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- since 1996 -
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Technical Discussions
ndttech
ndttech
16:37 Jul-19-2012
X or gamma ray

Hello all,

Currently on a project and doing radiographhy on pipework.
I have had a debate with several technicians over the use of gamma ray and x-ray.

The procedure recognises both but in my experience which is 20+ years i have always used x-ray where possible over gamma ray.

The new breed of technicians are asking me to show where it says x-ray over gamma ray in the procedure, my response is that this is protocol and always has been due to the image quality.

Having worked extensively throughout Europe i have seen a lot of guys that are happy using an isotope but when given a tube there is an instant look of shock horror on faces.

The above work i am talking about is all loose spools, small bore, Sch10-Sch40 up to 6" Sch 40 in a well equipped bunker.

Responses welcome.

 
 Reply 
 
Oliviero
NDT Inspector,
Quality Control srl, Italy, Joined Oct 2008, 414

Oliviero

NDT Inspector,
Quality Control srl,
Italy,
Joined Oct 2008
414
20:29 Jul-19-2012
Re: X or gamma ray
In Reply to ndttech at 16:37 Jul-19-2012 (Opening).

In a well equipped bunker, the loose spools up to 6" and low thicknesses, are well tested with X-rays without difficulties.
Isotopes need to be used in-field during assembly.
The required sensitivity could not be easily reached with the isotope and the X-rays in a well equipped bunker permit a better film quality versus an equal time spent.

 
 Reply 
 
Dent
Consultant, NDE Manager NDELevel III/3
NDT Consultant, Canada, Joined Nov 1998, 250

Dent

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
250
20:42 Jul-19-2012
Re: X or gamma ray
In Reply to ndttech at 16:37 Jul-19-2012 (Opening).

Quality aside for a minute, what about safety? Given that both are acceptable sources of radiation and both can meet the image quality requirements, I would always opt for the safest one. In my mind x ray would be the obvious choice from a purely safety point of view. If the complaint becomes that your shots are too good and you are seeing more than the other guy did with gamma, you may need to play the safety argument.

I have never seen it written that when both sources are available and acceptable that x ray must be used as protocol.

 
 Reply 
 
anjafo
NDT Inspector
Norway, Joined Aug 2009, 204

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
21:54 Jul-19-2012
Re: X or gamma ray
usually much faster with x-ray also.

 
 Reply 
 
ndttech
ndttech
22:07 Jul-19-2012
Re: X or gamma ray
In Reply to Dent at 20:42 Jul-19-2012 .

Dent,

You make a very valid point about safety which i have also pointed out to the guys.
In the procedure it says the radiation source which is x-ray and gamma but i am trying to get across that x-ray is the preferred method and as said on here, gamma is mainly for the tie-in and installation work.
Great responses from everyone and i am glad that i am not alone with the x-ray over gamma ray discussion.

Many thanks

 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
09:00 Jul-20-2012
Re: X or gamma ray
In Reply to ndttech at 22:07 Jul-19-2012 .

The decision of which radiation source is to be used (x-ray or gamma ray) is normally specified by the designer or end user taking into account all the points which have been brought about nicely in the discussion so far.

If you are a NDT Service provider and if the NDT procedure leaves the choice to you, you can of course choose either source depending on what you have, what licenses you have, the location etc.

If you are the welding contractor for the pipe-line, you would prefer that the radiography is done using gamma ray source since some detail is lost in the images (while still meeting the acceptance standards in terms of density, IQI visibility etc.). X-rays tend to show more detail and thus a few more discontinuities which attract the attention of the inspectors and may lead to extra repairs (and thus more cost to you the welding contractor).

So, the choice is really dependent on the perspective of the party involved and their role in the whole project.

Because of such ambiguities, we removed the choice in our specification (we were in a position to do so because we could convince the top management) for high temperature chemical reactors, which were prone to corrosion and which needed radiography during construction and also during service at intervals. The fabricators were not very happy but had no choice because we were ready to pay a higher price and give the order to those meeting our technical specification completely.

 
 Reply 
 
Dilip Sharma
Dilip Sharma
12:56 Aug-24-2012
Re: X or gamma ray
In Reply to S.V.Swamy at 09:00 Jul-20-2012 .

Dear sir,

Greetings for the day.

At the outset let me introduce myself. I am Dilip for JVS Engineers – India. We are in the field of manufacturing pressure valves, choke valves and well head assemblies being used on Oil Drilling Rigs and petroleum processing plants.
We have been certified by American Petroleum Institute for manufacturing these product.

We have manufacturing facilities to produce big range of products in various size in India, Singapore, UK & USA. However, as you know the prime characteristic of valve
is to have defect free body and other parts to sustain high amount of pressure. For which we are performing NDT test – however in order to enhance our testing facility/mechanism, we would like to introduce the Radiography testing bunker in our facility.

In this regard, may we request you to share us the details you have regarding the same.

Your support in this regard will be highly appreciated.

Hoping for the best.

Regards
Dilip Sharma

 
 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
10:23 Sep-02-2012
Re: X or gamma ray
In Reply to ndttech at 22:07 Jul-19-2012 .

On paper there is no real differences as by code you need to meet all the requirements for sensitivity, density etc. It is only when you run into issues with contrast that you might choose gamma over X, however depending on the control of the X unit this can be satisfied as well.
At the end of the day, safety besides, it is about production, X will do the same job day in day out and extremely fast with the right jigs, but the isotope will decay and you have to adjust exposures accordingly.

 
 Reply 
 
Gerald R. Reams
Engineering,
Industry, USA, Joined Aug 2012, 181

Gerald R. Reams

Engineering,
Industry,
USA,
Joined Aug 2012
181
14:43 Sep-02-2012
Re: X or gamma ray
In Reply to collin maloney at 10:23 Sep-02-2012 .

