June 2011, p. 42, Cleaner Times

Dr. Lydia Frenzel has been a significant force in the waterjetting industry since her early work in the 1970s and 1980s, which established waterjetting as a superior method for coatings removal. Lydia received her undergraduate and doctoral degrees in chemistry at the University of Texas in Austin and subsequently moved to southern Louisiana, where she worked with anti-fouling hull-coatings and then in pipeyards dealing largely with the effects of corrosion. After growing up on the Gulf Coast of Texas “with the chipping of rust in my ears,” this was a familiar battle.

While 3000–7000 psi water-blasting was used for cleaning pipes, Lydia reports, “When the pump companies started getting up to 20,000 psi around 1981–82, we started getting excited about coatings removal and surface preparation.” The lower pressure would clean and wash salts off, but Lydia observes, “When you go from 10,000 psi to 20,000 psi, magic occurs. You get a sonic wave on the surface and polymers would shear right off. The threshold pressure for most materials was 20,000 psi. I did a white paper for Butterworth on 20,000 psi surface preparation of metals for painting, and the result was that it could be done very elegantly.” Where technical papers typically have an audience of 50–100, around 3000 copies of Lydia’s “Water is True Grit” found their way to tradespersons and it is a classic Web item.

Charles Frenzel, a physicist from Vanderbilt as well as Lydia’s husband and coworker on the Advisory Council, notes, “I don’t know that anyone recognized at that time that we were opening an industry. No real science had been done on the idea of using waterjetting for coatings removal till that point. But when we cleaned the steel, we observed it had an immediate light yellowing that stayed that way for months. We have steel tests in storage that haven’t rusted in years.”

Lydia recalls, “We had a friend at the University of Kentucky who did the metallurgy on a cross section to prove that we had very clean surfaces. We had a small testing lab in New Orleans paint the surfaces for immersion testing, and we found the stuff was really cleaned off. With the waterjetting you not only got the salts knocked off, but the paint adhered better.”

“Immersion testing showed amazing performance!” Charles says, and this provided an application for equipment manufacturers to aim toward. Charles states, “Something had to come along to provide a reason for wanting more pressure, to control it in a certain way, and make a nozzle a certain way. Coatings removal gave people a handle on how this could be done and how it should go forward.”

After a typical cleaning by brushing or abrasive blasting, corrosion would often start within hours. Charles points out, “With abrasive blasting or brushing, they actually weren’t cleaning the salts off. People were looking at it in macroscopic terms—we can’t see anything so it must be ok. But corrosion starts at a microscopic level. By the next day the steel was black again.”

Though pump life was initially a problem with the higher pressures, Lydia notes, “The pump manufacturers have been very good at meeting needs for pumps, nozzles, and pump parts for this industry. They’ve responded to every request the industry has had.”

As waterjetting use expanded, Lydia continued work in related areas. “I worked for a coal mining plant in California and for Baker Sand Control in Lafayette, LA,” Lydia recalls. “My husband, Charles, and I had a computer consulting firm in New Orleans, and we were selling a water-based compound to keep pipes from corroding.”

Lydia became a committee chairperson for the Steel Structures Painting Council, now the Society of Protective Coatings (SSPC), and also for the National Association of Corrosion Engineers (NACE). “I’m still doing that and that’s still fun,” she comments. “Along the way I became the expert for the United States in this particular area—surface preparation by wet blasting—for the International Standards Organization (ISO).

“The waterjetting community was excited about this application, and those contractors who used it liked it, but they were few and far between,” Lydia observes. “One obstacle comes from contractors who  own dry blasting equipment and would have to buy new equipment and re-educate their workforce. Another obstacle is that when you remove the rust, everything on the steel underneath now shows up— where the metal may have been scratched or welded.” With dry blasting, old mistakes are erased since the surface of the metal itself is abraded rather than just exposed. Lydia comments, “It’s still not uncommon to get a certified inspector who doesn’t know what he’s looking at. The surface looks different. But the refineries love the waterblasting because they have to test the little cracks and you can find them easily.”

