CONAM Inspection of Furnace Radiant Tubes

Post by **qaisarabbas** » 22 Aug 2010, 17:22

We have been historically carrying out Conam (External Ultrasonic Inspection) of radiant tubes of our primary reforming furnace being catalyst within the tubes. The results of this inspection are reported in Creep grades (A,B,C,D) relevant to deterioration stages. The material of these tubes is HP Modified. Although the design life (10,000 Hrs) has been passed away, yet we have a consistent conam data and there are no tubes in grade C or D.

Now for next turnaround, the same service provider is proposing External Eddy Current Inspection instead of traditional conam inspection (UT based). He is claiming Eddy Current Testing as the better alternative of Ultrasonic Testing at later stage of tubes operating life for detection of voids & creep cracks.

I would like to know such experience by others and suggestion in this regard.

Thanks in advance,

Regards - Qaisar Abbas

ben · Post by **ben** » 25 Aug 2010, 06:41

In general, you must consider an H-Scan system which is an automated system combining ultrasonic attenuation, eddy current, ultrasonic thickness, and diametrical measurement.
This technique will detect creep damage and micro-fissuring. Additionally, significant diametrical growth is another sign of creep, although alloys like HK40 will fail in creep with little bulging whereas HP modified microalloyed tubes can bulge as much as 10 to 12% before retirement. They can also fail in creep with minimal deformation if stresses are high or from thermal stress or cycling.
Radiography is best used as a confirmation for creep cracking where advanced micro-fissuring is present, but not as the only method.
In short go for H-scan this time around and you would be getting much advanced inspection results.

mechcolor · Post by **mechcolor** » 25 Aug 2010, 07:15

I would like to add some of my comments:

1. Creep damage being the most likely to occur damage in reformer tubes must be looked for from its start.

2. Creep in the tube starts from isolated voids then to oriented voids which with the passage of time becomes microfissures then macro cracks and finally give up to the surface of the tube.

3. Now this whole process of creep failure must be detected at the right time even before isolated voids start to appear as oriented voids or generation of micro cracks starts near the end of tube life.

4. Interestingly, both ultrasonics and eddy current techniques are unable to detect for isolated voids even oriented voids also. These techniques are only useful for detection of micro crack growth and obviously macro cracks (which radiography can also pick up).

5. The option left to detect creep phenomenon is to select advanced techniques available in the market or to carefully select the frequency of inspection whether you are going for ultrasonic only or eddy-current / ultrasonic combination.

aterao · Post by **aterao** » 12 Nov 2010, 18:07

It is good that you have crossed 10 yrs.. tell me did you encounter any tube failure mid way?? API says usually 5% tube fails before reaching its design life... If there is no failure, hats off to your operation & inspection guys... you are doing a good job.. & call back CONAM and say no to 'H'SCAN..

piiengineers · Post by **piiengineers** » 15 Nov 2010, 07:18

Eddy current test is not good for HP Mod material due to high mangenetic permeability.Better to continue with UT which is proven for the past 30 years.

regards,

Post by **qaisarabbas** » 17 Nov 2010, 07:37

Thank you for value addition by ben, mechcolor, aterao & piiengineers.

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