Economics. Which gives the higher production rate? This can be different for different situations. With Gamma, the columnator is much easier to position and manipulate than a x-ray tube head. With the various sources of gamma-radiation available, sensitivity is comparable.

From my experience, bulky or installed items are easier to radiograph with sources. For small or easily manipulated parts, I usually prefer x-ray.

Gerald R. Reams
ASNT NDT Level III,
AWS-CWI, ASQ-CQA

 
 Reply 
 
upendra
upendra
19:12 Jan-28-2014
Re: X or gamma ray
In Reply to collin maloney at 10:23 Sep-02-2012 .

Please let me how the contrast will be better in case of Gamma ray as compared to x ray. In my case, i m getting opposite result. The film quality is much better when using X ray as compared to the later. Also let me know how the contrast quality of film can be improved in case of Gamma ray. I m getting a film which satisfies all the criteria in terms of density,sensitivity but the film appears to be very dark and the defects are not visible. Basically there is very slight difference in density between pipe and the weld, although there is good amount of weld reinforcement and good root penetration. How this small density difference can be enlarged in terms of contrast so that the defects become more clear.

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

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
868
20:00 Jan-28-2014
Re: X or gamma ray
In Reply to upendra at 19:12 Jan-28-2014 .

Upendra,

Maybe you should consider using a different film. Because you should be able to clearly see a difference in density between your weld and the base metal.

 
 Reply 
 
Tim
Tim
14:28 Jan-30-2014
Re: X or gamma ray
In Reply to upendra at 19:12 Jan-28-2014 .

As Michel has noted, film of a slower speed. Possibly an increase in focal film distance. (Check the Ug calculation)

 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
14:51 Jan-30-2014
Re: X or gamma ray
In Reply to Tim at 14:28 Jan-30-2014 .

I was always taught that a better imaged radiograph could be obtained with X-rays if choosing a small focal spot (or even microfocus) and suitable kV to alter the spectrum, whereas gamma sources have fixed discrete wavelengths.

Colin, are you referring to standard isotopes (Cobalt, Iridium, Ytterbium)? How does the use of these improve on the quality of suitable X-ray apparatus?

 
 Reply 
 
Tim
Tim
18:50 Jan-30-2014
Re: X or gamma ray
In Reply to Nigel Armstrong at 14:51 Jan-30-2014 .

Agreed and since you mention, smaller focal spot isotopes provide improved image.

 
 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
06:35 Feb-01-2014
Re: X or gamma ray
In Reply to Nigel Armstrong at 14:51 Jan-30-2014 .

Hi Nigel, might be in the way I was answering the original question.
You will get no debate from me that "X" will give better contrast, what I was trying to say about the original post was there is no prefered method between X or Gamma by Code, only that you meet the requirements for sensitivity, density etc. What comes into play are client requirements, its not uncommon for them to request X for stainless steel over Gamma as an example. This we know is based on better POD of fine cracks as opposed to Gamma that is Code acceptable but not as capable.

 
 Reply 
 
vijayaraghavan p
Consultant,
Freelance consultant, India, Joined Dec 2009, 12

vijayaraghavan p

Consultant,
Freelance consultant,
India,
Joined Dec 2009
12
07:29 Feb-20-2014
Re: X or gamma ray
In Reply to collin maloney at 06:35 Feb-01-2014 .

In Aeroospace, in the earlier specs mention was made to use x ray only for flight hardware. but in the lateste this astm e 1742, it is mentioned that gamma ray can be used provided , quality of the radiograph matches that of x ray. since this is hypothetical , we in aerospace use only x ray.

 
 Reply 
 
mudassir
mudassir
09:37 Oct-20-2019
Re: X or gamma ray
In Reply to upendra at 19:12 Jan-28-2014 .

We used gamma ray and now the client want that they follws x ray,so I expalianed him that gamma ray what we had done it has a good quality image,but he want a vallid reason why he can considered gamma ray over x ray.
I am not getting any point how to justify this point please any answers for this...help me guys

 
 Reply 
 
N B Rengaraju
NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA., India, Joined Sep 2014, 106

N B Rengaraju

NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA.,
India,
Joined Sep 2014
106
20:09 Oct-20-2019
Re: X or gamma ray
In Reply to mudassir at 09:37 Oct-20-2019 .

Check the contract with your client regarding application of Radiation Source. If you have committed to X-Ray as per contract, then your client is right in insisting for re-radiography.

Radiograhy Quality of Gamma Radiograhy will always be inferior to X-Ray & not vice-versa for a specific job, unless the job geometry has a latitude issue. So, no point in searching to prove gamma is better than xrays.

Regards

 
 Reply 
 
laurie
Australia, Joined Feb 2019, 36

laurie

Australia,
Joined Feb 2019
36
06:11 Oct-21-2019
Re: X or gamma ray
In Reply to ndttech at 16:37 Jul-19-2012 (Opening).

Unfortunately its not as simple as saying x-ray is better than gamma - latitude can also have a big effect although this can be mitigated with film choice or multifilm technique.
If you have a thin weld with a fair bit of reinforcement you can find that the reinforcement is very low density and the parent metal very high and you can hardly see anything.
Even if the reinforcement is relatively minor and the plate is thick then you easily find that a couple of mm difference causes the reinforcement to be very low density because its getting close to the upper useful range of the kV penetration.
A gamma source of say Ir192 can easily keep the density within limitations for say a 6mm plate with 4mm of reinforcement and a 40mm plate with 8mm of reinforcement which is difficult for lower energy x-ray sets.
Obviously these are extremes but gamma can be a lot more forgiving when you have varying parent metal and reinforcement and is probably why a lot of technicians prefer gamma despite the lower sensitivity.

 
 Reply 
 

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