probabilistic assessments for seam cracks

Probabilistic Assessmentsfor Seam Cracks

Jason SkowJan. 29, 2021

1. Crack Model Consortium

2. Probability of Failure for a Defect

3. Sizing Error

2Agenda

ê Improve integrity management of seam weld anomalies• Reduce risk from seam weld anomalies in

low toughness vintage pipe – other models are unconservative

• Reduce cost by avoiding unnecessary digs• Quantify benefits of maintenance actions,

such as pressure changes, hydrostatic tests and in-line inspection

ê Compile vintage pipe fracture toughness test data from across the industry

ê Enable Consortium members to present a united front to regulators

3Crack Model Consortium

ê An improved version of the PRCI MAT-8 model for seam weld anomalies:• realistic crack front profiles – better accuracy• predict the sharpening of blunt seam weld flaws

(ex. lack-of-fusion features) – reduced conservatism• crack geometries that deviate from hoop stress plane

(ex. hook cracks)ê The most comprehensive database of vintage pipe fracture toughness in the industry

ê ILI tool performance characterization: probability of detection (POD), probability of identification (POI), sizing

ê A software tool that:• implements a probabilistic version of the new PRCI MAT-8 model• evaluates mitigation: hydrostatic pressure tests, pressure reductions, future in-line

inspections • uses cloud computing to speed up calculation time

Deliverables of the Consortium 4

ê The PRCI MAT-8 fracture model represents the best available technology to predict burst pressure in pipe joints with longitudinal cracks.

ê The model will be improved:• Realistic crack front profiles• Fatigue sharpening at the tip of seam weld flaws

ê This modeling framework will continue to be refined, calibrated, and validated in the Consortium.

5Model Development and Analysis

Fatigue initiationRealistic crack front

Defe

ct L

engt

h

Defect Depth

Burst

WallThickness

Leak

7Probability of Failure

Defe

ct L

engt

h

Defect Depth

Burst

WallThickness

Leak


Defe

ct L

engt

h

Defect Depth

Burst

WallThickness

Small Leak


13Sizing Error

Measured Size

ILI S

ize 𝑦 = 𝑚𝑥 + 𝛽 + 𝑒

𝛽

1.5 mm

1.5 m

m

𝑚 =𝑎𝑏

𝑎𝑏

𝑦

𝑥

𝑒

slopeintercepterror

Unity plot

14Sizing Error

2.5

0.9 3.7

15Sizing Error

ê Model produces regression lines that could describe the data we have

ê Thousands of regression lines were calculated, only 50 are shown.

ê Lines close to the center are more likely – Intervals are calculated from these

ê Each model parameter is a distribution

AbrahamWald (1902-1950)

16Wald’s Memo

17Engines: 1.1 bullets per ft2

Fuselage: 1.7 bullets per ft2

Rest of the plane: 1.8 bullets per ft2

18Questions?

probabilistic assessments for seam cracks

Documents