Maintenance of buried corrugated steel bridges in … · Maintenance of buried corrugated steel...

Maintenance of buried corrugated steel bridges

in regional Victorian railway

By: Ali Chaboki- V/Line

Principal Engineer – Structures

Network Engineering – Asset Management

8th Australian Small Bridges Conference – 2017

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Introduction

About 400 buried corrugated steelpipes (Armco- trade mark) have beeninstalled in the V/Line network in 129locations

They were a cost effective solution forthe railway back in the 70s and 80s

Most are considered to be nearingtheir expected life

The issue with most locations is the zinccoating loss and corrosion has started

The asset management of these pipesand assessment of their reliability isdiscussed in this presentation

8th Australian Small Bridges Conference - 2017

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Topics V/Line network

Armco pipes in the V/Line network

Armco pipes – Asset management perspectives

Corrosion rate in zinc Layer and steel

Critical thickness/section loss

Case study- Morwell River

Remediation and replacement of corrosion-damaged pipes

Conclusion

8th Australian Small Bridges Conference – 2017

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V/Line


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• V/Line is largest regional public transport operator, in 2016-17 more than

19.3 million train and coach passenger trips were taken

• In addition to being a passenger service operator, V/Line maintains,

3,520 kilometres of rail track used by passengers and freight rail services

• About 1200 bridges and 5000 culverts are being maintained by V/Line

Facts about the ARMCO pipes in V/line network They were a cost effective solution for the railway back in the 70s and 80s

Number of locations: 129 locations, 400 pipes

Total Area : 41,000m2 – now 28,000 m2

Biggest Diameters : 5.5 meters

Longest pipe : 60 m (Parwan Creek)

Minimum diameter 0.6 m

Thickness 3 -5 mm

2…15,071

m2

Area of Armco pipes in the

V/line Network (2010)

Total Area (41,284 m2)

Pas…8th Australian Small Bridges Conference - 2017

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6,245

4,5814,860

11,446

3,2202,946 2,830

1,4211,125

458 339

1,058

151 217 183 75 34 68 26

4,888

3,187

2,362

8,119

2,4622,122

574

1,4211,124

4580

1,059

151 2170 75 0 68 26

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

Arm

co

pip

e t

ota

l A

rea

(m

2)

Line section

Line vs Armco pipe Area

original Area

remained Area

Facts about the ARMCO pipes in V/line network – cont’d

Risks to effective asset management

Not Knowing What You Have

Under Maintenance

Improper Risk Management

Improper Asset Lifecycle Management (ALM)


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An appropriate and accurate residual life prediction for an asset is

essential for cost effective and timely maintenance planning and

scheduling.

How Armco pipes fail

Consequences of failure

Likelihood of failure

Residual capacity

Effect of corrosion and section loss of their reliability

AM- Asset Management Perspectives

Assessment and evaluation of the rusted pipes:

Most are considered to be nearing their expected life –nominally between 30 to 50 years depending on environmental conditions.

The actual condition information of Armco pipes is less than accurate.

After a sudden line closure in 2013, because of an urgent defect, to manage the risks, we considered the more precise assessment, more frequent assessment


Possible Defects

Zinc coating loss

Rusting, corrosion and delamination specially at the invert

Severe deformation, bulging and out of roundness

Undermining of the track formation

due to corrosion, the moment of inertia and the cross-sectional area of the

wall are decreased with a resulting reduction in pipe strength.

In addition, this will increase the deformation of the pipe and soil under the

sleeper.

Risk management

• More effective assessment- more frequent inspection

• Life extension – asset life management

• Rehabilitation of defective pipes (short term, mid term and long term

mitigation and remedial plan)

Defects : zinc coating loss3 different exposures

Atmospheric exposure 1.5 μm/y - AS/NZS 4680

Exposure to water and sediment mostly at invert – to be discussed AS 2041

Exposure to fill material behind the pipe 2-4 μm/y - AS 2041 - depends on the soil PH, drainage


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Discussion : Exposure to water and

sediment : 25 to 30 years after installation of pipes, corrosion appeared on their invertZinc coating loss is about 3- 5

microns/year -75-micron initial thickness

based on AS 2041, “the invert of the structure below the usual waterline may, under certain conditions, be subject to abrasion and corrosion.”

NDT-Thickness assessment- Report sample


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Corrosion rate of exposed steel

Original

thickness

Corrosion

later

thickness

Zinc layer

loss

Expected

life of the

zinc layer

Corrosion

rate of bare

steel

Expected time to

loose 25% of the

section

Estimated Total

effective lifetime

3 mm 75- 85

micron

3 -5 micron 25-30 years 40-50

micron

12-15 years 35-45 years

5 mm 85 micron 3 -5 micro 25-30 years 40-50

micron

25-35 years 50-65 years


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• Residual lifetime? • Reliability of assets• Risk

The corrosion of bare unprotected steel without any protection is about 40-50 micron per year-

Critical thickness/section loss: Case study- Morwell River


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Critical thickness/section loss: Case study- Morwell River


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Thickness Buckling

load (kn)

Factor of

safety

4 mm 800 2.5

2.5 – lower part 500 1.3

1 mm lower part 210 0.7

Failure mode 1: Severely deformed and weak pipe:


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Failure mode 2: Major crushing

Maximum allowable section

loss

Based on the investigation, the factor of safety varies

from asset to asset, however, maximum 25% section

loss of thickness in large area can reduce the pipe

hoop and flexural strength about 40%.

Pipes have been designed using ASD. Factor of safety

is about 60%

However, is railway industry, dynamic factor load will

reduce this safety margin.


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Possible Remedial ActionsTemporary props

Plastic lining (Spiral or sprayed)

Polyvinyl Chloride Sleeve

Fold and Form

New Steel Plate

Relining with a pipe


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3 Major Remedial options V/line used in the past

1: Half/Invert Lining with reinforced shotcrete


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3 - Major Remedial Options we used in the past

2: Full lining with reinforcement shotcrete +

shear connectors- large culverts (Dia > 2 m)


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3 - major Remedial Options we used in the past

Replacement of the pipe with concrete pipes – Dia <2 m


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Long term planning

More effective Inspection and Assessment – ultrasonic and more

frequent inspections- NIWI-2707.10

Risk assessment

Plan to manage the risk including the replacement of

medium and small ones and lining of small ones


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Thank for Your Attention


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Any question ?

Maintenance of buried corrugated steel bridges in … · Maintenance of buried corrugated steel...

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