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

Transcription

1 Translated English of Chinese Standard: GB/T GB NATIONAL STANDARD OF THE PEOPLE S REPUBLIC OF CHINA ICS H 48 GB/T Replacing GB/T Welded Steel Pipes for Low Pressure Liquid Delivery (ISO 559:1991, Steel Tubes for Water and Sewage, NEQ) Issued on: September 11, 2015 Implemented on: June 1, 2016 Issued by: General Administration of Quality Supervision, Inspection and Quarantine; Standardization Administration of the People's Republic of China. Page 1 of 28

2 Table of Contents 1 Scope Normative References Order Content Dimension, Shape and Weight Diameter and Wall-thickness Length Bending Out-of-roundness Pipe End Weight Technical Requirements Designations and Chemical Compositions of Steels Manufacturing Process Delivery State Mechanical Property Technical Property Hydraulic Test Surface Quality Steel Pipe Butting Galvanized Zinc Coating Other Requirements Test Method Inspection Rules Inspection and Acceptance Group-batch Rules Sampling Quantity Re-inspection and Judgment Rules Packing, Marking and Quality Certificate Marking on Steel Pipes Packing and Quality Certificate of Steel Pipes Appendix A Appendix B Appendix C Page 2 of 28

3 Foreword This Standard is drafted in accordance with the rules specified in GB/T This Standard replaces GB/T Welded Steel Pipes for Low Pressure Liquid Delivery. The main technical differences between this Standard and GB/T are as follows: Revise the outer-diameter, wall-thickness and way of delivery of steel pipe 219.1mm or below; Revise the requirements on out-of-roundness of steel pipes; Revise the requirements on ends of steel pipes; Adjust part of steel designations; Revise delivery state of steel pipe; Add the requirements on zinc coating weight of galvanized steel pipe; Revise the rules on group-batch of steel pipes. This Standard was redrafted by reference to ISO 559:1991 Steel Tubes for Water and Sewage; it is not equivalent to ISO 559:1991. This Standard was proposed by China Iron & Steel Association. This Standard shall be under the jurisdiction of the National Technical Committee 183 on Iron and Steel of Standardization Administration of China (SAC/TC 183). Drafting organizations of this Standard: Tianjin YouFa Steel Pipe Group Co., Ltd., Panyu Chu Kong Steel Pipe Co., Ltd., Zhejiang Kingland Pipeline and Technologies Co., Ltd., Tianjin Juncheng Steel Pipe and Technologies Co., Ltd., Tianjin Lida Steel Pipe Group Co., Ltd., Jinghua Innovation Group Co., Ltd., Handan Zhengda Steel Pipe Co., Ltd., Baoji Petroleum Steel Pipe Co., Ltd. AND China Metallurgical Information and Standardization Research Institute. Chief drafting staffs of this Standard: Yin Jiuxiang, Chen Guangling, Wang Lishu, Shen Ganrong, Guo Jianjun, Yu Fuqiang, Wen Chaojiang, Jiang Haidong, Wang Hui, Dong Li, Zhao Fuliang, Zhang Songming, Yang Weifang, Wang Yaping and Hou Jie. The previous editions replaced by this Standard are as follows: GB/T , GB/T , GB/T , GB/T ; GB/T , GB/T ; Page 3 of 28

4 Welded Steel Pipes for Low Pressure Liquid Delivery 1 Scope This Standard specifies dimension, shape, weight, technical requirements, test methods, inspection rules, packing, marking and quality certificate of welded steel pipes for low pressure liquid delivery. This Standard is applicable to electric-welding longitudinal-seam steel pipe, submerged arc-welding longitudinal-seam (SAWL) steel pipe and submerged arcwelding helical-seam (SAWH) steel pipe for low pressure liquid delivery of water, air, heating steam, fuel gas, etc.; and it makes the marking to their respective different requirements; non-marking requirements are applicable to high-frequency electricwelding longitudinal-seam steel pipe, submerged arc-welding longitudinal-seam steel pipe and submerged arc-welding helical-seam steel pipe. 2 Normative References The following documents are essential for the application of this Standard. For dated references, only the edition cited applies. For the undated references, the latest editions of the normative documents (including all the amendments) are applicable to this document. GB/T 222 GB/T GB/T Permissible Tolerances for Chemical Composition of Steel Products Diantipyrylmethane Phosphomolybdate Gravimetric Method for the Determination of Phosphorus Content Steel and Iron - Determination of Acid-soluble Silicon and Total Silicon Content - Reduced Molybdosilicate Spectrophotometric Method GB/T Iron Steel and Alloy - Determination of Aluminium Content - Chrom Azurol S Photometric Method GB/T Iron Steel and Alloy - Determination of Chromium Content - Visual Titration or Potentiometric Titration Method GB/T Methods for Chemical Analysis of Iron, Steel And Alloy - The Sodium Carbonate Separation-diphenyl Carbazide Photometric Method For The Determination Of Chromium Page 5 of 28

