|
| |
Summaries:
Download this file:
top
Water has been used historically since the 1960's to clean
surfaces of loose dust, chalking, and dirt, and to repress dusting in
conventional air/abrasive systems.
With the pressure of environmental concerns and the evolution of new equipment
which is cost effective and reliable, high pressure waterjetting is more popular
than in earlier years.
Water by itself, or with soluble abrasives is used predominantly in maintenance
to remove heavy rust, old coatings, rubber, salts and other invisible
contaminants, not in new construction.
Water and hard abrasives can be used in new construction, particularly where
there is a concern about the dust levels.
"Because water jetting does not provide the primary anchor pattern known to
the coatings industry, this standard recommends its use primarily for recoating
or relining project where there is an adequate preexisting profile."
Never the less, waterjetting without abrasive does provide a 10 - 75 micron (0.5
- 3 mil) profile on aluminum and is the subject of US Patent 5,380,564.
Thermal spray coatings on a conventional grit-blasted surface have a tensile
pull adhesion of 3,000 psi; on the surface profile prepared by 50,000 psi
waterjetting, the surface pull adhesion is 6,000 psi.
Hempel's Paint visual Photographs- issued in late fall, 1996.
Currently NACE No. 5- SSPC- SP-12 is the joint written standard.
NACE written Standards take precedence over visual photographs (or standards)
which are used to supplement the written material.
NACE visual standard shall not conflict with NACE written standards.
NACE No. 5- SSPC SP-12 is unique in that it addresses both the Visible Surface
conditions, as is found in all the other blast cleaning standards, and the
Non-Visible Surface conditions which is designated as Surface Cleanliness.
This joint standard has undergone rigorous consensus scrutiny during
preparation.
Definitions for the various levels of cleaning are consistent with the
terminology of the industrial waterjetting community.
WJ-1 surface shall be free of all previously existing visible rust, coatings,
mill scale, and foreign matter and have a matte metal finish.
WJ-2 surface shall be cleaned to a matte finish with at least 95 percent of the
surface area free of all previously existing visible residues and the remaining
5 percent containing only randomly dispersed stains of rust, coatings, and
foreign matter.
WJ-3 surface shall be cleaned to a matte finish with at least two-thirds of the
surface free of all visible residues (except mill scale), and the remaining
one-third containing only randomly dispersed stains of previously existing rust,
coatings, and foreign matter.
WJ-4 surface shall have all loose rust, loose mill scale, and loose coatings
uniformly removed.
The three non-visible conditions do not have any guidance as to the suitability
for service conditions.
When the available papers were reviewed, it would appear that the SC-2 condition
was the area of concern in which coatings would start to experience blistering
or failure during testing.
At the SC-3 condition, most coatings failed during testing.
SC-1 The surface shall be free of all detectable levels of contaminants as
determined using available field test equipment with sensitivity approximating
laboratory test equipment.
SC-2 The surface shall have less than 7µg/cm2 chloride contaminants, less than
10 µg/cm2 of soluble ferrous ion levels, and less than 17 µg/cm2 of sulfate
contaminants as verified by field or laboratory analysis using reliable,
reproducible test equipment.
SC-3 The surface shall have less than 50 µg/cm2 chloride and sulfate
contaminants as verified by field or laboratory analysis using reliable,
reproducible test equipment.
Wet Abrasive Blast Cleaning SSPC- Technical Update Committee Report.
This technical committee report has been in preparation since 1985 and describes
sir-pressurized abrasive, water/abrasive, and water-pressurized abrasive blast
cleaning systems.
Procedures, equipment and materials are discussed and common consensus language
is suggested.
Because abrasives are doing most of the work in the cleaning process, the demand
for a set of visual photographs is not as great as for waterjetting.
This document covers processes which extend from almost all abrasive which is
just wetted with a little water to processes which are mostly water with a
little entrained abrasive.
In the former, the water is acting as a dust suppressant; in the latter, both
the water and abrasive do the cleaning.
It is felt that SSPC- SP 5, 10, 6, and 7 can serve as an accurate definition for
these cleaning processes.
The major visible difference is that the surfaces look darker.
Flash rusting from the water may sometimes develop.
This document has been balloted and final editorial negative comments are being
resolved.
It should be published in final form in late 1996 or early 1997.
The International Coatings slurry-blasting photograph should be sufficient to
provide companion reference guide.
The U.S. Navy funded a robotics controlled ultra-high pressure waterjetting
system that was integrated by Waterjet Systems, Inc.
Ultra High Pressure Water Jetting (UHP WJ) is thought to be an economical,
practical solution for compliance with environmental regulations promulgated by
the Federal Clean Air and Water Acts.
Open air abrasive blasting will essentially be no longer permitted under the
Federal Clean Air Act.
The adoption of Ultra High Pressure Water Jetting (UHP WJ) to strip paint
decreases or eliminates the used abrasive grit which is the largest waste stream
for many shipyards.
The Navy Sea Systems Command, Washington, D. C., material branch has responded
to the immediate need for guidance to the shipyards using waterjetting by
issuing an interim guidance document in December, 1994.
The amount of flash rusting is limited to light flash rusting.
Guide was drawn up as part of the research project "Development of a
high-pressure waterjetting tool, definition of surface standards for steel
surfaces prepared by high-pressure waterjetting and development of coatings
systems compatible with that method" and was sponsored by German Federal
Ministry of Research and Technology.
Tightly adherent black iron oxide is difficult to remove at pressures below
15,000 psi.
Visible water-insoluble foreign matter such as oil and grease shall have been
removed prior to high-pressure waterjetting.
Dw 1 Only poorly adhering mill scale, poorly adhering rust and poorly adhering
coatings are removed.
From firmly adhering old coatings, various spots, and in part, also larger areas
of the old systems or individual coats are present.
When viewed without magnification, a heavy layer of dark tan-brown rust will
completely obscure the original metallic surface.
This layer of rust will be loosely adherent and will easily mark objects brushed
against it.
The International Coatings definitions have provided the initiative for other
coatings manufacturers in the world market to adopt and issue new product
material data sheets incorporating these definitions of flash rusting.
