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Reference:30160FR (Rev. 02)
Date: 07 Febuary 2013
COMMERCIAL-IN-CONFIDENCE
Algo Mall Study
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BMT Fleet Technology Limited accepts no liability for any errors or omissions or for any loss, damage, claim or other
demand in connection with the usage of this report, insofar as those errors and omissions, claims or other demands are due toany incomplete or inaccurate information supplied to BMT Fleet Technology Limited for the purpose of preparing this report.
30160FR (Rev. 02)
ALGO MALL STUDY
07 Febuary 2013
Submitted to:
NORR Limited
Attention Dr. H Saffanni
175 Bloor St. East
Toronto, ON
M4W 3R8
Submitted by:
BMT FLEET TECHNOLOGY LIMITED
311 Legget Drive
Kanata, ON
K2K 1Z8
BMT Contact: Dr. L.N. PussegodaTel: 613-592-2830, Ext. 205
Fax: 613-592-4950
Email: [email protected]
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Algo Mall Study ii
REVISION HISTORY RECORD
Revision No. Date of Issue Description of Change
00 16 January 2013 Initial submission.01 29 January 2013 Revised submission including Client comments.
02 07 Febuary 2013 Revised submission considering Client comments.
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TABLE OF CONTENTS
ACRONYMS AND ABBREVIATIONS .....................................................................................vii
1 BACKGROUND................................................................................................................. 1
1.1 Selected Exhibits for Non-Destructive Evaluation (NDE) followed by DestructiveTesting............................................................................................................................ 1
1.2 Scope of Investigation.................................................................................................... 1
2 NON-DESTRUCTIVE EVALUATION (NDE)................................................................. 22.1 Exhibit A ........................................................................................................................ 22.2 Exhibit B......................................................................................................................... 42.3 Exhibit 543/525 .............................................................................................................. 92.4 Exhibit 527 ................................................................................................................... 112.5 Exhibit 530 Fillet Weld Measurements..................................................................... 112.6 Exhibit 530 and 511 Section Size Measurements ...................................................... 14
3 FAILURE SURFACE OBSERVATIONS ....................................................................... 153.1 Exhibit A ...................................................................................................................... 153.2 Exhibit 543 ................................................................................................................... 18
4 METALLOGRAPHIC EXAMINATIONS....................................................................... 224.1 Sample Preparation....................................................................................................... 22
4.1.1 Weld Connection - Exhibit A to B ...................................................................224.1.2 Weld Connection - Exhibit 543/525 and 527...................................................24
4.2 Assembly of Macrographs............................................................................................ 244.3 Microscopic Examinations ...........................................................................................29
4.3.1 Weld Connection - Exhibit A to B ...................................................................294.3.2 Weld Connection - Exhibit 543 to 527............................................................. 314.3.3 Exhibit A ..........................................................................................................34
4.4 Examination of the Surface of the Angle Cut out from Exhibit B ............................... 374.5 Material Chemical Analysis ......................................................................................... 394.6 Material Mechanical Properties.................................................................................... 40
4.6.1 Tensile Testing ................................................................................................. 404.6.2 Hardness Testing .............................................................................................. 42
5 CORROSION RATE ESTIMATE.................................................................................... 445.1 Structural Coating Life and Corrosion Rates ............................................................... 455.2 Comparison of Corrosion Rates ................................................................................... 46
6 CONCLUDING REMARKS RELATED TO CONNECTION DETAIL FAILURE
PROCESS ......................................................................................................................... 47
APPENDICES
APPENDIX A: EXHIBIT LIST
APPENDIX B: HARDNESS TESTING
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LIST OF FIGURES
Figure 2.1: Exhibit A - Full Section Column Flange (Thickness 13.4 mm)............................... 2
Figure 2.2(a): Measurements of the Height of the Remaining Weld Attached to the ColumnFlange (Exhibit A) ...................................................................................................... 3Figure 2.2(b): Measurements of the Leg Length of the Remaining Weld Attached to the Column
Flange (Exhibit A) ...................................................................................................... 3Figure 2.3: Two Views of Exhibit B.............................................................................................. 5Figure 2.4: Condition of the BoltHeads (Exhibit B); Side 1.......................................................... 6Figure 2.5: Exhibit B; After Cleaning by Wire Brushing to Remove Loose Corrosion Product...7Figure 2.6: Exhibit B - Thickness of Angle LegConnected Column Flange................................. 8Figure 2.7: Exhibit B - After Cleaning to Remove Corrosion Product from Nut..........................8Figure 2.8: Full Section Column Flange (Thickness 13.4 mm).................................................. 9Figure 2.9: Exhibits 543 and 525 Measurements of Weld Size................................................... 10Figure 2.10: Exhibit 527 .............................................................................................................. 11Figure 2.11: Intact Beam to Column Connection ........................................................................ 12Figure 2.12: Intact Connection Weld Height (Arrow Marks the Weld Height in
Figure 2.13(a)............................................................................................................ 12Figure 2.13: Exhibit 530 Measurements of the Weld Size .......................................................... 13Figure 3.1: Exhibit A Marked Out Before Cutting...................................................................... 15Figure 3.2: Exhibit A Section from 130 and 260 mm Measured from Top.............................. 16Figure 3.3: Exhibit A - Side 1 After Cleaning with Inhibited Acid............................................. 17Figure 3.4: Exhibit A - After Cleaning with Inhibited Acid........................................................ 18Figure 3.5: Exhibit 543 Marked with the White Line Before Cutting......................................... 19Figure 3.6: Exhibit 543 Section from 130 and 230 mm Measured from Top........................... 19Figure 3.7: Exhibit 543 Side 2 Before Cleaning....................................................................... 20Figure 3.8: Exhibit 543 Side 1 After Cleaning with Inhibited Acid......................................... 20Figure 3.9: Exhibit 543 Side 1 After Cleaning with Inhibited Acid......................................... 21Figure 4.1: Exhibit B Assembled After Cutting........................................................................... 22Figure 4.2: Exhibit B; Section Plane Approximately 130 mm from Top.................................... 22Figure 4.3: Exhibit A; Section Plane Approximately 130mm from Top.................................... 23Figure 4.4: Example of Metallographic Sections of the Failed Weld Connection at
Approximately 130 mm from Top in Weld Connection - Exhibit A to Exhibit B ... 23Figure 4.5: Example of Metallographic Sections of the Failed Weld Connection in Weld
Connection - Exhibit 543 to 527............................................................................... 24Figure 4.6: Failed Weld A130/B130............................................................................................ 25Figure 4.7: Failed Weld A260/B230............................................................................................ 26
