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

Input Pipe Parameters Input Defect Characteristics Pipe Stress Analysis Failure Prediction

Step II: Input Defect Characteristics

Input Type

Import File Manual Input

Use Scanned Pipe Wall Thickness Map (Patch Identification)

Browse:

?

Scanned Pipe Wall Thickness Map: Please upload the CSV file of the scanned thicknes map. csv file should be column (a): coordinates along circumferential (mm), row (1): Coordinates along pipe length (mm), and contents (row 2 and column b): penatration depth / wall thickness.

Please see this demo scanned wall thickness map: Trial patch wall loss.csv

(Click to see User Manual - Pipe failure analysis Section 1.1.1 for more information)

y3 mm -

y2 mm -

y1 mm -

|
x1 mm

|
x2 mm

|
x3 mm

|
x4 mm

×

Scanned Wall Thickness Map (Patch Identification)

Show Scanned Map Load Patches

Manually input patch geometry

Patch length (2a)

mm ?

Patch length (2a)

Patch length (2a) measured in mm, as according to the below image.

Note that patch length 2a should align with the pipe axis.

(Click to see User Manual - Pipe failure analysis Section 1.1.1 for more information)

Patch width (2b)

mm ?

Patch width (2b)

Patch width (2b) measured in mm, as according to the below image.

Note that patch length 2a should align with the pipe axis.

(Click to see User Manual - Pipe failure analysis Section 1.1.1 for more information)

Patch depth (c)

mm ?

Patch depth (c)

Patch depth (c) measured in mm, as according to the below image.

Note that patch length 2a should align with the pipe axis.

(Click to see User Manual - Pipe failure analysis Section 1.1.1 for more information)

Add Patch data

Step III. Nominal Stress Calculation

	Patch geometry [2a, 2b, c] (mm)	Nominal (hoop) stress (MPa)	SCF	Actual (hoop) stress (MPa)	Local Failure or Leak?	a	b	c

Re-calculate All Delete Row Clear All

Corrosion Parameters

Radial corrosion rate (mm/year) r_sv

?

Radial corrosion rate (mm/year): Increment of corrosion patch depth per year. Corrosion patch depth after t years c_t=c₀+r_sv×t, where c₀ is the current patch depth.

(Click to see User Manual - Pipe failure analysis Section 1.2.2 for more information)

Lateral extension rate (mm/year) r_sh

?

Lateral extension rate (mm/year): Increment of corrosion patch length and width per year. Corrosion patch half-length and half-width after t years can be calculated by a_t=a₀+r_sh×t, b_t=b₀+r_sh×t respectively, where a₀ and b₀ are the current half of the patch length and half of the patch width respectively.

(Click to see User Manual - Pipe failure analysis Section 1.2.2 for more information)

Compute Time to Failure

Step IV: Time to Failure Results

Time to Failure (years)

-
Years

Failure Type

-

Additional Output:

Crtitical Patch Length (2a')
- mm

Crititial Patch Width (2b')
- mm

Critial Patch Depth (c')
- mm

Critical Crack Length (L_c)
- mm

  View PDF   Back to Pipe Parameters   Go to Leak to Break

  Compute Probability of Failure   Go to Liner Selection   Exit

  Pipe Properties Mean value Deg. of uncertainty

Pipe nominal wall thickness (mm) T_n

?

Pipe nominal wall thickness (mm): Original wall thickness. Click to see the image Cross section of a corroded pipe for more information.


Accepted Values: 0 < T_n

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

Estimated external uniform corrosion (mm) T_ext

?

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.

Accepted Values: 0 < T_ext < T_n

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

Estimated internal uniform corrosion (mm) T_int

?

Estimated internal uniform corrosion (mm): Pipe wall thickness reduction caused by internal corrosion. Click to see the image Cross section of a corroded pipe for more information.


Accepted Values: 0 < T_int < T_n - T_ext

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

Pipe wall thickness allowing for uniform corrosion (mm) T

?