5 Content GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T GB/T Methods for Chemical Analysis of Iron, Steel And Alloy - The Ammonium Ferrous Sulfate Titration Method for the Determination of Vanadium Content Chromotropic Acid Photometric Method for the Determination of Titanium Content Methods for Chemical Analysis of Iron, Steel And Alloy - The Sodium Thiosulfate Separation Iodimetric Method for the Determination of Copper Content Methods for Chemical Analysis of Iron Steel And Alloy - The Neocuproine-chloroform Extraction Photometric Method for the Determination of Copper Content Iron Steel and Alloy - Determination of Nickel Content - The Dimethylglyoxime Spectrophotometric Method Extraction Separation - The Dimethylglyoxime Spectrophotometric Method for the Determination of Nickel Content Iron Steel and Alloy - Determination of Molybdenum Content - The Thiocyanate Spectrophotometric Method Hypophosphite Reduction-iodimetric Method for the Determination of Arsenic Content Neutral Titration Method for the Determination of Nitrogen Content after Distillation Separation Methods for Chemical Analysis of Iron Steel and Alloy - The Indophenal Blue Photometric Methods for the Determination of Nitrogen Content after Distillation Separation Iron Steel and Alloy - Determination of Niobium Content by the Sulphochlorophenol S Spectrophotometric Method Flame Atomic Absorption Spectrophotometric Method for the Page 6 of 28

6 Determination of Copper Content GB/T GB/T Methods for Chemical Analysis of Iron, steel and Alloy - The Flame Atomic Absorption Spectrophotometric Method for the Determination of Nickel Content Sodium Arsenite-sodium Nitrite Titrimetric Method for the Determination of Manganese Content GB/T Iron Steel and Alloy - Determination of Phosphorus Content - Bismuth Phosphomolybdate Blue Spectrophotometric Method and Antimony Phosphomolybdate Blue Spectrophotometric Method GB/T GB/T GB/T GB/T GB/T Perchloric Acid Dehydration Gravimetric Method for the Determination of Silicon Content Methods for Chemical Analysis of Iron, steel and Alloy - The Ammonium Phosphomolybdate Volumetric Method for The Determination of Phosphorus Content Butyl Acetate Extraction Photometric Method for the Determination of Phosphorus Content Sodium (potassium) Periodate Photometric Method for the Determination of Manganese Content Iron Steel and Alloyed - Determination of Manganese Content - Flame Atomic Absorption Spectrometric Method GB/T Iron Steel and Alloy - Determination of Sulfur Content - Methylene Blue Spectrophotometric Method GB/T Methods for Chemical Analysis of Iron, Steel And Alloy - The Potassium Iodate Titration Method after Combustion in the Pipe Furnace for the Determination of Sulfur Content GB/T Iron Steel and Alloy - Determination of Carbon Contents - Gas-volumetric Method after Combustion in the Pipe Furnace GB/T Methods for Chemical Analysis of Iron, steel and Alloy - The Gravimetric Method after Combustion in the Pipe Furnace for Page 7 of 28