Cavi-Tech Inc., Kennasaw, Georgia, is one of several contractors who have been
using waterjetting in surface preparation.
Cavi-Tech is particularly competitive in maintenance where spot blasting is
prevalent or where only part of the existing coating is removed.
They have defined seven stages from brush blast cleaning to bare metal.
They provide generic written descriptions and visual photographs, which are
prepared for specific industries.
These proprietary specifications are very useful in projects where economics is
the driving force.
Development of industry-wide consensus specifications for situations in which
the individual coatings manufacturer has to agree that the new coating will be
compatible with existing material on the surface is almost impossible.
Cavi-Tech, as does other contractors skilled in waterjetting, uses equipment
ranging from 15-20,000 psi to 30-35,000 psi to obtain the various levels of
cleanliness.
The Cavi-Tech blast cleaning specifications are numbered CB-1 to CB-4.
Some are closely equivalent to SSPC/NACE surface preparation specifications.
Removal of loose mill scale, loose rust, and loose paint to the degree hereafter
specified.
The surface should be abraded for adhesion.
CB-1.5 Sweep Off Blast- Modified to remove all Corrosion.
All rust, mill scale- except for carbon shadows-, streaks or discoloration
caused by rust stain, mill scale oxides, or slight tight residues of rust may be
found in bottom of pits.
Loose paint & coatings are removed completely.
CB-2 Blast and Sweep Cleaning-Loose paint shall be completely removed.
Tight Coating will be blasted back to show an underlying film surface evenly
abraded.
CB-2.5 Control Blast and Sweep Cleaning-Tight coatings will be blasted back to a
specified intermediate coat film surface.
Evenly abraded over the surface to provide good adhesion and bonding of paint.
CB-3 Blast and Cutback Cleaning-Old paint is removed down to existing primer
paint.
Prime coating shall be reduced to a dry film thickness, whereby all degraded
coating film has been removed.
Remaining prime coat shall be tight and evenly abraded.
CB-3.5 Control Blast and Cutback Cleaning- All old paint is to be removed down
to the existing primer.
The prime coating shall be removed to a dry film thickness of not more than 0.8
mils.
CB-4 Full Blast- At least 95 of each square inch of surface area shall be free
of visible coating residues, and the existing profile of the surface shall be
clearly evident.
Jotun Valspar has issued photographs for four grades of flash rusting- none,
slight, moderate, and considerable on a single, uniform steel panel.
Flash rusting is defined as rusting which occurs on metal within minutes to a
few hours after cleaning has been completed.
The speed with which flash rusting occurs may be indicative of salt
contamination on the surface, high humidity, or both.
The surface is of a blasted Grade A steel and the guide is intended to be a tool
for visual assessment.
The Guide is not restrictive to the use of water in the surface preparation.
All the photographs are of a uniform, yellow-brown rust.
They are NOT the splotchy, non-uniform, black rust that is indicative of active,
local corrosion cells.
The Steel surface shows a clearly perceptible change in color, but the original
metal surface is clearly visible under normal vision.
The surface exhibits a clearly visible metal shine when viewed at different
angles.
The steel surface shows a very clearly perceptible change in color, but the
original metal surface is still visible under normal vision.
The surface exhibits moderate metal shine when viewed at different angles.
The steel surface shows a pronounced change in color and the original metal
surface is completely covered by flash rust and not visible under normal vision.
The fall, 1996, issuance by Hempel of their "Photo Reference for Steel
Surface Cleaned by Water Jetting" further emphasizes the urgency of
intervention of the third party consensus process.
The third component, Invisible Contaminants, is one that people are still
unaware of.
Waterjetting CLEANS THE EXISTING PROFILE AND OPENS IT.
Jack Smith of Detyens estimated that the UHP WJ saved Detyens approximately 560
hours of cleanup wages.
Detyens did not have to pay for disposal of the abrasives at $14,000.
If you work in an area at or above 30 micrograms per cubic meter of air, your
employer must give you medical surveillance and training in the hazards of
working with lead.
Containment is used to direct the water to the impermeable collection areas.
The containment is best described as permeable materials, flexible containment,
natural input air, open seams, with no controls on exhaust-- not the expensive,
rigid, full containment system used in open air abrasive blasting.
Though not as good as in the first example these numbers are still are
impressive compared to dry abrasive blasting.
There was more exposure during sweeping and removal of the tarps and screens as
the spent paint and abrasive were dry.
Clean up was performed by rolling the plastic sheet to gather debris to one area
and then dry sweeping and shoveling.
The increase in air borne particle indicated that the dry spent abrasive/paint
should be wetted while sweeping and cleaning was occurring.
Essentially these airborne lead exposure numbers for wet abrasive blasting are
comparable to vacuum blasting.
The generated paint chips and abrasive was approximately 3 pounds/ square foot.
Regulated area samples were collected at the edge of the work area in the
direction of the prevailing wind.
All results were below the Action Limit for airborne lead., so that workers and
observers outside the regulated areas were not impacted.
The TCLP testing results indicate the waste generated was non-hazardous.
This waste was beneficially reused in cement kilns.
Air/water/abrasive blasting is a cleaning method in which water is injected into
the air/abrasive stream generated by conventional air-pressurized abrasive
blasting equipment.
Water/abrasive blasting is a cleaning method in which the abrasive is injected
into the water stream of a hydraulic pump.
All of these methods are sometimes called Slurry or Wet Abrasive BLASTING.
The abrasives can range from hard grit and sand to soft, soluble media.
A popular method LBP removal combines water and soluble soft abrasive such as
sodium bicarbonate.
The abrasive dissolves to leave just the water and paint for collection and
disposal.
The paint is removed from the water during the collection.
The water must be tested for lead levels, but typically only the paint solids
(and filters) are hazardous waste.
These systems can be configured as water systems to which abrasive is added at
the nozzle or as dry abrasive systems where the water is added at the nozzle.
Several different configurations are available ranging in water consumption of 1
quart to 8 gallons per minute and water pressures of 25 to 4500 psi.
As a particular example, the Jet Stripper® soft abrasive blasting systems uses
a water input of 200 to 5000 psi at a rate of 0.5 to 1 gallon per minute and 0.5
to 1 pound/minute of grit.