Figure 4.8: Demolition Separated Weld 543_220/527_220......................................................... 27Figure 4.9: Reference Weld 530 .................................................................................................. 28Figure 4.10: Micrographic Views at the Failure Surface Marked by White Arrows -
Exhibit A to B ........................................................................................................... 31Figure 4.11: Micrographic views in the Upper Portion of the Failure Surface on Side 1 marked
by arrows - Exhibit 543 to 527. Section plane 230 mm from top............................ 33
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Figure 4.12: Micrographic Views in the Lower Portion of the Failure Surface on Side 1 - Exhibit
543 to 527. Section plane 230 mm from top............................................................ 34
Figure 4.13: Assembly Showing the Removal Location of Sample from Exhibit A for
Metallography........................................................................................................... 35Figure 4.14: Mounted Sample from Exhibit A at Section Plane 30 mm from Top. .................... 36Figure 4.15: Micrographic Views of the Failure Surface of Angle - Exhibit A; Side 1 (Section
plane 30 mm from top) ............................................................................................. 37Figure 4.16: The Piece removed from Exhibit B; Side 1............................................................. 38Figure 4.17: Streoscopic View of the Surface shown in Figure 16(a). ........................................ 39Figure 4.18: Flange Sample Extracted From Exhibit 511............................................................ 41Figure 4.19: Stress-Strain Curve from Tension Specimen from Flange of Exhibit 511.............. 42Figure 4.20: Macrograph at Section Plane 630 mm from Top (Side 1) of Exhibit 530............... 43
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LIST OF TABLES
Table 2.1: Section Size Measurements for Exhibit 530 and 511 ................................................. 14
Table 4.1: Estimated Weld Sizes (Leg Lengths) at Fusion Faces................................................ 28Table 4.2: Estimated Section Thicknesses ................................................................................... 29Table 4.3: Chemical Analysis Results, wt% ................................................................................ 40Table 4.4: Measured Tensile Properties For Exhibit 511............................................................. 42Table 5.1: Estimated Decreased Weld Dimensins due to Corrosion and Corrosion Rate ........... 44Table 5.2: Estimated Decreased Section Thicknesses Due to Corrosion..................................... 44Table 5.3: Coating Life Statistics................................................................................................. 45Table 5.4: Corrosion Rate Statistics............................................................................................. 46Table 5.5: Pitting Corrosion Rate Data ........................................................................................ 46Table 5.6: Estimated Corrosion Rate Statistical Parameters........................................................ 46
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ACRONYMS AND ABBREVIATIONS
Al Aluminium
BM Base metal
BMT BMT Fleet TechnologyC Carbon
Cr Chromium
CSA Canadian Standards Association
Cu Copper
HAZ Het Affeted Zone
LAngle Weld leg size attached to angle section
LFlange Weld leg size attached to flange section
Mn Manganese
NDE Non-Destructive EvaluationNi Nickle
NRC National Research CouncilOPP Ontario Provincial Police
P Phosphorus
S Sulphur
Si Silicon
tAngle Thickness of angle leg section
tFlange Thickness of column flange
Ti Titanium
V Vanadium
VHN Vickers Hardness Number
W Distance between parallel sides ofnut from bolted connection
WM Weld Metal
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Algo Mall Study 1
1 BACKGROUNDBMT Fleet Technology Limited (BMT) was tasked to complete a metallurgical and structural
investigation of the steel structural elements removed from the Algo Mall and delivered to the
BMT test labs. A listing of the materials delivered to BMT by the Ontario Provincial Police(OPP) is presented in Appendix A as an Exhibit list.
The work performed in this investigation was coordinated and contracted through NORR
Limited. The initial meeting held at BMT s office on September 6, 2012 reviewed the
background of the investigation and developed an initial scope for the investigation as
documented in the meeting minutes. BMT s role in this investigation was focussed on the
connection detail (welded double angle beam connection) suspected to have precipitated the
collapse of the Mall roof top parking surface.
1.1 Selected Exhibits for Non-Destructive Evaluation (NDE) followed by DestructiveTesting
The Exhibit materials (Appendix A) selected for detailed investigation included:
Failed connection identified as Exhibits A (column) and B (beam and bolted angles to the
web). The separation occurred at the fillet welds connecting the two angles to the columnflange.
Similar beam to column connection consisting of Exhibits 543/525 (column flange) to527 (beam and bolted angles to the web). This separation was reported to have occurred
during demolition.
Exhibit 530 which is a beam to column connection.
Exhibit 511 which is a column. This was to be used for extraction of a sample for tensile
testing for confirm the material grade as 300W/44W (CSA G40.21).
These Exhibits are presented in Appendix A.
1.2 Scope of InvestigationThe agreed scope of work for the BMT investigation included the provision of engineering
opinions related to:
the mode and rate of degradation observed at the suspect connection (Exhibit A and
B);
the extent of degradation (corrosion) and the remaining capacity of the connection;
andthe mode and mechanism of failure of the connection.
BMT structural engineering, welding engineering and metallurgical engineering expertise and
experience were used to complete this investigation. The details of the findings of thisinvestigation are provided in the sections that follow.
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2 NON-DESTRUCTIVE EVALUATION (NDE)The first step in the investigation involved non-destructive measurement and evaluation of the
subject structural components as outlined in the sections that follow for each Exhibit.
2.1 Exhibit AMeasurements were made to determine the remaining weld sizes on the column flange presented
in Figure 2.1. The measurements were made using a calibrated vernier caliper along the two
vertical welds (marked by the white arrows in Figure 2.1) on each side and the results are
presented in Figure 2.2. The section to be cut out for cleaning the failure region (i.e., the weld
length along the section from 130 mm to 260 mm on Sides 1 and 2) using inhibited acid is
marked in Figure 2.2(a). Black scale deposits were removed from the region between the two
welds, i.e., the crevice area of the failed connection, and bagged for later analysis. Such typical
scale is marked by the green arrow. The scale deposits were sent for chemical analysis to the
NRC lab.
Figure 2.1: Exhibit A - Full Section Column Flange (Thickness 13.4 mm)
Side 2
Top
Side 1
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0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 50 100 150 200 250 300 350 400 450 500
Weldheigth,
(mm)
Length, (mm)
Exhibit A - weld height
side 1side 2
cut out piece
metallography planes
Figure 2.2(a): Measurements of the Height of the Remaining Weld Attached to the
Column Flange (Exhibit A)
The weld height (ordinate), in Figure 2.2(a) indicates the portion of the weld size, in the column
flange, that is remaining after the failure. The weld size in Figure 2.2(b) is the leg length of the
weld attached to the column flange. The weld length is measured as 460 mm.
0
2
4
6
8
10
12
14
16
0 50 100 150 200 250 300 350 400 450 500
Leglength,(mm)
Length, (mm)
Exhibit A - leg length
side 1side 2
Top weld length
Figure 2.2(b): Measurements of the Leg Length of the Remaining Weld Attached to the
Column Flange (Exhibit A)
Side 2 Side 1
Length
Top
Height
Side 2 Side 1
Length
Top
Leg Length (Size)
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2.2 Exhibit BTwo views ofExhibit B are presented in Figure 2.3. These consist of:
The beam connected to the column; and
The angles that connect the beam to the column.
It is noted that the failure occurred between the angles and the column flange along the fillet
welds (identified in Figure 2.1 as Side 1 and 2) except the area marked by the white ellipse in
Figure 2.3(a). The failure surface in the area marked by the white elipse was located in the Side
1 angle leg. The area marked by the white ellipse was cut out to be more closely examined using
the stereoscope. The objective of this detailed inspection was to identify any rubbing or surface
damage in this local region of the angle.
(a)
To
Side 1
Side 2
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(b)
Figure 2.3: Two Views of Exhibit B
As illustrated in Figures 2.3 and 2.4, the angle and the bolted connection were severely corroded.
Samples of the black and orange scale deposits shown on the angle in Figure 2.3(a) in the areas
marked by the yellow elipse were removed and bagged for chemical analysis at the NRC lab.