7 the Determination of Carbon Content GB/T Iron Steel and Alloy - Determination of Sulfur Content - Gravimetric Method GB/T GB/T 241 GB/T 244 GB/T 246 GB/T 700 GB/T 1591 GB/T 2102 GB/T 2651 GB/T 2653 GB/T 2975 GB/T 4336 GB/T GB/T GB/T GB/T Metallic Materials - Tensile Testing - Part 1 : Method of Test at Room Temperature Metal Materials - Tube - Hydrostatic Pressure Test Metallic Materials - Tube - Bend Test Metallic Materials - Tube - Flattening Test Carbon Structural Steels High Strength Low Alloy Structural Steels Acceptance Packing Marking and Quality Certification of Steel Pipe Tensile Test Method on Welded Joints Bend Test Methods on Welded Joints Steel and Steel Products - Location and Preparation of Test Pieces for Mechanical Testing Standard Test Method for Spark Discharge Atomic Emission Spectrometric Analysis of Carbon and Low-alloy Steel (Routine Method) Pipe Threads with 55 Degree Thread Angle Where Pressuretight Joints Are Made on the Threads - Part 2: Taper Internal and External Threads Steel Tubes - The Inspection Method on Eddy Current Test Steel and Iron - Sampling and Preparation of Samples for the Determination of Chemical Composition Steel and Iron- Determination of Total Carbon and Sulfur Content Infrared Absorption Method after Combustion in An Induction Furnace (Routine Method) GB/T Low-alloy Steel - Determination of Multi-element Contents - Inductively Coupled Plasma Atomic Emission Spectrometric Method Page 8 of 28

8 GB/T SY/T SY/T Dimensions and Masses Per Unit Length of Welded Steel Pipes Petroleum and Natural Gas Industries - Non-destructive testing (NDT) Methods of Steel Tubes Part 1: Radiographic Testing of Weld Seam of Welded Steel Tubes for Detection Of Imperfections Petroleum and Natural Gas Industries - Non-destructive Testing (NDT) Methods Of Steel Tubes Part 2: Automated Ultrasonic Testing of The Weld Seam of Welded Steel Tubes for The Detection of Longitudinal and/or Transverse Imperfections 3 Order Content The contract or order of steel pipe purchased according to this Standard shall include at least the following information: a) The number of this Standard; b) The product name; c) The steel designation (grade of quality); d) The quantity ordered (gross weight or total length); e) The dimension and specification; f) The length; g) The manufacturing process; h) The requirement on zinc coating weight (if applicable); i) Other requirements. 4 Dimension, Shape and Weight 4.1 Diameter and Wall-thickness Steel pipes whose outer-diameter (D) is not greater than 219.1mm shall be delivered according to nominal dimension (DN) and nominal wall-thickness (t); their nominal dimensions and nominal wall-thicknesses shall meet the requirements of Table 1. See Appendix A for the dimensions of the steel pipes whose pipe ends are Page 9 of 28

9 tensioned on total cross-section, their elongation after fractures are only for reference, it is not used as delivery condition Tensile test of welding joint Tensile test of welding joint shall be performed for steel pipes with outer-diameter not less than 219.1mm. Tensile specimen of welding joint (including weld seam of longitudinal-seam steel pipe, spiral weld of helical-seam steel pipe, and butt weld of steel strap) shall be cut from the steel pipe perpendicular to the weld seam and the weld seam on the center of the specimen. Tensile strength is only tested in tensile test of welding joint. The value of the test shall meet the requirements of Table Technical Property Bending test Bending test shall be performed for high-frequency electric-welding longitudinal-seam steel pipe with outer-diameter not greater than 60.3mm. In the test, the specimen shall be free of filler, its bend radius is 6 times of the pipe outer-diameter, the bend angle is 90, and the weld seam is on the outside face of the bending direction. After the test, the specimen shall have no crack Flattening test Flattening test shall be performed for high-frequency electric-welding longitudinalseam steel pipe with outer-diameter greater than 60.3mm. The length of the flattening specimen shall not be less than 64mm; and the weld seams on the two specimens shall be respectively on the positions forming 90 and 0 to the exerting force direction. During the test, when the distance between two flat plates is 2/3 of the pipe outerdiameter, there shall be no fissure or crack on weld seam; when the distance above is 1/3 of the pipe outer-diameter, there shall be no fissure or crack on parts except weld seam; the pipe continued to be flattened till the pipe walls closely contact; the pipe shall have no lamination or burnt metal in the whole flattening process Guided bending test Front guided bend test shall be performed for submerged arc-welding steel pipe. Guided bending specimen shall be cut from vertical weld (including weld seam of longitudinal-seam steel pipe, spiral weld of helical-seam steel pipe, and butt weld of steel strap) of steel pipe; the weld seam shall be on the center of the specimen; the specimen shall be free of repair weld; the reinforcement shall be removed. The specimen is bent 180 and the diameter of the bending mandrel shall be 8 times of the steel pipe wall-thickness. After the test, the specimen shall meet the following requirements: a) The specimen shall not break completely; Page 16 of 28

