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Technical Discussions
Lee Bird
Lee Bird
01:48 Apr-10-1999
Anamolies within pipe and plate wall

Greetings,
I am a level III UT,PT,MT and API 510 certified inspector.
I am researching a problem with steel plate and pipe that I hope someone may be able to share some expertise in. In our inspections as dictated by OSHA, and API we perform an "in service" examination of pipe and vessels within our facilities. By examining the outside surface of the material ultrasonically we can pick up wall loss due to corrosion, erosion or pitting. To have this type of discrimination we use a dual element technique . Using this technique Ultrasonic examination indicates numerous reflectors within the plate or steel wall. The OD and ID are not pitted, corroded or eroded.
I call this problem "dirty steel". This problem is occurring more and more often. Are there any guidelines other that ASME 435 that might yield some accept reject criteria? My e-mail address is lee.Bird@coastalcorp.com Has anyone else experienced this problem. I would be glad to share copies of my A-Scan traces for discussion.

Thank you



 
 Reply 
 
Steven Cook
Steven Cook
00:58 Apr-12-1999
Re: Anamolies within pipe and plate wall

Mr. Bird,

You are having one fundamental problem that many people overlook when
performing UT thickness measurements on piping.

Where you have material thicknesses less than 3 mm the dual element
transducers thickness readings are no longer linear. Please refer to ASTM
03.03 E-797. (Since I am at home right now, I am not 100% sure of the "E"
number, but it is for UT contact thickness method).

ASTM has a chart showing the inaccuracies that occur when using a dual
element transducer on thin materials.

So far, we have successfully used 6mm diameter x 10 MHz single crystal
transducers with a delay line to keep the near field out of the test material.

I believe that when you switch to a single crystal transducer your metals
will look a little cleaner.

However, if you should find that you are still getting "dirty steel" then
the only acceptance criteria that I am aware of is ASTM E 435.

If your company is the owner of the pipes, then a "Fitness for Use"
acceptance criteria can be established, based on sound engineering
requirements.

I hope this has been of some use.


Steven Cook
FLITE
7 Jalan Permas 12/5
81750 Permas Jaya, Johor
Malaysia
Phone: 60-7-289-2242
Fax: 60-7-289-2243
e-mail: cook@pd.jaring.my

--------------
: Greetings,
: I am a level III UT,PT,MT and API 510 certified inspector.
: I am researching a problem with steel plate and pipe that I hope someone may be able to share some expertise in. In our inspections as dictated by OSHA, and API we perform an "in service" examination of pipe and vessels within our facilities. By examining the outside surface of the material ultrasonically we can pick up wall loss due to corrosion, erosion or pitting. To have this type of discrimination we use a dual element technique . Using this technique Ultrasonic examination indicates numerous reflectors within the plate or steel wall. The OD and ID are not pitted, corroded or eroded.
: I call this problem "dirty steel". This problem is occurring more and more often. Are there any guidelines other that ASME 435 that might yield some accept reject criteria? My e-mail address is lee.Bird@coastalcorp.com Has anyone else experienced this problem. I would be glad to share copies of my A-Scan traces for discussion.

: Thank you



 
 Reply 
 
Manuel Haces
Manuel Haces
02:09 Apr-12-1999
Re: Anamolies within pipe and plate wall
: Greetings,
: I am a level III UT,PT,MT and API 510 certified inspector.
: I am researching a problem with steel plate and pipe that I hope someone may be able to share some expertise in. In our inspections as dictated by OSHA, and API we perform an "in service" examination of pipe and vessels within our facilities. By examining the outside surface of the material ultrasonically we can pick up wall loss due to corrosion, erosion or pitting. To have this type of discrimination we use a dual element technique . Using this technique Ultrasonic examination indicates numerous reflectors within the plate or steel wall. The OD and ID are not pitted, corroded or eroded.
: I call this problem "dirty steel". This problem is occurring more and more often. Are there any guidelines other that ASME 435 that might yield some accept reject criteria? My e-mail address is lee.Bird@coastalcorp.com Has anyone else experienced this problem. I would be glad to share copies of my A-Scan traces for discussion.

: Thank you

Please send me more information regarding the test, ID and OD of the pipe, thickness and a copy of
the A Scan, so I can send you my oppinion.



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

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
00:49 Apr-13-1999
Re: Anamolies within pipe and plate wall

: I call this problem "dirty steel". This problem is occurring more and more often. Are there any guidelines other that ASME 435 that might yield some accept reject criteria? My e-mail address is lee.Bird@coastalcorp.com Has anyone else experienced this problem. I would be glad to share copies of my A-Scan traces for discussion.

It would be helpful to have more details about what you're doing: transducer type (frequency and diameter), instrument type, instrument gain and PRF settings, and pipe wall thickness. Plus a copy of the A-scan, if you could post that.

Yes, this phenomenon has been observed elsewhere, and you can even see it sometimes on grain-free, inclusion-free materials like fused silica if you turn gain up high enough. Off the top of my head I can think of a couple causes that I've observed. You can sometimes catch multiple reverberations from trapped couplant pockets if the test surface is rough. If the surface is smooth, many duals will generate a small surface wave component that creates a crosstalk effect as it leaks into the receiver side of the transducer. If your instrument PRF rate is too high, you might be seeing wraparound noise. All of these effects typically show up in a significant way only when gain levels are very high, and they can all cause noise patterns that change as you move the transducer, due to minor changes in coupling and/or pipe surface topography. If you're using a worn transducer that forces you to crank up the gain to very high levels, that could also be a contributing cause.

--Tom Nelligan
Panametrics, Inc.





 
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