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Technical Discussions
Mohd Huzairi
Malaysia, Joined Apr 2015, 18

Mohd Huzairi

Malaysia,
Joined Apr 2015
18
06:29 Sep-09-2016
RT ellipse technique

Hello,

Using RT ellipse technique,how we can measure the best shifting or offset for gamma source to get good image of weld .What the relation between shifting of gamma source,SFD and pipe size or thickness.Is it any formula or calculation to get correct value for that shifting.What standard that best explain about ellipse technique.May refer below for example.Thanks.

case 1: 2" pipe SA-106 Gr B with thickness 5.54 mm
case 2: 2" pipe 316L with thickness 3.91 mm

number of film using ellipse technique: 2

 
 Reply 
 
N B Rengaraju
NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA., India, Joined Sep 2014, 107

N B Rengaraju

NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA.,
India,
Joined Sep 2014
107
09:19 Sep-09-2016
Re: RT ellipse technique
In Reply to Mohd Huzairi at 06:29 Sep-09-2016 (Opening).

Dear Mohd Huzairi,

The querry posed by you is a practical experience based one. A good technician shall be able to set up the geometry just by looking at the things. There is no standard relation nor formula. Thats why i said its a practical expertise. However, i can approximately state the given below based on practical experience:(for standard thickness)

1. For pipe sizes 1"NB and below, the shifting shall be 1/3 of SFD(corresponds to approx 20 deg)
2. For pipe sizes above 1"NB, the shifting shall be 1/4 of SFD(corresponds to approx 15deg)

Hope the above helps you.


 
 Reply 
 
Mohd Huzairi Rusli
Malaysia, Joined Apr 2015, 18

Mohd Huzairi Rusli

Malaysia,
Joined Apr 2015
18
09:47 Sep-09-2016
Re: RT ellipse technique
In Reply to N B Rengaraju at 09:19 Sep-09-2016 .

Rengaraju,

Thanks for the answer.I will try.However,during interpretation how much the opening between the weld image is acceptable for ellipse technique.Already tried once but the opening between welds is only 5 mm.I don't know is it accept or not.Thanks.

 
 Reply 
 
N B Rengaraju
NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA., India, Joined Sep 2014, 107

N B Rengaraju

NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA.,
India,
Joined Sep 2014
107
10:07 Sep-09-2016
Re: RT ellipse technique
In Reply to Mohd Huzairi Rusli at 09:47 Sep-09-2016 .

If you can see both the weld images clearly well separted, that is acceptable. Distance between the images is immaterial.

 
 Reply 
 
collin maloney
NDT Inspector, - Plant Inspector
Applus RTD, Australia, Joined Nov 2000, 147

collin maloney

NDT Inspector, - Plant Inspector
Applus RTD,
Australia,
Joined Nov 2000
147
08:56 Sep-11-2016
Re: RT ellipse technique
In Reply to N B Rengaraju at 10:07 Sep-09-2016 .

a quick rule of thumb is f/5 where f= source to film distance. the result gives you the amount of offset required from the perpendicular. This is a rule of thumb and as Rengaraju stated, this is more an experience based process. Again Rengaraju is correct in saying there is no code requirement for the weld separation on the elipse, but bear in mind that we normally view the weld and HAZ.

 
 Reply 
 
Shane Feder
, Quality Co-ordinator (SubSea)
Thailand, Joined Dec 2014, 89

Shane Feder

, Quality Co-ordinator (SubSea)
Thailand,
Joined Dec 2014
89
08:46 Sep-13-2016
Re: RT ellipse technique
In Reply to collin maloney at 08:56 Sep-11-2016 .

Not sure if "Distance between the images is immaterial." is correct.
The area of the ellipse has to be sufficient to view both "Areas of Interest" - whether that is HAZ and weld metal or just weld metal.
Please correct me if I am wrong but if the ellipse is too large is there not a danger of enlarging possible defects (eg. wormhole) if in a specific orientation, as the source side weld is transposed onto the film ?
Cheers,
Shane

 
 Reply 
 
N B Rengaraju
NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA., India, Joined Sep 2014, 107

N B Rengaraju

NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA.,
India,
Joined Sep 2014
107
09:17 Sep-13-2016
Re: RT ellipse technique
In Reply to Shane Feder at 08:46 Sep-13-2016 .

Dear Mr. Collin Maloney/Mr. Shane Feder.

When RT Inspection of Weld is discussed, its always understood that its Weld and HAZ. There is no need to specify HAZ everytime.

