TOFD 2

[Naif1981]

Hi
If u have 2 choose between TOFD (wich is now approved by ASME codes) and normal RT or UT
which one u will choose?
4000 m3 vessel (cylindrical-mounded for LPG)

does any one choose TOFD before?

 

[metengr]

Naif1981;
LPG service for new construction, I would use RT or conventional UT because you have no concerns with creep damage in service that would require periodic inspection.

I normally use TOFD phased array for in-service condition assessment of pressure retaining items subjected to creep where you are looking for subsurface creep cavitation damage in weld and BM heat affected zones.

 

[gr2vessels]

Naif,
There is a lot more to it than a simple choice;- the manual UT or even mechanised UT it is very tedious operation and require a highly specialised operator, to detect any flaw. Then you have to investigate each flaw, to ensure the type, size and location are within the limits. You can only record the detected flaws, hoping you haven't missed any.
The TOFD is a continuous operation which detects every flaw, size and location AND is continuously recording the process, like a continuous film. Not step by step like the UT.
I can imagine the amount of weld you have to inspect, so I would suggest an automatic continuous recording of the inspection using TOFD. You'll be saving heaps on time, perhaps on costs also.

 

[Naif1981]

Thank u all
What about RT only instead of TOFD or UT?

 

[gr2vessels]

Obviously, RT. But also, it depends on thickness, materials used, etc...
From your spelling and (not funny) abbreviations, I deduct that you work in India and the values/costs overthere are somehow different that anywhere else. I suspect that performing the most tedious and lenghty NDT's are the least expensive given the number of people which can be allocated to this task, 24/7.
I know however, that the quality of work in India is uncompromised, which ever NDT is performed, hence it makes it difficult to recommend one over the other method.
Still, my preference is for TOFD, being safer for the work environment, accurate and providing a continuous, real-time recording of the inspected seams. Any defect might be repaired during the same shift and the tests can be done while other work is performed on the vessel (no need to isolate the work place for RT or perform the RT overnight, when the vessel is available for inspection).
My two cents...
Cheers,
gr2vessels

 

[Naif1981]

Hi gr2vessels
Thank u, first, i am not from India, I am from Saudi Arabia, and the reason I asked for TOFD and UT, RT, cause I am involved in a big Project In mounded tank with capacity of 4000 m3 (10 Nos) and some bidders suggest the TOFD instead of UT,RT also our consultant recommend this

Last project was same in 2007 but we approved for UT,RT only.
there will be no extra cost if we choose UT,RT but for me I am looking for the best of these exams regardless the cost.

Thank you again for all of you

 

[gr2vessels]

Naif,
Just remember, you are a caring engineer striving to do your best;- the U and R abbreviations belong to the streets, you must upheld the engineering standard of YOU and ARE;- and wear the simbol of engineering by wearing the decent white shirt and tie no matter who and what wear anyone else. That way you will keep one head above everyone else and motivate yourself to lift your standads every day, proud example for the young ones.
Good on you,
cheers,
gr2vessels

 

[ndeguy]

Naif1981

Do you know about the TOFD near- and far-surface dead zones, extent of which depends on set-up parameters and can be minimised by adjustment but never completely avoided. Usually these zones are examined with simultaneous pulse-echo scans of weld root and cap regions.

With regards to TOFD advantages:

Proven superior probability of detection (POD) of planar flaws. If you plan on using a welding process prone to planar flaws, then advanced UT (TOFD/PA) is the way to go.

Finger-printing, every flaw present and not repaired can be monitored through subsequent inspections with a good probability of accurate through-wall thickness measurement.

Records - computerised you could store all the weld files on a few disks giving easy storage and recall compared to the boxes and boxes of flammable radiographs - unless you digitise the graphs.

I dont know the radiation laws in Saudi, but in Europe the essence is that unsealed sources outside of radiation bays are only allowed when there is no alternative - As Low As Reasonably Practical - ALARP. The combination of radiation and chemicals is avoided completely with advanced UT - shame the unwillingnes to change of many owners and manufacturers. Many RT workers are exposed to an unnecessary long term health hazard - hey, he's retired by the time his cancer is diagnosed so who cares!

Sorry it turned into a rant!

 

[stanweld]

TOFD/PA UT has been done on LNG tanks in the USA per API 620 and are currently being done on ASME I Power Boilers and B31.1 piping per Code Case 2235. In terms of schedule/productivity, we believe it superior to RT. Unlike RT, it is performed during normal construction activities and is highly suitable for assuring defect removal in repairs. We still use RT for dissimilar weld joints in boiler components using nickel base welding filler metals. Our AIs' like it as do our Owners'. For TOFD alone, I have required MT of the surfaces on Drums. Refer to ndeguy re near and far surface dead zones.

 

[roca]

gr2vessels:
I think you need to check your spelling..!

 

[gr2vessels]

Yes, I am a bit sloppy sometimes..(however, the standad is not really my standard). I have now included this in the new year resolution. Do we have a spelling checker on the post/reply editor?
Cheers,
gr2vessels

 

[Naif1981]

All of u. Thanks
now I am trying to see our consultant and replay to u.

 

[EngAddict]

gr2vessels, use Google chrome it checks spelling as you type. I think Firefox can do it too..

I can't spell w/o it. The curse of engineers..