Anode Retrofitting - PNWS-AWWA · •What is Anode Retrofitting? •Anode Retrofit Pilot Program...

Anode Retrofitting Lengthen Pipe Service Life at a Fraction of the Cost of Replacement

Matthew Palmer

Tualatin Valley Water District

Washington County, Oregon

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Presentation Outline

• Galvanic Corrosion Cells

• Premature Failure of Pipelines

• What is Anode Retrofitting?

• Anode Retrofit Pilot Program

• Cost Comparison vs. Pipe Replacement

• Identified Issues

• Further Research


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TVWD Location


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TVWD Background

• 2nd largest water district

• ± 200,000 people served1

• 28 pressure zones

• 12 pump stations

• ± 800 miles of pipe

• ± 19 MGD (ADD)

• 60 MG water storage

1 Seattle Public Utilities serves water to ± 1.3 million

Galvanic Corrosion Cells


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Corrosion is the deterioration of a substance or its properties as a result of an undesirable reaction with the environment. NACE International


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Anode Location where corrosion takes place

Cathode Location where corrosion does not occur

Electrolyte Soil, Water, Moisture, etc.

Metallic Path Pipe, wire, etc.

Galvanic Corrosion Cell (Metallic Pipe)

Four Elements for Corrosion to Occur


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23 year old Ductile Iron (Hillsboro)


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Unknown Age Ductile Iron (Tigard)


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Dissimilar Metal Corrosion


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The Galvanic Series Difference in voltage potential

Typical Service Material

Typical Main Material

CORRODES


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• Pipe life is expected to be a minimum of 50 years.

• Corrosive soils is causing pipe failure after 25-30 years.

• District cannot afford to replace piping on a 25- to 30-year replacement schedule.

Premature Failure of Pipelines

A Potential Solution?

Anode Retrofitting

What is Anode Retrofitting?


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Anode Retrofitting is the practice of:

• connecting sacrificial anodes to existing, corroding pipe

• to minimize or halt the effects of galvanic corrosion

• while minimizing disruption to the surface above existing pipe.


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The Galvanic Series Difference in voltage potential

Typical Service Material

Typical Main Material

Typical Anode Materials CORRODES


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Anode Location where corrosion takes place

Cathode Location where corrosion does not occur

Electrolyte Soil, Water, Moisture, etc.

Metallic Path Pipe, wire, etc.

Pipe with Sacrificial Anode Installed

ANODIC AREA

(CORRODING)

WELD TO PIPE


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Anode Retrofit Pilot Program


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Pilot Program Goals

The goal of the Anode Retrofit Pilot Program is to:

• Determine necessary tools/equipment/material

• Determine procedures for anode installation

• Determine average cost on a per LF basis

• Determine allowable anode spacing

• Generate policy for when to install anodes vs. replacing pipe vs. letting pipe go to failure


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Anode Retrofitting Beta Test

Beta Test Location: NW Damascus St., Portland, OR

January 6, 2015

What information was collected?

• Average time to excavate, install anode, and backfill

• Equipment used to perform the work

• Type of materials used and quantities

• Issues that our crews observed during installation


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Installation Procedure: 6 Easy Steps!

• STEP 1: Excavation

• STEP 2: Remove Asphaltic Coating from Pipe

• STEP 3: Weld Anode Lead Wire to Pipe

• STEP 4: Place Weld Patch Pad over Weld Location

• STEP 5: Place Anode

• STEP 6: Backfill and Surface Restoration


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STEP 1: Excavation

• Crews used a Hydro Excavator to excavate over top of weld locations.

– Minimize disturbance at surface

– Keeps excavation size to a minimum


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STEP 2: Remove Coating on Pipe

• Prior to welding anode lead wire to pipe, coating (typically asphaltic) must be removed.

• Grinder powered by portable generator.

Grinder-On-A-Stick™


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STEP 3: Weld Anode Lead Wire

Cadwelder-On-A-Stick™

• Anode lead wire to be exothermically welded to pipe using a handheld Cadwelder.

• Rubber bands break as weld is made.

• Works surprisingly well!