When Ellipse technique is spoken about, it is preassumed that the image represents what is known as elliptical shape. If Ellipse is too large or broad ellipse, then the shape itself is not Elliptical and is known as OVAL. Such Oval shaped images may go for Reshooting to correct it to Elliptical shape.

That's why I stated, primarily this is a Practical experience based querry.

Good Day to all

 
 Reply 
 
collin maloney
NDT Inspector, - Plant Inspector
Applus RTD, Australia, Joined Nov 2000, 147

collin maloney

NDT Inspector, - Plant Inspector
Applus RTD,
Australia,
Joined Nov 2000
147
09:55 Sep-13-2016
Re: RT ellipse technique
In Reply to N B Rengaraju at 09:17 Sep-13-2016 .

Totally agree with you N B Rengaraju, was just making the point the "split" needs to take into consideration the HAZ. There is however, no code description as to what constitutes an ellipse and thus it is "experience" that will dictate. As Mr Feder has noted, the larger the split, the greater the chance of enlarging the discontinuity, but once again this is "experience" and not a code requirement.
What we like to see and what the code calls for are sometimes a little different!

 
 Reply 
 
Shane Feder
, Quality Co-ordinator (SubSea)
Thailand, Joined Dec 2014, 89

Shane Feder

, Quality Co-ordinator (SubSea)
Thailand,
Joined Dec 2014
89
03:52 Sep-14-2016
Re: RT ellipse technique
In Reply to collin maloney at 09:55 Sep-13-2016 .

Guys,
Purely out of interest where does it state the HAZ must be interpreted when using RT ?
I have been through ASME V 2015 and there are numerous references to UT and PAUT needing to include the weld and HAZ but can find nothing related to RT ?

(1) For welds, the radiation beam may be offset from
the plane of the weld at an angle sufficient to separate the
images of the source-side and film-side portions of the
weld so that there is no overlap of the areas to be interpreted.

What are considered as "areas to be interpreted" ?

If we look at "Areas of Interest"

area of interest: the specific portion of the object that is to
be evaluated as defined by the referencing Code Section.

I have tried Code Sections - B31.3, B31.1 and ASME VIII and no mention of exactly what area must be interpreted on the radiographs.

What is noted in AS 2177 or the EN/ISO codes ?
Cheers,
Shane

 
 Reply 
 
collin maloney
NDT Inspector, - Plant Inspector
Applus RTD, Australia, Joined Nov 2000, 147

collin maloney

NDT Inspector, - Plant Inspector
Applus RTD,
Australia,
Joined Nov 2000
147
05:02 Sep-14-2016
Re: RT ellipse technique
In Reply to Shane Feder at 03:52 Sep-14-2016 .

Hi Shane
AS 2177 only references this in film coverage (3.6.2) where it says the film must be sufficient to cover the identification, weld and HAZ.
AS 4037 makes reference in the notes for acceptance tables for piping and vessels / boilers as follows: "Table is applicable to all imperfections in the welded joint including those in the fused weld metal and the heat affected zone"

 
 Reply 
 
Shane Feder
, Quality Co-ordinator (SubSea)
Thailand, Joined Dec 2014, 89

Shane Feder

, Quality Co-ordinator (SubSea)
Thailand,
Joined Dec 2014
89
05:26 Sep-14-2016
Re: RT ellipse technique
In Reply to collin maloney at 05:02 Sep-14-2016 .

Hi Colin,
ISO 17636 clearly states weld metal and heat affected zone but I can find nothing in ASME or API.
Would be interested if anyone else had found any reference in the American codes,
Cheers,
Shane

 
 Reply 
 
DHANANAJAY MOHANTY
Engineering,
jindal stainless steel , India, Joined Feb 2016, 4

DHANANAJAY MOHANTY

Engineering,
jindal stainless steel ,
India,
Joined Feb 2016
4
10:44 Sep-14-2016
Re: RT ellipse technique
In Reply to Shane Feder at 05:26 Sep-14-2016 .

For practical point of views : it is very important
Double wall image: For pipe less than 3.5 inch (89mm) as per code ASME SEC V DOUBLE WALL DOUBLE IMAGE TECHNIQUE IS ADOPTED.
FORMULA : OD/ID : Less then 1.41 ( Root over of 2) : Two shots at 90 deg Apart
: When OD/ID is Greater then 1.41 ( Root over of 2) , Then super imposed shot with minimum Three Exposures and number of exposure depend on : 1.7xOD/ID ( Next to the highest integer)
if Four segments are not covered by keeping the source in two locations at 90 deg Apart . Hence Elliptical shot not suitable . Both the source and film sides welds are superimposed and interpreted accordingly.