Corrosion product samples were similarly removed for chemical analysis at the NRC lab from
the nuts marked by the yellow elispses in Figure 2.3(b).
Figure 2.4 is presented to show a close up view of the condition of the bolt heads on the other
side (Side 1) of the connection displayed in Figure 2.3.
Side 2
Top
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Figure 2.4: Condition of the BoltHeads (Exhibit B); Side 1
The side shown in Figure 2.5 was cleaned by wire brushing to remove corrosion products in
order to make measurements of the remaining thickness of the angle leg bolted to the beam web
and the leg welded to the column flange. A calibrated micrometer was used to measure the angle
leg that was welded to the column flange and a vernier caliper was used to measure the angle leg
bolted to the web. The minimum thicknesses measured along the angle legs in the region shown
in Figure 2.5 was 4.8mm and 4.6mm for the angle legthat was welded to the column flange and
the angle leg bolted to the beam web, respectively. The thickness values of the angle leg that
was welded to the column flange are consistent with the weld heights displayed in Figure 2.2(a).
These measurements were recorded and stored in an MS Excel file. This file also includes
measurements of the thickness of the angle leg close to the corner of the angle along the entire
length of the angle. This data was measured using a micrometer. The results of these
measurements are shown in Figure 2.6 for both the angle leg thickness at the edge and corner.
These results suggest that the average thickness of the angle leg is marginally lower at its edge
than at the corner on Side 1 and almost the same on Side 2.
Side 1
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Figure 2.5: Exhibit B; After Cleaning by Wire Brushing to Remove Loose Corrosion
Product
0.0
1.0
2.0
3.0
4.05.0
6.0
7.0
8.0
0 50 100 150 200 250 300 350 400 450
Thickness,(mm)
Length, (mm)
edgecorner
Top
a) Side 1
Side 1
An le Ed e Thickness
An le Corner Thickness
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0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0 50 100 150 200 250 300 350 400 450
Thickness,(m
m)
Length, (mm)
edgecorner
Top
b) Side 2
Figure 2.6: Exhibit B - Thickness of Angle LegConnected Column Flange
One of the nuts in the bolted connection was cleaned to remove the corrosion products and the
distance between parallel side (W) measured using a vernier caliper was 25.3 mm as marked in
Figure 2.7.
Figure 2.7: Exhibit B - After Cleaning to Remove Corrosion Productfrom Nut
W
Side 2
An le Ed e Thickness
An le Corner Thickness
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2.3 Exhibit 543/525These Exhibits were examined because they were reported to be the connection supporting the
beam on the opposite column flange to the connection that failed (Exhibits A and B). This
connection was pulled apart during demolition activity, thus in-service, it was an intact welded
connection. The measurements taken at this connection detail were collected for comparisonwith the construction quality, connection details and degradation observed at Exhibits A and B.
Due to the lower levels of corrosion at this connection detail, compared to that at Exhibits A and
B, the structural geometry could be considered to be reflective of original construction.
Measurements were made to determine the weld sizes on the column flange shown in Figure 2.8.
The column flange (Exhibit 525) had been cut in half and bent before delivery to BMT.
Measurementsof the weld size were made using a vernier caliper along the two vertical welds on
each side and the results are presented in Figure 2.9, in a manner as for Exhibit A in Section 2.1
of the report.
Figure 2.8: Full Section Column Flange (Thickness 13.4 mm)
To
Side 1 Side 2
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0
1
2
3
4
5
6
7
8
0 50 100 150 200 250 300 350 400 450 500 550 600 650
Weldheigth,
(mm)
Length, (mm)
543 & 525- weld height
side 1side 2
a) Weld Height Attached to the Column Flange
0
2
4
6
8
10
12
14
16
0 50 100 150 200 250 300 350 400 450 500 550 600 650
Leglength,
(mm)
Length, (mm)
543 & 525- leg length
side 1side 2
b) Weld Leg Length Attached to the Column Flange
Figure 2.9: Exhibits 543 and 525 Measurements of Weld Size
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The total weld length is measured as 610 mm by assembling Exhibit 543 and 525 as one unit. It
was found that the weld size does not change significantly along the length on the weld. The
weld height was in the range of 6 mm to 7 mm and the leg length varied from 10 mm to 14 mm,
that is, the weld height was about double and the leg length was similar to that measured in
Exhibit A. Note that compared to Exhibit A there is only corrosion in the section between thetwo welds, i.e., the crevice created by welding the angles to the flange.
2.4 Exhibit 527The side view ofExhibit 527 is presented in Figure 2.10. It consists of the angles and beam that
were connected to Exhibits 543 and 525. It was noted that the length ofthe angle in Figure 2.10
is equal to the length ofthe weld along the flange shown in Figure 2.8.
Figure 2.10: Exhibit 527
After wire brushing to remove loose corrosion product and paint, measurements of the thickness
of the angle on both sides were made following the procedures adopted for Exhibit B and
described in Section 2.2 in this report. The measured average thickness ofthe two legs ofone
angle was 8.5 mm on the side bolted to the web and 7.5mm for the side that was welded to the
flange of Exhibits 543/525. These thickness values of the side connected to the column flange
are marginally greater than the weld height reported in Figure 2.9(a). These measurements were
recorded in an MS Excel file for future reference. This file also reported average thickness at the
corner of the angle tobe 8.1 mm.
2.5 Exhibit 530 Fillet Weld MeasurementsMeasurements were made to determine the weld size along fillet weld shown in Figure 2.11.
This detail is a beam to column connection with no corrosion but has a thicker column flange
than that of the failed connection. These measurements were taken to consider the as-built
geometry of the connection detail. A close up of the fillet weld is shown in Figure 2.12. The
measurements were made using a vernier caliper along the two welds on each side and the results
are presented in Figure 2.13, in a similar display as for Exhibit A in Section 2.1 of the report.
Side 2
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Figure 2.11: Intact Beam to Column Connection
Figure 2.12: Intact Connection Weld Height
(Arrow Marks the Weld Height in Figure 2.13(a)
Top
Side 1
Side 2
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0
1
2
3
4
5
6
7
8
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
Weldheigth,
(mm)
Length, (mm)
side 1side 2
(a) Weld Height Attached to the Angle
0
2
4
6
8
10
12
14
16
18
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
Leglength,
(mm)
Length, (mm)
side 1side 2
(b) Weld Height Attached to the Column Flange
Figure 2.13: Exhibit 530 Measurements of the Weld Size
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The weld height was in the range of 6 mm to 7.5 mm and leg length varied from 12 mm to
16 mm. In summary, the weld size was marginally larger to that measured in Exhibit 543/525.
2.6 Exhibit 530 and 511 Section Size MeasurementsSection size measurements were taken on the columns and beams of the above Exhibits 530 and
511, as requested by NORR Limited. Measurements of the thickness of the web and flange weremade using a vernier caliper. The section sizes (i.e., W and H) were dimensioned using a steel
ruler. The results presented in Table 2.1 also include the nominal dimensions.
