³gral. san martín austral gas pipeline
TRANSCRIPT
Rupture location
Pipeline: Gral San Martín Austral
Section: Río Seco - Bosque Petrificado
Diameter: 30” Year of Construction: 1973 Material: API 5lx52
Thickness: 8,74 mm
Accident
Characterization of
the Defect
Length: 138 mm
Maximum Width: 33 mm
Remaining thickness: 2,8 mm
Depth: 68 % of nominal depth
Two halves of the defect
were removed and then
aligned together to re-
create the original defect
prior to the rupture.
Analysis of the Defect
Section A seen through microscope Both defect faces
Close up external view of the
upper half of the fracture
surface.
It is believed that the fracture
initiated in this area. There was no evidence along
the remaining pipe surfaces of
wall thinning, due to gouging.
This suggest that the origin of
the failure has been an external corrosion defect.
Analysis of the Material
Steel microstructure analysis
100 μm
Lengthwise Photomicrographs
Photomicrographs without development of grain
Transversal Photomicrographs
50 μm 50 μm
Elongated manganese sulphide
inclusions are observed, in much
greater quantities that in other steels
with similar properties.
Field inspection
Low ground level
Temporary waterways
High chloride concentration
Area water pH: 6.1
High conductivity
Soil features
VERY AGRESSIVE SOIL
Running of MFL (Magnetic Flux Leakage Tools)
In- line inspection Running
Comment Depth Length
EXT ML 26% 129
EXT ML 19% 31
Without record
2007
1997
1994
In February 07, we ran a MFL
magnetic tool.
However, in April 07, we had a pipe
failure.
The original defect had been
reported as not significant.
Failure Conclusion
The origin of the rupture initiated in an axially oriented defect.
The defect had been produced by local corrosion, plus the combination of the
factors listed below:
Very aggressive clayish soil with high chloride concentration.
Coating Failure
Lack of proper cathodic protection for this type of field.
The inclusions in the material encouraged the occurrence of “preferential
corrosion” in lengthwise direction.
As the defect was axially oriented, the MFL tool could not characterize it
properly
Longitud del Defecto
An
ch
o d
e D
efe
cto
10 12 13 14 11
Defect
Gto. Austral
MFL
MFL tools CANNOT take proper measurements
of axial defects
TFI
Transversal Magnetic Flux Tool
Longitud del Defecto
An
ch
o d
e D
efe
cto
10 11 12 13 14
The transversal magnetic flux tool accurately measures axial defects
Defecto
Gto. Austral
MFL vs. TFI
Magnetic signals obtained for the same axial defect, with both MFL
and TFI tools
Axial Defects
Axial defect.
The magnetic signal obtained with the TFI tool, is larger than the
signal given by the MFL tool.
MFL SIGNALS TFI SIGNALS
MFL + TFI Combination of both technologies
The combination of
MFL + TFI technologies
improves accuracy in
the assessment of the
dimension of the
defects.
Run TFI
In Agost 07 we ran a TFI tool in the section where we had had
the explosion and we have detected another critical defect.
Large Depth Large Depth Large Depth
82 60% 216 75% 85 81%
Mar-07 Jul-07 Ago-07
TFI FIELDMFL
86mm
216mm
The individual corrosion signal
relates to boxes
According to the shape and magnitude of the signal, the analysis software
determines: depth, length, and width of each box
Cluster vs Box
The global dimension of the corrosion area corresponds to clusters. These clusters
are defined by using an interaction rule. The ILI reports clusters information.
The MFL tool is limited to determine the correct size of boxes
Box
Cluster