 
 Reply 
 
PANKAJ GAUTAM
NDT Inspector,
1002, India, Joined Jan 2019, 1

PANKAJ GAUTAM

NDT Inspector,
1002,
India,
Joined Jan 2019
1
16:07 Sep-26-2019
Re: RT ellipse technique
In Reply to N B Rengaraju at 09:19 Sep-09-2016 .

What Gap should be allowed in elliptical exposure between two wallet.?

 
 Reply 
 
Agbroko Kayo
Agbroko Kayo
08:59 Oct-26-2019
Re: RT ellipse technique
In Reply to PANKAJ GAUTAM at 16:07 Sep-26-2019 .

That's what I too want to know.
The measurement of the gap. Is is 5mm or more than?

 
 Reply 
 
Shane Feder
, Quality Co-ordinator (SubSea)
Thailand, Joined Dec 2014, 89

Shane Feder

, Quality Co-ordinator (SubSea)
Thailand,
Joined Dec 2014
89
12:02 Oct-26-2019
Re: RT ellipse technique
In Reply to Agbroko Kayo at 08:59 Oct-26-2019 .

This is a question that is not easy to answer.
The difference between base metal and HAZ cannot be viewed on a radiograph but certain codes require you to include the HAZ ?
My personal opinion is there is no minimum/maximum measurement requirement between the two welds on an elliptical shot.
If you have too big an ellipse there is a possibility you may " distort" the size of a defect / discontinuity so it is better to keep the two welds as close as you can.
5 mm as mentioned should be fine.
Hope that helps,
Cheers,
Shane

 
 Reply 
 
laurie
Australia, Joined Feb 2019, 39

laurie

Australia,
Joined Feb 2019
39
07:00 Oct-28-2019
Re: RT ellipse technique
In Reply to Mohd Huzairi at 06:29 Sep-09-2016 (Opening).

The angle will increase with the width of the cap, and reduce as the OD increases and the diagnostic length increases, and as DHANANAJAY MOHANTY said, the number of shots needs to increase as the OD/ID ratio increases.
You could work it out numerically but the thing that will destroy a nice formula is the weld width will vary and needs to be checked every time to vary the angle slightly.
The radiographers who always seem to get it right use a straight edge and line the exposure up by eye with about 5mm of separation, which agrees with what most everyone else is saying.

The HAZ by the way is defined in AS2177 3.6.2 as 6mm either side of the weld.
This figure looks suspiciously like someone picked 1/4" which was then converted to metric so my guess would be that this value was taken from another pre-decimal standard.
If you look at a lot of macros, by volume of welds produced, the HAZ, would be a lot less than 6mm but this would cover the vast majority even for thicker welds.

 
 Reply 
 
Kratus
Consultant,
Petrobras Petroleo Brasileiro, Brazil, Joined Jun 2015, 3

Kratus

Consultant,
Petrobras Petroleo Brasileiro,
Brazil,
Joined Jun 2015
3
12:52 Oct-28-2019
Re: RT ellipse technique
In Reply to laurie at 07:00 Oct-28-2019 .

Good morning, just as a reference, at Petrobras Brazil, we recommend a value for ellipse opening between 10 and 15 mm. The execution can be done by trigonometric relations or most of the time in practice.

 
 Reply 
 
ILLA NANIBABU
ILLA NANIBABU
07:46 Apr-04-2020
Re: RT ellipse technique
In Reply to N B Rengaraju at 09:19 Sep-09-2016 .

Hello sir, i'm Nani,
May i know about the Radiography image Eleptical length?
Imean how much length we need for up weld and down weld.

 
 Reply 
 
laurie
Australia, Joined Feb 2019, 39

laurie

Australia,
Joined Feb 2019
39
03:48 Apr-05-2020
Re: RT ellipse technique
In Reply to ILLA NANIBABU at 07:46 Apr-04-2020 .

zoom image

Ellipse

My interpretation is that if the gap is equal to or larger than your HAZ then a minimum of 2 exposures, but if not then a minimum of 3.

So aim for gap equal to your HAZ, but you must meet your density, Ug and sensitivity requirements and if you can't see your required wire then your gap is probably too big or your source is too close.

In practical terms, try for a couple of mm for DN15-25 and possibly up to 10 mm for DN80.

The black thick line in the image illustrates how to set up your angle where the gap at bottom of the weld is equal to your HAZ.
 
 Reply 
 

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