Charles points out that some corporate cultures do not favor overall efficiency. “They didn’t worry about whether it was cheaper to replace— due to damaging rust from poor surface maintenance—or to repair. It’s cheaper to maintain, but the people who are in operations don’t get promoted by saving money. They are enamored by the shiny and the new.”

However, the advantages of waterjetting were recognized by paint manufacturers and the U.S. Navy. The Naval aircraft carrier repair engineers couldn’t believe the results. Lydia reports, “International Paint, Hempel, Sherwin Williams, PPG, and Ameron said they accepted and actually preferred the waterblasting cleaning method. The coatings suppliers are key because they have to warranty the work. If they don’t like it, nothing’s going to happen.”

“We got a breakthrough in 1994 because the U.S. Navy didn’t want sand left over after they blasted ship hulls. They wanted something ecologically friendly and recyclable, and that’s water,” Lydia states. “They had a demonstration of a full vacuum recovery and full recycling system.” Charles adds, “The waste stream should have no other waste than the coating that comes off. Waterjetting accomplishes this. The paint can be separated out, compressed, dried, and that’s the minimum possible.

Instead of thousands of tons of contaminated abrasive, such as sand, you have 15 barrels of paint chips. Waterjetting is incredibly green.”

Charles and Lydia formed the Advisory Council in 1996 with the goal of promoting education, cooperation, and development of new technologies that conserve resources, primarily dealing with water blasting or wet abrasive blasting. Lydia says, “Charles and I took photographs for NACE/SSPC standards, which were funded by the National Shipbuilding Research Program (NSRP), a joint shipyard/navy program. NSRP is still funding projects favorable to waterjetting.”

Education efforts involve workshops all over the globe, massive e-mail, and multiple websites to introduce users to the waterjetting process, and an ongoing battle against the inertia of doing things the same way they’ve always been done. “After 20 years some people are still wondering if water will dissolve salts,” Lydia wryly comments. “The standards have been out since 1994, and I still have people saying, ‘I’m not sure we can paint over waterjetted surfaces.’”

As Charles points out, “It would be easier to change chemistry than some people’s opinions, and we educators don’t like that!”

Successful waterjetting also calls for a higher level of expertise, which takes time to develop. Lydia explains, “You can calculate what happens when the water hits and ‘splats.’ You can calculate the velocity, energy, and force from a nozzle, and the cohesive force to drill through a layer and the adhesive force to shear along an interface. You can take off exactly the layers you need at a very specific level.

“A lot of the time contractors are not into calculations,” Lydia observes. “They want to pick up the equipment and just have it work, but this is sophisticated. Most of the time blasters will start at an inconspicuous spot with low velocity and pressure, or they might start at 30,000 psi and see what it takes to remove one layer and not the next. It becomes an art.”

Since Europe has been ahead of the United States in their environmental awareness, they have also been ahead in the use of waterjetting technology. Lydia notes, “In the l980s a company in Canada put together a massive waterjetting system and came to the U.S. Now they maintain pipelines in Russia and the Middle East. They come along the pipeline and clean and recoat it, but people in the U.S. aren’t using it even though it’s proven technology.” Charles and Lydia both see restoration of the oil, gas, and chemical pipelines in the U.S. as a critical need where waterjetting could be instrumental. Lydia reports, “Our pipeline system is old and corroded. It’s a major crisis point in our infrastructure. It costs $7 billion annually to monitor, replace, and maintain the 484,000 miles of U.S. pipelines. In our country we’re patching rather than cleaning and repainting.”

Since pipeline ruptures range from disruptive to dangerous, Charles muses, “Why isn’t the refurbishment of the pipeline system of the U.S. recognized as one of the largest business opportunities of recent times?” Charles feels that a vision of what can be achieved is necessary for change to occur. “We’ve got a society that’s so litigation-conscious that they do the same, usual thing,” he remarks. “There’s no incentive to look at something new or different.”