It is a coaxial arrangement with the water being added at the nozzle.
The abrasive is carried to the nozzle by compressed air.
Commercial hard grit at 5-10% addition was added to remove mill scale and
achieve an anchor pattern.
Samples sites were located downwind from the work area.
The results were 2.6 µg/m3 for a 4-hour period on one day and 1.3 µg/m3 which
is well below the PEL and AL.
White Metal also supplied data for November, 1993, in removal of LBP from a
generating station.
" At these exposure levels, the painters are adequately protected with
half-mask respirators with HEPA filter cartridges and disposable rain
suits."
"Plant employees working around the blasting area are not exposed to any
dangerous levels of lead.
In addition, paint debris landing in areas outside of the polyethylene-lined
containment area are promptly picked up by sweeping with water mist to suppress
the dust."
Low-Pressure Water Cleaning (LP WC) is cleaning performed at pressures less than
5,000 psi (power washing).
Although I do not have direct knowledge or field case histories LPWC (power
washing) for LBP activities, I am aware that in Canada, LPWC is used to wash
bridges, plants, and tanks where LBP is present.
The loosely adherent paint comes off in larger chips, rather than as small
particles.
Even if no LBP is present, the Pollution Prevention Act requires that the
run-off water from industrial activities be tested for oil/grease and suspended
particles.
A sump pump, filter unit, and holding tank might be required to prepare water
for discharge into a sanitary sewer or for reuse.
Approximately 90 percent of the heavy metals are contained in the solid
particles.
; The Los Angeles County Sanitation District has a limit of 40 mg/L for a
discharge going into the sewer which will lead to the treatment facility which
is over the Federal hazardous limit.
In this case, the effluent water can typically be commingled with all the other
industrial water being used in the plant and sent to the plant treatment
facility.
As a contractor, Cavi-Tech matches the equipment to the job specification, and
has cleaned millions of square feet of coatings.
There was no need to erect containment screens around the tank.
After three days, the filtered blast water contained 0.17 mg/L; at the end of
the job, the level was 0.32 mg/L lead-- well below the hazardous level of 5
mg/L.
The LCRA considered HPWJ at 20,000 psi as it could remove the loose coatings;
would profile the remaining primer to two mils; and would permit intercoat
adhesion value of 400 to 600 psi.
The spend blast water and paint entered a sump, was pumped through filters to a
settling tank, then through three micron filters before going back to the water
blasting pump.
Ultra High Pressure Water Jetting (UHP WJ) is cleaning performed at pressures
above 25,000 to 30,000 psi.
A dike of approximately 50 ft by 100 ft was used on the ground as primary
containment for water and paint chips.
Dr. Frenzel extends her thanks to the waterjetting industry for their assistance
and cooperation.
Download this file:
top
Prepared and Presented at 1999 WJTA Conference; Houston TX.
Water Jetting, with and without abrasive addition, continues to impact the
maintenance industry and displace some of the traditional areas of dry abrasive
blasting.
This presentation focuses on the similarities and differences in the visual
reference photographs which are used in the global industry.
Since 1985, the continued improvement in nozzles, seals, and pumps make it
possible for reliable removal of coatings and rust.
Water jetting and wet abrasive blasting methods have gone from a rare oddity to
acceptance by the marine industry and becoming the preferred process for removal
of lead based paint or asbestos.
The Technology Publishing Company's (TPC) annual survey of painting contractors
indicates that fifty percent (50%) of the identified painting contractors use
some type of high pressure or ultra-high pressure waterjetting or wet abrasive
process.
One individual contracting firm says they have cleaned over 20 million square
feet of surface.
Coatings manufacturers, notably International Paint Co. (Akzo Nobel), Hempel's
Paints, and Jotun have produced videos, technical product literature, and visual
reference photographs to train their technical representatives and clients.
Ameron, Bridge-Cote of Canada, Devoe, Euro-Navy, Sigma, W&J Leigh & Co.,
Watson Coatings, and Wasser Hi-Tech Coatings are additional coating
manufacturing companies who actively embrace the use of water in surface
preparation.
Organizations such as SSPC (Society for Protective Coatings), NACE Int.
provide the grounds for consensus documents, that is, documents which are
defined as a "general agreement" or a "majority of opinion."
Consensus recommended practices and technology updates provide a Common Language
to describe problems.
Every industry tends to define the same problems in different terms.
Adopting consensus language saves time and money.
Environmental concerns are driving movement to include water.
Water Jetting and Wet Abrasive Blast Cleaning are displacing traditional
abrasive blasting in certain areas.
Adversarial points of views exist within the coatings industry.
It took ten years to build a consensus and issue the first standard on the use
of high pressure waterjetting jointly by NACE and SSPC in 1995.3 NACE and SSPC
have issued two other documents since that time.2,11 In 1998, ISO also started
work on a separate water jetting standard as they did not know the extent of the
American activities.
Over the years, European and American philosophies drifted apart in the adoption
of consensus language for abrasive blasted cleaned steel.
In simplistic terms, the Americans use standards language allowing a percentage
coverage of stains, while the Europeans use a criteria of tightly adherent
material.
The visual reference photographs for abrasive blast cleaning showed examples of
rusted steel, but not removal of coatings.
Projects involving removal of coatings for repainting often call for leaving
sound, adherent coatings on the substrate, not removing all of it to leave
slight stains.
We recognize that an independent set of photographs should be prepared so that
coatings manufacturers do not have to refer customers to material originally
prepared by a competitor.
In these documents, the distinction is made that blast cleaning or blasting
involves the use of solid abrasives whereas water cleaning or water jetting is
the use of water alone without abrasives.
Other generic terms to describe specific air/water/abrasive blast cleaning
methods are: Water Shroud or Wet-Head blasting, wet blasting, low volume water
abrasive blasting, and slurry blasting.
In the coatings industry, water jetting does not provide the primary anchor
pattern.
The use of water alone is primarily for recoating or relining projects for which
there is an adequate, preexisting profile.
It is frequently said that ninety percent (90%) of all coatings failures are the
fault of the surface preparation.
It is also said that "seventy-five percent (75%) of all coating failures
are the fault of the contractor."
