That scenario is really scary! While it could work for some discontinuity detection, I don't know how it could transpose over to some standard acceptance criteria common to US industrial and world wide ASME requirements. It would seem to be impossible for the results from this procedure to have a credible cross reference to AWS D 1.1 acceptance criteria.
This is China right??? The land of copyright and patent infringement. What is the problem with making an IIW block, or any other calibration block over there??? The way they make everything else, I would think calibration blocks would be as common as door stops.
"Calibration blocks? We don't need no stinkin calibration blocks amigo!"
China flanges, counterfeit bolts, tainted toothpaste and fruit juices, kid's jewelry made from lead alloys, and leaded paints all from China, what more can I say! Oh yea, I missed tainted drugs imported from China by U.S. pharmaceuticals are OK, but don't get caught trying to buy your own drugs in Canada (that's illegal!).
Al
I agree with Joe. Using an analog UT system you need a reference to compare to your indications.
I think they were giving you the Chinese 2 step.
Unless they were doing a straight beam examination, then they may be able to get away from it.
But for shear wave, I never heard of such a thing.
Since you've used the BWE (back wall echo) term, and stated your not talking about a weld, I am assume your talking about a plate lamination scan, and since a lam scan is as easy as it gets for UT, I'll reference the following standards: BS EN 10160, ASTM A435
To my knowledge, these are the only form of UT exams that do not directly specify a reference block. A quote from the 01 A435:
5.3 Conduct the examination with a test frequency and
instrument adjustment that will produce a minimum 50 to a
maximum 75 % of full scale reference back reflection from the
opposite side of a sound area of the plate. While calibrating the
instrument, sweep the crystal along the plate surface for a
distance of at least 1T or 6 in. [150 mm], whichever is the
greater, and note the position of the back reflection. A shift in
location of the back reflection during calibration shall be cause
for recalibration of the instrument.
Basically, your calibrating on the plate itself. The adding of DB is what doesn't make sense for this. That adding of DB implies a base DB for judgement of acceptability in the positive sense. I.E. lam scans rely on the negative in that it's a loss of backwall reflection being watched for, not the other way around.
Therefore the addition of DB implies they are attempting a DGS /AVG exam. Which is distance gain size typically in reference to a disk shapped reflector which would require a calibration block.
To sum it up, there are very limited standards and codes out there that do allow cal up on the part, but non that I am aware of anywhere in the EU, USA, Asia, or any other part of world I've worked in, that allow what you have described. Especially when you throw in the fact that they are making judgement calls for depth. That alone would require a block as there is no other way to determine depth without it.
Regards,
Gerald
China is the same as many other countries as they have national standards that they have to comply with. You should ask for the standard (which will be designated as a GB code). If you cannot read Chinese you should get it translated otherwise, to be honest, you are wasting your time and your company's money being there.
First - thanks for all the answers, I appreciate the help =)
Then to answer and clarify a bit the situation.
The inspections were on large cast steel parts (shafts, tyres, press rollers ...) using a straight beam probe and a analogic or a electronic device. In most cases it was the analogic and in these cases, especially for large parts, they were claiming they dont have big enough calibration blocks ...
About the standards, they knew the ones I was using as the company i was working for has been a regular customer and they have all the documentation in english and chinese.
As I have said, their judgement was based on a chart they have been using for years and years, telling them that a given % of the screen height peak and the depth of the flaw would be enough information to calculate the size of the defect. This method is way too different from what i learned and it is just impossible to cross check what they are doing. Some other inspector, foreign, with long experience, didnt seem to mind but i could never get the catch. I have asked other inspectors as well, and all give me answers like you are giving me.
I can speak a bit of chinese and what i have learned with the chinese guys doing the inspections is that their method is their own company's standard which is in accordance to China's standard ... although i havent cross checked that one as i wasnt using them.
So as for now, i know i was right ... hopefully the parts I have inspected didnt show any defect, otherwise it could have been an endless nightmare, debating the pro/against of their method with them with a possibility to reject the product in the end.
Thanks again and I will keep you posted if i can learn more about their methods.
