MaxeyGery_revB.pdf

International Pipeline Conference

2012 Willard A. (Bill} Maxey

Distinguished Lecture Series

"Fracture Initiation, Propagation, and Arrest" From

PRCI 5th Symposium on Line Pipe Research

November 1974

W. A. Maxey Battelle-Columbus, US

[Presented on behalf of Bill, by Gery Wilkowski]

Andmore...Athensbursttests ductile and brittle fracture propagation

Andmore... Dentandgougeflaws

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Solutions I tructural ntegrity

And more underwater burst test

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Thenandnow ...........

No computers,no internet,

no digital data acquisition,

no spreadsheets,

no finite element simulations,

just good

old fashion engineering

Introduction and Embellishments

Original paper outline below

Illtryandsayhowsomeofthesedifferenttopicsarestill used today and changes.

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Fracture Initiation Predicting Failure Pressure

Fracture Initiation referred to initiation of ductile fracture during pressurization to burst pressure

Not initiation of subcritical crack growth by fatigue, SCC, etc.

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Used Folias bulging factor for a through-wall crack in a thin shell

Bulging from pressure increased the axial-crack-driving force

From elastic shell-theory analyses, but incredibly works reasonably well in elastic-plastic and limit-load fracture regions!

Still used in many Codes and Standards

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When bulging factor put in Dugdale strip-yield model (also called the lnsec equation), then as toughness approached , then you have the limit-load solution

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Solutions I tructural


Hahn introduced the concept of flow stress as a stress level between yield and ultimate strength for an elastic-perfectly

plastic material, but we still needed practical definition of flow

stress

Maxey statistically determined that flow = yield + 10 ksi , which for the pipe materials at that time was about the same as flow =

(yield + ultimate)/2 used in more recent fracture mechanics models

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Next, needed a practical measure of ductile fracture toughness.

Bill looked at Charpy impact energy as that simple practical toughness measure.

From the full-scale pipe fracture tests with axial through-wall cracks the Charpy energy divided by the Charpy specimen fracture area correlated

incredibly well with the Kc calculated from pipe fracture tests.

This'was'also'called'an'apparent'toughness,'since'it'was'also'known'that there is stable ductile crack growth before burst pressure reached, but

analysis did not do crack growth calculations.

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The axial through-wall-crack model was extended to surface cracks, first by recognizing that the bulging factor for a surface

crack needed to be established.

Bill developed Equation 6 by looking at pipe test data where the toughness was high enough that limit-load should occur.

This formed the technical basis for B31G/RSTRENG, and axial surface crack solutions used in codes and standards throughout the world!

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When he combined all of the different aspects together (bulging, flow stress, toughness, surface cracks), the

resulting solutions was incredibly good!

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Fracture Initiation Leak-Before-Break (LBB)

LBB predictions of axial flawed pipe could also be made by comparing the surface crack failure curves to the through-wall-

crack failure curve.

Surface crack geometries that fail at pressures above the TWC curve are ruptures (breaks).

Failu

re s

tres

s/fl

ow

str

ess

Leak

Break

TWC curve

a/t = 0.9

a/t = 0.25

a/t = 0.1

a/t = 0.5

a/t = 0.75

2c/(Rt)0.5

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Fracture Initiation Transition Temperature

Bill (and Kiefner) presented some interesting pipe test results on how the transition temperature might be different for fracture

initiation than propagation

FPTT = fracture propagation transition temperature

FITT = fracture initiation transition temperature

Althoughhedidntgettoageneralsolutions,thoseresultsand others he developed were used to develop a Fracture Transition

Temperature Master Curve for axial or circumferential surface or

through-wall cracks in pipes and plates.

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The Long Lasting Aspects

The basic axial through-wall and surface cracks solutions are still being used today

B31G/RSTRENG corrosion flaws are the SC limit-load solution

Nuclear piping (ASME Section XI, JSME, French RCCM, German, Russian, etc. codes and standards

API 579 for chemical plant piping

Steam generator tubes

Pressure vessels

Ofcoursesometweakingbeingdone...

J-R curves used for fracture toughness that accounts for change in toughness as the crack grows in a stable manner up to maximum

pressure

Charpy to J-R curve relationships changing with new materials

Examining bulging factors for TWC and SC in elastic-plastic regions, with different SC a/t and 2c/Rt geometries

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Fracture Propagation and Arrest

Perhaps this is the area that Bill is most renown

Brittle Fracture

Not know as well for that work should be

Ductile Fracture

Developer of the Battelle-Two-Curve model

Started with ideal gas equations for lean natural gas

(mostly methane), and expanded to using equation-of-

state software developed by others, i.e., GasDecom

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Brittle Fracture Arrest

Since may old pipe lines only had Charpy data, and very occasionally DWTT data, Bill extended the Irwin-Corten linear-

elastic fracture mechanics solution to a practical brittle fracture

analysis tool.

Crack driving force = G = 0h2R/E Resistance was characterized as the Charpy energy that had the

same shear area as the DWTT at the operating temperature.

Could have used DWTT energy directly, but there was no API standard

to measure DWTT energy (even though most mills do it anyway).