Table 2.1: Section Size Measurements for Exhibit 530 and 511
H W Nominal Measured Nominal Measured
530Column
W10x89 276.4 261.1 15.6 14.8 25.3 27.3-27.8
530
Beam
Side 1
W24x84 611.9 229.1 11.9 11.7-11.8 19.6 19
530
Beam
Side2
W24x76 607.3 228.1 11.2 11.3-11.4 17.3 17.2-17.3
511
ColumnW10x49 254 254 8.6 9.4-9.6 14.2 15.5-15.7
511Beam
W24x76 607.3 228.1 11.2 11.1-11.8 17.3 16.9-17.2
Nominal Dimensions Web Thickness (mm) Flange ThicknessExhibit Section
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3 FAILURE SURFACE OBSERVATIONSThis section provides a description of the observations derived from the destructive examinationof the connection details.
3.1 Exhibit AIn order to carryout close up examination of the failed weld surface using a stereoscope, it wasnecessary to cut out a selected region as indicated in Figure 2.2(a) in Section 2.1. Exhibit A was
marked out at 130 mm and 260 mm from the top and the portion between 130 mm and 260 mm;i.e., between the two white lines, was cut by saw. The photo documentation of the cuts and the
cut section are shown in Figure 3.1 and Figure 3.2, respectively.
Figure 3.1: Exhibit A Marked Out Before Cutting
Side 1Side 2
To
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Figure 3.2: Exhibit A Section from 130 and 260 mm Measured from Top
((The arrow points to the bottom orientation.)
The examination of the failed surface before cleaning using the stereoscope did not reveal anyfracture surface features, therefore the weld region on both sides were cleaned using inhibited
acid solution (50/50 water and Hydrochloric acid with Rodine). Rodine is an inhibitor that has
been found to be effective in not removing metal (iron).
Figure 3.3 shows the failed connection (Side 1) region after cleaning with the inhibited acid
solution. Side 2 (not shown) also shows similar appearance. As the initial cleaning appeared to
be insufficient, a more rigorous cleaning using a synthetic material brush while immersed in a
cleaning solution was successful in exposing bare metal in some regions while in the base/root of
the weld, a black deposit (see white arrows in Figure 3.3) remains. The magnetite deposit
extends from the root of the weld into the weld throat. This suggests that the weld throat
seperation (initiating from the weld root) was exposed to a corrosive environment for asignificant period of time (i.e., greater than one year). The formation of magnetite (Fe3O4)
occurs after the formation of red or orange oxide by converting its iron ions.1 Thus magnetite is
an older form of oxide.
1Jones, Deny A, Principles and Prevention of Corrosion , Macmillan Publishing Company, New York, 1992.
Side 1Side 2
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(a)Initial cleaning
(b)Final Cleaning
Figure 3.3: Exhibit A - Side 1 After Cleaning with Inhibited Acid
(The left end is the cut at 130 mm from top side of column)
The black regions (marked by the white arrow in Figure 3.3) are magnetite deposits. Magnetiteis a magnetic form of oxide which can be differentiated from the red/orange oxide commonly
referred to as red rust. The magnetite is difficult to clean from the surface and is an older form
of corrosion product compared to red rust. The metallic region (marked by the green arrow in
Figure 3.3) has been cleaned effectively by the inhibited acid solution. Figure 3.4 provides a
detail view of the region close to the 130 mm end. The failure surface in the metallic regions
may not have the virgin failure features due to dissolution of the steel in a corrosion process.
The bright spots in Figure 3.4(b) are indicative of minute corrosion pits when viewed with the
stereoscope.
Side 1
Side 1
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(a)Initial Cleaning
(b)Final Cleaning
Figure 3.4: Exhibit A - After Cleaning with Inhibited Acid.
(A closer view than Figure 3.3. The left end is the cut at 130 mm from top side of column.)
3.2 Exhibit 543In a similar way to that described in Section 3.1, a 100mm long section was cut outby saw. The
photo documentation of the cuts and the cut section are shown in Figure 3.5 and Figure 3.6,
respectively. This connection was pulled apart during demolition activity, thus in-service it was
an intact welded connection.
Side 1
Side 1
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Figure 3.5: Exhibit 543 Marked with the White Line Before Cutting
Figure 3.6: Exhibit 543 Section from 130 and 230 mm Measured from Top
The examination of the failed surface using the stereoscope revealed fracture surface features, asshown in Figure 3.7. Compared to Exhibit A where the failed surface had black oxide
(magnetite), the fracture surface in Exhibit 543 indicated only the presence of red oxide. This
was expected as the oxide on the fracture surface of Exhibit 543 would have formed only after
demolition. Side 1 was cleaned using inhibited acid solution in two stages as described in
Section 3.1.
Side 1 Side 2
Side 1 Side 2
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Figure 3.7: Exhibit 543 Side 2 Before Cleaning
(The left end is at 220 mm from top side of column)
(a)Initial Cleaning
(b)Final Cleaning
Figure 3.8: Exhibit 543 Side 1 After Cleaning with Inhibited Acid.
(The left end is at 220 mm from top side of column)
The black oxide (magnetite) in Figure 3.8 is confined to the area on the column flange adjacent
to the weld root (Figure 3.7) and thus could have been formed in service. The initial cleaning
was effective in cleaning only a strip at the top of the failure, as marked by the green arrow as
illustrated in Figure 3.8(a). The final clean was effective in removing the red oxide in the rough
fracture region, as marked by white arrow in Figure 3.8(b).
Figure 3.9 illustrates a detail view of the region close to the 220 mm end. The strip at the top ofthe fracture (marked by green arrow in Figure 3.8(a)) indicates a smooth surface compared to the
rough surface below it. There is a step, marked by the white arrow in Figure 3.9(b), and is in an
oblique plane to the rest of the failed surface. The black region in Figure 3.9(b) is clearly visible
as a black scale formed in the column flange and in this view appears to extend to the bottom of
the failed surface. The black scale was removed and was found to be magnetic and is likely to be
magnetite. These two fracture surface regions are reviewed by microscopic examination in
Section 4.3.2.
Side 2
Side 1
Side 1
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(a)Initial Cleaning
(b)Final Cleaning
Figure 3.9: Exhibit 543 Side 1 After Cleaning with Inhibited Acid
(A closer view of Figure 3.8. The left end is at 220 mm from top side of column.)
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4 METALLOGRAPHIC EXAMINATIONSTo further examine the connection details, metallurgical samples were removed for examination
as described in the sections that follow.
4.1 Sample Preparation4.1.1 Weld Connection - Exhibit A to BThe failure of this welded connection is believed to be the cause for the collapse of the concrete
slab. Metallographic sections were prepared on both welds (Side 1 and Side 2) of Exhibit A at
the two locations marked in Figure 2.2(a). These two locations represent the minimum and
maximum weld height along the length of the weld. Metallographic specimens were also
prepared at approximately the same locations, with respect to the distance along the weld in
Exhibit B. To remove these specimens, Exhibit B had to be cut by saw similar to Exhibit A as
described in Section 3. Photographic records were made during this process. Figure 4.1 displays
Exhibit B assembled after saw cutting and may be compared with Figure 2.3(a). Figure 4.2presents a cross-sectional view of a cut surface through Exhibit B.
Figure 4.1: Exhibit B Assembled After Cutting.
Figure 4.2: Exhibit B; Section Plane Approximately 130 mm from Top.
(Location for extraction of metallographic samples is marked by the two circles.)
