Soluble Substances Table 1  (P & W Hand Held Hydroblast Unit)
[table=1]
  Total Sample Area  (cm2) 112.5
 Total µg/ cm2   2.61
 Chloride µg/ cm2  0.85

Soluble Substances Table 2 (ABB Hand Held Grit Blast Unit)
[table=3] 
 Total Sample  Area (cm2) 50
 Total µg/ cm2   120.71
 Chloride  µg/ cm2  62.55

December 29, 2008

Prepared for
Advanced Technology Institute
SSA: No. 2008-326

Prepared by
Lydia M. Frenzel, Ph.D.
Fat Squirrel 22, LLC
On behalf of
Project Participants:
Todd Pacific Shipyard- Lead Shipyard

Project Goals and Objective:

This document is a supplement to SSPC-VIS No. 4 NACE VIS 7 (or ISO 8501-4).

SSPC-VIS No. 4 NACE VIS 7, ISO 8501-4, International Paint Hydroblasting photos, and Hempel photos do not illustrate: 1. an example of lightly wiping; 2. an example of the surface after excess flash rust with loose rust dust has been mitigated by pressure washing.

For this manual, “Flash Rust” is the rust that occurs from the time the waterjet (WJ) or wet abrasive blast (WAB) cleaning process starts to the time the water used for the cleaning process dries. Flash rust often looks like a rust bloom.

Look at SSPC-VIS No. 4 NACE VIS 7, ISO 8501-4, and NACE No. 5- SSPC- SP-12 for a more detailed definition of flash rust.

“Rust-Back” is used in dry abrasive blast standards. Rust-Back occurs on surfaces that appear to be dry. Rust Back is the rust that occurs when DRY, bare steel is exposed to conditions of high humidity, moisture, or a corrosive atmosphere.

“Rust Bloom” is somewhat uniform rust spread evenly over a large section of the surface. Rust Bloom is a generic description. The observer doesn’t know if it originates from flash rust or rust-back.

Coatings manufacturers will designation the level of Flash Rust that is acceptable for the coating in a specific environment.

How much “Flash Rust” is formed is directly related to time of wetness. Engineering controls and project scheduling are key in reducing the time of wetness. Look at Blast and Dry, Clean Blasting, and Drying Effects.mpg

Inspecting for “Flash rust” is not rocket science.
It is deceptively simple or deceptively hard, because the decision is subjective.
? Prior to painting, look at the rust bloom on the steel.
? Find out the environmental history-if there was rain, pressure washing, waterjet cleaning, or no water involved at all.
? If there is no water involved, you reject the “Rust-Back.”
? If there is water involved in the surface cleaning, you place VIS-4 up to the surface nest to the rust and make an initial judgment concerning light, moderate, and heavy.
? If necessary, you wipe the “Flash Rust” to continue the determination between light, moderate, and heavy.
? Be consistent in the determination methods.
? Mitigate the flash rust to the amount required by the project specifications.

This manual does not address whether or not the amount of flash rust is suitable for coatings. Coatings manufacturers DO NOT recommend painting over HEAVY flash rust. The coatings must wet to the substrate, consolidate the dust, and be thick enough to cover the rust dust.

SSPC, NACE, ISO and Coatings Manufacturers published several guides to “Flash Rust” with photos.
All guides are to be used in the same manner. All lead to the same answer!

Download this manual here:

[download id="5"]

Can you remove all of a top coating and leave all of the tightly adherent base coat? Are elastomeric coatings tightly adherent by abrasive blasting standards and easily removed by wet blasting?

The advantage of waste streams that contain only the original coating: Dams and tidal structures.

Paint removal that creates opportunity for corrosion. Brushing and scraping.

UHP WJ is routinely used to remove surface radiation from steel in nuclear plants.

John S. Oechsle Jr., who is now retired, worked with S.G. Pinney & Assoc. in Florida and prior to that in the 1950’s worked with Metalweld and DuPont in the nuclear industry.  IN 1999, he talked to me about what happened to the surface, removal of Corrosion, and surface radiation. The exterior surface of any metal starts to change as soon as it comes out of the mill.  The change is at the outer boundary and as you go into the material, you reach the bulk property region.

Metalweld and DuPont in the 1950′s showed that corrosion invades the surface by about 2.5 mils at the grain boundary. To remove all contamination by dry blasting, it required 5 consecutive blasts consuming 47.5 lb. of abrasive/ft.² to remove enough steel to eliminate the surface corrosion contamination. NACE No. 1/ SSPC-SP 5 was the standard.

Ultrahigh-pressure water at 36000 to 55000 psi removed the surface contamination in one full pass. On a project in Japan, 28 tons of structural steel had been in immersion in a nuclear plant for 19 years. The steel was corroded and radioactive. The customer wanted to clean the steel to less than detectable radiation for removal from the site. All steel was ultrahigh-pressure blasted at 55000 psi. 27.5 tons were moved off site at less than detectable radiation so only one-half ton of steel was removed in total.

One of the major UHP pump manufacturers has studied this erosion and energy concentration at length as they sell both cleaning and cutting equipment.

A typical surface cleaning application is 0.8 liters/minute (3 gallons per minute) at 280 MPa (40,000 psi) at a rate of 22 square meters (200 square feet) per hour.  To erode MILD steel, you would need about 150 times more energy in terms of square area per minute per hydraulic horsepower.  In other words, you would need to slow down to about 0.15 sq meter per hour at the same parameters in order to get erosion.

Personally, I don’t think anyone would want to slow down production rates this much!