Combining the driving force and resistance for minimum toughness for brittle fracture arrest gives:

CVP*SA%(of DWTT at operating temperature)/Ac = 0h2R/E

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Not only did that separate arrest versus brittle fracture propagation, but Bill also could determine if there was 1, 2, or

more brittle fracture that would propagate axial at the same time

if the toughness was a fraction of the crack driving force.

2 or more cracks 8 or more cracks

These two figures from

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Ductile Fracture Arrest The Two-Curve Method

Bill developed the ductile fracture arrest model currently called the Battelle Two-Curve (BTC) analysis. Bill never called it that, it

was simply the ductile fracture arrest analysis.

So what are these two curves in the BTC model?

There is one curve that represents the gas decompression behavior. That is essentially the crack-driving force

The second curve is a combination of pipe geometry, strength,

toughness, and backfill restraint that Bill developed

BillliketocallthesecondcurveaJ-curvebecauseoftheshape.

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Ductile Fracture Arrest Gas Decompression

Gas decompression needs to be considered since ductile fractures propagate slower than initial acoustic velocity (Va) in gas,

As gas expands is cools and the instantaneous or decompressed acoustic velocity (Vd) decreases since the gas density increases,

Decompressed wave speed of gas is instantaneous acoustic velocity minus outward flow velocity

Initial Va natural gas about 1,300 fps ductile fractures typically 300 to 1000 fps

Ideal gas is isentropic expansion, and Bill used 1D, full-opening steady-state decompression curve

No effects of surface roughness or pipe diameter

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Ductile Fracture Arrest Gas Decompression

Gas decompression analyses became more complicated with different fluids in the pipe

Rich natural gas needs an equation-of-state program to obtain the decompression curve isentropic expansion of the fluid, which

coolsdownanditsdensitychanges. Thedensityisthenusedto

determine the instantaneous acoustic velocity.

GASDECOM was implemented from the work at ExxonMobil, and still

pretty darn good!

Bill also applied the dynamic ductile crack propagation work to nuclear pipes pressurized with subcooled water.

As the fracture progressed, the subcooled liquid water would very

rapidly drop to the saturation pressure and stay there for a long range of

decompressed velocities (Vd x fluid density changes when going from 0

to 100% quality steam).

Then the approach was expanded to liquid CO2 pipeline applications, which was very similar decompression behavior to

subcooled water for a nuclear plant

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Ductile Fracture Arrest BillsJ-curve

BillsJ-curve came from dynamic measurements of ductile fracture speeds and decompressed pressures measured as the

crack was travelling at that speed.

The curves were different for buried pipes than pipes with no backfill leading to a backfill coefficient (the constant)

As pressure drops, there was a minimum fracture speed related to a parameter Bill called the Arrest Pressure or Arrest Stress (Pa or oa)

that was rooted in the concept that there was an effective crack

length during dynamic crack propagation.

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Ductile Fracture Arrest BillsJ-curve

DatausedtoestablishtheArrestStressbyuseofthe ln-sec fracture initiation equation

For high toughness cases crd /crflow = 0.30 which is 1/MT (bulging factor of a dynamic running crack); or MT = 3.33

Knowing MT from limit-load case, he solved for toughness-dependent cases using Charpy energy

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Ductile Fracture Arrest - Examples

Examples of Two-Curve analyses predictions for;

propagation, quick arrest, and

eventual steady-state arrest

Propagation at 700 fps

Quick Arrest

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Simplified Equation Developed

Bill conducted statistical analyses using BTC equations to establish a simplified equation for lean

natural gas pipelines

Implemented into Codes and Standards, typically with restriction for; lean gases, diameters less than 42-inch,

pressures 72% SMYS or lower soil backfill....

Many other simplified equations developed afterwards

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But how quickly can a ductile fracture arrest?

Bill showed data where arrest distance was function of

(actualCVP)/(Cvmin for eventual arrest) Depended if arrest;

in origin pipe joint (need to develop full-bore opening),

or arrested after going thru a prior joint of pipe away from the origin effects

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The Long Lasting Aspects and Tweaking

After ~40 years the BTC method is still the industry standard approach

OfcoursesometweakingbeingdonetoBillsTwo-CurveApproach...

Different backfill coefficients developed

Effect of different soil types, effect of soil burial depth, frozen soil, water

backfill Toughness aspects Dynamic toughness not proportion to Charpy energy for high Charpy energy

materials (Fearnehough, Wilkowski, Leis,..)

Separations on fracture surface of controlled-rolled steels separations appear at different temperatures in Charpy test than full thickness pipe or DWTT - first

reason why DWTT energy proposed

Grade effect corrections for X80 & X100 but showing it may really be steel-making changes over the decades that now affects even some X60-X70

Recent work showing dynamic toughness changes as a function of fracture speed

empirically accounted by Bill for older steels, but what about new steels?

Gas decompression curve improvements

GASDECOM rewri t ten to be more stable in PRCI code PipeDFrac

to be released Many other equat ions -of-state developed Ef fects

of pipe diameter and roughness

Even new sophisticated dynamic FE models of crack propagation

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Billandsomeofhisfriends... wellmisshim!

J. Kiefner, A. Duffy, J. Ryan, R. Eiber, F. Syler, G. Kramer, P. Krishnaswamy, J. Rue, B. Gertler, P. Vieth, M. Rosenfeld, D. Shoemaker,C.Baxley,J.Wood,... me . Sorryifwedidntgetyouinapicturehere!

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