GB/T Translated English of Chinese Standard: GB/T NATIONAL STANDARD OF THE

Transcription

1 Translated English of Chinese Standard: GB/T NATIONAL STANDARD OF THE GB PEOPLE S REPUBLIC OF CHINA ICS A 29 GB/T Replacing GB/T Metallic Coatings - Hot Dip Galvanized Coatings on Fabricated Iron and Steel Articles - Specifications and Test Methods 金属覆盖层钢铁制件热浸镀锌层技术要求及试验方法 (ISO 1461:1999, Hot dip galvanized coatings on fabricated iron and steel articles - Specifications and test methods, MOD) Issued on: April 10, 2002 Implemented on: December 1, 2002 Issued by: General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China Page 1 of 27

2 Table of Contents Foreword Scope Normative References Terms and Definitions General Requirements Samples Coating Requirements Test Methods Qualification Certificates Appendix A Appendix B Appendix C Appendix D Appendix E References Page 2 of 27

3 Foreword This Standard modifies and adopts ISO 1461:1999 "Hot Dip Galvanized Coatings on Fabricated Iron and Steel Articles - Specifications and Test Methods". This Standard is redrafted according to ISO 1461:1999. The differences between this Standard and ISO 1461 are listed in Appendix A. The following modifications are made in this Standard; the technical differences between this Standard and ISO 1461 as well as the reasons are listed in Appendix B. The standard name is changed to "Metallic Coatings - Hot Dip Galvanized Coatings on Fabricated Iron and Steel Articles - Specifications and Test Methods" according to the existing domestic series standards; Delete the foreword of ISO 1461; Use "this Standard" to replace "this International Standard"; Quote the Chinese standards that partially adopt international standards; Combine the contents of Section 4.2 and Appendix A of ISO 1461:1999 into Section 4.1 of this Standard; Divide the contents of chapter 6 of ISO 1461:1999 into Chapter 6 and Chapter 7 of this Standard; Requirements are put forward to the coating thickness of the hot dip galvanized articles which adopt the zinc explosion to replace the centrifuging treatment or adopt both of them at the same time; Safety requirements are put forward to the hot dip galvanizing for incompletely dried articles. This Standard replaces GB/T "Metallic Coatings - Hot Dip Galvanized Coatings on Fabricated Iron and Steel Articles - Specifications". The main changes of this Standard, compared with GB/T , are as follows: If the coating thickness is larger than the specified value, then the galvanized article surface is allowed to have dark or grayish color-unevenness; Safety requirements are put forward to the hot dip galvanizing production process; The area of each uncoated surface is required not to exceed 10cm 2 ; Page 3 of 27

4 Metallic Coatings - Hot Dip Galvanized Coatings on Fabricated Iron and Steel Articles - Specifications and Test Methods 1 Scope This Standard specifies the specifications and test methods of the hot dip galvanized coatings (the total content of other alloying elements shall not be more than 20) on the fabricated iron and steel articles. This Standard is not applicable to the following conditions: a) Plates, strips, wire rods, pipes and rods that are produced by continuous hot dipping; b) Hot dip galvanized products that adopt particular standards; c) Hot dip galvanized products which have additional requirements or are inconsistent with the requirements of this Standard. Note: Some product standards may specify the product hot dip galvanized coatings through reference in this Standard or amendment of partial articles in this Standard. This Standard does not specify the after-treatment and additional over-coating for the hot dip galvanized products. 2 Normative References The following provisions, through reference in this text, constitute the provisions of this Standard. For the dated reference, all the subsequent amendments (not including the corrigendum contents) or revisions of these publications do not apply. However, parties who enter into an agreement based on this Standard are encouraged to study whether the latest revisions of these documents apply. For undated reference, the latest revisions apply to this Standard. GB/T 470 Zinc ingots (eqv ISO 752) GB/T 4955 Metallic coatings - Measurement of coating thickness - Coulometric method by anodic dissolution (eqv ISO 2177) GB/T 4956 Non-magnetic coatings on magnetic substrates - Measurement of coating thickness - Magnetic method (eqv ISO 2178) Page 5 of 27