Chang ;)
Id be very much interesting in reading this "standard". Could you post it's publisher and document number?
Unfortunately, I have left it over there, it was too dirty for any copy machine ... I was told I would go back to this supplier, ill try to remember it and get a copy of it.
Hi 803056,
Amigo! u missed that you should visit China this summer Olympic and see how beautiful the city =) the olympic stadium, CCTV building and the world tallest building in shanghai =). I don't think they are stupid.
Regards
Joey
I think the tallest building is in Dubai now. Not to rain on China's parade though, because one of my city's best imports is 7'6" Yao Ming.
I don't believe anyone said they were stupid. Far from it. They have the fastest growing economy in the world and some of them are actually reaping the economic benefits from the industrialization of their country.
We're the dummies. We traded our strong industrial based economy for short term profits and low prices for toys and clothing for low paying jobs in the service sector sweeping floors, flipping hamburgers and shuffling paper. The value of the US dollar is a fraction of what it was and those low prices have evaporated because it takes more de-valued dollars to pay for the good that we've mortgaged our futures to purchase.
Welding rods - made in China, welding gloves - made in China, work boots - made in China, shirt - OK, so Malaysia was thrown a bone on that one.
Best regards - Al
Anyway ...
I was again at a factory to check on a steel slab, 150mm thick .. same story, no calibration block.
As for who is smart and who isnt ? Well, lets face it, people come to china because its cheaper. But why is it cheaper ? Not only because of
the workers being cheaper, but because the quality is cheaper (although it is related i know, especially in welding). So in the end, customers are asking for cheaper and cheaper, but better and better ... it is just not feasable ... when the west will understand that good quality has a price,
then they will get what they pay for. In the meantime, its a waste of money, papers, task-force that companies are ready to pay to get a little cheaper than what they would pay in the west.
But stay this way, otherwise i dont have a job here =)
Some standards will, in fact, let you use the part to be examined itself as a calibration standard. If the chinese companies' customers agree. This part (a shaft for example) may have an inherent dimension that is perfect for this calibration. I think you may have been ill prepared for this assignment (communication wise).
The thing is it was not for a chinese customer, it was not according to JB code (chinese national standard). It was for a european company on ASME code ...
As long as it is a simple slab, it is still doable to do a check and see the overall health of the piece, but when it comes to finding a flaw and analyzing it, without calibration block, it is quite tough ... if not impossible.
By tomas
Date 07-15-2008 10:14
Yes, some ASME codes will allow calibration on part to be inspected. However, using a backwall echo as a reference reflector seems, well, you may as well just put a blindfold on. If this is what they are doing to size flaws then tell them "no tiki, no laundry"!
By ndeguy 
Date 08-08-2008 10:30
Edited 08-08-2008 10:38
Chang
Sorry to come so late - hopefully better than never. First I envy your trips to China - never had the good fortune to be visit that ancient and enormous country - I certainly dont agree with some of the vitriol demonstrated against China on this forum - but then its human nature to be afraid of that which we dont understand.
Crackerbarrel philosophy over - could the local techs scrap of paper be a DGS (Distance-Gain-Size) diagram displaying a series of curves representing the response from a backwall and different diameter flat-bottomed holes? In German - originating country of the DGS system its known as AVG diagram. Very simply, each probe and material velocity has its own diagram. For straight-beam probes you set your sensitivity from the backwall of the item and then read off the difference between the response from the indication at the sound path to that of the backwall at the same soundpath to give you the equivalent reflector size.
The chart may have been those dB differences taken from the curves reduced to a simple chart. I used to work in Germany and I had such a chart produced from the curves where everything below a certain equivalent reflector size (e.g. 2mm diameter flat-bttomed hole) was acceptable, so the chart quickly told you the difference between the indication dB amplitude and that of the equivalent reflector to judge whether it was reportable or not.
I agree with Joe...you can find discontinuities, but how do you know when you find something if it is acceptable or not, if you haven't calibrated the machine to a set standard? For any UT inspection done where AWS D1.1 structural welding code is required, that practice will not work at all.