The major surface profile on a metal substrate is defined by the abrasive and is
typically formed by a dry, abrasive blast technique.
Because of environmental restraints on visible dust, Wet Abrasive Blasting (WAB)
is finding a market in new steel construction.
An analogy is throwing a baseball at a mud flat.
Throw a large softball relatively slow and you will make a rounded impression
with a lip.
Throw a small hard ball relatively fast and you will make a deeper rounded
impression.
Throw a sharpened pyramid at an angle, and you will create a ridge.
Some of the mud will splatter off, but most of the mud gets shifted to the new
profile.
Abrasives do not necessarily remove the metal because metal is malleable, but
you are creating a macroscopic pattern.
This pattern may or may not remove existing corrosion cells.
This initial profile provides the cleaned nib to which the paint adheres.
There are many situations where abrasives are needed when older surfaces are
being blasted.
Abrasives are used in tight corners and for the back side of plates where the
particles can be rebound or ricochet.
In marine areas, there is frequently a very tightly adherent black layer of rust
which is resistant to removal by water jetting alone.
Addition of a little abrasive into the water stream will speed the production
rate and help break this brittle layer.
Abrasives can be used to ricochet on all sides of a small compartment whereas it
may be difficult to direct a jet stream of water towards all the surfaces.
Abrasives erodes or abrades the surface from the top.
A US Standard 100 mesh screen has openings for 125 micron particles.
When the contractor is cleaning with 125 micron particles, contaminants which
are in cracks or crevices or pits simply cannot be reached or removed.
Crevices become filled with spent abrasive when a contractor is trying to remove
pack rust between plates.
Subsequently the paint gets applied over "clean" abrasive and fails
prematurely.
If there are invisible contaminants on the surface, abrasive blasting can drive
the contaminants into the surface or form a pocket of metal in which the
contaminant is buried.
Waterjetting can be described as a series of small droplets in the 5-10 micron
range hitting the surface at supersonic speeds.
The droplets implode (cavitate) and drill through coatings or rust; then spread
laterally and shear at the interface, much like ultrasonic cleaning, to lift
materials.
A series of microscopic "pock marks" form on the macro surface.
The measured profile in gross terms, for example 0.002inch (50 microns), is
still the same for a surface cleaned by abrasive and by water jetting, but the
microscopic details are different.
Tom Aldinger reported that water blasting would give as good or better adhesion
than abrasive blast to SSPC SP10 (near-white) on 60 year-old pen stock.
The ability to remove chemical contaminants (salts), particularly from badly
pitted and corroded steel, is a major advantage of the water jetting process.
WJ and WAB do such a good job of removing invisible contaminants from the
surface, even if intact coatings are left on, that blisters from chemical
contaminants and delamination from oil and grease disappear.
Contractors, inspectors, and coatings personnel use the SSPC/NACE and ISO
written standards and visual reference photographs for training and acceptance
on jobs.
Abrasives hit from the top, erode the surface, provide plastic flow to the
metals, tend to make the surface look uniform and "erase" different
areas.
The experienced observer sees black stains on the top where heavy rust was
present, or coatings on the top of the surface- rather than stains in the bottom
of the pits so the observer see something which is a new experience even though
the pits are cleaned.
Water jetting is used primarily in removal of coatings, where frequently the
objective is to retain as much tightly adherent coating as possible.
When viewed without magnification, the surface shall be free from visible oil,
grease and dirt, and shall be free from mill scale, rust, paint coatings and
foreign matter.
The perception of percentage coverage is an unrecognized problem.
Every experienced inspector thinks that he can tell what 5% and 33% coverage is.
This was very evident as the new photos were being screened.
Coverage is a topic to itself and is depicted in illustrations of 5% and 30%
coverage from "The Book of Spots."
Whether the spots are sharp or diffuse, nearly the same color or contrasting
colors, on a uniform, lightly profiled or a non-uniform, heavy pitted surface,
will make a difference.
Since 1996, Dr. Frenzel has been educating the experienced personnel first on
the NSRP Technical Advisory Committee and subsequently the NACE/SSPC task group
on percentage coverage.
Figures 5, 6, and 7 illustrate three different representations of five
percentage coverage.
In practice, the marine coatings industry embraced NACE No. 5/ SSPS SP-12 and
immediately interpreted it to allow islands of tightly adherent paint to remain
as compared to stains of paint because it is used in maintenance and repainting.
The original "staining" language arose because solid particles don't
get into the crevices.
The paint remains as stains in the pits and crevices.
In WJ without abrasive, intact coating remains on the top of the surface.
The new photos under consideration where coatings are being removed all depict
the retention of coatings.
Coatings manufacturers have positively endorsed this position.
With the advent of computer digitization, new photos are also being considered
for SSPC- VIS 2/ASTM D 610 "Standard Method of Evaluating Degree of Rusting
On painted Steel Surfaces."
The concept of percentages with large, medium, and small, pinpoint spots is a
challenge because the appearance in pin point corrosion at 30% is that the
entire surface is covered.
The written definitions are similar in that they describe four visual
cleanliness conditions.
They differ with respect to the presence of mill scale and tightly adherent
coating as compared to percentage staining.
Based on the discussion of the task group members, it is the author's opinion
that the current ISO photographs and the SSPC/NACE written definitions are
inadequate to address the problems of retention of sound coatings in
maintenance.
The appearance of old metal surfaces cleaned by WJ without any abrasive is very
different from those cleaned with abrasives.
There is no discrepancy when all coatings and rust layers are removed by WJ or
WAB.
However, WJ finds its forte in partial removal of coatings.
It is the partial removal and spot blasting with WJ and WAB with soft abrasives
that is forcing the adoption of new visual photographs and a revision of the
written standards language.
The WJ task groups of NACE, SSPC, and ISO are addressing this question.
Water jet cleaning is bringing the European and United States standards
organizations together into a coalition effort.
Thanks to International Paint, Jotun, Hempel's, Cavi-Tech Inc. for permission to
use their photographs in non-commercial presentations.
The members of the SSPC and NACE task groups have volunteered thousands of
hours.
