Structural Designs that Accelerate Corrosion (PowerPoint)

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					Maintenance Coating- Spot Repair
and Primer as an Alternative to Full
Coating Removal

Presented by: Tony Serdenes, Greenman-
Pedersen
 Learning Outcomes
• At the end of this webinar, you will be
  able to:
  – Recognize the proper steps to take when
    developing a maintenance coating plan
  – Determine when to perform spot repair,
    spot repair and overcoating or complete
    recoat of structure
Introduction
• The webinar will define maintenance painting and
  explain the differences between repairing by
  overcoating versus full coating removal and recoat.
  Overcoating is generally defined as the practice of
  painting over an existing coating as a means of
  extending its useful service life. Overcoating may
  be a cost-effective alternative to complete coating
  removal and repainting.
Major Steps in Maintenance
Coating
• Six major steps in a maintenance coating program:
   Step 1: Plan and conduct condition assessment
     survey
   Step 2: List potential maintenance painting
     options
   Step 3: Select appropriate maintenance painting
     options
   Step 4: Establish implementation procedures
   Step 5: Implement maintenance painting options
   Step 6: Plan and implement follow-up activities
Step 1
• Used for several purposes:
  – To determine the need for recoating
  – To determine the extent of corrosion and
    corrosion damage
  – To determine the performance of various
    coating systems
  – To prioritize coating requirements where
    insufficient funds are available to do all
    the desired work
Step 1
• Three types of
  surveys:
  – General Overview
  – Detailed Visual
    Survey
  – Physical
    Coating/Structura
    l Inspection
General Overview
• During a general coating condition
  assessment:
  – Only one or two parameters are rated
    (e.g., general condition or rusting)
  – Structure normally observed from the
    ground
  – A qualitative rating
  – Done in a few hours or less
Detailed Visual Survey
• During a detailed visual
  assessment:
   – Relies exclusively on
     visual observations
   – Numerous structural
     elements are separately
     rated according to SSPC-
     VIS 2, ASTM D610 or
     equivalent
   – Obtain a semi-quantitative
     rating of the percent of
     surface deteriorated
   – May be used to develop
     preliminary cost estimates
     for recoating
Examples of Pictorial Guides
Physical Inspection
• Physical testing is
  required to
  determine
  whether the
  coating can be
  overcoated or
  repaired, or
  whether it is too
  weak to accept
  another coating
Physical Inspection
• A physical inspection of the structure
  and aged coating system should be
  conducted to determine:
  – Film thickness
  – Number of layers of paint
  – Adhesion
  – Underlying substrate condition
  – Coating type
  – Presence of soluble salt contamination
Physical Inspection
• SSPC TU-3, Overcoating provides
  discussion of the value of physical
  testing, as well as the procedures for
  testing
• Table 1 in Appendix A.1 contains a
  table assessing the risk of overcoating
  based on film thickness and adhesion
  of the existing coating
SSPC TU-3, Table 1
Structural Inspection
• Coating
  assessment
  should be included
  as part of any
  general structural
  inspection for loss
  of:
  – Metal
  – Broken joints
Structural Inspection
• Evaluate and record the ratings of
  individual structures or structural
  elements
• Create a sub unit sampling plan,
  identifying the portions of the
  structure or facility that will be rated
  and the type of rating scheme to be
  used
Step 2
• List potential
  maintenance
  painting options:
  – Spot repair only
  – Spot repair and
    overcoating
  – Complete recoat of
    structure
Spot Repair Only
• Surface preparation and touch-up
  coating of localized areas of
  deteriorated coating and corrosion

• Primarily a “stop-gap” method
  – Re-evaluate within 3 to 5 years
Spot Repair Only
• Reasons why spot repair may be
  selected are:
  – Repair are hidden or in a low-visibility
    area
  – Corrosion and degradation are limited to
    isolated areas
    • Less than 1% of total area
Spot Repair And Overcoating
• Involves spot repair of deteriorated
  coating and corroded areas followed
  by the application of a full finish
  coating over the entire surface,
  including spot repaired areas and
  intact coating areas

• Expected to give 5 years or more
  additional life
Complete Recoat of
Structure
• When corrosion and deterioration
  exceed 16% of the total area
Determining Maintenance
Painting Options
Step 3
• Evaluate economics of available
  options