5 GB/T 6462 Metallic and oxide coatings - Measurement of coating thickness - Microscopical method (eqv ISO 1463) GB/T 9793 Metallic and other inorganic coatings - Thermal spraying - Zinc, aluminum and their alloys (eqv ISO 2063) GB/T Metallic and other inorganic coatings - Definitions and conventions concerning the measurement of thickness (eqv ISO 2064) GB/T Metallic coatings - Determination of the mass for hot dip galvanized coatings on ferrous materials - Gravimetric method (eqv ISO 1460) GB/T Steel and steel products - Types of inspection data (eqv ISO 10747) ISO Sampling procedure for characteristic inspection - Part 1: Lot inspection sampling plan according to the determined acceptable quality level (AQL) ISO Sampling procedure of characteristic inspection - Part 3: Sampling procedure of discontinuous lots 3 Terms and Definitions The following terms and definitions as well as the ones specified in GB /T apply to this Standard. 3.1 Hot Dip Galvanizing It is a kind of process and method that zinc and (or) zinc-ferrum alloy coating is formed on the surfaces of the pretreated steel or cast iron articles by immerging them into the molten zinc bath. 3.2 Hot Dip Galvanized Coating It refers to the zinc and (or) zinc-ferrum alloy coating that is obtained on the surfaces of the iron and steel articles by adopting the hot dip galvanizing method. Note: It is abbreviated as coating in this Standard. 3.3 Coating Mass It is the total mass of the zinc and (or) zinc-ferrum alloy coating on per unit area of the steel surface, in g/m Coating Thickness It is the total thickness of the zinc and (or) zinc-ferrum alloy coating on the steel Page 6 of 27

6 surface, in µm. 3.5 Significant Surface It is part of the article surface which is hot dip galvanized or will be hot dip galvanized. The coating on such surface is of great importance for the appearance and (or) service performance of the article. 3.6 Control Sample It is the hot dip galvanized article or article group that are used for tests in a random selection from the inspection lot. 3.7 Reference Area It is the area that is subjected to test and experiment according to the specified times. 3.8 Local Coating Thickness It is the arithmetic mean value of the coating thickness, measured by the magnetic method as designed; or the equivalent value of the coating mass thickness, measured by primary measurement on a certain reference area. 3.9 Mean Coating Thickness It is the arithmetic mean value of the local coating thickness of a certain large article or a sample from a certain galvanized article lot. Note: The large article in this Standard refers to the article of which the significant surface area is larger than 2m 2 (see ) Local Coating Mass It is the coating mass of a certain area through primary measurement by the gravimetric method Mean Coating Mass It is the arithmetic mean value of the local coating mass or the equivalent value of the mean coating thickness, measured by the gravimetric method according to the sampling specified in Chapter Minimum Value It is the minimum value of the equivalent value of the coating mass thickness, measured by the gravimetric method; or the minimum value of the arithmetic mean value of the coating thickness, measured by the magnetic method as designed on a certain reference area. Page 7 of 27

7 3.13 Inspection Lot It is referred to as "lot" and is the hot dip galvanized articles in an order or in a delivery Acceptance Inspection It is the inspection which shall be made for the hot dip galvanized articles of a certain inspection lot in the manufacturing factory without any other requirement Uncoated Areas It is the area where the fabricated iron-steel article surfaces have not reacted with the molten zinc. 4. General Requirements 4.1 Data provided by the Buyer to the Supplier Necessary Data The standard number of this Standard Additional Data In case the buyer has any special requirement, the buyer shall supply the following data: a) Chemical compositions and performance of substrate metal may affect the hot dip galvanizing (see Appendix C); b) Marking of significant surface: it may use drawing sheet to mark-indicate or provide the sample with appropriate marks; c) Use drawing sheet or other methods to mark the region that its surface, flat or not, will affect the usability of galvanized article. The reasons for the unevenness are zinc tumor formed in the process of galvanizing and traces left by the touch between articles in the process of galvanizing etc.; these issues shall be negotiated by both parties of the buyer and the supplier; d) Smooth degree of surface satisfying the product requirements shall be labeled by samples or other methods; e) If there are special pretreatment requirements; f) If there are special requirements of the coating thickness (See: note of 6.2 and Appendix C); Page 8 of 27

8 6.4 Adhesion The general-thick hot dip galvanizing article has no exfoliation and oxidation phenomena under normal running conditions. And the coating exfoliation and oxidation phenomena generated by bending and deformation processing after the galvanizing do not denote a bad coating adhesion. If the buyer has any special requirement that the coating adhesion must be tested, then negotiation shall be done between the supplier and the buyer. 6.5 Acceptance Criteria Several reference areas shall be selected according to the requirements of and tests shall be made on these reference areas according to the test methods specified in The measured coating thickness shall not be less than the specified value in Table 2 and Table 3. In case of disputes, the gravimetric method test is allowed to be made by cutting the samples. Otherwise, the non-destructive test method shall be adopted for all the samples. If the steel thickness of the articles is different, then articles of the same thickness shall be taken as a separate lot and their coating thickness shall be in accordance with the corresponding value specified in Table 2 and Table 3 respectively. If the control sample coating thickness does not comply with these requirements, then double samples shall be selected in this lot (if the article quantity is less than the minimum sampling quantity, then all the articles shall be selected for test). If most of the control samples pass the test, then the lot articles can be regarded as qualified; or else, the unqualified articles shall be scrapped or re-galvanized approved by the buyers. 7 Test Methods 7.1 Appearance Test Inspect the articles by the corrected vision under normal reading environment. 7.2 Coating Thickness Test General Test Conditions If allowable, the coating thickness measurement shall not be made in area where is less than 10 mm from the margin, on the flame cutting surface or on the corner (see Appendix C.1.2) Reference Area (see 3.7) In order to obtain a typical mean coating thickness (see 3.9) or mass (see 3.11), if the Page 13 of 27

