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Time to Failure Module

Given pipe and soil properties, loading and corrosion patch geometry, the Time to Failure Module is capable of predicting the actual hoop (maximum) tensile stress in the pipe. Given corrosion rates, the Time to Failure Model can:

  • Predict the time window from current pipe condition to when a failure occurs.
  • Determine the critical crack length for a possible burst based on fracture mechanics criterion.
  • Determine the type of failure (leak or burst) caused by corrosion.

When a leak rather than a burst occurs, the Time to Failure Module allows the user to further assess the potential burst failure of corroded cast iron pipes caused by pressure transients and determines the time window for leak before break. The Time to Failure Module also incorporates the analysis of uncertainty of key physical parameters and predict the probability of failure and hazard rate over the specified number of years.

Time to Failure Module Workflow
Pipe Material: Host pipe material type. This includes metallic pipes, cement pipes, etc. In the Monash Pipe Evaluation Platform, the following pipe materials are implemented: Cast Iron (CI, CICL), Asbestos cement (AC) and Mild Steel (MS, MSCL).

Accepted Values: CICL, CI, MS, MSCL

(Click to see User Manual - Pipe failure analysis for more information)
Pipe segment installation year: Construction year of the pipe, burial year of the pipe or pipe installation year.

Accepted Values: 1800 to 2021

(Click to see User Manual - Pipe failure analysis for more information)
Pipe nominal diameter (mm): Internal diameter of the pipe. Typically, the nominal diameter is expressed in mm conveniently rounded to roughly the manufactured internal diameter, however the imperial terms use inches.

Accepted Values: 0 > D

(Click to see User Manual - Pipe failure analysis for more information)
Traffic load (kN): Indicated by the wheel load. Click to see the image A buried pipe under internal pressure and traffic load for more information.

Accepted Values: 0 ≤ W < 100 kN
Diagram of loading

(Click to see User Manual - Pipe failure analysis for more information)
Maximum allowable pressure (kPa): The maximum pressure in the pipe taking into account surge pressure. Click to see the image Pressure explanations for more information.

Accepted Values: 0 ≤ Pmax
Diagram of pressure types
(Click to see User Manual - Pipe failure analysis for more information)
Soil Type: The soil type names are from AS 4419 (2018). The users can select a soil type from the list and the soil properties will be prefilled. Soil type could be any of the following soils:

Accepted Values: sand, loamy sand, sandy loam, fine sandy loam, loam, silty loam, sandy clay loam, fine sandy clay loam, clay loam, silty clay loam, sandy clay, light clay, silty clay, medium clay, heavy clay

(Click to see User Manual - Pipe failure analysis for more information)
Advanced Parameters Click to show
Pipe Properties
Pipe nominal wall thickness (mm): Original wall thickness. Click to see the image Cross section of a corroded pipe for more information.

Diagram of corrosion
Accepted Values: 0 < Tn

(Click to see User Manual - Pipe failure analysis for more information)
Estimated external uniform corrosion (mm): Pipe wall thickness reduction caused by external corrosion. Click to see the image Cross section of a corroded pipe for more information.
Diagram of corrosion
Accepted Values: 0 < Text < Tn

(Click to see User Manual - Pipe failure analysis for more information)
Pipe wall thickness reduction caused by internal corrosion. Click to see the image Cross section of a corroded pipe for more information.

Diagram of corrosion
Accepted Values: 0 < Tint < Tn - Text

(Click to see User Manual - Pipe failure analysis for more information)
Pipe wall thickness allowing for uniform corrosion (mm): Actual pipe wall thickness after accounting for external and internal corrosion. Note that T = Tn - Text - Tint . Click to see the image Cross section of a corroded pipe for more information.

(Click to see User Manual - Pipe failure analysis for more information)
Burial depth (mm): The depth from the ground surface level to the crown of the pipe. Click to see the image A buried pipe under internal pressure and traffic load for more information.

Accepted Values: 0 ≤ D ≤ 10000 mm
Diagram of loading
(Click to see User Manual - Pipe failure analysis for more information)
Ultimate tensile strength (MPa): Maximum stress that a material can withstand while being stretched or pulled before breaking.

Accepted Values: 0 < σt

(Click to see User Manual - Pipe failure analysis for more information)
Pipe elastic modulus (GPa): Also known as Young’s Modulus or Modulus of Elasticity. It is the slope of stress–strain curve in the elastic deformation region for the pipe material. Note: for cast iron, 50 ≤ Ep ≤ 250 GPa while for steel, 190 ≤ Ep ≤ 210 MPa

Accepted Values: 50 ≤ Ep ≤ 300 GPa

(Click to see User Manual - Pipe failure analysis for more information)
Poisson's ratio: Measurement of deformation in pipe material in a direction perpendicular to the direction of the applied force. Note: for cast iron, 0.21 ≤ νp ≤ 0.26 while for steel, 0.27 ≤ νp ≤ 0.3.

Accepted Values: 0.15 ≤ νp ≤ 0.4

(Click to see User Manual - Pipe failure analysis for more information)
Fracture toughness (MPa√m): Resistance of materials to the propagation of cracks under an applied stress.

Accepted Values: 0 < KIC

(Click to see User Manual - Pipe failure analysis for more information)
Soil Properties
Soil modulus (MPa): An elastic soil parameter used in the settlement, compression or movement of soils. It is the slope of stress–strain curve in the elastic deformation region for the soil.

Accepted Values: 0 < Es < 300 MPa

(Click to see User Manual - Pipe failure analysis for more information)
Lateral earth pressure coefficient: The lateral earth pressure coefficient at rest and can be calculated by: k = ( 1 - sin⁡∅ ) where ∅ is the soil friction angle.

Accepted Values: 0 ≤ k ≤ 1

(Click to see User Manual - Pipe failure analysis for more information)
Soil unit weight (kN/m3): The ratio of the total weight of soil to the total volume of soil. Soil unit weight or bulk unit weight is the unit weight of soil and varies for different soil types. The values are typically between 15 kN/m3 to 20 kN/m3.

Accepted Values: 0 < γs ≤ 30 kN/m3

(Click to see User Manual - Pipe failure analysis for more information)

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