Special thanks to Aqua-Dyne, Butterworth Jetting, Carolina Equipment &
Supply, Flow Int., and NLB Corporation, Doug & June Koppang, Aulson Co.,
Cavi-Tech, Fluidyne, Freemyer Co., Hartman-Walsh Painting, UHP Projects, Valley
Systems,, Leo Kosowan, Roland Hernandez, and Dan Bernard for support and
discussion.
Download this file:
top
Prepared by Lydia M. Frenzel, Ph.D. Advisory Council
This paper is a recap of the growth of cleaning coatings by waterjetting and the
support of the shipbuilding panel.
It also talks about the revision of SSPC- SP-12 NACE No. 5
Who's involved in making a project successful?
Today and tomorrow, we are going to discuss innovative technology- Waterjetting
and wet abrasive blasting- that meets current environmental demands.
So Let's step back for a moment and see how we came to this New Technology.
From an article in CLEANER TIMES- on the history of water blasting.
As early as the 1930s, the Aldrich Pump Company (later acquired by
Ingersoll-Rand) was combining high pressure pumping units with nozzles to
transform streams of water into chisels that would remove scale and slag from
steel mills.
In 1956 a Monsanto engineer from St. Louis came to Houston to speak to the local
coating society.
His purpose --to promote the use of water for preparing steel.
Due to Houston's close proximity to the Gulf Coast, if the steel was not
thoroughly cleaned prior to painting, it would result in intercoat contamination
and create adhesion problems which would "show up down the road,"
explains Dick Paseman (HOUSTON) who was working as an industrial painting
contractor at that time.
"That was a nice idea in 1956," he adds, "but it was just another
cost to go through."
By 1961, Goss and Paseman formed American Powerstage Company to develop a high
pressure pump and introduced their first unit which they named and copyrighted
as the "Water Blaster."
So you can see that these changes began at least 40 years ago.
In 1972, Change was still in the air.
I started looking at the future of coatings, blasting, and the environmental
regulatory climate.
I worked on testing for new NUCLEAR power plant coatings, NEW organo-tin
compounds for ship hulls, water- rinses for corrosion prevention, and
water-borne coatings for pipe yards.
My introductory years in coatings was with traditional blasting in Texas,
Mississippi, Oklahoma, and the swamps of Louisiana.
I learned it is hard to remember the objective is to drain the swamp when you
are up to your ass in alligators.
After years of observation, investigation, and experience, I HAVE COME TO THE
CONCLUSION that "WATER IS TRUE GRIT."
Believe me when I tell you that I didn't start out with that in mind.
The Advisory Council defines Surface preparation: Creating the situation in
which the coatings will perform as expected.
Expectations for the quality of surface preparation have escalated in the past
few years.
This is the trend of the future.
Preparing for change is preparing for the future.
Today as you participate in this workshop, think of the future of your business.
Adapt what you see and hear to your particular needs.
As the expectations for surface preparation goes up- the expectation for YOUR
performance goes up.
Environmental expectations are going up- OR Rather- Going down- to lower
air-borne contaminants and smaller solid waste streams.
An informal discussion with European experts in 1997 revealed " the
coatings removal business in Europe is reaching $2 billion annually.
WJ is already capturing about 10% of this.
We've seen only the tip of the iceberg.
Some NACE Instructors are predicting in 10 years that waterjetting and wet
abrasive blasting will dominate the maintenance market.
Business will look very different than it does today.
Change is not a comfortable topic but it is necessary.
We are all afraid of trying something new.
WHY- MISTAKES COME BACK TO HAUNT US.
No one remembers the million square feet of coatings that are done correctly.
They only remember, and hear about, the five square feet that failed.
When you try something new, you want to be sure that you understand how to go
about it because understanding the process will enhance your bottom line.
If it was the environmental regulations which forced this industry to start to
change, then it is now the coatings manufacturers who are driving the change in
surface preparation.
In 1985, I gave talks on waterjetting and paint removal to NACE spring corrosion
course, SSPC, and the NPCA marine coatings conference.
Change didn't escalate until 1994 when International Paint accepted the
substrate for their coatings.
Coatings manufacturers tell me that they see coatings lasting 20% longer, but
they are still collecting data.
Look at September Issue of Materials Performance- Max Winkeler- p. 120- when he
is asked "What developments do you foresee in the area of surface
preparation."
Who's involved in making a project successful?
While chairing the Task Group on Wet Blasting, I heard a senior engineer say
"We never let the contractor select the test method or pressure.
We leave them out of specification development."
Isn't this leaving out one-third of the people responsible for the success of a
project?
Abrasives today are not the same abrasives from 1985.
All aspects of the coatings industry are here today- abrasives, waterjetting,
wet abrasive blasting, shipyards, owners, fabricators, specifiers, inspectors,
blasters, containment, dehumidification, painting contractors,
environmentalists, coatings suppliers, permitting agencies.
In one instance, you are using low pressure water cleaning: in the other,
high-pressure waterjetting, in another triple action waterjetting pistols.
NACE No. 5- SSPC SP-12 is being revised along with adoption of photos.
Very Thorough or Substantial Cleaning: A WJ-2 surface shall be cleaned by
waterjetting to a matte (dull, speckled) finish which, when viewed without
magnification, is free of all visible oil, grease, dirt, and rust except for
randomly dispersed stains of rust, tightly adherent thin coatings, and other
tightly adherent foreign matter.
Acceptable variations in appearance that do not affect surface cleanliness
include variations caused by type of steel, original surface condition,
thickness of the steel, weld metal, mill fabrication marks, heat treating,
heat-affected zones, and differences in the cleaning pattern.
A brown-black discoloration of ferric oxide may remain as a tightly adherent
thin film on corroded and pitted steel and is not considered part of the
percentage staining.
UHP WJ at pressures in excess of 240 MPa (35,000 psi) is capable of removing
loosely adherent mill scale, but production rates are not always cost effective.
Mill scale, rust, and coating are considered tightly adherent if they cannot be
removed by lifting with a dull putty knife.
The reference photos were delivered to SSPC in Summer of 1997 after review by
the Technical Advisory Committee of NSRP.
It took a while to have SSPC make prints from the slides.
In spring 1998 and fall 1998, the joint task group found fault with almost every
photo even though many of the joint task group members were also present in the
NSRP Technical Advisory Committee discussions.