To
Side 1
Side 2
Side 1Side 2
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Metallography samples were extracted at locations indicated by the circles in Figures 4.2 and
4.3. Four samples were extracted from the two cut planes shown in Figure 4.1. It is noted that
the edges of the angles at these locations were welded to the column flange by fillet welds. In a
similar way, four metallographic samples were also extracted to display the weld profile in
Exhibit A. Figure 4.3 is presented to show a cut plane in Exhibit A.
Figure 4.3: Exhibit A; Section Plane Approximately 130mm from Top
(Location for extraction of metallographic samples is marked by the two circles.)
The samples were cut and prepared for metallographic examination. The steps involve mounting
the extracted samples in Bakelite and then grinding with a 1200 grit paper using metallurgicalpreparation equipment. The samples are then etched in 10% nital solution (10% volume nitric
acid in methanol) to reveal the macro-structure. Two examples of this are provided in
Figure 4.4. The weld metal is the region marked by the arrow and the halo around it is the
visible heat affected zone (HAZ) due to welding. It is to be noted that this is the minimum weldheight location as displayed in Figure 2.2(a).
(a)Exhibit B - Side 2
(b)Exhibit A - Side 2
Figure 4.4: Example of Metallographic Sections of the Failed Weld Connection at
Approximately 130 mm from Top in Weld Connection - Exhibit A to Exhibit B
Side 2Side 1
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4.1.2 Weld Connection - Exhibit 543/525 and 527A similar procedure described in Section 4.1 was adopted to prepare metallography samples at a
section plane 220 mm from the top with reference to Figure 2.7. The resulting metallographic
samples are presented in Figure 4.5. The weld metal regions are marked by the arrows.
(a)Exhibit 527 - Side 1
(b)Exhibit 543 - Side 1
Figure 4.5: Example of Metallographic Sections of the Failed Weld Connection in Weld
Connection - Exhibit 543 to 5274.2 Assembly of MacrographsSample specimens from each of the angle leg and the column flange that were sectioned and
photographed are used to develop an understanding of the connection geometry at the time of the
failure and at construction. Figures 4.6 and Figure 4.7 illustrate the sectioned specimens taken
from the separated welds, designated as Welds A130/B130 and A260/B230 (combining Exhibit
A and B sections at positions 130 mm and 260 mm from the top), respectively. In each case,
specimens from the two sides (Side 1 and Side 2) of the welded connection are shown. The
estimated original (i.e., at construction) section thicknesses and fillet weld profile have been
added to the figures to illustrate the estimated amount of material lost to corrosion.
Figure 4.8 similarly illustrates the sectioned specimens taken from the weld separated during
demolition, designated as Weld 543_220/527_220 (Exhibits 543 and 527 at a position of 220mm from the top of the weld). As shown in Figure 4.8, the effects of corrosion are negligible.
Figure 4.9 illustrates a reference weld, designated Weld 530 (one side only), which shows anintact fillet welded connection with no corrosion.
In each figure, the separated components in a connection have been positioned by closelyaligning the contours of the fusion line (within the thickness of the steel sections) and the
contours of the heat-affected zones. In assembling these composite figures, care was taken to
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ensure that the adjacent images were presented at the same level of magnification. The
rectangular blue backgrounds positioned behind each sectioned component provide the nominal
dimension of the component. Similarly, the red triangular backgrounds are used to illustrate the
nominal weld sizes considered to have been used in construction. Where the nominal weld (red
triangle) is obscured by the weld, a black dashed line has been used to represent the nominalfillet weld trangle boundaries.
(a) Side 2
(b) Side 1
Figure 4.6: Failed Weld A130/B130
Angle Leg
(as-constructed)
Fusion face for
determining weld leg
length (excluding any gap)
Angle Leg
(as-received)
Column Flange
(as-received)
Corroded fillet weld
Fusion line contour
Heat-affected zonecontour
Idealized Fillet
Weld Profile
Column Flange
(as-constructed)
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(a) Side 2
(b) Side 1
Figure 4.7: Failed Weld A260/B230
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(a) Side 1
(b) Side 2
Figure 4.8: Demolition Separated Weld 543_220/527_220
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Figure 4.9: Reference Weld 530
The as-received weld sizes (weld sizes measured by BMT), taken as the leg lengths along the
fusion face (and not accounting for gaps between the components), have been estimated from the
photographs of the specimens. The nominal weld sizes, which are assumed from the idealized
fillet weld (red background triangle) shown in the photographs, have been estimated similarly.
The estimated leg lengths are listed in Table 4.1 for each weld specimen, for each side.
Table 4.1: Estimated Weld Sizes (Leg Lengths) at Fusion Faces
Nominal Weld Size1
[mm] As-Received Weld Size1
[mm]
Side 1 Side 2 Side 1 Side 2Weld Specimen
LAngle LFlange LAngle LFlange LAngle LFlange LAngle LFlange
Failed
Weld
A130 /
B1307 13 7 13 3.5 8.0 3.5 8.0
A260 /
B2307 13 7 13 4.5 12.0 5.0 12.5
Demolition
Separated
Weld
543_220 /
527_2207 13 7 13 7 13 7.0 13
Reference
Weld530 7 13 7 13
1. The weld size (leg length) is estimated based on the weld at the fusion face with no gapassumed between the angle leg and the column flange.
Table 4.2 lists the thickness for each angle leg and column flange section from each specimen for
the estimated original (i.e., at construction) condition and in the as-received (i.e., corroded)
condition.
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Table 4.2: Estimated Section Thicknesses
Estimated Original
Thickness [mm]
As-Received Thickness [mm]
Side 1 Side 2 Side 1 Side 2Weld Specimen
tAngle tFlange tAngle tFlange tAngle tFlange1
tAngle tFlange1
Failed
WeldA130 / B130 7.9 14.2 7.9 14.2 2.5 9.5 4.0 9.0
A260 / B230 7.9 14.2 7.9 14.2 4.0 12.5 5.4 12.9
Demolition
Separated
Weld
543_220 /
527_2207.9 14.2 7.9 14.2 7.9 13.5 7.9 14.0
Reference
Weld530 7.9 25.3 8.0 -
1. The as-received column flange thickness is measured from the minimum thickness shownin the photographs.
The exact fit between the separated components cannot be known with certainty and it is
similarly not known when the welds failed. It is noted from the photographs of the failed and
separated welds, shown in Figure 4.6 and Figure 4.7, that significant corrosion of the structuralmembers and the weld profile has occurred. Further, evidence of pitting corrosion is seen on the
surfaces of the weld failures, indicating that the wastage may have progressed through the entire
thickness of the weld throat during the service life. In particular, the weld illustrated in Figure
4.6(b), corresponding to specimen A130/B130 at Side 1, shows significant corrosion of the angle
leg indicating that a corrosive environment was present on both surfaces. This suggests that the
corrosion process would have reduced the weld size from both the face and root.
4.3 Microscopic ExaminationsMicroscopic examination of the fracture path to attempt to identify the mode of failure and
contributing factors was completed, by examination of metallographic sections, and is reported
subsequently.
4.3.1 Weld Connection - Exhibit A to BA pair of the macro-structure observation samples was prepared for microscopic examination.