Lydia’s concern is, “After 30 years I don’t see how waterjetting is new any more, but I keep finding people who’ve never thought about waterjetting for their cleaning and coatings removal.”

Lydia served on the WJTA Board for 12 years and says, “I really enjoy working with the waterjetting industry. They’re very competitive, but they will get together and talk about what’s good for the industry. Through the years they’ve been very cooperative.”

Because of its versatility, waterjetting has quite diverse applications. “I love it that you can go into someone’s research lab and they may be cutting stained glass or parts for a motorcycle fender,” Lydia exclaims. “It’s used as a cutting tool for blue jeans, mashing potatoes, and pulverizing orange juice. One of the biggest uses of waterjets is cutting baby diapers because you have a fast stream of water that doesn’t get anything wet. It’s a knife blade that never gets dull. I would love to see more water used on bridges, structures, and roads. It pains me to see someone with a jackhammer on a highway. With waterjetting you can remove what you want without fracturing the rest of the surrounding concrete.”

Lydia has enjoyed serving as an expert on unique projects where waterjetting could provide both the precision and power needed. “We were involved in the conservation of the Titanic Big Piece and the Saturn V rocket,” she recalls. “I found the Saturn V to be the most interesting because you’re working on an icon—a part of history. We worked with the conservators to use waterjetting and not damage the artifact. We were letting them know how you could get one coat off without tearing the rest to pieces.”

The reason for Lydia and Charles’s promotion of waterjetting is not just professional interest; Charles says, “You might think we’re just technologists, but we think about the welfare of people. We search for excellence.” Since Lydia has been a District Governor with Rotary International, they have visited hundreds of clubs and Charles observes, “Community-aware people do not come from the engineering and science professions, but they have the biggest impact on lives. Scientists are often not aware of social implications because living in a gated community doesn’t give a picture of what’s going on at the food bank.”

“We really hate to see the ill effects of misapplied techniques and old ideas because people don’t want to change,” he continues. “That’s why we got involved—we were concerned about the waste of money and lives. We needed to develop a network to bring this community together to look at conservation of resources and the infrastructure of the United States.”

Lydia has been recognized as “Distinguished Citizen” by Alpha Gamma Delta sorority and was honored in 2004 as one of the 20 most influential people in the coatings industry by the Journal of Protective Coatings and Linings. As well as giving workshops and providing expert advice, Lydia and Charles have found time to write seven fiction books, with the latest released January 2011. Charles accurately says, “We do a lot of things!” From the ground up, Lydia has been pushing the water-jetting frontier forward, and she welcomes others to join her to build the future with action and vision!

Drs. Charles and Lydia Frenzel live in San Marcos, TX, and can be reached at Frenzelfrenzel@advisorycouncil.org.

IWA Jun 2011 45

Conference and Exhibition

October 31-November 3, 2011

Houston Marriott West Loop, Houston, Texas, USA

 Call for paper (http://www.clarion.org/ERRP/ERRP-2011/index.php)

Papers are now invited for this international forum which will address key issues in oil and gas pipeline-rehabilitation.  The conference program will be divided into the following broad areas of interest:

• Inspection – internal and external
• Integrity assessment
• Repair and rehabilitation practices and technologies
• Internal issues – including black powder, microbial corrosion
• External issues – including coatings, DCVG, direct assessment.

The link contains additional information on the submission of abstracts and the conference.

Prepared by Lydia Frenzel from a specific Proprietary Inhibitor and Cleaner manufacturer’s sheet. Most of the manufacturers have letters or tests results from specific coatings manufacturers. If you contact me, I will send you the link to the source material.

OBJECTIVE: This document provides guidelines for testing Proprietary Inhibitor and Cleaner used according to its manufacturer’s instructions. These test guidelines are necessary because applicable ASTM test procedures specifically require that tests be conducted in a manner consistent with the manufacturer=s instructions for use of the product tested. Since the performance of the product is application sensitive, this step by step test procedure should be helpful in the evaluation of its performance in various surface preparation methods.