Some people wanted to use all of the photos including both a red and green
primer because "Some industries use red and some use green."
During the NSRP review, we had been requested to make the background steel gray,
rather than with a "yellow or brown tinge" which arises from
open-cycle equipment.
Later on, we were asked to put the yellow back in as a color correction.
We had our initial selection for the US around April 1999.
In fall of 1998, we started correspondence with a new ISO WJ group and sent
copies of the slides to Europe in March 1999.
The US task group wanted to go out with one set of photos between ISO and SSPC/NACE.
Despite considerable efforts by the US delegateion, a single set of coherent
photos between ISO and SSPC/NACE will not happen.
Seeking cooperation cost us about a year (March 1999- June 2000) in time.
ISO will use a subset of the Hempel photos and one set of three flash rust
pictures from International Paint WJ photos.
The Joint NACE/SSPC Task Group will use the set of the photos originated by NSRP
and one set of Hempel photos so that we have an example of brittle and
non-brittle thoroughly degraded coating.
We will continue to use VIS (4) as visual reference photos.
Ballot on this WJ set is due out any day now.
I would hope to have negatives resolved by end of year and the photos published.
If all goes well, we will publish the photos this spring.
You have seen the NSRP photos- so I will go over the one additional set from
Hempel.
We had photos of a degraded, brittle coating.
Hempel has photos of a less brittle, degraded coating.
The SSPC/NACE photos show a coating that doesn't feather easily whereas the
Hempel photos show an eroded surface.
The Joint Task Group members felt that both should be included.
The Ballot on Wet Abrasive Blast Reference Photos went out around Sept. 7th.
Every standard is reviewed every five years.
NACE No. 5 revision is due out in 2001.
Abrasive change the profile from the top down.
Anything that is present on the surface can be driven into the folds.
Waterjetting cleans from the bottom of the pits up.
It separates the coating and lifts it from the surface.
Use photos from Advisory Council Volume 3 on Adhesion and Profile.
Waterjetting is fractal, so it can more effectively remove corrosion sites.
Ultra-high pressure waterjetting leaves the crevices clean; the original gross
profile unchanged, and removes the chemical contaminants.
The above statement has fundamental implications in the microscopic details of
the profile.
When steel has started to rust, can straight abrasive blasting will produce a
suitable surface which is free of corrosion sites?
Probably not- because corrosion growth is fractal.
I like to say "Abrasive blasting and waterjetting are two types of cleaning
mechanisms.
It is the story of the pit and the pendulum.
They lead to two different appearances and two different results."
Emphasize- The main profile stays the same but the details change.
Compare Tator Panel with abrasive cleaning- with Tator Panel with WJ-These
photos come from Advisory Council Volume II and III educational training
Modules.
"The striking point is that the detail of the eroded surface increases with
increasing magnification, suggest the waterjet erosion produces a fractal
surface.
The feature size is at least an order of magnitude finer in the waterjet
surface.
In contrast, the grit-blasted surface would actually appear smoother as the
magnification is increased, going from a long-range roughness pattern to smooth
plateaus and facets, although there is micro-grooving due to the abrasion of the
grit particle.
Thiokol was concerned with damage to the metal substrate.
Thiokol verified that the minimum allowable erosion of 0.0001 inch (2.5 micron)
would not be exceeded during the cleaning process.
If the paint is about to fall off, a low pressure water washer- less than 5,000
psi can be sufficient.
It depends on the adhesion, cohesion, and molecular binding energy of the
coatings.
The following table is for a typical 2-inch spinning nozzle with multiple
orifices.
It is the Jet Energy Intensity that erodes coating and stresses the binding
force of the coating.
Download this file:
top
The Lower Colorado River Authority, Austin, Texas, refurbished
the Comal County Utility Plant located in New Braunfels so that is can be used
for public, commercial businesses.
The story is the transformation of a power plant, built in 1926, which contained
asbestos and lead based paint (lbp) and had been closed for decades, into an
asset for the community.
Every project starts out with a where, when, what, how statement.
This coatings project involved removal by manually held ultra-high-pressure
waterjetting (UHP WJ) of approximately 410,000 square feet of lead based paint
from the historically significant Comal County Power Plant located in New
Braunfels, Texas.
The project combines renovation, but not restoration, and historic preservation.
The owner is Lower Colorado River Authority, the coating manufacturer is Wasser
High-Tech Coatings, the contractor is UHP Projects Inc.
The coating removal portion started around September, 1999, and continued
through June, 2000.
This project was the first time the contractor had worked with the owner.
Every project has more to the story than "just the facts."
Every project involves interaction and representation of the three points of
view that must come together in the bid specification for the surface
preparation and coating application to be successful and flow smoothly.
Certainly any project that deviates from a traditional blasting and painting
must have the upper management of the owner firmly in support of the process.
The owner or operator of the facility initiates and controls the project often
with the assistance of an engineering or planning firm who may act for the
owner.
In this project, the owner selected early in the process a coating system based
on past history.
The question then became how to write the specifications for public bidding and
how to select a qualified contractor.
The Bid Specification language allows people to work together on projects.
When all three viewpoints- owner, contractor, and coatings manufacturer come
together- a "new or emerging" process becomes an accepted process.
Responsibility is shared between the three parties.
The owner, coatings manufacturer, and contractor can get together and discuss
solutions that are mutually beneficial.
Often the result is that the coatings manufacturer and the contractor work
together to supply cooperative warranties or guarantees to the owner.
Who is the Owner and What Role does the Comal Plant play in the community?
The Owner is a conservation and reclamation district that generates
hydroelectric power, manages the waters of the Colorado River, operates parks
and assist communities in economic development.
Water is a major recreational and economic source for New Braunfels founded in
1845.
For many New Braunfels residents, the Comal Plant has been a city landmark,
guarding the entrance to Landa Park, the "Largest in Texas" for more
than seven decades.
Community interaction and response was a top priority for the owner.
The power plant is 20 feet from the pristine Comal River with three endangered
species and sixty-three species of flora and fauna in the immediate vicinity.
Comal Springs feeds a 1.5 million gallon pool in the park.