This is done by re-grinding the etched sample in 1200 grip paper and polishing to a 1 micron
finish using metallurgical preparation equipment. The samples are then etched in 2% nital
solution to reveal the microstructure. The pairs selected were the section plane 260 mm from topfor Exhibit A and plane 230 mm from top for Exhibit B from Side 2. The focus of the
examination was to assess the microstructure at the failure surface of both Exhibits. The
observations indicated the following:
The failure surface in Exhibit A was entirely in the weld, i.e., the microstructure alongthe failure surface display weld metal (see Figure 4.10a). This microstructure is
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characterized as columnar morphology that is typical of as-deposited weld metal
microstructure.
There were pits along the failure surface (marked by green arrow). The pit marked by thegreen arrow is filled with oxide. This suggests that the failure surface was exposed to a
corrosive environment for a significant period of time for pitting to occur and forcorrosion deposits to be present in the pits.
There was no observable grain deformation at the failure surface.
The failure surface in Exhibit B was entirely in the HAZ, i.e., the microstructure alongthe failure surface did not display weld metal (see Figure 4.10b). This observation
combined with that in the first bullet suggests that the fracture path followed the weld
fusion line (i.e., boundary between the weld metal and base material of the angle).
The pits along the failure surface in Exhibit A supports the observations presented in
Figure 3.4(b) in Section 3. The failure surface was exposed to a corrosive environment for a
significant period of time. Therefore it is clear that the original failure surface (i.e., failuresurface before corrosion) in Exhibit A is not present due to corrosion and hence any inference
from fractography (observations made on the cleaned fracture surface) could be misleading.
(a)Exhibit A Side 2 - Section plane 260 mm from Top
200 m
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(b) Exhibit B Side 2 - Section Plane 230 mm from Top
Figure 4.10: Micrographic Views at the Failure Surface Marked by White Arrows -
Exhibit A to B4.3.2 Weld Connection - Exhibit 543 to 527A pair of the macro-structure observation samples was prepared for microscopic examination as
described in Section 4.3.1. The pair selected was section plane 220 mm from top for Exhibit 543
and plane 220 mm from top for Exhibit 527 from Side 1. This is because the macrograph
presented in Figure 4.8(a) indicated weld metal in Exhibit 527 at the edge of the angle in theupper portion of the failure path. It is noted that there is no expected metal loss after demolition
and therefore the failure path represents the actual path as compared to those observations made
in Section 4.3.1 for connection Exhibit A to B. The observations indicated the following:
The failure surface in Exhibit 543 and 527 was in the weld in one portion of the fracture;
i.e., the microstructure along both halves of the failure surface display weld metal, as
illustrated in Figure 4.11. This region represents the smooth failure surface at the top side
of the fractograph presented in Figure 3.9. (Note that in Figure 3.9, the corrosion on this
surface is removed by cleaning in inhibited acid solution, while the metallographic
section was prepared before removal of surface rust.)
There is observable grain deformation at the failure surface in this portion of the fracture.The deformation of the grain structure is local and only a few (i.e. 5 to 10) microns deep
and can be found on both sides of the failure surface. The grain deformation morphology
indicates shear at the two failure surfaces suggesting a ductile failure process.
200 m
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There is evidence of a layer of non-metallic film (corrosion product) at the failure surface
in Exhibit 527 as illustrated in Figure 4.11(b) and as marked by the green arrow. Thenon-metallic film is 5 to 10 microns and it is likely to be a layer of red rust.
The failure surface in the portion of the fracture that appears rough in Figure 3.9 is in the
HAZ in both halves of the failure surface (see Figure 4.12). The transition from the
smooth surface to the rough surface presented in Figure 3.9 indicates an oblique surface
as described in Section 3.2.
The failure surface profile in Figure 4.12 indicates evidence of the rough surface markedby the arrows.
The failure surface profile also indicates planer facets and subsidiary cracks marked bythe arrow in Figure 4.12. This is indicative of the cleavage (brittle) mode of fracture and
is likely in the HAZ adjacent to the weld.
Two modes of failure are possible in the two regions presented in Figures 4.11 and 4.12
for the failure in the weld and HAZ as a result of different toughness in the twomicrostructural regions.
(a) Exhibit 543
100 m
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(b) Exhibit 527
Figure 4.11: Micrographic Views in the Upper Portion of the Failure Surface on Side 1
Marked by Arrows - Exhibit 543 to 527. Section Plane 230 mm from Top
(a) Exhibit 543
100 m
100 m
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(b) Exhibit 527
Figure 4.12: Micrographic Views in the Lower Portion of the Failure Surface on Side 1 -
Exhibit 543 to 527. Section plane 230 mm from top4.3.3 Exhibit AAs a result of a progress meeting with Norr and Giatec, a request was made to extract a sample
from Exhibit A. The objective was to observe the fracture path that occurred in the angle welded
to Side 1. The location of the sample extraction with respect to the top region of this Exhibit isdocumented in Figure 4.13. The sample removal location is marked by the black arrow and the
plane for microscopic examination is indicated by the red arrow. The green arrow in Figure 4.13
indicates the location where the fracture deviated to the angle section. It is to be noted that this is
the only location where the failure occurred outside of the weld zone as was also noted in Figure
2.3(a) in Section 2.2. Also, the opposite side of this fracture was in the region enclosed in thewhite ellipse in Figure 2.3(a).
100 m
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Figure 4.13: Assembly Showing the Removal Location of Sample from Exhibit A for
Metallography
(The white arrow points to the bottom orientation of the column.)
Side 2 Side 1
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The metallographic sample is presented in Figure 4.14 with the failure surface to be examined
marked by the arrow is from the angle section. There was apparent rotation or prying of the
angle from the column during the failure, as can be interpreted from Figure 4.14. This suggests
that the angle section fracture was the last element of the connection failure.
Figure 4.14: Mounted Sample from Exhibit A at Section Plane 30 mm from Top.(The arrow points to the failure surface to be examined on Side 1.)The metallographic examination of the failure path in this section plane revealed the following:
The failure surface has non-metallic material (likely oxide), as indicated by the white
arrows in Figure 4.15; and
The grain structure has apparent deformation at the surface layer as observed by
compressed shape of the grains, indicated by the black arrow, compared to the grain
structure present 50 microns below the failure surface.
Side 1
Side 1
100 m
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(a)Lower Magnification
(b)Higher Magnification
Figure 4.15: Micrographic Views of the Failure Surface of Angle - Exhibit A; Side 1
(Section plane 30 mm from top)
4.4 Examination of the Surface of the Angle Cut out from Exhibit BThe region enclosed in the white ellipse in Figure 2.3 (Section 2.2) was cut out for close
examination. The surface of the cut out that needed to be examined to detect indication of anyrubbing is presented in Figure 4.16 before and after cleaning in inhibited acid. The black marks
enclosed inside the white circle were marks made by a marker to identify a cut line.
Side 1
50 m
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(a)Before Cleaning
(b)After Cleaning
Figure 4.16: The Piece removed from Exhibit B; Side 1
The shiny spots in Figure 4.16(a) were examined under the stereoscope and appeared to have ametallic appearance (see Figure 4.17). However there were no indications that these were a
result of rubbing of this surface on the column flange in Exhibit A. After cleaning in inhibited
acid more black oxide regions appeared as can be infered by comparing Figure 4.16(a) and
4.16(b). It is likely that the black regions in Figure 4.16(b) were covered by red rust in Figure
4/16(a).
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Figure 4.17: Streoscopic View of the Surface shown in Figure 16(a).