Background: This gives the specific background of the Proprietary Inhibitor and Cleaner.

TEST PROCEDURE: Panel Preparation Steel test panels should be used when testing for rust formation. The size of the panels may vary but generally are 3″ x 5″ x 0.25″. Ten panels per coating is generally adequate to test for both salt removal and coating adhesion. All panels, with the exception of the control panel, should be immersed for 100 hours in an 8-10% weight by weight (w/w) sodium chloride solution to accelerate rust development. The control panel which was not immersed in salt water solution will establish the baseline reading for salts and other contaminants levels. In addition to the control panel, leave one test panel out of the blast sequence to measure the salt levels deposited after 100 hours of immersion. The other eight panels will be blasted to SSPC-SP10 (NACE 2)(Near White) using the either the water-abrasive blasting method or the dry blast method.

For Water-Abrasive Blasting: Per manufacturer’s recommendation for water-abrasive blasting, Proprietary Inhibitor and Cleaner should be used in both the blast and the wash down cycles. In the blast cycle the product can be injected into the blast stream by using an injection pump at low dilution of 50:1 ratio of Proprietary Inhibitor and Cleaner to water or higher (as high as 250:1) only with potable water.

Pre-mixing of the product is also acceptable as long as the mixing ratio is the same (50 parts potable water or higher with 1 part Proprietary Inhibitor and Cleaner or higher).

In the wash down cycle in water-abrasive blasting it is critical that the mixing ratio not exceed 100:1, because the wash down cycle is the final rinse of the surface. Wash down not only cleans contaminants that were present before the blast but also removes shattered abrasive particles embedded in the surface profile during the blast cycle. These embedded particles have a potential to form rust on the surface because they are wet, may contain chlorides, sulfates, and other contaminants, and will attract oxygen in the air. Therefore, to get these particles out of the surface profile and achieve a perfectly cleaned surface a wash down is necessary.

Wash down as defined by the manufacturer should have at least 500 psi pressure @ 1-3 g.p.m. of water (potable) mixed with Proprietary Inhibitor and Cleaner at a 50:1 to 100:1 ratio (see manufacturer’s instructions).

WARNING: Dipping the test panels in Proprietary Inhibitor and Cleaner solution without using a pressure rinse will not remove the embedded abrasive particles and the salts trapped in the corrosion pits but will only wet them, virtually guaranteeing premature coating failure. Using Proprietary Inhibitor and Cleaner both in the blast and wash down cycles is a failsafe method to obtain maximum cleanliness of the substrate. After the wash down cycle is completed, allow the test panels to dry, usually 15-30 minutes, before they are coated or subjected to any other test. Failure to allow the surface to dry will also lead to premature coating failure. Understandably, for test purposes, higher than recommended concentrations may be used. The greater the concentration, the longer the drying time, but under no circumstances should a coating be applied over a wet or damp surface.

For UHP Water Jetting, waterjetting, water blasting (water with little or no abrasive at 25,000+ p.s.i.)

Typically chemicals are NOT used in the BLAST CYCLE.

Blast cycle: (optional) (applicable if, and only if, pump manufacturer approves.) Start with 250:1 Proprietary Inhibitor and Cleaner. If flash occurs, decrease water portion (increase portion) until there is no flash.

Wash down (rinse) cycle: Begin as soon as practical after the blast. If Proprietary Inhibitor and Cleaner was used in blast cycle, start with 200:1. If Proprietary Inhibitor and Cleaner was not used in blast cycle, start with 100:1. (In either case, wash downwater pressure should be at least 500 p.s.i. with a water flow rate of at least 2 g.p.m..). If the surface is highly contaminated with chlorides and/or the water is very hard (contains elevated levels of carbonates or bicarbonates) and/or the surface is deeply pitted or profiled and/or weather conditions are marginal, it may be necessary to decrease water and increase Proprietary Inhibitor and Cleaner from the recommended start ratios to 100:1 or 50:1, respectively.