The nearby Schlitterbahn Waterpark Resort is one of the nation's largest
waterparks, featuring 65 acres of water recreational areas.
The Comal plant is very visible as it is located two blocks from the historic
town square and across the street from Wurstfest Hall, a major Texas celebration
and tourist attraction.
Williams described the interaction of the LCRA with the community.
The Comal power plant was built in 1926, before the owner was created.
The owner subleased Comal from the Guadalupe-Blanco River Authority in 1942 and
gained full title in late 1972.
After prices on natural gas continued to spiral, the owner pulled the plug in
1974, but not their involvement and commitment to the community.
The owner has a strong eco-friendly policy.
They do the right thing for air quality, water quality, the community,
occupational safety and health, and general environmental enhancement.
"We're recycling a power plant,"said John Gosdin, LCRA manager of
parks and conservation services, who has overseen the work.
In the late 1970's, LCRA leased the 37 acre site to the City of New Braunfels
and New Braunfels utilities.
It was discovered in 1986, that salvagers of the equipment and steel had damaged
some interior insulation, included friable asbestos in the 1979-82 time period.
Starting in 1989, the owner removed 6,300 cubic yards of contaminated
asbestos-containing insulation and contaminated materials.
Soil contaminated with fuel oil and PCB's, and on-site landfills were remediated.
The removal of the paint and repainting is just one step in a multi-year,
multi-stage project.
For this refurbishment project, the owner has spent more than a decade on the
environmental cleanup and other site work, including the asbestos, PCBs,
landfills, and repairs on the Comal Dam, which helps control the level of nearby
Landa Lake.
Removing remaining equipment, stripping the building to its exterior walls,
concrete floors and structural steel- would cost an estimated $7 million.
Asbestos and lead in the air did not exceed permissible exposure limits if there
is no activity in the building to stir up the dust.
The amount of structural steel contained in the structure is deceptive.
Imagine, cleaning 7.6 football fields of area all in the shape of the goalposts.
Physical safety concerns including hazards from falling objects, i.e. fire
bricks, holes in the floors, and water or bird/animal feces.
Health hazards from lead paint, asbestos, and the presence of large amount of
bird feces.
Between 1990 and 1995, the owner noticed a great increase in the dollar amount
to remove paint and disposal of the waste streams.
The owner already had a history of 5-6 years performance with moisture-cured
(MC), single component, micaceous iron oxide (MIO) urethane coatings in prior
industrial and dam projects over a waterjetted cleaned surface.
Primer: one coat of moisture cured urethane- MC- Miozinc which is zinc-rich/micaous
iron oxide, single component, applied for 3 mils DFT.
The coating, a single-component moisture-cured urethane (MCU) is very reliable,
easy to use, and very user friendly.
The contractor can pop the lid on the can; stir it up; and put it into
suspension.
The paint can be applied with brush, roller, or spray without addition of
thinner with a very long pot life.
The coating can be applied under adverse conditions, of rain or cool, damp
weather.
There is very little to no down time from a contractor's point of view.
Cost savings is found in less thinner, less downtime, and the MCU system is
typically one-half the thickness of an epoxy system.
The public bid process included responses of dry abrasive blasting, but the
selected process was UHP WJ.
The contractor was SSPC QP-1 and QP-2 qualified with a history of similar
projects throughout the world.
One of the principals has over 25 years experience as a general contractor with
dry abrasive blasting.
Over the past seven years, he has found UHP WJ to work well in all sorts of
maintenance projects.
The contractor started in 1993 and has grown to 150 employees, multiple vacuum
systems, and 12-13 UHP WJ pumps.
The two principals met in 1989-90 on the USS Enterprise in which 265,000 square
feet of bilges and machinery rooms was cleaned with WJ and painted.
The coatings have lasted without failure to date.
The contractor handles on-shore and offshore projects, large and small, from the
one-two day to multi-year contracts.
The first impression during the pre-bid conference when the estimators walked
into the Comal Plant was the Gomer Pyle Syndrome "GOLLY!"
UHP Manager Bob Ashworth said "We Looked up- It was a large job.
Piping was being removed along with the last of the asbestos.
There is a lot of steel in this plant- maybe more so than on a ship or bridge.
The steel just goes on forever and ever.
It was a challenge to see all the building."
Ashworth feels "There is no other company in the world that has the caliber
of the people that we do.
It was a job that we are very well suited for.
Our people are trained in these types of jobs.
It was a difficult job and a kind of job that we like to take on."
Their projects managers bring dedication, loyalty, and outstanding experience to
each site.
This attitude comes out in their work and public response.
The contractor breaks down all large projects as multiple small jobs in each
small section and put it all together for estimation.
The contractor made several trips to the site.
As Ashworth said, "LBP does not strike the fear in us as they may in an
abrasive blaster.
When you use water to remove lbp, it's not the hazard it is with dry blasting.
Your people are not exposed to the hazard of air borne contaminants.
One of the challenges of the bid was to meet the acceptance criteria for lead
wipe levels as negotiated with the owner.
They built the gutter work for the windows.
A comprehensive health and safety plan is implemented early, especially for the
people they hired from the community.
The contractor hired several people from the community and trained them to be
waterjetters, and hired local painters and general labor.
There were 60-65 people total working at one time between the WJ, painting,
scaffolding, electricians, and environmental personnel.
A full time safety person was on the job each and every day and held a 15-minute
safety meeting each andevery morning.
The coatings technical representative was there several times.
The contractor rigged troughs under each window to catch both interior and
exterior water from the cleaning operations and direct the water into the
building for the collection sump.
The surfaces varied from old steel with multi-layered paint, to hard brick, to
horse hair filled mortar and very soft, old brick.
For the most part, the existing paint system was easily removed to the NACE No.
5- SSPC SP-12 surface preparation of WJ-3 with retention of tightly adherent
primer.
The third party inspector from a nation-wide engineering firm that deals with
power plants representing the owner had not seen WJ before.
Because he had been getting a WJ-2 visual cleanliness, the third party
inspector, simply through lack of experience, did not want to accept a WJ-3
surface.
The bid called for WJ-3 or SP-6 in the surface preparation section and complete
removal of all lead-based paint (lbp) in the remediation and abatement section.