10 Burr outside of steel pipe weld seam shall be cleared; the residual height of burr shall not be greater than 0.5mm. If the supply and demand parties agree, and it is specified in the contract, considering the demand party's requirement, burr in steel pipe weld seam may be cleared. After burr in weld seam is cleared, the residual height shall not be greater than 1.5mm; where the wall-thickness is not greater than 4mm, the depth of slot scraping after clearing burr shall not be greater than 0.2mm; where the wallthickness is greater than 4mm, the depth of slot scraping shall not be greater than 0.4mm Weld reinforcement of submerged arc-welding steel pipe Where the wall-thickness is not greater than 12.5mm, inside and outside weld reinforcement beyond the original surface profile shall not be greater than 3.2mm; where the wall-thickness is greater than 12.5mm, the inside and outside weld reinforcement above shall not be greater than 3.5mm. Exceeded part of weld reinforcement may be grinded Misalignment As for electric-welding longitudinal steel pipe, radial misalignment of steel strap edge on weld seam shall not be such that remaining thickness on both sides is less than 90% of the steel pipe wall-thickness. As for submerged arc-welding steel pipe, where wall-thickness is not greater than 12.5mm, radial misalignment of steel strap edge on weld seam shall not be greater than 1.6mm; where the wall-thickness is greater than 12.5mm, radial misalignment of steel strap edge on weld seam shall not be greater than time of the steel pipe wall-thickness Butt weld of steel strap Submerged arc-welding helical-seam steel pipe may have steel strap butt weld, but the distance from the pipe end to the connection point of the steel strap butt weld and helical seam shall be larger than 150mm; where the steel strap butt weld is positioned on the pipe end, there shall be a circumferential interval of at least 150mm to the helical seam of corresponding pipe end Surface defect Internal and external surfaces of steel pipe shall be smooth, and free of folding, crack, lamination, lap weld, arc breaking, burn-off and other defects with depth after grinding exceeding the deviation of the wall-thickness. These defects shall be cleared completely; the residual wall-thickness on the cleared position shall not be less than the minimal permissible value of the wall-thickness deviation. There may be other local defects with a depth not exceeding the deviation of the wall-thickness. Page 18 of 28

11 5.7.3 Repair welding of defect Repair welding shall be applied to steel pipes with outer-diameter not greater than 219.1mm As for steel pipes with outer-diameter greater than 219.1mm, defects on base metal and weld seam may be repaired. Before repair welding, the position to be repaired shall be treated to make it conform to the welding requirements. The shortest length of the repair welding seam shall not be less than 50mm; the maximum length of repair welding seam on electric welded steel pipe shall not be greater than 150mm; repair welding on a steel pipe shall not be more than 3 points; repair welding shall not be applied on the part within 200mm to the pipe end. Repair welding pass shall be grinded, the grinded welding pass shall smoothly transit with the original profile; hydraulic test shall be performed according to the requirements specified in Steel Pipe Butting If the supply and demand parties agree, and it is specified in the contract, considering the demand party's requirement, steel pipes may be delivered in a butted way. The length of the stubs for butting shall not be less than 1.5m; only two stubs may be butted. Before butting, pipe ends shall be treated to make them conform to the welding requirements. In the butting process, steel pipe weld seam (including weld seam of longitudinal-seam steel pipe, spiral weld of helical-seam steel pipe, and butt weld of steel strap) shall have a mutual interval of 50mm~200mm on the butting position. After butting, the butt weld shall be uniform and even along the circumferential direction, and meet the requirements of The bending of butted steel pipe shall meet the requirements of 4.3, and be applied with hydraulic test according to Galvanized Zinc Coating Galvanizing method Hot dip galvanizing method shall be used for steel pipes Determination of zinc coating weight Weight of zinc coating shall be measured for galvanized steel pipe. Unit-area total weight of zinc coating on external surface of steel pipe shall not be less than 300g/m If the supply and demand parties agree, and it is specified in the contract, considering the demand party's requirements, the supply party may supply galvanized steel pipes whose unit-area total weight of zinc coating on external surface of steel pipe is not less than 500g/m 2. When pipes are delivered according to unit-area total weight of zinc coating 500g/m 2, only one specimen among them may have total weight of zinc coating less than 500g/m 2, but the total weight shall not be less than 480g/m 2. Page 19 of 28

