Stan Kusters, Sintra Engineers

This Presentation

Introduction

Input from study B

Deterministic analysis

Probabilistic analysis

Conclusions

2

Legenda: Experience

Checking

Theoretical part

Practical part

• Part D

• Field verification

• Part C

• Fracture Mech validation

• Part B

• Evaluation projects

• Part A

• Inventory literature

Part E

Concept Std.

Evaluation

Legenda: Experience

Checking

Theoretical part

Practical part

• Part D

• Field verification

• Part C

• Fracture Mech validation

• Part B

• Evaluation projects

• Part A

• Inventory literature

Part E

Concept Std.

Evaluation

Goal: Develop Good WorkmanShip acceptance criteria for

PAUT, leading to same quality level as RT, to be

published as EN/ISO norm

ScopeThin walled low alloy steel between 3.2-8.0 mm

Original plan: Four project “phases”

Theoretical – practical

Past experience – testing/validating

Phase A & B provide proposed AC and supporting

information

Phase C & D validate rejection rate (D) and

Probablity of Failure for standard case (C)

The KINT ACPA project

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Introduction Study C

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Validation of acceptance criterion for Phased Array

Ultrasonic Testing (PAUT) using fracture mechanics:

One acceptance criterion applicable for different components

(cylinder and flat plate)

Deterministic analysis performed to determine the

allowable defect size

Probabilistic approach to compare Radiographic Testing

(RT) and Phased Array Ultrasonic Testing (PAUT)

Probability of Failure (PoF)

False Call Rate (FCR)

Rejection Rate (RR)

Input from study B All defects in study C will be classified as a through wall crack-like flaw

Not possible to reliably determine the defects depth/height by PAUT

Reliable characterization of the defect is not possible with PAUT

With RT a distinction between a planar flaw and a non-planar flaw can be made.

Probability of Detection for PAUT and RT

Flaw distribution

Planar flaws (RT): 21 % (Of all defects)

Deviation defect length (sizing error)

Length Length

Depth

Height

Rest ligamentIf depth or rest ligament

<20% of wall thickness

→ through wall crack

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Components All combinations of parameters below have been assessed

3 configurations:

Flat plate

Longitudinal weld in cylinder

circumferential weld in cylinder

Wall thickness: 3 mm, 5 mm, 7 mm en 9 mm

Outside diameter: 100 mm, 200 mm and 1,000 mm

Yield strength: 200 MPa (Low) and 500 MPa (High)

Fracture toughness: Based on API579; Material Class A (Low) and D (High)

Load: Membrane stress + bending stress and residual

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Deterministic analysis

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Fracture toughness Based on API579 material is ranked from A to D

The two extremes (material class A and D) have been chosen for the determination of the

fracture toughness

Lower bound fracture toughness determined for all 4 material combinations: Low yield strength and low fracture toughness

Low yield strength and high fracture toughness

High yield strength and low fracture toughness

High yield strength and high fracture toughness

Toughness

Material class A Material class D

Strength200 MPa 1,263 MPa√mm 2,000 MPa√mm

500 MPa 1,394 MPa√mm 3,021 MPa√mm

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Applied stresses Primary stress:

Based on maximal design criterion EN/RTOD

Membrane stress: 2/3 of yield strength

Bending stress: 1/3 of yield strength

Residual stress:

Based on API579-1/ASME FFS-1:2016. Conservative assumption (upper bound)

For a flat plate a uniform stress of yield strength + 69 MPa has been assumed

For the circumferential weld and longitudinal weld as shown in figures below.

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Results For the different materials the maximum allowable through wall defect length is determined.

Material with high yield strength and low fracture toughness is most critical

Maximum allowable through wall defect length is less than 1 mm. This is not realistic as acceptance

criterion.

Material

Yield

strength

Fracture

toughness

Critical defect

length [mm]

[MPa] [MPa√mm] Pm Pm + Pb

1200

1,263 1.8 1.2

2 2,000 5.7 3.6

3500

1,394 0.5 0.3

4 3,021 2.6 1.7

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Probabilistic analysis

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Fracture mechanics assessments Probabilisitc analysis performed → Monte Carlo analyses

120 million fracture mechanic assessments

Performing Fracture mechanics assessment

where statistical selection of parameters is

done:

- Flaw length (2C0)

- Membrane stress

- Bending stress

- Fracture Toughness

Flaw distribution

Membrane stress

Bending stress

Fracture toughnessFailure or No Failure

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Flaw distribution Obtained by study B: Based on CT data

Mainly defects with a length below the 5 mm

Weibull distribution used in Monte Carlo assessment

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Fracture mechanic assessmentsPhased Array Ultrasonic Testing

Defect

Rejected

PoD

Fracture mechanic

Length resizing

Accepted

Correctly Not Correctly

Found

Measured length less

than acceptance

criterion?

