Advanced NDTs for Inspection of Catalyst Tubes of Reformer Furnace

CATEGORY: NDT – NON-DESTRUCTIVE TESTING
Asia Pacific Conference on Non-Destructive Testing (APCNDT 2013), Mumbai, India, November 18-22, 2013
Advanced NDTs for Inspection of Catalyst Tubes of Reformer Furnace
Gautam Das (1), D. Dutt (2) , Kaushik Boral (3), Gourab Seal (4)
dasgautam@indianoil.in
duttad2@indianoil.in
boralk@indianoil.in
sealg@indianoil.in
1 Dy. General Manager (Inspection), Haldia Refinery, Indian Oil Corporation Limited
2 Chief Inspection Manager, Haldia Refinery, Indian Oil Corporation Limited
3 Sr. Inspection Manager, Haldia Refinery, Indian Oil Corporation Limited
4 Sr. Inspection Engineer, Haldia Refinery, Indian Oil Corporation Limited
Abstract
The Reformer tubes used in the refining, petrochemical and fertilizer industries are manufactured by the centrifugal casting process of heat-resistant austenitic alloys such as HK -40, HP-40, and HP -Niobium modified materials. These tubes are prone to various degradation mechanisms like creep, hydrogen attack, corrosion, fatigue etc and the useful life of these tubes is largely dependent on operation and maintenance. Also, as these tubes are operated at severe conditions, the determination of the serviceability of these tubes beyond their design life of 100,000 operating hours is of vital importance. A range of NDTs are presently available which provides the opportunity to improve the reliable service life of reformer tubes. Thus, rather than to remove tubes from service for sectioning and metallurgical examination at every plant turnaround, it is advantageous to use NDE techniques to screen the tube condition for environmental damages such as creep.
Proper determination of tube condition and its ultimate life requires specific in-situ examinations. Reformer tube condition can currently be assessed in-situ by qualitative NDE assessment using various techniques like Diametrical Growth Measurement (diameter change with creep in some cases), Wall Thickness Measurement (apparent decrease in wall thickness with creep), Replication (final stages of creep damage; i.e., macro-cracking), Radiography (final stages of creep damage; i.e., macro-cracking), Eddy Current Testing (responds to chromium migration due to overheating and conductivity changes) and Ultrasonic Testing (responds to attenuation and scattering).
Extensive trials have been conducted to determine the viability and optimization of the various techniques and it has been established that the tube condition cannot be conclusively determined by one stand-alone technique, but by effective combination of multiple techniques depending on the degree of damage. One such combined advanced NDE technique is 'H' SCAN Technology, which is now widely used for damage assessment of Reformer tubes. Another breakthrough technology in this field is Laser Optic Tube Inspection System (LOTIS). The advantages and disadvantages of each technique, when compared against each other, reduces the occurrence of false calls, improves tube condition assessment and can increase overall furnace reliability.
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