Pipe wall thickness allowing for uniform corrosion (mm): Actual pipe wall thickness after accounting for external and internal corrosion. Note that T = T_n - T_ext - T_int . 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)

None Low Moderate High

Pipe nominal diameter (mm) D

?

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)

None Low Moderate High

Burial depth (mm) H

?

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

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

None Low Moderate High

Ultimate tensile strength (MPa) σ_t

?

Ultimate tensile strength (MPa): Maximum stress that a material can withstand while being stretched or pulled before breaking.

Accepted Values: 0 < σ_t

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

None Low Moderate High

Pipe elastic modulus (GPa) E_p

?

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 ≤ E_p ≤ 250 GPa while for steel, 190 ≤ E_p ≤ 210 MPa

Accepted Values: 50 ≤ E_p ≤ 300 GPa

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

None Low Moderate High

Poisson's ratio v_p

?

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 ≤ ν_p ≤ 0.26 while for steel, 0.27 ≤ ν_p ≤ 0.3.

Accepted Values: 0.15 ≤ ν_p ≤ 0.4

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

None Low Moderate High

Fracture toughness (MPa√m) K_IC

?

Fracture toughness (MPa√m): Resistance of materials to the propagation of cracks under an applied stress.

Accepted Values: 0 < K_IC

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

None Low Moderate High

Corrosion Parameters

Radial corrosion rate (mm/year) r_sv

?

Radial corrosion rate (mm/year): Increment of corrosion patch depth per year. Corrosion patch depth after t years c_t=c₀+r_sv×t, where c₀ is the current patch depth.

(Click to see User Manual - Pipe failure analysis Section 1.2.2 for more information)

None Low Moderate High

Lateral extension rate (mm/year) r_sh

?

Lateral extension rate (mm/year): Increment of corrosion patch length and width per year. Corrosion patch half-length and half-width after t years can be calculated by a_t=a₀+r_sh×t, b_t=b₀+r_sh×t respectively, where a₀ and b₀ are the current half of the patch length and half of the patch width respectively.

(Click to see User Manual - Pipe failure analysis Section 1.2.2 for more information)

None Low Moderate High

  Soil Properties Mean value Deg. of uncertainty

Soil modulus (MPa) E_s

?

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 < E_s < 300 MPa

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

None Low Moderate High

Lateral earth pressure coefficient k

?

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)

None Low Moderate High

Soil unit weight (k/m³) γ_s

?

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 < γ_s ≤ 30 kN/m³

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

None Low Moderate High

Loading

Traffic load (kN) W

?

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


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

None Low Moderate High

Maximum allowable pressure (kPa) P_max

?

Maximum allowable pressure (kPa): strong>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 ≤ P_max

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

None Low Moderate High

Corroded Patch Geometry

Patch half-length (mm) a

?

Patch half-length (mm):

(Click to see User Manual for more information)

None Low Moderate High

Patch half-width (mm) b

?

Patch half-width (mm):

(Click to see User Manual for more information)

None Low Moderate High

Patch depth (mm) c

?

Patch depth (mm): Patch depth (c) measured in mm, as according to the below image.

Note that patch length 2a should align with the pipe axis.

(Click to see User Manual - Pipe failure analysis Section 1.1.1 for more information)

None Low Moderate High

Additional Parameters

Curent age (years)

?

Current age (years): The period of time from pipe installation to current time (years). The input value should be non-negative.

(Click to see User Manual - Pipe failure analysis Section 1.3.1 for more information)

Decay curve for next # years

?

Decay curve for next # Years: The period of time the Decay Curves (Probability of Curves) will be predicted for (years). The input value should be non-negative.

(Click to see User Manual - Pipe failure analysis Section 1.3.1 for more information)

   Back Compute Probability of Failure (Hazard Rate)

Results

Probability of Failure

-
Hazard Rate

Decay Curve for Next # Years

Locate by Pipe ID:

(Found in pipe library) (Not found in pipe library)

Pipe material:

?

