-2002
Re: Pipe Scale and NDT Readings
: I am a consulting engineer with over 20 years experience in steam piping engineering, design, and maintenance. Is it possible to have a UT reading for a steam line show a larger-than-installed wall thicknes due to internal scale build up or does the UT process/quipment eliminate this scale due to it's dissimilar density than the original pipeline? Thanks...
.
: Carl Olson Jr.
: Cubex, Inc.
: colson@cubexcontrols.com
.
The short answer seems to be YES...
THe longer answer is that some of our customers have a technique to measure what is metal and what is scale or other ID buildup...the other obvious question seems there is a difference in what was recorded as noimal in the beginning...




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

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
07:13 Jan-14-2002
Re: Pipe Scale and NDT Readings
: I am a consulting engineer with over 20 years experience in steam piping engineering, design, and maintenance. Is it possible to have a UT reading for a steam line show a larger-than-installed wall thicknes due to internal scale build up or does the UT process/quipment eliminate this scale due to it's dissimilar density than the original pipeline? Thanks...


Yes, it's possible. The acoustic impedance of the scale is relatively close to that of the steel, so that the echo from the steel/scale boundary is fairly small as compared to the scale/air echo. Many gages will by default grab the larger scale/air echo and read that thickness. However if you use a gage with a waveform display and adjustable setups, you can often adjust gain and blanking parameters so that you read metal thickness only.

Also, remember that sound velocity in steel and other materials decreases with temperature, so if the gage is calibrated on room temperature material and then used on hot metal, the incorrect velocity calibration will cause the hot steel to appear thicker than it actually is. Incorrect compensation for transducer delay line heating during testing will have the same effect.

--Tom Nelligan
Panametrics, Inc.


    
 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
08:54 Jan-20-2002
Re: Pipe Scale and NDT Readings
It is better to have a small section of the pipe as mock-up where the different layers are visible so that the readings are correlated. A-scan display systems which show upto 5 or 6 different layers are available, but actual velocities of the various materials at the respective temperatures needs to be input so that the transit time can be translated into correct thicknesses.

: : I am a consulting engineer with over 20 years experience in steam piping engineering, design, and maintenance. Is it possible to have a UT reading for a steam line show a larger-than-installed wall thicknes due to internal scale build up or does the UT process/quipment eliminate this scale due to it's dissimilar density than the original pipeline? Thanks...
: .
: : Carl Olson Jr.
: : Cubex, Inc.
: : colson@cubexcontrols.com
: .
: The short answer seems to be YES...
: THe longer answer is that some of our customers have a technique to measure what is metal and what is scale or other ID buildup...the other obvious question seems there is a difference in what was recorded as noimal in the beginning...
.



    
 
 Reply 
 

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