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STEP 4: Install Weld Patch Pad

• Once the weld is made, grinded pipe area must be protected.

• Multiple products on the market today for this exact use.

• Handy Cap IP and Trenton Patch Pad have been tried by the District.


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STEP 5: Place Anode

• Pre-packaged anode is dropped into place, offset from the existing pipeline.

• Depending on the size of the existing pipe and soil corrosivity, different size anodes will be used.


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STEP 6: Backfill and Surface Restoration

• Anode is backfilled with sand and native soil. Water is dumped into anode pit to consolidate material.

• Trench is backfilled with crushed aggregate.

• Surface restoration:

– Gravel, native soil

– Asphalt, concrete

Cost Comparison to Pipe Replacement


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• District uses $23/in-dia to estimate per LF pipe replacement costs

– Historical project financial data used to generate value

• Includes all pipe, excavation, service reconnections, backfill, surface restoration

Cost of Pipe Replacement

Pipe Diameter Cost per LF

6” $138

8” $184

12” $276


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Cost Type Includes… Cost per Hour Cost per AnodeA

Labor Staff time (5 person crew) and benefits $341.13 $85.28

Equipment Hydro Excavator, Dump trucks, etc. $166.50 $41.63B

Material Anodes, sand, rock, welding cartridges - $138.39C

Total (per anode) $265.30

Total (per LF of pipe) $14.74

Cost of Anode Retrofitting

Assumptions:

A Crews installed anodes every 15 minutes.

B Cost assumes excavation is within gravel. C Cost assumes 17 pound anodes, installed every 18 feet.


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Pipe Diameter Cost per LF Anode per LF % of Replacement

6” $138 $14.74 10.7%

8” $184 $14.74 8.0%

12” $276 $14.74 5.3%

16” $368 $18.00 4.9%

Anode Retrofit versus Pipe Replacement

• Spoiler Alert! Anode Retrofitting is cheaper than Pipe Replacement

Upsize to 32 Lb. Anode


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0

50

100

150

200

250

300

350

400

6" 8" 12" 16"

$ p

er

foot

Pipe Diameter

Anode Retrofitting vs. Pipe Replacement

Replacement Anode Retrofit


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• Anchorage Water & Wastewater Utility (AWWU) states 10% the cost of pipe replacement (2014).

• Des Moines Water Works (DMWW) states less than 10% the cost of pipe replacement (2005).

• TVWD has found that it is less than 10% the cost of pipe replacement, depending on pipe diameter.

– Assuming gravel surface, more if in asphalt/concrete

What have other utilities found?


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How much life does it add?

• Much factors into this answer:

– Condition of pipe at time of anode retrofitting

– Corrosivity of native soil

– Native backfill vs. crushed aggregate backfill

– Proper sizing and placement of anodes

• Des Moines Water Works (DMWW) states an additional 20 years (2005).

• Others have estimated 25 years of added life


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• Anode retrofitting is a valuable tool in lieu of pipe replacement in some situations.

• Cost savings are large but variable (dependent on pipe dia.)

• Very cost effective for large diameter pipes, especially welded joint pipes (steel transmission mains, larger spacing possible).

• Years of life added is not clearly defined, some other pilot programs have stated 20 to 25 years.

TVWD Conclusions


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• Local jurisdictions: max core size of 8” diameter.

– 8” hole not feasible, not enough room to place anode

– May require full lane grind and inlay

• Wet pipes don’t get along well with Patch pads

– Pipe needs to dry prior to placing patch pad

Identified Issues


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• Electrical continuity across non-bonded pipe joints

– If continuity is found to be acceptable, increasing spacing of anodes to lower retrofitting costs is an option.

• Determine better method to estimate remaining pipe life

– Better prioritize anode retrofitting projects

– Acoustic pipe wall assessment, electromagnetic inspection, etc.

– Currently based on visual inspection.

Further Research


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Thank you

Ryan Smith, Tualatin Valley Water District

Mike Britch, P.E., Tualatin Valley Water District

George Richards, Cascade Corrosion Consulting Services, Inc.


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