Yes No

No Failure Failure

Not Found

All failures divided by total

defects gives PoF

All rejected defects

divided by total

defects gives RR

All not correctly rejected

defects divided by total

defects gives FCR

Varied

Repair14

Fracture mechanic assessmentsRadiographic Testing

Defect

Rejected

PoD

Fracture mechanic

Length resizing

Accepted

Correctly Not Correctly

Found

Measured length less

than acceptance

criterion?

Yes No

No Failure Failure

Not Found

All failures divided by total

defects gives PoF

All rejected defects

divided by total

defects gives RR

All not correctly rejected

defects divided by total

defects gives FCR

2 mm

Repair

Planar?

Yes

No

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PoD graphs from study B

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Pro

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Det

ect

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[-]

Actual Defect Length [mm]

Probability of Detection

RT PAUT (Double sided)

Radiographic Testing

Mean: -1.32 mm (CT measures a longer defect)

Standard deviation: 2.95 mm

Phased Array Ultrasonic testing (Double sided)

Mean: -0.47 mm (CT measures a longer defect)

Standard deviation: 7.22 mm

Length resizing

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Only results of high strength/low toughness material and flat plate shown (most critical)

Probability of failure (PoF) of PAUT and RT are compared

Ratio of PoF (PAUT divided by RT)

If PoF ratio is 1, the PoF of PAUT and RT are the same Acceptance criterion is approximately 5.5 mm

Probabilistic analysis: Results

1 million

defects

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Percentage planar defects

From 21 % (based on all defects) to 14 % (based on detected defects with RT)

No significant effect on acceptance criterion

Resizing of defect length

From independent on defect length (normal distributed) to dependent on defect length (uniform

distributed)

Optimisation of Prob. analysis

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PoF ratio is 1 for an acceptance criterion (PAUT double sided) of approximately 5 mm

Significant decrease of FCR ratio

(max ratio was 3)

Decrease of RR ratio

Results Optimisation

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Fracture toughness

For small wall thickness (<10 mm) the fracture toughness is higher than the assumed (Lower bound)

fracture toughness. (plane strain/plane stress)

Resizing defect length

A uniform distribution of the sizing error (dependent on crack length) has been applied. It’s more likely

that in practice the distribution will be a normal distribution (dependent on crack length). Data set of study

B is not sufficient to determine the mean and standard deviation of the normal distribution per defect

length.

Sensitivity ass. of Prob. Analysis

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Fracture toughness

Has no influence on FCR and RR

PoF ratio is 1 for an acceptance criterion (PAUT double sided) of approximately 5.5 mm

Results Sensitivity assessments

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Resizing defect length

PoF ratio is 1 for an acceptance criterion (PAUT double sided)

of approximately 6mm

Results Sensitivity assessments

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Single Sided

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PoD graphs from study B

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0 2 4 6 8 10 12 14 16 18 20

Pro

bab

ility

of

Det

ect

ion

[-]

Actual Defect Length [mm]

Probability of Detection

RT PAUT (Double sided) PAUT Single sided

Acceptance criterion for single sided PAUT is based on double

sided PAUT

Study D and E came to an acceptance criterion for an inspection level 1,

level 2 and level 3 inspection level of respectively 6 mm, 7 mm and 8 mm

The PoF of single sided compared/equalized to double sided

Acceptance criterion single sided PAUT Inspection level 1: ≈ 2.5mm

Inspection level 2: ≈ 3.9mm

Inspection level 3: ≈ 5.3mm

Single Sided

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Based on a probabilistic analysis an acceptance criterion for PAUT double sided

of around 6mm gives the same probability of failure as RT

Not possible to compare FCR and RR with study B and study D

The sizing error of the two inspections have an influence on the False Call Rate and Rejection

Rate. Sizing error is not known accurately enough

Not possible to align the definition of RR and FCR with study B and study D

Single sided PAUT compared/equalized to double sided PAUT

Acceptance criterion single sided PAUT Inspection level 1: ≈ 2.5 mm

Inspection level 2: ≈ 3.9 mm

Inspection level 3: ≈ 5.3 mm

Conclusions

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Questions?

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Study C project team – Stijn Hertelé, Alfons Krom, Paul

Stevens, Casper Wassink and Pascal Schreurs

Project leads – Leo Ton, Casper Wassink and Erik

Zeelenberg

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Thank you!