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5-Year Water Storage Tank Inspection 250,000 Gallon Michael St tank
Norwalk, CT CorrTech Report No. 13568-FOR-01
Prepared For:
South Norwalk Electric & Water
164 Water St. Norwalk, CT 06856-0468
25 South Street Hopkinton, MA 01748
November 2018
STATEMENT OF LIMITATION
The conclusions presented in this document are based on the services described and not on tasks or procedures beyond the scope of the described procedures or the time and budgetary constraints imposed by the contract limitations. CorrTech, Inc. has performed this assessment in a professional manner using that degree of skill and care exercised for similar projects under similar conditions by reputable and competent consultants, and in accordance with the procedures established within CorrTech’s quality assurance, quality control protocol. CorrTech, Inc. shall not be responsible for conditions or consequences arising from relevant facts that were concealed, withheld or not fully disclosed at the time the evaluation was performed.
Report Reviewed by: Ted Lund NACE CIP Level III #050
July 2019
TABLE OF CONTENTS
INTRODUCTION ....................................................................................................................... 1
EXECUTIVE SUMMARY ........................................................................................................... 1
OBSERVATIONS ....................................................................................................................... 2
RECOMMENDATIONS .............................................................................................................. 4
APPENDIX I
Photographs APPENDIX II Dry Film Thickness
Michael St
South Norwalk Electric & Water.
CorrTech Report No. 13568-FOR-01
Page 1
INTRODUCTION On November 8, 2018 CorrTech representatives Garth Lund and Ben Palmer performed a corrosion and structural assessment of the exterior and interior of the South Norwalk Electric & Water Michael St tank in Norwalk, CT. The inspection was conducted to establish the current condition of the tank's steel structure and coating systems. The tank inspected included:
Michael St Tank This work was completed under an agreement between South Norwalk Electric & Water and CorrTech Inc., referenced under South Norwalk Electric & Water PO number 009013 dated 8-31-2018 and performed under CorrTech job number 132568. The tank was inspected in accordance with the latest version of AWWA D101 53 (86R) standard for water tank inspections CT DPH RCSA Section 19-12, and the M42 AWWA Tank Guidance Manual. The interior of the reservoir was inspected with the TankRover, remotely operated vehicle, while in-service. TankRover is the only piece of equipment like it in the United States and was developed by CorrTech. By using the TankRover the interior of the tank was inspected with no special preparation, additional disinfection or downtime. The TankRover is equipped with a surface-cleaning tool used to remove loose rust or debris in order to view the potential metal loss under the coating. The unit has high-powered thrusters, which are used to maneuver throughout the tank and are used to wash away bottom sediment for observations. The exterior portions of the tank were inspected by walking the roof. Shell portions were visually inspected from the ground. The objectives of the assessment were to: 1. Perform field inspections and tests to assess the structural and coating integrity of the
tank. 2. Review the safety compliance of tank ladders and access. 3. Review sanitary conditions and protection. 4. Provide recommendations for rehabilitation. EXECUTIVE SUMMARY
Condition and recommendations for the tank are briefly summarized in this section. For detailed
information regarding tank conditions and specific recommendations please refer to the
designated tank section.
Three small holes were observed on the roof near deformations at the knuckle, which need to
be sealed as soon as possible. Holes appear to be the result of weld deformation not corrosion
penetration.
Overall exterior coating is failing with extensive rust penetrating the coating on all surfaces.
Coating is very brittle and aged with micro-cracking. Tank should be scheduled for complete
Michael St
South Norwalk Electric & Water.
CorrTech Report No. 13568-FOR-01
Page 2
exterior recoating. Interior coating is not in need of replacement but it may be more economical
to repaint full tank at same time.
Anchor nuts are corroding away or are completely gone. Anchors need to be repaired to provide
original overturn prevention.
Roof vent is combined with access hatch into the wet area of the tank. Roof vent does not meet
current CT DPH requirements. Vent screen is exposed to wind driven rain and does not have
insect screen. We do not suggest covering the existing vent screen with 24-mesh screen as it
may frost over. Existing dents and deformation in the roof may be indicators of past negative
pressure events during the winter.
OBSERVATIONS Photos provided in the report were created from a digital camera and interior pictures were captured in digital format from the interior video. Interior images are as clear as our printed technology will allow. Copies in the report provide a reference for our comments. Keep in mind that for underwater video snaps, the video provides the greatest detail and should be viewed as part of the report. Narration on the video is done in the field and some of the comments may be different than the written report.
