FAILURE CAUSES

“Gral. San Martín Austral” Gas Pipeline Río Seco – Bosque Petrificado Section

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

Rupture Dimensions

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

MFL

Circumferential Defects

TFI

Axial Defects

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

“Gral. San Martín Austral” Gas Pipeline Río Seco – Bosque Petrificado Section

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