Anode Retrofitting - PNWS- · PDF file•What is Anode Retrofitting? •Anode Retrofit...

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Transcript of Anode Retrofitting - PNWS- · PDF file•What is Anode Retrofitting? •Anode Retrofit...

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

    Matthew Palmer

    Tualatin Valley Water District

  • Washington County, Oregon

    2

    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

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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)

  • Washington County, Oregon

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    Unknown Age Ductile Iron (Tigard)

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  • Washington County, Oregon

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    Dissimilar Metal Corrosion

  • Washington County, Oregon

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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?

  • Washington County, Oregon

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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.

  • Washington County, Oregon

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    The Galvanic Series Difference in voltage potential

    Typical Service Material

    Typical Main Material

    Typical Anode Materials CORRODES

  • 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.

    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

  • 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!

  • Washington County, Oregon

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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.

  • Washington County, Oregon

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  • Washington County, Oregon

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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.

  • Washington County, Oregon

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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

  • Washington County, Oregon

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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

  • Washington County, Oregon

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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.

  • Washington County, Oregon

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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

  • Washington County, Oregon

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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?

  • Washington County, Oregon

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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