250K Gallon Michael St Tank Michael ST is a pedisphere structure located at 12 Michael St, Norwalk, CT. The tank is approximately 129-ft tall and 45-ft in diameter. Tank construction date was not provided but it is reported that the tank was repainted in 1991. Last full inspection was performed in 2013. INTERIOR Inspection ROV was deployed into the tank through the existing 24-in round combination roof hatch/vent. Roof hatch is equipped with a 2-in sanitary curb and a 2-in overlapping hatch cover. Hatch was not equipped with a lock but tank security is provide by the locked bottom steel door. Roof (ceiling) Roof is a self-supporting dome structure with a radial stiffeners around the perimeter. Edge corrosion has formed along 10% of the roof lap joint seams. Three small holes were observed in the roof plates near the deformed locations in the knuckle. Holes are less than ¼-in in diameter and located right on weld seams. Ladders Interior wet area ladder is intact with no section loss. Shell
Michael St
South Norwalk Electric & Water.
CorrTech Report No. 13568-FOR-01
Page 3
Shell coating has heavy iron and sediment staining with less than 1% active corrosion. Active corrosion is minor and primarily on the weld seams. Floor/Bowl Floor/bowl of the tank has a sediment buildup of over 6-in around the riser pipe. Review of the 2013 inspection report shows the sediment depth to be similar with little additional accumulation. Inlet/ Outlet Tank has a combination inlet/outlet pipe located near the floor to shell seam on the cone. This pipe is 10-12 inches above the sediment blanket. EXTERIOR Roof Roof has overall coating delamination on 35% of the surface with15% of the delamination topcoat delamination to the mid-coat and 20% of the delamination is to the steel substrate. Several areas of plate deformation were observed on the knuckle near the circumference weld. These deformations were also noted in the 2013 inspection along with one small hole. Dry film thickness readings were taken on the roof coating. High reading was 27.9 mils, low reading was 8.3 mils and the average was 13.9 mils, see Appendix II. Vent Tank is equipped with a finial vent screen that is an extension of the wet area hatch neck. The vent collar is formed from a perforated steel plate. Vent plate openings are roughly equal to a 6-8 mesh screen. Ladders and Railings Tank ladder begins at grade inside the locked column base. Ladder rungs are 11-in rung to rung, 8-in rung to shell wall, and 15-in wide. No section loss was observed on the ladder. Ladder is equipped with a notched rail style fall arrest system. Overflow Pipe Overflow pipe consist of a pipe that runs down the riser pipe to the base of the column and discharges above ground into a storm drain. Overflow has 14-in airgap and an internal insect screen for protection. Shell/Bowl Shell has coating general corrosion on 50% of the surfaces with rust bleeding through the coating. Coating is cracked and brittle allowing moisture through to the steel. No large areas of coating delamination where observed.
Michael St
South Norwalk Electric & Water.
CorrTech Report No. 13568-FOR-01
Page 4
Stem Tank is supported by a tubular steel column. Column is anchored to the foundation via (14) 1.5-in diameter anchor bolts. Two of the 14 bolts have nuts with heavy corrosion with significant metal loss, in fact one is 100% gone. Interior column s accessed by a standard door that is equipped with a lock. Dry film thickness readings were taken on the column coating. High reading was 24.1 mils, low reading was 9.9 mils and the average was 18.7 mils, see Appendix II. Foundation Concrete ring wall foundation had no cracking or spalling. Interior chime plate has active corrosion on 15-20%. Exterior chime plate has active corrosion on 5%. RECOMMENDATIONS Roof holes need to be sealed immediately with a caulking product such as Sikaflex 1a or Manusbond 75A. When the tank is repainted the holes should be welded. Estimated cost $1,500 Tank exterior should be fully blasted and coated in the next 2-5 years using a properly written job specification and certified coating inspection. Ensure proper surface preparation and coating application for maximum service life from the new coating. Make sure to include extensive stripe coating of exterior plate lap seams and structure welds. All contractors should follow the AWWA D102-latest, AWWA Standard for Painting Steel Water-Storage Tanks with a full-time coatings inspector to ensure proper surface preparation and application. Estimated Cost $350,000. Roof vent does not meet current CT DPH or AWWA D100 standard for sanitary protection. Exposed vent screen is subject to wind driven rain. Insect screens are now part of the normal sanitary standard and in order to use safely these fine screens a special vent assembly is needed. Vents should be installed which can relieve both a positive or negative pressure should the fine mesh screen become clogged. An AWWA vacuum/pressure relief vent provides for the safe use of insect screen and should be designed for easy inspection and maintenance. A new vent should be installed away from the wet area access hatch. Estimated cost $6,000 When tank is repainted OSHA 5,000 lb rated swivel anchors should be added to the roof to allow for proper tie off by climbers. Estimated cost $500 Cracked dry riser hatch cover should be replaced and a restraint chain installed.