For Dry Abrasive Blasting (wash down only, of course) Start with 50:1. Wash down pressure should be no less than 500 p.s.i. at 2+ g.p.m. 1,500+ p.s.i. is highly recommended to totally remove the dust and contaminants from the anchor profile. Then increase water portion (or decrease Proprietary Inhibitor and Cleaner ) until flash appears or appears before you wish it to (i.e., until your blast window is unsatisfactory.)

Three most critical points for wash downs:

1. Always use the appropriate ratio of Proprietary Inhibitor and Cleaner for the specific blasting application with potable water.

2. Always use recommended minimum pressure and flow corresponding to the blasting application used.

3. Do not dip in or brush the surface with Proprietary Inhibitor and Cleaner as a substitute for a pressurized rinse..

RECOMMENDED COATING TESTS: Test panels prepared in the earlier section can now be subjected to the following tests. These are ASTM tests, approved and recommended by both SSPC and NACE. Coating compatibility approvals of Proprietary Inhibitor and Cleaner from several coating manufacturer’s i.e. Sherwin-Williams, Carboline, Ameron, PPG, Tnemec, etc. are based on the result of these tests (please see Representative Coating Compatibility Chart). Some tests were completed at the coating company’s laboratory and some of them were conducted at an independent laboratory under the supervision of coating company corrosion specialist. The test results are available on request.

1. ASTM D 5894 – 96 Standard Practice for Cyclic Salt Fog / UV Exposure of Painted Metal, (Alternating Exposures in a Fog / Dry Cabinet and a UV / Condensation Cabinet)

2. ASTM D 4541 – 95 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers

3. ASTM D 610 – 95 Standard Test Method for Evaluating Degree of Rusting on Painted Steel Surfaces

4. ASTM D 714 – 87 Standard Test Method for Evaluating Degree of Blistering of Paints

5. ASTM D 1654 – 92 Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments

RECOMMENDED CHLORIDE REMOVAL TESTS: The following tests are recommended if the panels are tested for soluble salts or any other contaminant which Proprietary Inhibitor and Cleaner may effectively remove. These test are also described in SSPC-TU 4 – Field Methods for Retrieval and Analysis of Soluble Salts on Substrates.

1. ISO 8502-6 Bresle Sampling Method, (SSPC-TU 4, Section 3.3 – Adhesively Bonded Cell)

2. ISO 8502-5 Chloride Ion Detection Tube (SSPC-TU 4, Section 4.3 – Field Detection of Chloride Ion by Kitigawa Tube)

3. ISO 8502-1 Field Test for Iron II Salts in Abrasive Blast Cleaned Surfaces (Field Test for Soluble Iron Corrosion Products) (SSPC-TU 4, Section 4.8 Qualitative Field Detection of Ferrous Ion)

4. Quantab Strip (SSPC-TU 4, Section 4.4 – Field Detection of Chlorine Ion by Quantab Method)

If you are interested in our Coffee Club, you’ll find some ongoing materials on Fat Squirrel Publishing as Napoleon Forest combines forces with a few interesting characters like Jaqi LeMans, a lover of muscle cars and the only woman to win the Texas 500, in ferreting out what the secretive Free Range Party has to do with the latest Texas political conspiracy.

Many people contributed to this module.  The technical team members include:
National Shipbuilding Research Program SP-3 Panel, Todd Pacific Shipyard, Detyens Shipyard, Atlantic Marine Florida LLC, Carolina Equipment and Supply Co. (CESCO), UHP Projects, and NLB Corporation. My apologies if I missed someone.

There are many other factors of inspection of the substrate when wet abrasive or waterjet methods are used.  For workshops or further details or training, contact Dr. Lydia Frenzel.

