Two Case Studies on Metallurgical Failures

Author: Dr Janet Cotton

Date: 27th August 2011

Fractured Bollard

Fracture site

Bollard Failure

What caused the catastrophic

fracture of the bollard?

What does the fracture surface say about the failure

What was the load requirements for bollard

What was the bollard made from, what are its properties

Fracture Surface

Fracture site

Bollard Material

Grey Cast Iron

Sample Rupture Strength (UTS) MPa Strain to Failure (Elastic)

1 116MPa 2.05%

2 117MPa 1.73%

3 118MPa 0.60%

4 132MPa 0.37%

Grey Cast Iron

Grey Cast Iron

Sample Rupture Strength (UTS) MPa Strain to Failure (Elastic)

1 116MPa 2.05%

2 117MPa 1.73%

3 118MPa 0.60%

4 132MPa 0.37%

Grey Cast Iron

KIC = applied stress x SQRT (flaw size x PI)

Bollard Materials

BS Marine Structures BS 6349

Fenders, bollards, fairlead etc

First published in 1985 Revised 1994

Recommendations for Bollard Materials

BS 1452 – Cast Iron BS 2789 – Ductile Iron BS 3100 – Cast Steel

Bollard Installed 1961

Bollard Materials

Manufacturer Material Description Relevant Standard

Trelleborg Ductile Cast Iron ASTM A 536, 65-45-12 or 80-55-6

BS EN 1563

Trelleborg Grey Cast Iron None given

Trelleborg Cast Steel None given

Fendercare Grey Cast Iron EN GJL 250

BS EN 1561

Fendercare Spheriodal Graphite

Cast Iron

EN GJS 450-10

BS EN 1563 – 1997

Fendercare Cast Steel GE 300

EN 10293-1991

Bollard Materials

Standard Material Value

BS 1452 1961 grade 10 Grey Cast Iron 170MPa

BS 1452 1961 grade 12 Grey Cast Iron 205MPa

BS 1452 1990 grade 180 Grey Cast Iron

BS 1561 Grey Cast Iron 250-300MPa

ASTM 48 A class 150 Grey Cast Iron 150MPa

BS 1563 1997 Spheroid Cast Iron 450MP

Tested Bollard Strength Grey Cast Iron 116MPa -132MPa

Standard Mooring Arrangement – BS 6349-4 1985

Mooring Rope

Standard Mooring Arrangement – BS 6349-4 1985

Finite Element Analysis

Finite Element Analysis

Standard Mooring Arrangement – BS 6349-4 1985

Bollard Material

Fracture site

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Heat Exchanger

Hot Dip Galvanising

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• Brown Deposit • Iron / Si Rich – rust from pipes (hematite)

• Light Brown Deposit •Iron / Si Rich with Cl – rust from pipes contaminated with Cl

• Black Deposit •Iron rich – rust from pipes (magnetite)

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DETERMINANDS METHOD Baltimore Specification CTO623 CTO624 No 7 Condenser

pH at 25°C SANS 5011:2005 6.5-9.0 7,0 5,9 7.07

Conductivity at 25°C in mS/m SANS 7888:2005 132 18,3 185

Dissolved solids at 180 °C in mg/L SANS 5213:2005 1200ppm max TO FOLLOW TO FOLLOW 1060

Calcium as Ca in mg/L SANS 11885:2008 30-500ppm 26,65 3,964 31.85

Magnesium as Mg in mg/L SANS 11885:2008 35,13 4,857 43.29

Sodium as Na in mg/L SANS 11885:2008 162,2 23,68 200

Chloride as Cl in mg/L SANS 9297:2007 274 44 337

Sulphate as SO4 in mg/L SANS 6310:2005 250ppm max 84 6 270

Total alkalinity as CaCO3 in mg/L SM 2320:1995 250ppm max 41 5 38

Iron as Fe in mg/L SANS 11885:2008 500ppm 0,107 <0,01 1.39

Selenium (recoverable) as Se in mg/L SANS 11885:2008 <0,01 <0,01 <10

Zinc as Zn in mg/L SANS 11885:2008 18,85 0,049 2.15

Total hardness as CaCO3 in mg/L Calculation 211,2 29,90 78.63

Sulphur mg/L 20

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steel pipe

zinc coating steel pipe

zinc coating

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Corr

osio

n R

ate

pH of water

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• Mass of Zinc = 372 kg

• Volume of Zinc when new – 85 micron x 312 m3 = 2.6 x10-2 m3

• Life cycle of condenser – 15 years – accepted corrosion rate 5 micron / year

• pH 14 (maximum) – corrosion rate of 5 times that of pH of 8/9

•25 microns per year – 0.48 microns per week

• At pH 14 it would take more than 1 year to remove the volume of Zinc on condensers

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pH

Ammonia (kg)

Ammonia (kg) Vs Condenser pH

pH ~ 12.5 @ ~ 2800 kg

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steel pipe zinc coating

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Position Fe wt% Zn wt% Si wt%

1 15.14 84.50 0.36 2 97.71 2.02 0.28 3 8.05 91.61 0.34 4 7.06 92.59 0.35 5 32.00 50.03 17.96

2 3 4 5

1

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• Poor water treatment • The effect of ammonia on feed water • “Poor Sample Preparation” • Sand in the Feedwater • Galvanic effect of the box on pipe array

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