Types of cracking and detection by Acoustic Emission on coking drums Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 1
In historical cases have been found various types of cracking on coking drums. These can be classified according to the following schematic drawing. Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 2
Types of cracking founded on coking drums 4) 7) 5) 1) 6) 2) 8) 3) Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 3
Clasification We can give a quick sorting by location: On the walls of the drum a) Where there is welding Metal / Welding Clad / welding b) Where there is not welding Clad c) At the joints of the drum with accessories Nozzles Skirt The description of these failures are discussed below. Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 4
a) On the walls of the drum, where there is welding 1 2 3 Tipo Crack in the clad interface and propagates through the circumferential weld bead Crack in clad under circumferential weld bead Crack in weld layer under the longitudinal weld bead Descripción This type of crack is usually presented, or at least is favored when the drum is suffering from bulging. When the cords of inner and outer welding are aligned This type of crack is usually presented, or at least is favored when the drum undergoes bulging Due to thermal fatigue and bulging Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 5
b) On the walls of the drum, where there is not welding 4 Tipo Surface crack in the clad Descripción Occurs by corrosion on the surface of the clad and is magnified by distortion in the walls due to temperature changes 5 Crack detachment Presented by improper manufacturing process 6 Pitting in the clad Es debida a la corrosión interna Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 6
c) c) At the joints of the drum with accessories 7 8 Tipo Crack in the weld of nozzle Crack in the skirt weld (the most common) Descripción Corrosion occurs on the surface of the clad and is magnified by distortion by temperature changes Presented by thermal fatigue Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 7
Monitoring and inspection It is strongly recommended that monitoring of the cracks that connect to the shell are made using acoustic emission, without removing the drum operation. It must inspect 100% of all welds and clad using volumetric inspection acoustic emission Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 8
Detection of cracks in drums coking by Acoustic Emission Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 9
Objective Applications of Acoustic Emission Test to aid in the evaluation of mechanical integrity and reliability of coking drums in service, out of service or during manufacture Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 10
Fatigue Cracks Fatigue cracks in circumferential welds of coking drums, can be detected by Acoustic Emission from the beginning, before detect for Visual Inspection. Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 11
Placement of transducers for AE test Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 12
Application of AE on drums Coking During Hydrostatic Testing To detect manufacturing discontinuities These are the failures which, eventually, initiate and grow as thermal fatigue cracks Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 13
Distribution of 36 AE transducers on coking drums including the cone (shown in red) Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 14
Acoustic Emission Testing in Service Performed while in service during regular operations. Uses stresses developing during thermal transients at quench and heat up It relies on detecting actual crack growth due to thermal fatigue. Since cycles can be substantially different from each other, 3+ cycles are required to screen the drum. AET can separate ID from OD connected flaws by means of determining when in the cycle, crack growth occurred It provides full coverage of the shell, head and cone, or partial coverage focusing on known problem areas (bulges, skirt, nozzles, etc.) Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 15
Case 1 Cracked skirt attachment weld Cracks in key hole slots Client need to know if and when skirt cracks are growing Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 16
Case 1 Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 17
Case 1 Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 18
Case 1 Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 19
Case 2 In service monitoring of coke drum for 6 cycles. Rare design with top derrick supported by top head by means of a cylindrical skirt. Significant cracking found at top skirttohead attachment welds Difficult location to inspect, not planned. Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 20
Case 2 Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 21
Case 3 22
Case 4 Overhead piping system in Coker Unit subjected to vibration induced fatigue cracking Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 23
Conclusions Detection of active cracks, connected by internal and external diameter, covering 100% of the surface of the drums. Location mapping of areas with active cracks Prioritization of active discontinuities in order to plan appropriately for inspection and repair during downtime Determine the presence and approximate location of manufacturing defects in new coking drums, in order that repairs can be executed properly. Aims to avoid the presence of small defects that can act as "nucleation sites" for future growth of thermal fatigue cracks Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 24