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)

CICL CI MS MSCL

Pipe segment installation year:

?

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): DN

?

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) W

?

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


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

Maximum allowable pressure (kPa) P_max

?

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 ≤ P_max

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

Internal (minimum) Pressure (kPa) P_min

?

Internal (minimum) Pressure (kPa): The minimum pressure in the pipe taking into account surge pressure. Click to see the image Pressure explanations for more information.

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

Soil Type:

?

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)

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

Advanced Parameters Click to show

Pipe Properties

Pipe nominal wall thickness (mm) T_n

?

Pipe nominal wall thickness (mm): Original wall thickness. Click to see the image Cross section of a corroded pipe for more information.


Accepted Values: 0 < T_n

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

Estimated external uniform corrosion (mm) T_ext

?

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.

Accepted Values: 0 < T_ext < T_n

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

Estimated internal uniform corrosion (mm) T_int

?

Pipe wall thickness reduction caused by internal corrosion. Click to see the image Cross section of a corroded pipe for more information.


Accepted Values: 0 < T_int < T_n - T_ext

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

Pipe wall thickness allowing for uniform corrosion (mm) T

?

Pipe wall thickness allowing for uniform corrosion (mm): Actual pipe wall thickness after accounting for external and internal corrosion. Note that T = T_n - T_ext - T_int . 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) H

?

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

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

Ultimate tensile strength (MPa) σ_t

?

Ultimate tensile strength (MPa): Maximum stress that a material can withstand while being stretched or pulled before breaking.

Accepted Values: 0 < σ_t

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

Pipe elastic modulus (GPa) E_p

?

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 ≤ E_p ≤ 250 GPa while for steel, 190 ≤ E_p ≤ 210 MPa

Accepted Values: 50 ≤ E_p ≤ 300 GPa

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

Poisson's ratio v_p

?

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 ≤ ν_p ≤ 0.26 while for steel, 0.27 ≤ ν_p ≤ 0.3.

Accepted Values: 0.15 ≤ ν_p ≤ 0.4

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

Fracture toughness (MPa√m) K_IC

?

Fracture toughness (MPa√m): Resistance of materials to the propagation of cracks under an applied stress.

Accepted Values: 0 < K_IC

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

Soil Properties

Soil modulus (MPa) E_s

?

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 < E_s < 300 MPa

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

Lateral earth pressure coefficient k

?

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) γ_s

?

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 < γ_s ≤ 30 kN/m³

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

Step 2 : Proceed to Failure Analysis

Step V: Estimate Remaining Life after Leak due to Pressure Transient

Pipe Properties

Fracture toughness (MPa√m) K_IC

Loading

Maximum allowable pressure (kPa) P_max

?

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 ≤ P_max

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

Minimum internal pressure (kPa) P_min

?

Minimum internal pressure (kPa): The minimum pressure applied the pipe due to recurring surge pressures. Click to see the image Pressure explanations for more information.

Accepted Values: 0 ≤ P_min

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

Fatigue Parameters

Number of recurring surge pressure cycles per day n_PC

?

Number of recurring cyclic surge pressure cycles (/day): Number of pressure transients per day are used to determine if the host pipe or liner will fail from fatigue. Consistent pressure transients may reduce the life of the host pipe and liner. The default value is set at 2 per day, for pump start-up and pump shutdown.

Accepted Values: 0 ≤ n_PC

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

Fatigue constant m_f

?

Fatigue constant: A fatigue constant in Paris’ law. This fatigue constant is unitless.

Accepted Values: 0 < m_f

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

Fatigue constant (m/cycle) C_f

?

Fatigue constant (m/cycle): A fatigue constant in Paris’ law. Units are in m/cycle.

Accepted Values: 0 < C_f ≤ 0.00001 m/cycle

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

Estimated remaining life after leak due to pressure transient

Years

  Back Compute Time from Leak to Burst