12 5.9.3 Adherence test of zinc coating Adherence test of zinc-coating shall be performed for galvanized steel pipe. In the test, the specimen (except the weld seam part) shall be immersed for 5 times continuously in cupric sulfate solution; it shall not turn red (copper coating color) after immersion Adhesive force inspection of zinc coating After being galvanized, steel pipes with outer-diameter not greater than 60.3mm shall be applied with zinc coating adhesive force inspection by bending test. In the test, the bending specimen shall be free of filler, its bend radius is 8 times of the pipe outer-diameter, the bend angle is 90, and the weld seam is on the outside face of the bending direction. After the test, the specimen shall not have zinc coating flakingoff If the supply and demand parties agree, and it is specified in the contract, considering the demand party's requirements, steel pipes with outer-diameter greater than 60.3mm after being galvanized shall be applied with zinc coating adhesive force inspection by flattening test. The length of the flattening specimen shall not be less than 64mm. When the distance between two flat plates is 3/4 of the pipe outer-diameter in the test, the specimen shall not have zinc coating flaking-off Surface quality of zinc coating Zinc coating in internal and external surfaces of steel pipe shall be intact, there shall be no non-galvanized black dot or bubble, there may be small uneven surface or local zinc tumor Galvanized surface of steel pipe may be passivated Inspection before galvanizing Inspections on dimension, shape, surface, mechanical property and process property shall be performed for steel pipes before galvanizing Other Requirements If the supply and demand parties agree, and it is specified in the contract, considering the demand party's requirements, the requirements like adding impact test and increasing pressure value of hydraulic test may be specified for steel pipes additionally. 6 Test Method 6.1 Dimension and shape of steel pipe, burr height of electric welded steel pipe, weld reinforcement of submerged arc-welding steel pipe shall be measured with measuring device or apparatus with the accuracy meeting the requirements. Page 20 of 28

13 7 Inspection Rules 7.1 Inspection and Acceptance Inspection and acceptance for steel pipes shall be performed by the supplier's quality and technical supervision department. 7.2 Group-batch Rules Steel pipes shall be inspected and accepted by batches. Each batch is consisted of steel pipes with the same designation, same heat number, same specification, same welding procedure, same heat treating system (if applicable) and same zinc coating (if applicable). The quantity of each batch of steel pipe shall not be beyond the following requirements: a) Steel pipes produced by a shift, the outer-diameter is not greater than 219.1mm; b) 200 pieces, the outer-diameter is greater than 219.1mm but not greater than 406.4mm; c) 100 pieces, the outer-diameter is greater than 406.4mm. 7.3 Sampling Quantity Sampling quantity for each inspection of steel pipe shall meet the requirements of Table Re-inspection and Judgment Rules The re-inspection and decision rules of steel pipe shall meet the provisions in GB/T Packing, Marking and Quality Certificate 8.1 Marking on Steel Pipes Marking on steel pipe shall include at least the following information: The name or trademark of manufacture, the standard number applying to the product, steel designation, product specification and traceable identification number. Other requirements on steel pipe marking shall meet the requirements of GB/T Packing and Quality Certificate of Steel Pipes Packing and quality certificate of steel pipe shall meet the requirements of GB/T Page 22 of 28

