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Down-Tube
End Coating Specification
Rev.
10-21-01
DESCRIPTION
OF WORK
The
ARCOR® down-tube end coating system is currently a
8-10 mil system applied at 6- 8” down the tube
tied in with a 30-40 mils Tubesheet coating system.
The milage is achieved with 2-3 coats. Appropriate
surface preparation will be completed prior to
coating application and environmental controls will
be maintained in accordance with ARCOR®s’
Application Specifications.
Based
on information from visual inspection and the
Tubesheet layout drawings, ascertain the Tubesheet
size and the tube I.D. ranges for the purpose of
supplying proper size tube rollers & flap wheels and
to get an accurate material calculation and abrasive
needs.
Calculated
total surface area of each tubesheet (includes tube
openings).
Calculated
total internal surface area to be coated down each
tube.
Calculate
the Waterbox to Tubesheet joint as number of linear
feet.
Determine
size and location of manway access points.
These manways will serve as ingress and
egress for personnel and equipment.
Determine
accessible locations for equipment as needed
including dust collection, dehumidification, blast,
compressor, sprayer, pressure wash.
Determine
needs for electrical hookups for equipment such as
dust collection, dehumidifier, sprayer, lighting.
Determine
needs for air hookups for equipment such as air tool
manifold.
Determine
needs for scaffolding inside waterboxes to easily
reach all areas of Tubesheet.
APPROACH
TO WORK
ARCOR®
can provide all material, technical support,
supervision, equipment and labor to install the
down-tube protective coating system.
ARCOR®
proposes to coat the tubesheets and waterboxes using
the S-30Ô
Prime / EE-11 coating system; a 100%
solids, multifunctional Novolac epoxy system
designed specifically as a protective coating for
metals in aggressive service/cooling water
environments, particularly in tubesheet environments
where a flexible, resilient coating is
required to resist the long term effects of metal
flex, expansion, contraction and high temperature
gradients between the hot & cold sides.
ARCOR®S-30
PrimeÔ
will be used as the prime coat.
In addition to being a Novolac epoxy, the
S-30 PrimeÔ
contains Zinc Phosphate, which inhibits corrosion
and effectively eliminates undercutting. (Data Sheet
and MSDS on ARCOR® CD-ROM).
ARCOR®EE-11
will be used as the build & topcoat. EE-11 was
designed with the use of reactive plastisizers. This
gives EE-11 flexibility and resiliency while
maintaining its chemical & temperature
resistance (up to 265°F
Immersion, pH 1.0-13.5). This resiliency &
flexibility is crucial in resisting the effects of
flexural & thermal stresses of condenser
tubesheets, particularly at the critical tube/tubesheet
joint. (Data Sheet and MSDS on ARCOR® CD-ROM).
Both
the S-30 Prime®
and EE-11 products can be roller and/or spray
applied greatly reducing application time.
ARCOR®
Test Data (found on the ARCOR® CD-ROM) includes a
copy of a Lehigh University study (1992 & 1993
& summary condensed version) of Atlas Cell
coating disbondment resistance commissioned by
Pennsylvania Power & Light, Northeast Utilities
and Baltimore Gas & Electric. Seven of the most widely used commercial protective coatings
were tested in thin film and thick film variations. ARCORâ’s
S-30Ô
Prime system tested highest in all
categories.
- Down-Tube
Coating System (8 +/- 2 mils):
ARCOR® recommends application of a
three-coat ARCOR®S-30Ô/EE-11 system, for a final dry film thickness of 6-10 mils.
The coating shall cover 6” down each
tube-end (specific conditions may vary the total
length of the tube coating such as level of wear,
presence of tube insert, customer specification
etc.).
Surface
Preparation:
The tubes are prepared for
coating in as follows with certain steps dependant
on whether there is an existing coating present
down-tube.
1.
All tube ends should be trimmed to flush with
Tubesheet. This done for two reasons;
a.
it will allow for a more complete cleaning of
corrosion at the tube/Tubesheet joint and prevent
‘shadowing’ during blast ;
b.
it will allow a smoother more complete tie-in
of the Tubesheet and down-tube coating; peaks and
edges are weak points in any coating system.
A
tube ID cutter is used, no lubricant required. The
mandrel and blades are sized for the specific tube
OD/ID and depth of cut so it is important to obtain
accurate information. Do not rely on specifications
and drawings. Measure yourself.