9 a) Gravimetric method is an arbitral method and it shall be carried out according to the requirements of GB/T The measured galvanized coating mass according to this method shall convert the coating density (7.2g/cm 3 ) to the coating thickness (see Appendix E.2). As this method is a destructive test method, if the article quantity is less than 10, the damage caused by this method and the resultant remedy cost is unacceptable for the buyers, then the buyers shall not be forced to accept the gravimetric method. b) Magnetic method is a non-destructive test method and it shall be carried out according to the requirements of GB/T The measuring reference area shall be in the representative area where can be selected as the reference area by the gravimetric method. If the magnetic method is adopted to measure the coating thickness of over 1000mm 2 reference area, then at least 5 measuring points shall be selected and the arithmetic mean value of them is the local coating thickness (see 3.9) of this reference area. So long as this average value is not less than the required local thickness value specified in Table 2 or Table 3, the measured value of specific measuring point is allowed to be less than the value specified in Table 2 or Table 3. The magnetic method is best applicable to the on-line quality control in the plant. Since the measured area using this method is very small, there may be one or two measured value less than the local coating thickness or the mean coating thickness. If adequate measuring has been made on one reference area by the magnetic method, then the measured local thickness value will approach to the value got by the gravimetric method. c) Cross section microscopical method is a destructive test method and it just measures a certain point. So it is not applicable to the routine inspection of the large articles or heavy articles. But it can observe the metallographic phase of a certain point according to the requirements of GB/T d) Anodic dissolution coulometric method is a destructive test method and it shall be carried out according to the requirements of GB/T Note: Electromagnetic method, a non-destructive test method, may also be adopted (see Appendix E.1). In the aforesaid measuring methods, the destructive test methods may contribute damages to the hot dip galvanized articles. So generally, the non-destructive test methods shall be adopted. However, the gravimetric method shall be adopted for arbitration if there is any dispute. If the article is very small, and more than 5 article significant surface areas must be provided for a 1000mm 2 reference area with each article having its reference area suitable for adopting the magnetic method, then the magnetic method may be adopted, or else, the gravimetric method shall be adopted. The conversion method between the coating thickness and the coating mass is specified in Appendix E. Page 15 of 27

10 7.3 Adhesion Test So long as the adhesion of the galvanized coating and the substrate can meet the article's service and general operational requirements, it is not necessary to be tested specifically. If the buyer has any special requirement, then the adhesion test method shall be determined according to the negotiation between the supplier and the buyer (see Appendix C.6). The adhesion test shall be carried out on the significant surfaces where adhesion is required during the using process. 8 Qualification Certificates As required, the hot dip galvanizing manufacturers shall provide qualification certificate meeting the requirements of this Standard. Page 16 of 27

11 C.1.4 Influence of active elements in the substrate metal on galvanized coating thickness and coating appearance Most of the steels can be hot dip galvanized approvingly, but some active elements, such as silicon (Si) and phosphorus (P) in the steels will affect the hot dip galvanizing. The steel surface components will influence the galvanized coating thickness and its appearance. For example, Si and P may lead to uneven and (or) grayish coating to a certain component range. Such coating may be much friable and thicker. The steels applicable to the hot dip galvanizing and their performance guide are presented in Normes Francaises NFA :1994 (see references). But the influence of particular elements in the steels is still being studied [see ISO (see references)]. C.1.5 Internal stress in the substrate metal Partial stress in the substrate metal may be remove during the hot dip galvanizing process and may also cause the deformation of the galvanized articles. The steel articles will be crisp after a certain degree of cold-working (for instance, flexion); this depends on the steel variety and cold-working degree. The hot dip galvanizing is a heat treatment process. If the galvanized steels are sensitive to the deformation aging, the hot dip galvanizing will accelerate the occurrence of the deformation aging and make the steel and iron articles brittle. For fear of such embrittlement hazard, steels which are not sensitive to the deformation aging-rigidification may be applied. If certain kinds of steels are considered to be sensitive to the deformation aging, then they shall be kept clear of deep cold-working if possible. If they could not be kept clear of the deep cold-working, then stress-relief heat-treatment shall be made before the pickling and the hot dip galvanizing. Note: The deformation aging-rigidification sensibility and the resultant friability are mainly caused by the nitrogen in the steel. More precisely, they depend on the steel producing process. Generally, such a problem is not occurred in modern industrial production. Aluminum killed steel may decline the deformation aging to the minimum degree. As for those steels which are strengthened by the heat treatment and cold-working, they may also tempering after being heated and reduce the acquired strength. As for those quenched steels and (or) deep-stretched steels, they have large internal stress, which may increase the cracking risk of the steel articles in the pickling and hot dip galvanizing processes. And this cracking risk can be decreased by the stress-relieving treatment for the articles before the pickling and hot dip galvanizing. But the hot dip galvanizing treatment shall be consulted from the experts. Generally, structural steel will not be brittle for hydrogen absorption in the process of pickling. Residual hydrogen (if any remained) does not affect structural steel. In view Page 20 of 27

