Detail of GB/T 8923.4-2013

Introduction of GB/T 8923.4-2013

Preparation of steel substrates before application of paints and related products - Visual assessment of surface cleanliness - Part 4: Initial surface conditions, preparation grades and flash rust grades in connection with high-pressure water jetting 1 Scope This part of GB/T 8923 specifies a series of preparation grades for steel surfaces after removal/partial removal of water-soluble contaminants, rust, previous paint coatings and foreign matter by high-pressure water jetting. The various grades are defined by written descriptions together with photographs that are representative examples within the tolerances for each grade as described in words. In addition, this part specifies both initial surface conditions and after-cleaning flash rust grades, also defined by written descriptions together with representative photographic examples. Note 1: Examples of foreign matter are salt, grime, dirt, mill scale, oil, grease and marine growth, e.g. algae. This part relates the cleanliness of the surface to its visual appearance. In many instances, this is sufficient for the purpose but, for coatings likely to be exposed to severe environments, such as water immersion and continuous condensation conditions, consideration should be given to testing for soluble salts and other invisible contaminants on the visually clean surface by the physical and chemical methods which form the subjects of the various parts of ISO 8502. The roughness characteristics of the surface should also be considered by reference to ISO 8503, although it must be noted that preparation by high-pressure water jetting does not create a profile or significantly change an existing profile. Note 2: Water pressure, water volume, nozzle design, stand-off distance and traverse rate are factors which will affect the efficiency of removal of contaminants such as water-soluble matter, rust and paint coatings. The removal efficiency also depends on whether detergents are being used in the cleaning process. If so, rinsing afterwards with clean water is necessary.   2 Normative References The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 4628-3 Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size of defects, and of intensity of uniform changes in appearance - Part 3: Assessment of degree of rusting ISO 8501-1 Preparation of steel substrates before application of paints and related products - Visual assessment of surface cleanliness - Part 1: Rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous coatings ISO 8502 Preparation of steel substrates before application of paints and related products - Tests for the assessment of surface cleanliness ISO 8503 Preparation of steel substrates before application of paints and related products - Surface roughness characteristics of blast-cleaned steel substrates 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 water jetting (preferred) hydrojetting aquajetting water blast-cleaning (deprecated) hydroblasting (deprecated) aquablasting (deprecated) cleaning a steel substrate by directing a high-speed jet of water onto its surface 3.1.1 high-pressure water jetting water jetting that involves the use of water pressurized to above 70 MPa Note: Water jetting using higher pressures might remove loose mill scale from a steel surface, but it does not impart a surface profile to the substrate. 3.2 initial surface condition visual appearance of a coated steel surface which has been degraded or damaged by rusting, blistering or flaking 3.3 preparation grade visual appearance of a steel surface after contaminants on the surface have been removed by a preparation method 3.4 flash rust grade visual appearance of a steel surface with respect to flash rust after the surface has been subjected to water jetting (see 3.1) 4 Initial surface conditions Five initial surface conditions are defined. Three initial surface conditions, designated DC A, DC B and DC C, are specified for steel surfaces that have degraded since being blast-cleaned and, in the case of DC A and DC B, painted with a protective paint system. Note: DC C is intended for use both in situations when a protective paint system has been applied previously and in situations when no protective paint system has been applied. Two initial surface conditions, designated DP I and DP Z, are specified for steel surfaces that have degraded since being blast-cleaned and painted with an iron oxide prefabrication primer (DP I) or a zinc silicate primer (DP Z) alone. The initial surface conditions are defined by written descriptions given in Table 1 together with the representative photographic examples appended to this part. Table 1 Descriptions of initial surface conditions

Contents of GB/T 8923.4-2013

Foreword II 1 Scope 2 Normative References 3 Terms and definitions 4 Initial surface conditions 5 Preparation grades 6 Flash rust grades 7 Procedure for the visual assessment of steel substrates 8 Photographs Annex A (Informative) Guidance on cleaning with water