The material presented in this training module is intended to be non-commercial and, as indicated by the diverse source of photographs and list of contributors, is derived from a cross-section of equipment and materials suppliers to the pressurized water cleaning industry manufacturers, experienced contractors, as well as NSRP volunteers and staff.
The use of a specific photo or video does not constitute endorsement or preference for a particular supplier.  They are intended as illustrative examples and to acknowledge the companies with individuals who contributed to this program and the advancement of the industry.

Companies who contributed to the review and discussion include:

National Shipbuilding Research Program SP-3 Panel

Todd Pacific Shipyard
Detyens Shipyard
Atlantic Marine Florida LLC
Carolina Equipment and Supply Co. (CESCO)
NLB Corporation
UHP Projects
Flow International
KMT Aqua-Dyne
Hammelmann Corp.
Surface Technologies Corp.
Elzly Corp.
Applied Research Lab- Penn State
Hydrochem Industrial Services
Parker Polyflex
International Paint
Hempel
Jotun
PPG Protective & Marine Coatings
General Shipyards
NASSCO
Chlor*Rid
Holdtight Solutions
Chariot Robotics LLC
Journal of Protective Coatings and Linings (JPCL)
CleanerTimes
Sarafina
Alcoa
Stolt Nielson Tanker
National Surface Treatment Center
Society of Protective Coatings (SSPC)
National Association of Corrosion Engineers (NACE)
Navy Sea Systems Command (NAVSEA)

Bibliography
These papers are included for further reading with permission from JPCL, CleanerTimes, and Marine Log. All rights are retained by the publishers.

Gilbert, Doug, New Hydroblasting and Slurryblasting Standards Issued, JPCL, Jan., 1995, p. 64-69
Kelly, John, There’s More than One Kind Of Rust, Marine Log, May, 1996, p. 18
Swearingen, Mark, UHP Water Jetting Offers Advantages, Marine Log, May, 1996, p. 20
Tanner, John, Flash Rust, A Primer, CleanerTimes, April, 2001, p. 20
Frenzel, Lydia, The ABC’s of Surface Preparation, CleanerTimes, April, 2001, p. 42-44
Frenzel, Lydia, Flash Rust: Color, CleanerTimes, May 2001, p. 26 & 27
Frenzel, Lydia, Flash Rust: Amount, CleanerTimes, June 2001, p.32 & 33
Frenzel, Lydia, Remote Waterjetting Offers Inconspicuous Coatings removal on LNG tank, JPCL, Dec., 2002, p. 57-65
Frenzel, Lydia M, Flash Rust, CleanerTimes, Sept, 2004 p 24-27

The Pressure Sensitive Tape Test described by Hempel is a modification of ISO 8502-3 (Pressure Sensitive Tape test for dust) and is not mentioned in VIS-4.  The tape test can be used as a permanent record.  If lint deposition is a concern, the project specification may require use of a different technique to determine the level of flash rust, such as the pressure-sensitive tape test. Those responsible for establishing the requirements and those responsible for performing the work can agree to the use of a different technique to determine the level of flash rust

Place a piece of tape (as specified in ASTM D 3359) in a length of at least 5 cm (2 in) on the surface and rub thoroughly with a fingertip–not a nail–to make the tape adhere firmly.  Peel off the tape and place it on a piece of white paper for reference. Repeat this process 9 additional times (for a total of 10 tests) using a fresh piece of tape each time and apply the tape to the same spot.  Assess the appearance of the tape and the surface.

The results from the pressure sensitive tape test lead to the same conclusions as the tape tests.  For further details or training on this item, contact Dr. Frenzel.

Tape Test from a Moderate Flash Rust (MFR) Surface (Below).

 4. Based on the subjective methods, Flash Rust is classified as
           • None
           • Light
           • Moderate
           • Heavy

The following metric table was developed by Pete Ault, Elzly Technology Corporation. Click Table to enlarge.