12 Note 1: When internal thread cooperates with the external thread, the coating of the external thread form catholic protection to the internal thread, hereby there can be no galvanized coating on the internal thread. Note 2: There shall be adequate strength on the hot dip galvanized screw thread articles to meet the requirement of original design. C.2.3 Process heating influence The hot dip galvanizing shall not be made for those materials which are likely to be affected by the heating in the hot dip galvanizing bath. C.3 Hot dip galvanizing bath In the condition of special requirements, the buyer can specify the content of the additive elements and impurities in the galvanizing bath and galvanized coating. Especially in the condition that the hot dip galvanizing treatment shall be made for the boiler (namely, boiler and tank) which shall be used for the drinking water system together with the hot dip galvanized steel pipes., the buyer can claim the coating compositions to comply with the composition requirements of EN (see references) for the pipe coating. C.4 After-treatment Generally, articles shall not be piled together if they are still hot and wet. Small articles may be loosened in the charging basket or on the material frame, as soon as they are taken out from the hot dip galvanized bath, the redundant zinc shall be removed by centrifuging treatment or zinc explosion method immediately. To prevent articles from generating white rust on their surfaces in wet environment, proper surface treatment shall be supplied for articles which don t need painting any more after being galvanized. If articles are to be painted or powder sprayed after being galvanized, the buyer shall impart the supplier before hot dip galvanizing. C.5 Repair of uncoated area and injury area If the articles need painting after being galvanized, the supplier shall impart the buyer to allow the repair for the injury area as well as the recommended methods and materials to repair the uncoated area and injury area. The buyer and next coating-painting party shall ensure the consistency between the next coating system and the adopted repair methods and materials. Article 6.3 specifies the acceptance requirements of the repair layer thickness. The same method can be adopted to repair the injury area on the spot. Size of the repair Page 22 of 27

13 Appendix D (Normative Appendix) Safety Requirements D.1 The manufacturing process of hot dip galvanizing shall be carried out according to the regulation and standard requirements of national related safety, environment protection and human health. D.2 The hot dip galvanizing is strictly prohibited for the articles embodied sealing intra-cavity except when there is proper open pore on sealing intra-cavity to prevent it from explosion which is caused by the increasing pressure of internal heated pressure. In addition, those proper open pores can insure zinc liquid in the intra-cavity to outflow favorably after the hot dip galvanizing. On condition that no specific relevant national safety law and health law relating to the problem of exhaust and diversion in the intra-cavity, the buyer shall supply the pore-opening methods or other treatment measures, otherwise the supplier shall deal with it by themselves. The method of pore-opening, exhaust and diversion may refer to ISO (see References) D.3 As for those incompletely dried articles, if there is solvent or other water contents on their surfaces, they will explode after entering the zinc bath. Therefore, necessary measures shall be adopted to prevent people from being scalded by the zinc liquid splashing. Page 24 of 27

14 References 1 ISO 2808:1997 Paints and varnishes - Determination of film thickness 2 ISO 4964:1984 Steel hardness conversion 3 ISO 14713:1999 Protection against corrosion of iron and steel in structures - Zinc and aluminum coatings - Guidelines 4 ISO :1998 Paints and varnishes - Corrosion protection of steel structures by painting system - Part 4: Type of surface and surface preparation 5 ISO :1998 Paints and varnishes - Corrosion prevention of steel structures by painting system - Part 5: Protection painting system 6 EN Steel pipes - Inside and (or) outside protective layers - Hot dip galvanized steel pipes of the automated equipment mass - Specifications 7 NFA :1994 Steel and iron - Steel for hot dip galvanizing END Page 27 of 27