Types of cracking and detection by Acoustic Emission …hybridpetroleum.com/pdfs/Tipos de...
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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
1)
2)
3)
4)
5)
6)
8)
7)
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
Tipo Descripción
1Crack in the clad interface and
propagates through the circumferential weld bead
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
2 Crack in clad under circumferential weld bead
This type of crack is usually presented, or at least is favored when the drum
undergoes bulging
3 Crack in weld layer under the longitudinal weld bead 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
Tipo Descripción
4 Surface crack in the clad
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
Tipo Descripción
7 Crack in the weld of nozzle
Corrosion occurs on the surface of the clad and is magnified by distortion by temperature changes
8 Crack in the skirt weld (the most common) 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 thatmonitoring of the cracks that connect tothe shell are made using acousticemission, without removing the drumoperation.
• It must inspect 100% of all welds andclad using volumetric inspection acousticemission
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
Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 10
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. 11
Fatigue cracks in circumferential welds of coking drums, can
be detected by Acoustic Emission from the beginning, before
detect for Visual Inspection.
Fatigue Cracks
Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 12
Placement of transducers for AE test
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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. 14
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. 15
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. 16
Case 1
•Cracked skirt attachmentweld
•Cracks in “key hole” slots•Client need to know if andwhen skirt cracks are growing
Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F. 20
Case 2
In‐service monitoring of coke drum for 6 cycles.• Rare design with top derrick supported bytop head by means of a cylindrical skirt.• Significant cracking found at top skirt‐tohead attachment welds• Difficult location to inspect, not planned.
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Case 4
Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F.
Overhead piping system in Coker Unit subjected to vibration induced fatigue cracking
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Conclusions
Ajusco 15, Colonia Portales, Delegación Benito Juárez, C.P. 03300, México, D.F.
• 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