The
tube/Tubesheet joint is the most critical area, the
most prone to failure, so it is extremely important
that the area be as clean and profiled as possible.
2.
Debur tubes as needed and repair any damaged
ends. Use medium grit flapper wheels and abrasive
grinding cones attached to an air drill attached via
a custom mandrel allowing extension down a full
12” of the tube. The goal is to get a uniform
smooth clean surface free of major surface defects
that can hinder the coating process.
3.
Existing coating is removed by a 10-12,000
PSI Hydro Laser, down the entire tube length,
with a 360°
tip. This will remove 90% of the existing tube
coating with the added benefit of cleaning the
entire tube length. If there is a concern of high
chloride levels and the potential for chloride
contamination, Chlor*Ridâ
should be added to the water. This will neutralize
chlorides. If working with a new or newly re-tubed
unit use a degreaser in first wash.
4.
Coating remaining in the tube ends (difficult
to get with hydro lance process) is cleaned with
handguns using a more concentrated tip. This will
remove all remaining material in the tubes. Any
residual at the tube/tubesheet interface will be
cleaned during the Blast of the tubesheets.
5.
All water in the tubes will then be sucked
out using a Vac truck with a 6” hose. Air horns
are then installed to facilitate full drying over a
48-hour period.
6.
The tubes are profiled using abrasive
blasting. After the sheets are cleaned each tube is
profiled using a lance. Use fine-medium grit Black
Beauty to attain a 1-2 mil profile. The lance is a
12” (longer if coating over 10” down-tube)
3/8” stainless steel tube welded to an adapter to
allow it to be attached to the end of the blast
hose.
The
lance is to be inserted to within 2” of the end of
the tube coating i.e. 4” if coating 6”. The
lance method will result in an approximate 30-40°
blast pattern. Inserting within 2” will allow the
blast to pattern to reach the final 2” and
minimize disturbance of the tube beyond the area to
be coated. Mark the lance with a brite colored tape
at the insertion depth so the blaster can readily
see haw far to insert.
The
blaster inserts the lance to the tape mark then
pulls the trigger and removes the lance at an even
speed. The blaster should count, ‘1001, 1002,
1003’ and be out. Test blast 10 tubes with this
count then stop and inspect. Check for even look to
profile and color over length of area to coat. Check
profile with Testex tape. Adjust count up or down
depending on results i.e. longer count if profile is
<1 mil and color is uneven, shorter if profile is
>2mil. Do
another 10 tube test and review. Continue until
satisfied with consistent results.
7.
The tubes are then blown down with compressed
air. They are then checked for cleanliness and
touched up with an Acetone soaked roller. This will
insure there is no residue in the tube, which could
inhibit proper adhesion.
Down-Tube
Coating:
1.
A Prime coat of the S-30 Prime® will be
roller-applied at a thickness of 2-3 mils to a depth
of 6.0” The depth is controlled via a locking
guide, which slides on the end of the custom made
mandrel. The roller will stop when the guide hits
the tube end. The rollers are a lint-free tube
roller with a ½” nap.
2.
An Intermediate coat of EE-11 will be
roller-applied at a thickness of 2-3 mils to a depth
of 5.5”. The depth is reduced from the Prime coat
to allow for a tapering of the coating as it
terminates within the tube. The locking guide is
moved down the mandrel so the roller will stop when
the guide hits the tube end.
3.
A Topcoat of EE-11 will be roller-applied at
a thickness of 2-3 mils to a depth of 11.0”. The
depth is reduced from the Intermediate coat to allow
for a tapering of the coating as it terminates
within the tube. The locking guide is moved down the
mandrel so the roller will stop when the guide hits
the tube end.
4.
At the completion of the tubesheet coating,
the tube ends are then inspected for runs and or
puddling on the bottom of the tube, as well as any
‘donut’ rings around the tube end.
All defects are addressed with ‘flapper’
wheels and cone grinders to touch-up and smooth out
the tube coating. If necessary additional coating
should be applied.
5.
The amount of material required to coat
tubes @ 10 mils is calculated as follows:
1604/10
mils = 160.4 square feet per gallon,
160.4
x (1.0 - .30) = 160.4 x .7 = 112.3 sf/gal with 30%
waste. Waste in down-tube coating is considerably
higher than in general coating.