14 Appendix B (Normative) Determination of Zinc Coating Weight - Antimonic Chloride Method B.1 Preparation of specimen Determination of zinc coating weight shall be performed after galvanizing steel pipe. Two steel pipes are selected from each lot, a pipe section with a length of 30mm~60mm (depending on the specification) is cut into a specimen from each end of each steel pipe; the surface of specimen shall have no uneven surface and zinc tumor. The specimen surface shall be cleaned with pure dissolvent like benzene, petrobenzene, ethylene trichloride or carbon tetrachloride, rinsed with alcohol, then flushed with clear water; finally, the ends of the specimen is coated with varnished (phenol) and then dried. B.2 Preparation of test solution Dissolve 32g of trichloride antimony (SbCl 3 ) or 20g of antimony trioxide (Sb 2 O 3 ) in 1,000mL of hydrochloric acid with a density of 1.18kg/dm 3, to be raw liquor. Prior to the test, add 5mL of the raw liquor into 100mL of hydrochloric acid with a density of 1.18kg/dm 3, to be test solution. B.3 Operation procedure of test B.3.1 Weigh the weight of specimen with a balance, round off to 0.01g (closest). B.3.2 Immerse the specimen into the test solution, a specimen each time; make the liquid level higher than the specimen. The temperature of the solution shall not be greater than 38 C during the test. B.3.3 When the hydrogen generation from the specimen becomes little in the solution and the zinc coating has disappeared, the specimen is taken out. The specimen is flushed in water, and dried up with cotton or clean cloth; when it becomes dry completely, it is weighed with a balance, and rounded off to the nearest 0.01g. B.3.4 After the zinc coating is delaminated from the specimen, outside and innerdiameters of the specimen shall be measured on the ends respectively at two mutually perpendicular directions; the mean is taken as the actual outer-diameter and innerdiameter, rounded off to 0.01mm (closest). B.3.5 If the test solution is easy to remove zinc coating, it may be reused. B.4 Calculation of test results Page 24 of 28

15 Appendix C (Normative) Adherence Test of Zinc Coating - Cupric Sulfate Immersion Method C.1 Preparation of specimens Adherence test for zinc coating shall be performed after galvanizing steel pipe. Two steel pipes are selected from each batch; a specimen with a length of not less than 150mm is cut from one end of each steel pipe. Oil stain and others on specimen surface shall be removed, and wiped up with clean soft cloth. C.2 Preparation of test solution Dissolve 33g crystal cupric sulfate (CuSO 4 5H 2 O) or about 36g industrial cupric sulfate in 100mL of distilled water, add excessive powdery cupric hydroxide [Cu(OH) 2 ] or copper carbonate (chemical pure) [CuCO 3 -Cu(OH) 2 ], to neutralize free acid. Add 10g cupric hydroxide for each 10L solution; if copper carbonate is added, about 12g of cupric hydroxide is added for each 10L solution; whether it is excessive depends on the deposition on the container bottom. Stir it, keep it still for 24h and filter and clarify it. If powdery cupric oxide (CuO) replaces cupric hydroxide, about 8g is added for each 10L solution, but keep it still for 48h and then filter it. The density of the prepared test solution is 1.170kg/dm 3 at 15 C. C.3 Test container C.3.1 The test container shall be made of material inert to cupric sulfate. C.3.2 The inside dimensions of the container shall be such that any wall of the container is kept 25 mm from the specimen immersed in the solution. C.4 Operation procedure of test C.4.1 The cut end of the specimen points shall be kept downwards, the immersed length shall not be less than 100mm; the specimen shall be immersed for 5 times continuously in cupric sulfate solution. The temperature of the specimen and the solution shall be kept 15 C~21 C during the test; the solution shall not be stirred. The immersion time each time shall last 1 min; the specimen shall be cleaned in running clean water immediately after being taken out; clean up black deposit with soft bush; wipe it dry with soft cloth. C.4.2 Except last immersion, the specimen shall be re-immersed immediately in the solution. Page 27 of 28

16 C.4.3 After immersion for 20 times, the test solution shall be discarded. C.5 Judgment of test result C.5.1 After the specimen have been immersed for 5 times continuously, clean and wipe-dry; it shall not display red (copper coating color). It is an exception that there is red metal copper on the positions 25mm within the specimen end and 10mm within the solution level. C.5.2 If there is red metal copper on the specimen after the test above, its adherence may be judged by the following method: the specimen is cleaned in running clean water immediately after being immersed for 15s in 1:10 hydrochloric acid solution; if the zinc coating reappears on the bottom surface, the specimen is judged eligible. C.5.3 If there is doubt on whether there is zinc coating on the bottom surface under the red metal copper deposition, the red metal copper deposition may be scraped off, one or more drops of diluted hydrochloric acid is applied on such position; if there is zinc coating, live gaseous hydrogen will be generated. Besides, zinc qualitative test may be used for judgment, i.e. dropped acid fluid is collected with a piece of filter paper or a pick-up tube, and neutralized with ammonium hydroxide to make it weak acidic. Hydrogen sulphide is introduced into this solution to observe whether white zinc sulphide deposit is generated. END Page 28 of 28