GB/T 23257-2017Polyethylene coating for buried steel pipelines (English PDF)

1 Scope

China's national standard for the polyethylene anticorrosion coating applied to buried steel pipelines. It specifies the classification, the materials, the requirements, the test methods, the inspection rules and the marking, packaging, transport and storage of the coating, together with the requirements for its application. A buried steel pipeline is protected by two systems working together: a coating that isolates the steel from the soil, and cathodic protection that handles what the coating misses. The coating does almost all of the work, and the three-layer polyethylene system this standard covers is the dominant choice worldwide for a reason. The first layer is fusion-bonded epoxy applied to the blast-cleaned hot steel, which gives the adhesion to the metal and the resistance to under-film corrosion; the second is a copolymer adhesive; the third is extruded polyethylene several millimetres thick, which gives the mechanical protection and the water barrier. Each layer does a job the others cannot, and the failure of the system is nearly always a failure of the bond between them or of the surface preparation beneath the first. That is why the standard's requirements sit where they do. The surface preparation and its cleanliness and profile come before everything. The coating thickness, the peel strength at ambient and at elevated temperature, the cathodic disbondment - the measure of how far the coating lifts from the steel at a holiday under cathodic protection, which is the single best predictor of long-term performance - the impact and indentation resistance, the holiday detection over the whole surface, and the thermal ageing. The field joint, which is coated on site rather than in a plant, is the weakest point of any pipeline and is covered accordingly. Issued on 12 May 2017 and in force since 1 December 2017, it replaces GB/T 23257-2009.

This standard specifies the minimum technical requirements for steel pipe extrusion polyethylene anti-corrosion layer and radiation cross-linked polyethylene heat shrinkable tape (set). This standard is applicable to the design, production and inspection of extruded polyethylene pipe anti-corrosion layer, and the design, construction and on-site filling test. Other laying forms of extruded polyethylene anti-corrosion coatings can be referred to. Extrusion polyethylene anti-corrosion layer can be divided into normal temperature type (N) with maximum design temperature not exceeding 60 °C and maximum design temperature not exceeding 80 °C High temperature type (H) two types.

2 Normative references

The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article. Pieces. For undated references, the latest edition (including all amendments) applies to this document. Determination of tensile properties of plastics - Part 2. Test conditions for moulding and extruded plastics

GB/T 1408.1 Test methods for electrical strength of insulating materials - Part 1

GB/T 1410 solid insulating material volume resistivity and surface resistivity test method

GB/T 1633 Determination of Vicat softening temperature (VST) of thermoplastics

GB/T 1725 Determination of non-volatile content of paints, varnishes and plastics

GB/T 1842 plastic polyethylene environmental stress cracking test method

GB/T 3682 Thermoplastic melt mass flow rate and melt volume flow rate determination

GB/T 4472 Determination of density and relative density of chemical products Determination of embrittlement temperature of

GB/T 5470 plastic impact method

GB 6514 Painting operation safety regulations Painting process safety and ventilation purification

GB/T 6554 - Resin-based composites for electrical insulation - Part 2. Test method

GB/T 7124 Determination of tensile shear strength of adhesives (rigid materials to rigid materials)

GB 7692 Painting operation safety regulations Pre-painting process safety and ventilation purification

GB/T 8923.1.Determination of surface cleanliness of steels - Part 1 . Uncoated steel Corrosion grade and treatment grade of the surface of the steel after surface and overall removal of the original coating

3 Terms and definitions

The following terms and definitions apply to this document.

3.1 Extruded polyethylene coating with extrudedpolyethylenecoating In the extruder, by heating and pressurizing, the polyethylene is continuously flowed through the extrusion die to form a coating on the pipe. The coating layer comprises a longitudinal extrusion coating and a lateral wrapping coating.

3.2 Maximum design temperature maximumdesigntemperature The maximum temperature that the coating may reach during pipeline transportation, handling, construction, and operation.

3.3 Maximum operating temperature maximumoperationtemperature The highest temperature reached by a pipe or pipeline system during operation.

Note. The maximum operating temperature does not exceed the maximum design temperature.

3.4 Low temperature coated epoxy powder coating lowtemperatureappliedepoxypowdercoating It is used as the bottom layer of the three-layer polyethylene anti-corrosion layer specified in this standard, and can be applied to epoxy powder coatings below.200 °C.

3.5 Fracture nominal strain nonlineartensilestrainatbreak Tensile nominal strain corresponding to tensile fracture stress.

3.6 Cohesive failure cohesivefailure The adhesive layer itself ruptures and adhesive bonds exist on both surfaces of the adherend.

3.7 Interface destruction interfacialfailure A visually visible damage occurs at the interface between the adhesive layer and the adherend. 4 anti-corrosion layer structure

4.1 Extruded polyethylene anti-corrosion layer is divided into two layers and two layers. The bottom layer of the two-layer structure is an adhesive layer, and the outer layer is a polyethylene layer; The bottom layer of the three-layer structure is usually an epoxy powder coating, the middle layer is an adhesive layer, and the outer layer is a polyethylene layer. Pipes above DN500 are not suitable A two-layer polyethylene anti-corrosion layer is used.