4.5 Material Chemical AnalysisSamples were removed from the following:
weld connection between Exhibits A and B
weld connection between Exhibits 543/525 and 527
base metal: Exhibits A(column flange), B (angle), 543 (column flange) and 527(angle).
Information collected from the original construction drawings indicated that the structural
sections were made from Grade 300W material and that a 7018 electrode was used for
fabrication. The properties of these materials are used as the basis for comparison of the
measured material properties.
Weld nuggets were removed from Exhibit A and 543 column flange by sawing off a length
sufficient to have more than 2 g. The location of these nuggets with respect to the top of the
weld are approximately 100 mm.
For Exhibit A and 543 the flange material was removed from one of the locations where the weld
macroscopic samples were removed. The same procedure was adopted for removing angle
material from Exhibit B and 527.
The samples were sent to Exova Labs in Burlington, Ontario for chemical analysis. The results
are presented in Table 4.3. The base metal compositions meet the CSA 300W requirements.
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These requirements are C (max) 0.22, Mn 0.5 to 1.5, P (max) 0.04, S (max) 0.05 and Si (max)
0.40.
Table 4.3: Chemical Analysis Results, wt%
Sample C Si Mn S P Cr Cu Ni Al V Ti
A (flange) 0.20 0.03 1.11 0.02 0.01 0.03 0.26 0.05
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Figure 4.18: Flange Sample Extracted From Exhibit 511
The tensile test was performed at quasi-static rate following ASTM E8. The load and specimen
gauge length extension was acquired during the test. The acquired data was post processed toobtain the stress-strain curve, yield strength (0.2% off set) and the tensile strength. The total
elongation at fracture on a 50 mm gauge length was measured after the test was completed.
Figure 4.19 displays the stress-strain curve and Table 4.4 presents the yield strength, tensile
strength and elongation. The results met the CSA 300W requirements. These requirements are,
300 MPa (min) yield strength, 450 620 MPa tensile strength and 23% (min) elongation (50 mm
gauge length).
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Figure 4.19: Stress-Strain Curve from Tension Specimen from Flange of Exhibit 511Information collected from the original construction drawings indicated that the structural
sections were made from Grade 300W material and that a 7018 electrode was used for
fabrication. The properties of these materials are used as the basis for comparison of the
measured material properties.
Table 4.4: Measured Tensile Properties For Exhibit 511
Sample Yield Strength(MPa)
Tensile Strength(MPa)
Total Elongation (%)
511 (flange) 327 487 42.5
CSA 300W >300 450 620 >23
4.6.2 Hardness TestingThe metallographic sample shown in Figure 4.9 was used to perform hardness traverse across the
weld, HAZ and base metal. The macrograph of this sample is again presented in Figure 4.20 to
illustrate the hardness traverse locations. Hardness was carried out in a calibrated Vickers
Machine using the 5 kg load. The locations of the traverse are marked by the red broken lines.The locations represent (1) sub-surface regions of the column flange and (2) mid-thicknessregion of the angle.
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Figure 4.20: Macrograph at Section Plane 630 mm from Top (Side 1) of Exhibit 530
The detailed results of the hardness testing are presented in Appendix B where the individual
hardness readings are provided for each indentation of the two traverses. The results show that
for the column flange sub-surface traverse (identified as 1 in Figure 4.20), the average base metal
hardness is VHN 175 and average weld metal hardness is VHN 226. The peak hardness observedon this traverse was VHN 260 at the fusion boundary (coarse grained heat affected zone), as is
typical for welded connections.
For the hardness traverse along line 2 (as identified in Figure 4.20) an average hardness value of
VHN 165 was measured for the angle base material and an average harness value of VHN 226
was measured for the weld metal. The peak hardness, observed at the weld fusion boundary
(coarse grained heat affected zone) was VHN 237.
These hardness measurement results indicate that an over-matched weld was deposited in
construction, as is accepted construction practice. The weld metal ultimate strength exceeds that
of the column flange and angle material. The lower hardness of the angle, compared to theflange indicates that the tensile strength of the angle is lower than that of the column flange.
Vickers hardenss measurement was also carried out on metallographic sections from Exhibits A
and 543. These sections are presented for Exhibits A and 543 in Figure 4.7 (section plane 260
mm) and Figure 4.8 (section plane 220 mm), respectively. For Exhibit A the average base metal
hardness is VHN 154 and the weld metal average hardness is VHN 218. For Exhibit 543 the
average base metal hardness is VHN 153 and the weld metal average hardness is 227. Theresults indicate that the weld metal is over-matched, as would be expected in these two welds as
well.
2
1
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5 CORROSION RATE ESTIMATEBased upon the measured weld sizes and structural section thicknesses at the time of this
investigation (i.e., as-received ) and the nominal weld sizes and estimated original section
thicknesses (i.e., at construction ), uniform corrosion rates have been estimated. The estimatedcorrosion rates are listed in Table 5.1 and Table 5.2 for the weld leg lengths and for the section
thicknesses, respectively. Table 5.1 and Table 5.2 include the diminished weld lengths and
section thicknesses; i.e., the change in length and thickness, as calculated from the nominal less
the as-received and estimated original dimensions presented in Tables 4.1 and 4.2. In estimating
the corrosion rates, it is assumed that the components have been subjected to corrosion
uniformly. Further, the corrosion rate as determined is based on a service life of 32 years; i.e.,
assuming construction during 1980. The corrosion rate is therefore estimated using the
following equation:
Table 5.1: Estimated Decreased Weld Dimensions due to Corrosion and Corrosion Rate
Corroded Length [mm] Weld Corrosion Rate[mm/y]
Side 1 Side 2 Side 1 Side 2Weld Specimen
LAngle LFlange LAngle LFlange LAngle LFlange LAngle LFlange
Failed
WeldA130 / B130 3.5 5.0 3.5 5.0 0.109 0.156 0.109 0.156
A260 / B230 2.5 1.0 2.0 0.5 0.063 0.031 0.063 0.016
Table 5.2: Estimated Decreased Section Thicknesses Due to Corrosion
Corroded Thickness [mm] Section Corrosion Rate [mm/y]
Side 1 Side 2 Side 1 Side 2Weld Specimen
tAngle tFlange tAngle tFlange tAngle tFlange tAngle tFlange
Failed
WeldA130 / B130 5.4 4.9 3.9 4.9 0.169 0.153 0.122 0.153
A260 / B230 3.6 0.9 2.4 0.5 0.113 0.028 0.075 0.016
The corrosion rates expressed in Tables 5.1 and 5.2 differ in that the Section Corrosion Rates
(Table 5.2) are based upon corrosion attached on two surfaces while the Weld Corrosion Ratesare based upon single surface corrosion. Therefore when comparing these rates, the Section
Corrosion Rate (Table 5.2) should be divided by 2.
These estimated corrosion rates are approximate values and should be considered lower bound
values. While these calculations assume a uniform corrosion rate from the date of construction
until they were removed from the failure site, it is known that the structural components were
coated. The coating would be expected to play a role in preventing the onset of corrosion,
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although it would have a finite life. If the coating life was assumed to be approximately five
years on average, the estimated corrosion rates presented in Tables 5.1 and 5.2 would increase by
18.5%.
