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

Washington County, Oregon

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TVWD Location

Washington County, Oregon

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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

Washington County, Oregon

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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

Washington County, Oregon

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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

Washington County, Oregon

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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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Dissimilar Metal Corrosion

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Dissimilar Metal Corrosion

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Dissimilar Metal Corrosion

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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

Washington County, Oregon

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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

Washington County, Oregon

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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

Washington County, Oregon

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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

Washington County, Oregon

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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 dont get along well with Patch pads

Pipe needs to dry prior to placing patc