2.
Tubesheet
Coating System (30+/- 5 mils):
ARCOR® proposes to apply a three (3) coat ARCOR®S-30
Prime/EE-11Ô
system, for a final dry film thickness of 45 mils.
The coating shall cover the entire Tubesheet.
1.
The Tubesheets will be Hydro Lased at
35-40,000 PSI to remove all existing coating and
fully clean the surface. This step is recommended if
an existing cladding system is present i.e. 100+
mils, or if the existing coating is very well
adhered. The Hydro Laser removes coating quickly and
without resulting large quantities of waste
abrasive. If there is a concern of high chloride
levels and the potential for chloride contamination,
Chlor*Ridâ
should be added to the water. This will neutralize
chlorides. If working with a new or newly re-tubed
unit use a degreaser in first wash.
2.
Each Tubesheet is the abrasive blasted with
1243 medium grit Black Beauty (Coal Slag) to profile
the tubesheet face at 3+ mils.
3.
A prime coat of the S-30 PrimeÔ
will be roller-applied at a thickness of 15 mils.
This coat is applied during the Primer down-tube
coat. Coating down the tubes results in a
significant quantity of material getting onto the
Tubesheet. This excess is spread by roller and
squeegee as the down-tube process progresses. After
all tubes in a sheet are done a final light coat of
S-30 Prime is rolled over the entire face to smooth
it out.
4.
A second coat of EE-11 @ 15 mils is applied.
This again is done during application of the
intermediate down-tube coat.
5.
A third coat of EE-11 @ 15 mils is applied.
This again is done during application of the final
down-tube coat.
6.
After the down-tube coating is completed
additional milage can be added to the Tubesheets as
needed per specification. For best results the EE-11
can be spray applied. Plural spray application
allows a smooth coat to be applied with minimal
effect to the tube coating. Although EE-11 can be
spray applied at 80 mils, the milage should be kept
to 20-25 mils per coat to minimize any puddling
and/or donut in the tube.
7.
After allowing the coating to cure a minimum
of 24 hours it is the inspected for defects and/or
voids. The multi- coat process will minimize any
potential voids. If any are found they are touched
up with EE-11. This is done after the tubes are
inspected and cleaned of any residual coating.
8.
If there is significant tube end
sanding/grinding, an additional mist coat of EE-11
should be spray applied at 10 mils. This will give a
final smooth gloss finish to the entire sheet and
tube ends.
9.
The
amount of material required to coat a Tubesheet @ 45
mils is calculated as follows:
1604/45mils
= 35.6 square feet per gallon
35.6
x (1.0 - .20) = 35.6 x .8 = 28.5 sf/gal with
20% waste
3.
Waterbox to Tubesheet Joint Sealing:
The Waterbox to Tubesheet joint is sealed
using ARCOR® ARCTHANE®,
a 100% solids high elongation, elastomeric
hybridized epoxy/urethane joint sealer that combines
the wear resistance of epoxy with the flexibility of
urethane. This material can be applied at up to 500 mils per coat
without slump.
1.
ARCTHANE®
will be applied with a caulk tube and gun in two,
500 mil coats for a final dry film thickness of 1000
mils and a width of 1 inch.
Estimate 16 linear feet per gallon with a 25%
waste factor.
2.
The specification for Application of this
joint is provided on the enclosed ARCOR® CD-ROM
under ‘Specifications’
4.
Quality Control:
- Quality Assurance should
be maintained throughout the project. The ARCOR® CD-ROM contains copies of all necessary QC
forms and checklists.
- ARCOR® can
provide all the necessary inspection equipment
and reference materials to verify compliance
with the requirements for surface cleanliness,
surface profile, abrasive cleanliness, air
supply cleanliness, environmental conditions,
surface temperatures, wet film thickness, dry
film thickness and coating continuity.
- maintain
a material log which will include material name,
kit size, batch number, date of manufacture and
shelf life.
- Refer to ARCOR®’s
General Application Specification. This document
contains detailed surface preparation and
application information along with quality
control holds points.
- Refer to ARCOR®’s Spray
Application Procedure for details of spray
application procedure.
- supply
dehumidification, heating and dust control
equipment for use in establishing and
maintaining proper environmental controls.
Temperature and humidity conditions must
be established and controlled as appropriate in
accordance with the material technical
specifications.
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