presented by: tony serdenes, greenman- pedersen maintenance coating- spot repair and primer as an...
TRANSCRIPT
Presented by: Tony Serdenes, Greenman-Pedersen
Maintenance Coating- Spot Repair and Primer as an Alternative to Full Coating Removal
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
surveyStep 2: List potential maintenance painting
optionsStep 3: Select appropriate maintenance
painting optionsStep 4: Establish implementation proceduresStep 5: Implement maintenance painting
optionsStep 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/Structural 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
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 layer
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
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
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 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
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.