Tank should be inspected in 2023 in accordance with AWWA standards
Appendix I Photographs
SNEW--Michael St
DP#01Tank overall
DP#02General corrosion on the exterior of watersphere
DP#03Top of stem and hatch
DP#04Column base
SNEW--Michael St
DP#05Intact anchor bolt
DP#06Topcoat delamination on base cone
DP#07Bowl with corrosion
DP#08Anchor bolt with active corrosion, complete nutloss
SNEW--Michael St
DP#09Overflow discharge point
DP#10Intact overflow screen
DP#11Coating delamination on lower base cone
DP#12Interior of column base
SNEW--Michael St
DP#13Dry riser
DP#14Corrosion on interior chime
DP#15Corrosion on interior chime
DP#16Corrosion on exterior chime
SNEW--Michael St
DP#17Hatch at top of stem
DP#18Roof plates with active corrosion
DP#19Plate deformation on weld seam where smallhole was seen
DP#20Combination wet area hatch and vent
SNEW--Michael St
DP#21Open roof hatch to dry riser
DP#22Active corrosion on roof plates
DP#23Coating delamination on roof plates
DP#24Deformation on plate and hole location
SNEW--Michael St
DP#25Dry riser ladder
DP#26Dry riser cover cracked
DP#27Closed roof hatch to water cavity
DP#28Locked column base door
SNEW--Michael St
00:36Open roof hatch, dry riser ladder and hole inroof
01:22Corrosion staining on roof plates
01:41Hole in roof plates on exterior dent
03:08Open roof hatch, interior ladder, and overflow,3-holes visible
SNEW--Michael St
04:42Typical condition of the shell
10:25Staining on lower shell
24:20Sediment in bowl to riser seam
24:39Inlet/outlet pipe above sediment
SNEW--Michael St
25:19Sediment 6-in +
26:39Overflow floor penetration
Appendix IIDry Film Thickness
Powered by DeFelsko 1
B26 ShellB27 Roof
SNEW-Micheal st Summary# x σ ↓ ↑
Coating Thickness (mils) 90 16.394 3.959 8.31 27.96
Powered by DeFelsko 2
B27Created: 2018-11-08 20:37:30
PosiTector Body S/N: 722083Probe Type: PosiTector 6000 FS
Probe S/N: 178008CAL: Cal 1
Summary# x σ ↓ ↑
Thickness (mils) 45 13.994 3.414 8.31 27.96
Readings# Thickness Time
(mils)
1 12.70 2018-11-08 20:37:332 9.77 20:37:343 8.82 20:37:354 10.97 20:37:365 10.27 20:37:376 8.31 20:37:387 9.30 20:37:398 10.81 20:37:409 13.73 20:37:42
10 10.93 20:37:4311 16.42 20:37:4412 12.21 20:37:4613 12.66 20:37:4714 11.73 20:37:4815 13.08 20:37:4916 17.99 20:37:5017 13.86 20:37:5118 13.73 20:37:5219 16.64 20:37:5320 13.28 20:37:5421 18.07 20:37:5522 15.34 20:37:5623 14.39 20:37:5724 16.40 20:37:5825 13.24 20:37:5926 18.44 20:38:0027 13.25 20:38:0128 13.95 20:38:0229 13.01 20:38:0330 15.70 20:38:0431 21.16 20:38:0532 15.06 20:38:0633 12.78 20:38:0734 14.01 20:38:0835 11.99 20:38:0936 12.27 20:38:10
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B27 Readings# Thickness Time
(mils)
37 14.08 20:38:1138 11.37 20:38:1239 15.86 20:38:1340 12.72 20:38:1441 27.96 20:38:1542 14.23 20:38:1643 16.07 20:38:1744 14.45 20:38:1845 16.74 20:38:19
Powered by DeFelsko 4
B26Created: 2018-11-08 19:05:32
PosiTector Body S/N: 722083Probe Type: PosiTector 6000 FS
Probe S/N: 178008CAL: Cal 1
Summary# x σ ↓ ↑
Thickness (mils) 45 18.794 2.877 9.99 24.10
Readings# Thickness Time
(mils)
1 9.99 2018-11-08 19:06:062 13.36 19:06:073 16.27 19:06:084 14.67 19:06:105 13.11 19:06:106 16.98 19:06:137 19.44 19:06:148 22.41 19:06:159 19.26 19:06:18
10 16.26 19:06:1911 14.63 19:06:2012 20.49 19:06:2313 15.46 19:06:2414 18.54 19:06:2515 19.13 19:06:2916 17.92 19:06:3017 19.54 19:06:3218 17.12 19:06:3319 20.96 19:06:3420 17.23 19:06:3521 19.18 19:06:3622 17.53 19:06:3723 17.25 19:06:3724 16.77 19:06:3825 16.62 19:06:4426 20.29 19:06:4527 20.04 19:06:4628 20.64 19:06:4729 23.72 19:06:4830 19.73 19:06:4931 21.04 19:06:5232 20.21 19:06:5333 21.57 19:06:5434 20.78 19:06:5835 20.30 19:06:5936 21.36 19:07:00
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B26 Readings# Thickness Time
(mils)
37 24.10 19:07:0138 18.83 19:07:0239 22.19 19:07:0340 21.35 19:07:0841 17.56 19:07:0842 20.21 19:07:0943 20.77 19:07:1144 21.74 19:07:1145 19.16 19:07:12
