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Technical Discussions
Tony Li
Tony Li
01:32 Nov-19-2007
ASTM A388/API 6A

I would appreciate if anyone can help on the below.

We sell lots of steel forged bars into USA and sometime it's very confused of the NDT rejection criteria.

for bars larger than 150mm, our rejection criteria is set at:

No single indication exceeding DAC @ 6.4mm(or 1/4"), and

No mutliple indication exceeding DAC @ 3.2mm(or 1/8")

Because customers do not specify the total numbers of single indication & multiple indications allowed, what we should do on this issue ?

Or there is a rejection criteria ? can anyone tell ?

Thanks a lot.

Tony



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

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
280
05:09 Nov-21-2007
Re: ASTM A388/API 6A
API 6A Page 69 makes it clear - any single indication larger than that required is rejectable. Any mutiple indications (2 or more) larger than the second criteria is cause for rejection.

API 6A also requires manufacturers to establish manufacturing procedures reflecting each quality level with the accept/reject criteria clearly defined.

Similar rules are quoted in numerous ASTM material specifications and the interpretation is I believe consistent with the above.


 
 Reply 
 
Tony Li
Tony Li
04:55 Nov-22-2007
Re: ASTM A388/API 6A
----------- Start Original Message -----------
: API 6A Page 69 makes it clear - any single indication larger than that required is rejectable. Any mutiple indications (2 or more) larger than the second criteria is cause for rejection.
: API 6A also requires manufacturers to establish manufacturing procedures reflecting each quality level with the accept/reject criteria clearly defined.
: Similar rules are quoted in numerous ASTM material specifications and the interpretation is I believe consistent with the above.
------------ End Original Message ------------

Thanks for the input.

We adopted the criteria, but sometime material is still being rejected, and we don't know why.

Does anyone know what the definition is for "traveling type indications", we wonder this maybe the cause of rejection.

Thanks

Tony Li


 
 Reply 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 183

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
183
07:53 Nov-22-2007
Re: ASTM A388/API 6A
reply:

What is a 'travelling indication'?

When doing ultrasonic testing with a moving angle beam probe using an instrument with an A-Scan representation the distance (time-of-flight) to a reflector is changing with probe movement.
That makes the screen indication from the reflector -which of course is at constant position - 'travelling'.
But really the probe is travelling.
Or the other way round: The same reflector is seen by the probe from different positions (directions).

Best regards

Udo Schlengermann

European Application Laboratory
GE Inspection Technologies GmbH
Huerth, Germany

----------- Start Original Message -----------
: : API 6A Page 69 makes it clear - any single indication larger than that required is rejectable. Any mutiple indications (2 or more) larger than the second criteria is cause for rejection.
: : API 6A also requires manufacturers to establish manufacturing procedures reflecting each quality level with the accept/reject criteria clearly defined.
: : Similar rules are quoted in numerous ASTM material specifications and the interpretation is I believe consistent with the above.
: Thanks for the input.
: We adopted the criteria, but sometime material is still being rejected, and we don't know why.
: Does anyone know what the definition is for "traveling type indications", we wonder this maybe the cause of rejection.
: Thanks
: Tony Li
------------ End Original Message ------------




 
 Reply 
 
Larry Mullins
Larry Mullins
00:24 Nov-23-2007
Re: ASTM A388/API 6A
----------- Start Original Message -----------
: reply:

When using a straight beam transducer a lamination is "static" or non-moving. Indications which move on the A-scan when using straight beam indicate a flaw with through-wall projection and would be seen as moving and therefore more objectionable than a lamination. So if travelling is used in conjuction with straight beam examination this is a traveling indication.

: What is a 'travelling indication'?
: When doing ultrasonic testing with a moving angle beam probe using an instrument with an A-Scan representation the distance (time-of-flight) to a reflector is changing with probe movement.
: That makes the screen indication from the reflector -which of course is at constant position - 'travelling'.
: But really the probe is travelling.
: Or the other way round: The same reflector is seen by the probe from different positions (directions).
: Best regards
: Udo Schlengermann
: European Application Laboratory
: GE Inspection Technologies GmbH
: Huerth, Germany
: : : API 6A Page 69 makes it clear - any single indication larger than that required is rejectable. Any mutiple indications (2 or more) larger than the second criteria is cause for rejection.
: : : API 6A also requires manufacturers to establish manufacturing procedures reflecting each quality level with the accept/reject criteria clearly defined.
: : : Similar rules are quoted in numerous ASTM material specifications and the interpretation is I believe consistent with the above.
: : Thanks for the input.
: : We adopted the criteria, but sometime material is still being rejected, and we don't know why.
: : Does anyone know what the definition is for "traveling type indications", we wonder this maybe the cause of rejection.
: : Thanks
: : Tony Li
------------ End Original Message ------------




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

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
280
06:31 Nov-23-2007
Re: ASTM A388/API 6A
The guys have defined the condition correctly - the problem you are facing is a difference in interpretation of an incomplete specification.

API 6A and ASTM discuss flaws only in terms of a DAC reference level and dimension in one plane. The fact is that many flaws have length, width and depth and hence especially in heavy wall materials the occurence of travelling indications. The assumption is often that these are more harmful than straight planar flaws unless their origin and true nature can be identified - not always possible. The client side therefore tends to err on the side of caution and reject. Whether that is truely a defensible position as the specifications define the flaws is arguable.

As a manufacturer you probably should use API 6A better and establish clear acceptance/rejection criteria in the PSL specs which outline how these are dealt with and get them accepted by your customers so there is real clarity. For many purchasers if the issue is addressed up front they will be happy.


 
 Reply 
 
Tony Li
Tony Li
08:28 Nov-26-2007
Re: ASTM A388/API 6A
----------- Start Original Message -----------
: The guys have defined the condition correctly - the problem you are facing is a difference in interpretation of an incomplete specification.
: API 6A and ASTM discuss flaws only in terms of a DAC reference level and dimension in one plane. The fact is that many flaws have length, width and depth and hence especially in heavy wall materials the occurence of travelling indications. The assumption is often that these are more harmful than straight planar flaws unless their origin and true nature can be identified - not always possible. The client side therefore tends to err on the side of caution and reject. Whether that is truely a defensible position as the specifications define the flaws is arguable.
: As a manufacturer you probably should use API 6A better and establish clear acceptance/rejection criteria in the PSL specs which outline how these are dealt with and get them accepted by your customers so there is real clarity. For many purchasers if the issue is addressed up front they will be happy.
------------ End Original Message ------------

Thanks to all of you for your inputs here. It really help us a lot.

Tony Li


 
 Reply 
 

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