Hydroblasting

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  HydroblastingStandards www.international-pc.com  123Hydroblasting Standards Contents1.Introduction5.Notes2.Format6.References3.Explanatory Text7.Visual Standards4.Procedure For Using The Standards Introduction Hydroblasting is a technique for cleaning surfaces,which relies entirely on the energy ofwater striking a surface to achieve its cleaning effect.Abrasives are NOT used inhydroblasting systems.Consequently the problems caused by dust pollution and by the disposal ofspent abrasives are eliminated.Two different hydroblasting operatingpressures are commonly encountered. ã High pressure hydroblasting,operating at pressures between 680 bar (10,000 p.s.i.) and 1700 bar (25,000 p.s.i.) ã Ultra high pressure hydroblasting,operating at pressures above 1700 bar (25,000 p.s.i.)See note 5.1This visual standard has been prepared by the use ofultra high pressurehydroblasting equipment.The standard however is applicable to surfaces producedby a whole range ofhydroblasting pressures,providing the equipment used is capableofcleaning to the visual standard depicted.The steel surfaces produced by hydroblasting do NOT look the same as thoseproduced by dry abrasive blasting or slurry blasting.This is because water on its owncannot cut,or deform steel like abrasives.Hydroblasted surfaces therefore tend tolook dull,even before they ‘flash rust’.In addition,Grade D steel,with active corrosionpitting,shows a mottled appearance after hydroblasting.Mottling occurs when thecorrosion products are washed out ofthe pits leaving a bright patch and thesurrounding areas are left a dull grey,brown to black colour.See note 5.10.Thispattern is the reverse ofthat left by abrasive blasting where anodic pits are often darkdue to corrosion products not being entirely removed and the surrounding areas arebright.‘Flash rusting’,i.e.light oxidation ofthe steel which occurs as hydroblastedsteel dries offwill quickly change this initial appearance.This standard has been produced to help International Paint Technical Service andTechnical Sales personnel advise on the recommended standard ofhydroblasting andthe acceptable level offlash rusting allowed prior to the application ofour productrange.All surface preparation and coating application work is the responsibilityoftheapplicator.All products and advice supplied are subject to our standard conditions ofsale. Format The standard consists ofa series ofcolour photographs,which depict the condition ofunpainted steel surfaces prior to and immediately after surface preparation byhydroblasting.See note 5.2.It then shows these surfaces with varying degrees of flash rusting. Explanatory Text 3.1 Initial Rust Grades The standard illustrates two initial rust grades ofsteel which have had the millscaleremoved by abrasive blasting and which have been allowed to rust to the relevantstandard.See note 5.8.They are designated as Grades C and D,and are comparableto the rust grades C and D described in the ISO 8501-1:1988 surface preparationstandard and the SSPC VIS-1-89 surface preparation standard ofthe Steel StructuresPainting Council.  The definitions are: Rust Grade C: Steel surface completely covered with rust but with little or slight pitting under normal vision. Rust Grade D: Steel surface completely covered with rust on which general pitting is visible under normal vision. 3.2 Blast Standards The standard illustrates grade C and D surfaces prepared by hydroblasting to twodifferent degrees ofcleanliness.These are designated HB2 and HB2 1 / 2 and arecomparable to Sa2 and Sa2 1 / 2 described in the ISO 8501-1:1988 surface preparationstandard and to SSPC-SP6 and SSPC-SP10 ofthe Steel Structures Painting Councilsurface preparation standards.The definitions are: HB2 Thorough Hydroblast Cleaning When viewed without magnification the surface shall be free from visible oil,grease,dirt,paint coatings and foreign matter and from most ofthe rust.Any remainingcontamination and staining shall be firmly adherent.See notes 5.9 and 5.10. A brown-black discoloration offerric oxide may remain as a tightly adherent thin filmon corroded and pitted steel.See notes 5.9 and 5.10. HB2 1 / 2 Very Thorough Hydroblast Cleaning When viewed without magnification the surface shall be free from visible oil,grease,dirt,loose rust,paint coatings and foreign matter except for staining.A brown-blackdiscoloration offerric oxide may remain as a tightly adherent thin film on corrodedand pitted steel.See notes 5.9 and 5.10. 3.3 Degrees ofFlash Rusting The standard illustrates three grades offlash rusting.Light flash rusting,designated L,moderate flash rusting,designated M,and heavy flash rusting,designated H.The definitions are: L:Light Flash Rusting When viewed without magnification small quantities oflight tan-brown rust willpartially discolour the srcinal metallic surface.The discoloration may be evenlydistributed,or in patches,but it will be tightly adherent and will not be heavy enoughto easily mark objects brushed against it. M:Moderate Flash Rusting When viewed without magnification small quantities oflight tan-brown rust willobscure the srcinal metallic surface.This layer may be evenly distributed or patchy in appearance but it will be heavy enough to mark objects brushed against it. H:Heavy Flash Rusting When viewed without magnification a heavy layer ofdark tan-brown rust willcompletely obscure the original metallic surface.This layer ofrust will be looselyadherent and will easily mark objects brushed against it. Procedure for Using the Standard 4.1 Select the photograph ofrust grade that most closely resembles the rust grade ofsteel to be cleaned.Previously painted steel can be classed as either C or Dgrade depending upon the degree ofpitting.See note 5.2. 4.2 Select the photograph depicting the degree ofcleaning that has been specified.For example,ifthe initial rust grade is D and thorough hydroblast cleaning isspecified (HB2) use photograph D HB2. 4
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