• The variables involved in protective
  coatings often require a variety of
  solutions, each of which will carry
  unique cost-benefit factors
Step 3
• Economic Analysis
  – Initial Vs. Service Life Costs
  – Initial Cost Factors
  – Time Value of Money
  – Analysis
Step 3
• Initial cost factors are:
  – Mobilization/Demobilization
  – Access
  – Preparation
  – Material Costs
     • Container Vs. Coverage
     • Service life of coatings
     • Initial Vs. Service life per square foot
Step 3
• Example of Container
  Vs. Coverage
  Calculation
   – Urethane finish @ 2
     mils
   – Coating A at $30 per
     gallon and 42%
     volume solids
   – Coating B at $35 per
     gallon and 56%
     volume solids
Step 3
• Calculate coverage and assume 20% loss
  factor:

• 1604 X % Volume Solids X (1- Loss Factor)
  / DFT

• Cost analysis of paint material should be
  based on coverage cost NOT cost per
  gallon
Step 3
• Coating A
  – 1604 X 0.42 X 0.74 / 2 = 252.63 square
    feet
  – $30 / 252.663 = $0.119 per square feet
• Coating B
  – 1604 X 0.56 X 0.75 / 2 = 336.84 square
    feet
  – $35 / 336.84 = $0.1039 per square feet
Step 3
• Initial cost factors
  – Surface preparation
  – Application
  – Equipment
  – Curing / drying
  – Interference / downtime
  – Environmental / health / safety
  – Indirect
Step 3
• Net Present Value
   – The value today of a future payment or series of
     payments discounted at the appropriate discount rate
       • Discounting
           – The process of finding the present value of a payment or series
             of future cash flows; the reverse of compounding
• Net Future Value
   – The amount to which a payment or series of payments will
     grow over a given future time period when compounded at
     a given interest rate
       • Compounding
           – The arithmetic process of determining the final value of a
             payment or series of payment when compound interest is
             applied
Step 3
• Economic Analysis
   – Projected life of structure
   – Consider systems
      • Original painting
      • Touch-up (Spot/Spot)
      • Touch-up (Spot/Full)
      • Full repainting
   – Cost calculations
      • Current cost levels
      • Net future levels
      • Net present levels
      • Average equivalent annual cost
Step 4
• Select appropriate maintenance
  painting options and establish
  implementation procedures
  – Identify relevant factors for coating
    system selection
  – Select surface preparation methods and
    coating materials
  – Prepare specification
Identify Relevant Factors for
Coating System Selection
• Coating system selection is influenced
  by special factors such as:
  – Environmental, health and safety
    regulations
  – Budgets
  – Exposure environments
  – Weather
  – Configuration of structure
  – Surface contaminants
Select Surface Preparation
Method
•   Solvent cleaning
•   Hand and power tool cleaning
•   Abrasive blast cleaning
•   Wet abrasive blast cleaning
•   Waterjetting
Select Coating Materials
• The selection of the coating system
  involves two phases:
  – Identify the generic types
  – Identify the criteria for selecting
    materials
Prepare Specification
• Provides a complete
  description of the
  desired work by
  prescribing specific
  procedures,
  processes and
  materials
• Provides criteria for
  acceptance or
  rejection of work
Step 5
• Implement maintenance painting
  options
  – Clean and coat the structure
Step 6
• Plan and implement follow-up
  activities:
  – Establish need for periodic inspection
  – Establish schedules for condition
    assessment
  – Ensure proper documentation and filing
    of historical information
  – Institute preventative maintenance
    measures
Establish Need For Periodic
Inspection
• Inspection should be made of the
  structure within 6 to 12 months after
  application
Establish Schedules For
Condition Assessment
• First condition assessment would
  normally be conducted about 5 years
  after the original application and
  every 3 years thereafter
Ensure Proper
Documentation And Filing Of
Historical Information
• Records of the daily inspection logs
  and coatings should be stored in
  owners files
• Retained coating samples should be
  properly labeled and stored for at
  least 3 years
Institute Preventative
Maintenance
• Regular removal of contaminants
 Summary
• Following a maintenance coating program
  enables the coating to perform its expected
  life and avoid early coating failure. At times
  when repair of the coating is needed an
  evaluation of the condition of the coating
  shall be performed to aid in determining the
  method of repair. Often spot repair or spot
  repair and overcoating is an economical
  alternative to full removal and recoat.

				
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posted:5/28/2012
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