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Technical Discussions
Paul
NDT Inspector,
USA, Joined Mar 2016, 21

Paul

NDT Inspector,
USA,
Joined Mar 2016
21
20:33 Jan-09-2020
Ultrasonic inspection of round bar per API 6A Stems

If anyone has experience with API 6A, Specification for Wellhead and Tree Equipment, 21st Edition 21st - Please explain what section 10.4.3.2.2 is saying.

We are doing a volumetric scan using contact single pulse transducer on round bar 3" diameter 30" in length. The spec calls out stems(or bar from which the stems are machined) shall be inspected from the outside diameter and ends by the straight-beam technique. Stems that cannot be examined axially using the straight-beam technique shall be examined using the angle-beam technique.

The DAC shall be based on a maximum 1/8" FBH straight beam and a maximum 1/16" side drilled hole, 1" deep(angle beam).

The FBH's I understand. The side drilled hole is confusing. What does it mean by 1" deep? Does this mean the hole should be 1" in distance from contact surface, through hole across the entire diameter, or does this mean you would locate 1" deep side drilled holes at different metal travel distances from contact surface, similar to the PDF attached.

 
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Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 868

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
868
04:42 Jan-10-2020
Re: Ultrasonic inspection of round bar per API 6A Stems
In Reply to Paul at 20:33 Jan-09-2020 (Opening).

Paul,

The inspection calls for a UT straight beam inspection from the end and from the transverse axis. The last sentence of your paragraph give you the answer.

"Stems that cannot be examined axially using the straight-beam technique shall be examined using the angle-beam technique".

Therefore, if you can inspect your stems with a straight beam technique, you do not worry about the SDH. Because it is to draw your DAC for the angle beam inspection.

All you do is a DAC using a 1/8" FBH. Then scan with your straight beam transducer.

 
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Paul
NDT Inspector,
USA, Joined Mar 2016, 21

Paul

NDT Inspector,
USA,
Joined Mar 2016
21
14:55 Jan-10-2020
Re: Ultrasonic inspection of round bar per API 6A Stems
In Reply to Michel Couture at 04:42 Jan-10-2020 .

Michel,
We are not able to scan the 30" bar and reasonably locate a 1/8" FBH. Even at 16" MTD and scanning from both ends we have doubts. If we could use the straight-beam method on the ends, we would, to save inspection time. I was hoping to get an explanation of what type of reference standard we should use if angle beam. I don't understand what (1"deep) is referring to. Does this have any bearing on the depth of the side drilled hole or is this referring to distance from contact surface?

 
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THEO MICOTTIS
Italy, Joined May 2013, 81

THEO MICOTTIS

Italy,
Joined May 2013
81
17:36 Jan-10-2020
Re: Ultrasonic inspection of round bar per API 6A Stems
In Reply to Paul at 14:55 Jan-10-2020 .

Dear Paul, which straight beam probe are you using for axial scan? Sounds strange to me that you cannot locate 1/8" FBH at 30". Are the ends of the stem machined?
I would do as following: 1/16" SDH at 1" deep from diameter surface and construct my DAC.
Regards Theo

 
 Reply 
 
Paul
NDT Inspector,
USA, Joined Mar 2016, 21

Paul

NDT Inspector,
USA,
Joined Mar 2016
21
18:52 Jan-10-2020
Re: Ultrasonic inspection of round bar per API 6A Stems
In Reply to THEO MICOTTIS at 17:36 Jan-10-2020 .

Download

Theo,
It is saw cut. The consistency of surface finish and perpendicularity of end to axis is not always similar from one bar to the other or smooth enough. This is why we considered using an angle beam rather than axial.

I have 1" diameter 2.25MHz and 5MHz probes or .375" in the same frequencies.

Excuse my inexperience, I have limited angle beam OTJ training. The side drilled hole is through the entire bar, perpendicular to the axis of the bar, and located 1" from the contact surface? Then I would create a DAC using the one hole? I was given this diagram for 1.5" diameter round stock as an example from a level 3, but I didn't understand how a curve would be created or if the orientation of the hole was correct.
 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 868

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
868
04:36 Jan-11-2020
Re: Ultrasonic inspection of round bar per API 6A Stems
In Reply to Paul at 18:52 Jan-10-2020 .

Paul,

Have a look at ASTM A-388 standard. It is similar to what you are doing and may give you some insight.

 
 Reply 
 
THEO MICOTTIS
Italy, Joined May 2013, 81

THEO MICOTTIS

Italy,
Joined May 2013
81
08:28 Jan-11-2020
Re: Ultrasonic inspection of round bar per API 6A Stems
In Reply to Paul at 18:52 Jan-10-2020 .

Paul, the SDH required should be enough to construct your DAC curve / reference line.
As Michel suggested, have a look at ASTM A388 pa.9.3.3 for hole orientation and related DAC.
Regards Theo

 
 Reply 
 

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