Water Blasting/Jetting Flashcards
(72 cards)
Using water as the principal ingredient to prepare surfaces for coating application is a relatively ___ ___.
Recent Development.
Using water to prepare surfaces was developed for two principle reasons:
1st: Water dampens ___ ___ and allows use of abrasive blast cleaning techniques in places where blast dust is considered a nuisance or hazardous.
2nd: The water can wash away ___ ___, which dry blast cannot remove easily.
1st: Dust Emissions.
2nd: Soluble contaminants.
The significance of soluble contaminants (not easily seen on a dry blast cleaned surface) have been increasingly recognized as a reason why coatings fail to provide ___-___ ____. Their removal is now considered to be an essential element of successful surface prep for the best coating systems.
Long Term Performance.
The waterjetting standard addresses both ___ (WJs) and ___ (NV) levels of cleanliness.
Visible and nonvisible
There are two forms of water blast cleaning:
- Water Blasting which?
- Waterjetting which?
- Uses abrasive combined with water.
2. Uses water alone.
NACE/SSPC, etc, have divided waterjetting into categories for the sake of accuracy and consistency.
- Low Pressure Water Cleaning.
- High pressure water cleaning.
- High pressure waterjetting.
- Ultrahigh pressure water jetting.
- LP WC: Pressures below 5,000 psi.
- HP WC: Pressures of 5,000 to 10,000 psi.
- HP WJ: Pressures of 10,000 to 30,000 psi.
- UHP WJ: Pressures above 30,000 psi.
LP WC used for surface prep is primarily a 1___ ___. At below 5,000 water removes 2 ____ ___ . It will reliably remove 3___ of ___ ___ leaving the surface coating intact.
Is often used to wash the underside of ships and will remove 4. ___ ___ and some deteriorated 5 ___ ___ ___ prior to recoating.
- Washing technique.
- Soluble contaminants and some loosely adherent surface contaminants.
- Chalking of aged coatings.
- Marine Growth
- Anti-Fouling Coatings.
Advantages of waterjetting include:
- Uses water as a cleaning material, since suitable water is generally available in cheep/large quantities.
- No ___ ___ to contaminate surrounding area.
- Absence of ___ and ___ hazards at the nozzle tip.
- Abrasive particles.
3. Dust and Spark hazards.
HP WC is used to prepare 1___ ___ prior to coating. A properly focused HP WC nozzle can cut through 2___ ___ so the technique is both efficient and dangerous.
When used for surface prep for coatings over 3___ surfaces, the production rate is relatively 4___.
In addition, only 5___ contaminates can be successfully removed when preparing 1___ surfaces for painting.
- Concrete Surfaces.
- Concrete Blocks
- Steel
- Low
- Loose
HP WJ is seldom used for surface prep for 1___ seldom uses HP WJ equipment. It does not clean better than equipment operating at 2___ ___, and the production rate is not cost effective.
- Coatings.
2. Lower Presure
UHP WJ used water pressure at 1__ ____ and above, up to 2__ ___. Because of the high pressures required, safe practice demands great care in controlling the 3. ___ ____, since a person struck by high velocity water at short range could be seriously injured.
- 30,000
- 50,000
- WJ Nozzle.
Most UHP WJ equipment operates with a 1___ nozzle and 2___ water streams. The highly efficient nozzle design produces an effective cleaning pattern while using relatively little water, perhaps no more than 3___ ___ per minute.
- Rotating.
- Dual.
- 2 Gallons.
UHP WJ requires the nozzle be held close to the surface being cleaned since cleaning efficiency decreases rapidly when the nozzle is held further than ___ ___ from the surface.
18 Inches
UHP WJ:
The most efficient cleaning is achieved when the nozzle is a max of 1____ from the surface. However, the blast patters in then very narrow and 2___ ___ may decrease.
- 2 inches.
2. Production Rates
UHP WJ:
At these pressures, water removes most 1___ such as chemical salts, dirt, grease, etc. It will not produce a 2___ ___ but can restore any previously existing 2___ ___ if the equipment is designed to clean the surface to a high standard. Use the highest pressures 3___ and above to achieve this high standard.
- Contaminants.
- Surface Profile.
- 35,000
UHP WJ:
An unexpected benefit of using very high pressures is the 1___ it generates. This limits rust deterioration, and the surface remains relatively clean (though with some ginger discoloration)
- Heat
Pure waterjetting at pressures below 1___ is seldom used for surface prep prior to coating, except as a 2___ ____. It is commonly used 3___, however, to remove marine growth on ships and oil-related structures.
- 7,000
- Wash Technique
- Underwater
Use pressures between 1___ and 2___ to clean marine growth from a ships hull or off-shore structure.
- 2,900
2. 7,200
The performance of Watterjetting in immersion conditions depends on two main factors.
- The ___ of the driver and ___.
- The ___ of the fouling and degree of barnacle or shell growth.
- Maneuverability of the diver and visibility.
2. The density of fouling and degree of barnacle/shell growth.
On ships’ hulls in dry dock, a cleaning rate of up to 1___ can be achieved with HP WJ. Working underwater, however, adds many other factors to consider, and these factors usually 2___ ___.
- 2,000 ft2/h
2. Reduce Performance
Because there is no 1___ ___ with an UW blast unit (the design compensates for reverse thrust), the operation is performed with considerably less 2. ___ ___ when compared so similar work above the surface.
- Reaction Force
2. Physical Effort
UW concrete cutting is another operation for WJ; Equipment has been used for this purpose at depths of up to ___.
450 ft.
A section of damaged concrete coating on a 30in steel pipeline beneath a rig in the North Sea was successfully cut and jet blasted away without damage to the underlying steel pipe. Pressures of up to 11,000 psi were used, and one diver at a time from the team handled the gun and did the cutting.
Just an example. No questions.
When steel must be brought to a white metal finish underwater, use specially developed equipment that injects ___ into the water stream.
Abrasives.
