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CL BLOG Continued from page 41
with ~80 psi (552 kPa) nozzle pressure using a 7/16-in (11-
mm) nozzle with ~250 cfm ÆW_ There are some black patches in the upper surfaces of the evaporators that are pretty hard and tough. This takes ~80 kg of garnet per m2
and ~30 min per m2 .
There were worse results with slags. I wonder if anyone has had any experience with this type of project and could provide advice on how to proceed. My ideas for a solution are changing the parameters of the pressure nozzles, type of abrasive, chemical cleaning procedures, strippers, power tool, or mechanical cleaning methods. Most of these changes may give marginal improvement, but at this stage I am really looking at something that would [XMML \PQVO[ ]X [QOVQÅKIV\Ta JMKI][M the evaporators need to get back into service quickly.
\W X[Q KTMIVQVO MNÅKQMVKa LZWX[ LZI- matically. I believe that a smaller nozzle _QTT JM \PM UW[\ MNNMK\Q^M Y]QKS Å` ) 3/8-in (9-mm) venturi nozzle may pro- vide the solution for you. The other important variable is the
A
very high levels of salt contamination. I would highly suggest testing for salt con- tamination immediately after blasting the black patches off of the substrate. I would recommend testing for levels of chlorides,
A NACE International, Vol. 51, No. 4 April 2012 MATERIALS PERFORMANCE 43
abrasive feed rate. If the feed rate is too low or too high, productivity will suffer. The National Shipbuilding Research pro- gram has determined the following results: using copper slag at 80 psi and a feed rate of 30 lb/min (14 kg/min), a production rate of ~3 ft2
/min (0.27 m2 /min (0.37 m2 /min). /min) can be
expected. At 45 lb/min (18 kg/min), the cleaning rate can increase to more than 4 ft2
It is hard to tell from the descrip- tion alone, but it sounds like you have the typical "black rust," which often forms because of
The compressor is too small for this nozzle size and blast hose length combination. With a pres- sure drop of <100 psi (689 kPa)
sulfates, and nitrates. Not knowing all the factors involved, any or all of these con- taminants may be present. You also did not state the level of humidity or if the black patches reform in a short time pe- riod. This information would be helpful in making suggestions. If contamination is found, it should be removed or it will most likely cause any coating application
to fail prematurely. I would suggest that blasting be immediately followed by a wash with a chemical soluble salt re- UW^MZ ) ZMJTI[\ \W ZMUW^M XW[[QJTM ÆI[P rust may or may not be needed, depend- ing on many factors.
Continued on page 45