Table of Metrics used in Flash Rust

ALL of the VISUAL GUIDES are used in the SAME WAY!
 Look at the flash rust
• straight on,
• within arm’s length,
• in good lighting,
• prior to painting.
 Allow time to remove, if necessary, excess loose flash rust prior to painting

Look at the surface and decide if you can see through the rust or if it obscures the surface.  Make sure that the rust is not splotchy black.

Look at the color.   Color can vary depending on the type of steel. The color is affected by the age and type of steel and, in the field, certainly might appear differently than the descriptive terms. Current language being adopted by NACE and SSPC will remove the COLOR language. 

Determine Quantity of loose rust dust. Lightly wipe the surface with a cloth.

The methods to evaluate Flash Rust are Subjective.
• Visual Appearance and
• Assessment of amount of Loose Dust
 Cloth Wipe in hand
 Cloth Swatch in hand
 Cloth around a Brush
 Tape

Below: the substrate is dry- but it is  darker (overall) than the original substrate.
This surface is dry within 5 minutes. The standard pictures in VIS-4 do not provide these types of illustrations of pressure-washed surfaces. The upper half is not washed; the lower half has been pressure washed.

Brush test on the Pressure Washed Surface.

Brush Test before Pressure Wash.

After Pressure Wash- there is very little faint color on cloth
After pressure washing the substrate, there is a faint marking at the upper edge of the cloth where the brush bristles contacted the surface.
The area has been mitigated from moderate to light flash rust.

 Prior to the application of paint, the substrate must meet the procurement specifications.
 Typical field remediation includes:
 Pressure washing
 Broom brushing
 Blowing off with pressurized air
 Solvent cloth or dry cloth wiping
 Vacuum

Upon polling contractors, it appears that pressure washing is the preferred practice. The appearance after pressure washing when the surface dries will be DIFFERENT; rust dust is washed away.  Typically the surface has a darker appearance.  The metallic sheen might disappear.  The standard pictures in VIS-4 do not provide illustrations of pressure-washed surfaces.
In the first two pictures, the substrate was pressure washed (ca 1000 psi) to remove the loose dust so that the substrate would meet a “light” flash rust requirement..
The substrate dried in a few minutes.  Flat surface can take longer to dry.

INSPECT the AREA AFTER PRESSURE WASHING.
Note that the loose dust is removed.
However, the stains on the right have remained.
The inspector, contractor, paint manufacturers, and owners (all the responsible parties in a coatings project) should note streaked areas and obvious runs. 

In this example, the source of the water that created the original flash rust came from a hole in the ship that most likely had salts or oil and greases.  Special attention should be given to those areas. Look to the project specifications as to what other inspections might be required.

At the right, notice that some areas are not washed, some have dried, and some are still drying.

Here are more pictures showing the same type of situation, where some areas are not yet washed, some are dry, and some are still drying.

Close up of area on right in picture above.

To Repeat: the inspector, contractor, paint manufacturers, and owners (all the responsible parties in a coatings project) should note streaked areas and obvious runs. 

In this example, the source of the water that created the original flash rust came from a hole in the ship that most likely had salts or oil and greases.  Special attention should be given to those areas. Look to the project specifications as to what other inspections might be required.
All the defects can be seen.  There are stains, but NO loose rust dust.

All the defects can be seen.  There are stains, but NO loose rust dust.

This is the result of the Brush Wipe Test on Heavily Stained & Heavy Flash Rust Area

Before Pressure Washing

Before Pressure Washing.

After Pressure Washing. Hand wiping test.

After Pressure washing. Brust test.

A direct comparison between hand wipe and brush test on pressure washed moderate flash rust indicates no differences.

 None
 Light
 Moderate
 Heavy
Adopt the method with which you feel most comfortable and that is portable to different projects and sites.

Examples of LFR on Swatch, wipe, and Brush

Example of MFR on swatch and brush wipe.

HFR on Swatch

HFR on Brush Wipe

HFR with Swatch, Brush, and Wipe