norr report algo mall study

7/29/2019 NORR Report Algo Mall Study

1/70

Reference:30160FR (Rev. 02)

Date: 07 Febuary 2013

COMMERCIAL-IN-CONFIDENCE

Algo Mall Study


2/70


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]


3/70


4/70


BMT Fleet Technology Limited 30160FR (Rev 02)

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.


5/70



Algo Mall Study iii

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


6/70



Algo Mall Study iv

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


7/70



Algo Mall Study v

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


8/70



Algo Mall Study vi

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


9/70



Algo Mall Study vii

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


10/70



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.


11/70



Algo Mall Study 2

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


12/70



Algo Mall Study 3

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)


13/70



Algo Mall Study 4

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


14/70



Algo Mall Study 5

(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


15/70



Algo Mall Study 6

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


16/70



Algo Mall Study 7

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


17/70



Algo Mall Study 8

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


18/70



Algo Mall Study 9

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


19/70



Algo Mall Study 10

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


20/70



Algo Mall Study 11

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


21/70



Algo Mall Study 12

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


22/70



Algo Mall Study 13

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


23/70



Algo Mall Study 14

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


24/70



Algo Mall Study 15

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


25/70



Algo Mall Study 16

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


26/70



Algo Mall Study 17

(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


27/70



Algo Mall Study 18

(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


28/70



Algo Mall Study 19

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


29/70



Algo Mall Study 20

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


30/70



Algo Mall Study 21

(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.)


31/70



Algo Mall Study 22

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


32/70



Algo Mall Study 23

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


33/70



Algo Mall Study 24

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


34/70



Algo Mall Study 25

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)


35/70



Algo Mall Study 26

(a) Side 2

(b) Side 1

Figure 4.7: Failed Weld A260/B230


36/70



Algo Mall Study 27

(a) Side 1

(b) Side 2

Figure 4.8: Demolition Separated Weld 543_220/527_220


37/70



Algo Mall Study 28

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.


38/70



Algo Mall Study 29

Table 4.2: Estimated Section Thicknesses

Estimated Original

Thickness [mm]

As-Received Thickness [mm]


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


39/70



Algo Mall Study 30

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


40/70



Algo Mall Study 31

(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


41/70



Algo Mall Study 32

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


42/70



Algo Mall Study 33

(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


43/70



Algo Mall Study 34

(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


44/70



Algo Mall Study 35

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


45/70



Algo Mall Study 36

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


46/70



Algo Mall Study 37

(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


47/70



Algo Mall Study 38

(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).


48/70



Algo Mall Study 39

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.


49/70



Algo Mall Study 40

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


50/70



Algo Mall Study 41

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).


51/70



Algo Mall Study 42

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.


52/70



Algo Mall Study 43

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


53/70



Algo Mall Study 44

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]


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]


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,


54/70



Algo Mall Study 45

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


55/70



Algo Mall Study 46

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.


56/70



Algo Mall Study 47

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.


57/70



Algo Mall Study A-1

APPENDIX A

EXHIBIT LIST


58/70



Algo Mall Study A-2


59/70



Algo Mall Study A-3


60/70



Algo Mall Study A-4


61/70



Algo Mall Study A-5


62/70



Algo Mall Study A-6

Figure A.1: 527 End View

Figure A.2: 527 Side View


63/70



Algo Mall Study A-7

Figure A.3: Sample 530


64/70



Algo Mall Study A-8

Figure A.4: Sample 525 and 543


65/70



Algo Mall Study A-9

Figure A.5: Exhibit 511


66/70



Algo Mall Study A-10

Figure A.6: Sample A

Figure A.7: Sample B


67/70



Algo Mall Study A-11

Figure A.8: Sample B (side)


68/70



Algo Mall Study B-1

APPENDIX B

HARDNESS TESTING


69/70



Algo Mall Study B-2

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:


70/70

norr report algo mall study

Documents