5.1 Structural Coating Life and Corrosion RatesA literature review of available corrosion rate data was used to identify statistics related to
structural coating life, general corrosion and pitting corrosion rates. Since structural detail
corrosion rates and coating quality data is not generally available for steel civil structures, data
used to infer steel corrosion wastage rates were drawn from the marine industry. 3,4,5 This
comparison is considered appropriate if the failed structural connection was assumed to operate
in a humid environment in the presence of salts or chlorine ions.
The marine industry coating life statistics for a given structural connection are defined basedupon the connection detail location and environment. These coating life values are considered to
be statistically distributed based upon a normal distribution that theoretically represents thevariability in the paint application quality. Data collected from the literature indicates that the
mean life of coatings ranges from 5 to 10 years. This range in coating life is related to the
component location and environment. From literature, the coating life normal distribution
statistics outlined in Table 5.3 can be used.
Table 5.3: Coating Life Statistics
Coating Life [years]Locations
Mean Coeff. of VariationLiving Space 10 0.2Exterior Deck 9 0.2Interior Deck 10 0.2Dry Cargo Space 1* 0.3Ballast Tank 5 0.3Liquid Cargo Space 7 0.3
* Low coating life is due to expected abrasion in cargo loading and unloading.
The marine industry mean corrosion rates, once coating failure has occurred, are assigned to a
component based on location and environment. In addition, a coefficient of variation incorrosion rate (COV = standard deviation/mean) can be assigned to each component. The
corrosion rate mean and coefficient of variation data can be drawn from the data collected fromthe literature and presented in Table 5.4.
3Tanker Structure Cooperative Forum, Condition Evaluation and Maintenance of Tanker Structures , TSCF,
Published by Witherby & Co, 1992.4
Ge Wang, John Spencer, Tarek Elsayed, Estimation Of Corrosion Rates Of Structural Members In Oil Tankers ,
22nd International Conference on Offshore Mechanics and Arctic Engineering, 2003.5 A. Dinovitzer, Life Expectancy Assessment of Ship Structures , US Ship Structure Committee SSC-427
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Table 5.4: Corrosion Rate Statistics
Liquid Cargo [mm/y] Ballast[mm/y]
Ullage/Dry Space
[mm/y]Structure Type Class Mean COV Class Mean COV Class Mean COV
Deck 1 0.05 1.7 5 0.19 1.1 9 0.02 0.6Deck Stiffener 2 0.09 2 6 0.16 1.4 10 0.02 0.6Side 3 0.06 0.6 7 0.07 0.04 11 0.02 0.6Bottom 4 0.05 1.7 8 0.19 1.1 12 0.02 0.6
The potential for pitting or weld zone preferential corrosion was considered in the marine
industry data with a pitting corrosion rate for those components whose coatings have broken
down. The rate of pitting corrosion assignment can be based on the corrosion data collected in
the literature review. Pitting corrosion affects the integrity of the structure by reducing the
effectiveness of the weldment. Pitting corrosion rate data available for consideration is shown inTable 5.5.
Table 5.5: Pitting Corrosion Rate Data
Liquid Cargo [mm/year]* Ballast [mm/year] Ullage/Dry SpaceStructure Type
Mean COV Mean COV Mean COVAll Connections 1.5 0.11 2 0.2 0 0
5.2 Comparison of Corrosion RatesBased on the estimated corrosion rates listed in Tables 5.1 and 5.2 for the weld sizes and for
section thicknesses respectively, the mean and standard deviations of the data are listed in Table5.6. As noted previously, these corrosion rates ignore the protection afforded by the coating and
assuming a 5-year coating life would be 18.5% higher if the corrosion wastage occurred over a
time duration that was five years shorter.
Table 5.6: Estimated Corrosion Rate Statistical Parameters
Mean Standard Deviation COV
[mm/year] [mm/year] [-]
Weld Sizes 0.088 0.053 0.61
Section Thicknesses 0.104 0.058 0.56
Combined (Weld Sizes andSection Thicknesses) 0.096 0.055 0.57
Given the statistics listed in Table 5.4, the estimated corrosion rates provided in Table 5.6 are
aligned with those corresponding to liquid cargo structural corrosion rates in the marine industry
or those associated with a ballast tank, but certainly exceed those for a marine structural dry
(high humidity) space.
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6 CONCLUDING REMARKS RELATED TO CONNECTION DETAIL FAILUREPROCESS
The investigation completed by BMT Fleet Technology Limited did not identify any specific
issues with the original construction quality of the welded connection that failed. The measuredmaterial properties were in good agreement with the specified properties of the materials listed in
the original design drawings (Section 4.5).
The connection detail that failed experienced a significant level of corrosion degradation
(Section 5.1) reducing the load carrying capacity of the connection detail. The weld corrosion
rate was accelerated due to the marine (Section 5.2) like environment (moisture and salinity)
and the welding electrode chemistry that resulted in localized preferential corrosion of the weld
metal after the connection protective coating became ineffective (Section 4.4).
The fractographic evidence in the weld failure region, from 130 to 260 mm from the top of the
weld, showed the failure surface was pitted due to corrosion and included black oxide indicatingthat the failure occurred along the weld some months before final separation (Section 3.1)
The macrographic presentations also indicate metal loss in the assembled weld connections
(Section 4.2). The larger losses are seen at a section plane 130 mm where the leg length of the
connection to angle section is at the minimum. This observation suggests that a significant
amount of material was lost due to the corrosion process that continued after the weld fracture.
The micrographic examination (Section 4.3.3) indicates that it is most likely that the last
ligament of the connection to fail was the upper end of the angle section of Side 1. This
comment is supported by several factors including the rotation (or prying) of the remaining piece
of the angle section form the column flange, and the absence of corrosion pits on this failuresurface. In order for the deformation observed in the angle component to occur, the bulk of the
welded connection must have failed prior to separation of this ligament.
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APPENDIX A
EXHIBIT LIST
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Figure A.1: 527 End View
Figure A.2: 527 Side View
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Figure A.3: Sample 530
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Figure A.4: Sample 525 and 543
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Figure A.5: Exhibit 511
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Figure A.6: Sample A
Figure A.7: Sample B
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Figure A.8: Sample B (side)
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APPENDIX B
HARDNESS TESTING
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NP
Loc ation Oc ular Reading Hardnes s c ular Readin Har dnes s
BM-1 233 171 BM-19 (T/4 ) 240 161
BM-2 232 172 BM-20 (T/4 ) 238 164
BM-3 226 182 BM-21 (T/4 ) 234 169
HAZ-4 214 202
HAZ-5 215 201 HAZ-22 229 177
HAZ-6 204 223 HAZ-23 225 183
HAZ-7 192 252 HAZ-24 218 195
HAZ-8 189 260 HAZ-25 208 214
FL-9 194 246 HAZ-26 198 237
W-10 203 225
W-11 201 229W-12 200 232 W-27 203 225 Comments:
W-13 203 225 W-28 202 227
W-14 206 218 W-29 201 229
FL-15 195 244 W-30 199 234
HAZ-16 201 229
HAZ-17 219 193
BM-18 225 183 ACCEPT
Average #DIV/0! Average REJECT
sub S traverse on column flange traverse on angle
Load 5 (kg)
Procedure:
Date:
Report Number: 30160 Exhibit '530' Side 1 60mm from to
ASTM E92
JC
530_S1 60mm from end Macro sketch
Vickers 5 kg load
13-Dec-12
Checked by:
Applicable Standard:
Technician:
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