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Technical Discussions
NDT Inspector, -
PT SEAMLESS PIPE INDONESIA JAYA, Indonesia, Joined Apr 2007, 5


NDT Inspector, -
Joined Apr 2007
13:33 Dec-17-2009
Need Explanation

Can any one help me to explain about this clause, that "Coupling shall be monitored through the back wall signal amplitude. A pipe from
production will be scanned for the back wall signal height. The minimum amplitude found will be
taken as the reference. Then the coupling warning threshold shall be set at the above reference
amplitude minus N dB. N dB being in the flow detection channels, the difference between the
reference signal(s) from reflector(s) and the detection threshold."
And/or give me an illustration of calculation regarding "N"

Best Regards,

John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 280

John O'Brien

Consultant, -
Chevron ETC ,
Joined Jan 2000
13:12 Dec-24-2009
Re: Need Explanation
In Reply to kusnadie at 13:33 Dec-17-2009 (Opening).

This is common for AUT systems in pipe mills. The clause requires that the AUT system be designed with an alarm that monitors a coupling channel if the amplitude falls below the reference level. Normally a zero degree probe is set up looking at the back wall echo from the pipe and is then corrected for the amplitude from reference reflectors i.e a 5% or 10% notch or 3.2 mmm SDH dependent upon specifications. The idea is that the difference between the alarm level from the reference reflectors is allowed for so that if you lose coupling to an extent you will not see the amplitude of the reference reflectors the coupling alarm will be triggered.


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