All existing paint shall be substantially removed to the metal substrate (SSPC
SP-6/ SSPC SP-12/WJ-3).
Conduct wipe tests on abated steel substrates following application of primer to
ensure complete removal of lead-based coatings.
The contractor interpreted this to mean that the check for visible lbp would be
made at closure after the primer and topcoat had been applied.
The third party inspector interpreted the abatement statement to mean a SSPC-
SP-10 or WJ-1 should be achieved prior to painting.
Ambient Air monitoring was measured for the first ten days.
After the air monitoring results were reviewed on this project, project
management made the decision to remove the respirator requirements initially
enforced during the testing procedures and to implement a random sampling as
necessary to insure personnel safety.
Another 10,000 gallons (estimated 50 tons) of hazardous waste sludge comprised
of the solids that settled from the water was disposed by the owner.
The total estimated costs for this hazardous waste disposal was estimated at
approximately $20,000.
Let's compare the above with the waste disposal profile of the scenario of using
dry abrasive blasting.
If dry abrasive blasting had been used for the surface preparation, an estimated
6-10 pounds abrasive/square foot for the coating removal would have been
required.
With the assumption of 8 pounds per square foot, the spent abrasive, which would
have been mingled with lead paint, would amount to 3,280,000 pounds (1640 ton).
The containment and cleanup of this abrasive and generated dust would have
presented a major effort and would have been very labor and time consuming.
For comparison, non-hazardous abrasive disposal varies somewhat and costs
approximately $65 to $75 per ton in the Norfolk, Virginia area.
This calculates to $106,600 for non-hazardous abrasive disposal.
It costs about $0.25/pound if the abrasive stream is hazardous, or an estimated
cost of $820,000.
Look at this project from a waste minimization viewpoint.
The assumption is made that the amount of waste paint and thinner materials
would be the same whether using WJ or abrasive blasting.
Compare the volumes 10,000 gallons of hazardous sludge generated on the project
with the calculated 3,280,000 pounds of abrasive.
Assuming 100 pounds abrasive per cubic foot, this calculates to 32,800 cubic
feet or 246,000 gallons.
The project, in terms of 50 gallons drums, would have generated 200 drums WJ
sludge compared to an estimated 4920 drums of spent abrasive.
The volume of hazardous spent material is reduced 25 times.
All three participants, the owner, the coatings supplier and the contractor
approached this project with a "win-win" attitude.
Work towards a solution to educate the inexperienced personnel.
The project turned out good with an extremely well appointed building.
This section is a summary of interview remarks made by the New Braunfels
coatings technical representative near the end of the project.
We are taking an old building that had all the hustle and bustle of a power
plant.
For years, it has been essentially abandoned and had deteriorated into a
derelict condition.
Now the building is being recycled as a viable entity.
The owner is bringing it back into the life of the community providing future
service to New Braunfels.
To go in this building and dry blast it, in my mind, would have probably
polluted the building and the surroundings with abrasive media to the point that
it would have been falling out of the cracks for years to come.
The UHP WJ, is very effectively removing the old lbp.
WJ allows the contractor to get the paint down on the floor.
They are putting the paint and water into a large cistern.
They are not getting the media permeated into the nooks and crannies of the
building.
Another advantage is the coating and UHP WJ is almost a marriage made in heaven.
The coating can go on in damp environments.
You can literally apply it in parts of the building while they are WJ in other
parts of the building.
You couldn't do that with dry abrasive blasting.
Dry blasting would have extended the time out considerably longer if they tried
to blast and then coat.
It would take forever to get the dust to settle.
HP or UHP WJ is very clean when you compare to the dry blast.
The coatings technical representative has been associated with slurry blast and
you still have a lot of stuff to clean up.
With the HP WJ, not only does it clean the pores of the steel, you do not have
the problems of residual dust which gets into everything.
The side issue of a little rust bloom is minimal.
Because you are doing manual WJ, you tend to get a light rust bloom afterwards.
Wasser's moisture cured urethane coatings are made for that environment of a
light rust bloom.
It works long term on steel which is not perfectly prepared so you do not need a
SP-5 or SP-10, or WJ-1 or WJ-2.
The single component, zinc based, micaceous iron oxide moisture cured urethane
provides a tenacious coating.
The barrier properties are combined with active corrosion protection in case of
a breach.
From a coatings and cleaning aspect, the contractor had very little down time
from equipment.
When you go in and look at their work, it is very clean.
It is a joy to see someone like the owner who takes the time to re-designate
what the building is to be used for, and to recycle it to be an asset to the
community.
There are savings in the project costs attributed to reduced health risks
associated with generation of lead dust and reduction in the amount of
containment.
The lead remediation was completed with no detrimental effect to the surrounding
tourist and recreational areas and the pristine river with its 3 endangered and
63 species of flora and fauna.
Coatings manufacturers have accepted this surface preparation technology and are
approving their products in conjunction with properly prepared surfaces using
UHP WJ.
Download this document
top
We will examine how this continual improvement evolution came
about and what the change means to the marine construction industry in terms of
waste minimization and pollution prevention.
We will look at the volumes of water produced by waterjetting compared to storm
water run-off.
You have to make the decision whether this is just for the effluent water from
the jetting or if it will include the storm water runoff also.
Let's estimate conservatively that the contractor will run 2 UHP Waterjetting
pumps for 16 hours non-stop.
One of the major costs involved in a treatment system is how low the discharge
contaminate numbers are that must be met.
System cost coupled with technical expertise to run the system really does not
make it a practical option.
After determining how much water will be generated and what you plan to do with
it after treatment, you can look at the treatment system.
The wastewater is drawn from the holding tank at the prescribed flow rate
determined and sent to a retention tank with constant agitation.
For more difficult applications it typically would pass though a gravity sand
filter to capture any extremely fine particles.
In small boatyards or on site jobs such as blasting paint off buildings,
bridges, or roads batch treatment is often utilized in batch tanks of 350 to
1500 gallon batches.
3. Design a treatment system that is big enough to treat the amount of waste
water you will generate, and be sure its design will remove all contaminates you
need to have removed for discharge.
It is possible to run a UHP WJ unit with vacuum recovery on only 50 gallons a
day.
|