Thames River Project

The problem:

The Thames barrier was erected in 1989 to provide flood control to the upper reaches of the Thames River including the heavily populated areas of London. The gates could be raised from the riverbed into a vertical defense position in the event high surge tides threatened the London metropolitan area.

In October of 1997 a sand dredger, the Sand Kite, wrecked into one of the main gates of the Thames barrier. The ship was damaged and dumped its load of sand and aggregate, then sank onto the gate where it sat for several days atop its load. This caused paint failure and premature corrosion on the flat face of the gate. The failure of this gate could have had potentially disastrous effects on London, with flooding damage estimated at UK$21 Billion and extensive loss of life.

The UK’s Environment Agency had several requirements for the any repairs that were undertaken on the damaged gate. The barrier gate could not be taken out of service and had to be able to be closed at any time with a 1-hour notice to the cleaning contractor. In addition, there could be no environmental pollution or potential release into the environment during the surface preparation procedures. The twice-daily 21-foot tides and heavily traveled river created logistics problems for any repair to the gates. Because of these constraints any surface preparation that required stationary staging was rejected.

The solution:

The remotely controlled, vacuum attached JetTractm system provided by UHP Projects, Inc. was used to clean and prepare the surface of the gate for recoating. This system uses Ultra High Pressure (40,000 PSI) waterjets to strip the coatings from the surface. A patented seal allows the remote JetTractm crawler to attach itself to the gate using vacuum supplied by a remote vacuum skid. The paint and water is completely contained in a vacuum shroud and removed down a hose to a vacuum system located on a barge. The JetTractm crawler is remotely controlled and can move in any direction in both the horizontal and vertical positions as well as overhead.

Handy Table on Surface Contamination

NAVY SEA Systems Command
Materials Engineering Group
Codes SEA 03M12.5
2531 Jefferson Davis Highway
Arlington, VA 22242-5160

Soluble Substances Table 1  (P & W Hand Held Hydroblast Unit)
  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)
 Total Sample  Area (cm2) 50
 Total µg/ cm2   120.71
 Chloride  µg/ cm2  62.55

How is this going to be spent?

A few days ago we decided that we needed to take some action on the new budget.

The government is going to need a lot of help if it is to know how to spend some of the following:

$6 Billion on energy efficiency in public housing.
$5 Billion on weatherization grants to homeowners.
$8 Billion on public transit and ancillary infrastructure.
$40 Billion assisting school districts to modernize.
$2 Billion rehabing foreclosed properties.
$29 Billion for roads and bridges.

Personally, I don’t think we should have very much faith in the decision process. We’ll tend to get storm windows on houses in Lake Charles, La. and screens on houses in Montana. New benches at bus stops will feature eye catching designs and no shelter roofs. Old-but-serviceable will become targets for new-and-novel. The public will get a whole slew of new buzz words and politicians won’t have to get colds kissing babies for a while. Dedicating a few new acres of asphalt is safer than repainting the food bank.

Inspection Manual for Flash Rust

Inspection Manual for Flash RustSupplement to Standard Photograph Guides
Supplement to VIS-4

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:

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