4.2 The minimum thickness of the coating shall comply with the requirements of Table 1. The thickness of the anti-corrosion layer at the weld site shall not be less than 80% of the value specified in Table 1. should According to the pipeline construction environment and operating conditions, select the grade of the anti-corrosion layer. Table

1 Thickness of anti-corrosion layer Steel pipe nominal diameter DN Epoxy coating a Mm Adhesive layer Mm Minimum thickness of coating Mm Ordinary (G) Enhanced (S) DN<=100 100 \u003cDN<=250 250 \u003cDN\u003c500 500<=DN< 800 800<=DN<=1200 DN >1200 >=120 >=150 >=170 1.8 2.5 2.0 2.7 2.2 2.9 2.5 3.2 3.0 3.7 3.3

4.2 a Not applicable to two-layer polyethylene anti-corrosion coating.

7 Quality inspection

7.1 The quality inspection of steel pipe surface treatment shall meet the following requirements.

a) The steel pipe after throwing (spraying) and rusting shall be tested on the surface derusting level by root, using the corresponding photo or standard in GB/T 8923.1 For visual comparison of the board, the surface derusting quality should meet the Sa21 level requirements; the surface anchor depth should be per shift (not more than 12h). Less measurement twice, each time measuring two steel pipes, should be measured by roughness tester or anchor depth test paper, the anchor depth should be up to To 50µm~90µm; the surface temperature of the steel pipe before surface treatment should be monitored, and the surface temperature of the steel pipe should not be lower than the dew point temperature. Above 3 °C.

b) The surface dust degree of the steel pipe shall be tested at least twice per shift (not exceeding 12h), and two steel pipes shall be tested each time. Should be in accordance with GB/T 18570.3 The specified method is used to evaluate the surface dustiness, and the surface dust degree should be no less than 2 grades.

c) Each batch of steel pipes entering the plant shall be tested at least on the surface of the two steel pipes after surface treatment. Steel pipes are stacked or coated by sea, seaside When the construction site is in the saline-alkali zone, the salt content of the surface of the two steel pipes shall be tested at least every shift (not exceeding 12h). according to The method specified in GB/T 18570.9 or other suitable method for the determination of salt content on the surface of steel pipes, the salt content on the surface of steel pipes shall not More than 20mg/m2.

7.2 After derusting, the surface defects of the steel pipe shall be inspected. The surface defects and irregularities (heavy skin, damage, scratches, etc.) of the steel pipe shall not be applied after being repaired.

7.3 During the coating process, the heating temperature of the steel pipe shall be continuously...

10 Appendix F Moisture content <=

0.1 Appendix G Tensile strength a MPa >=17 GB/T 1040.2 Fracture nominal strain a >=600 GB/T 1040.2 a Stretching speed 50mm/min.

5.2.4 Polyethylene The properties of polyethylene special materials and their pressed sheets shall comply with the requirements of Tables 5 and 6. The coating plant gathers for each production batch (not more than 500t) Ethylene special materials shall be re-tested for the first 4 items specified in Table 5 and the first 4 items specified in Table 6. If necessary, other properties may be applied. Carry out a retest. Table

5 Performance indicators of polyethylene special materials Project performance index test method density g/cm3 0.940~

0.960 GB/T 4472 Melt flow rate (190 ° C,

2.16 kg) g/10min >=

0.15 GB/T 3682 Carbon black content >=

14 Appendix A (Normative) Test Method for Curing Time of Epoxy Powders

15 Appendix B (Normative) Test methods for thermal properties of epoxy powders and their coatings

17 Appendix C (Normative) Method for determination of adhesion of anti-corrosion coatings

20 Appendix D (Normative Appendix) Anti-corrosion layer cathodic disbonding test method

21 Appendix E (Normative Appendix) Anti-corrosion test method for anti-corrosion layer

23 Appendix F (Normative Appendix) Method for determination of oxidation induction period

25 Appendix G (Normative Appendix) Test Method for Determination of Moisture Content of Plastics

26 Appendix H (Normative) Determination of indentation hardness

27 Appendix I (Normative) Test Method for Chemical Resistance of Polyethylene to Chemicals

28 Appendix J (Normative Appendix) Test Method for Ultraviolet Light Aging Resistance of Polyethylene

29 Appendix K (normative appendix) Method for determination of peel strength of anti-corrosion layer

30 Appendix L (normative appendix) Test method for impact strength of anti-corrosion layer

32 Appendix M (Normative) Test method for hot water immersion of polyethylene anti-corrosion layer

33 Appendix N (Normative Appendix) Heat Shrink Tape (Set) Thermal Shock Test Method

34 Appendix O (Normative) Test method for embrittlement temperature of hot melt adhesives

15 Appendix D Anti-bending (-20 ° C, 2.5 °) No crack Appendix E

Note. The coating thickness of the laboratory sprayed test piece should be 300µm~400µm, and the coating temperature is the temperature specified in the product specification. When not specified, normal temperature coating The powder application temperature was.200 ° C, and the low temperature coating powder coating temperature was lower than.200 ° C.

5.2.3 Adhesive The properties of the adhesive shall comply with the requirements of Table 4. The coating factory shall, in accordance with the provisions of Table 4, apply adhesives for each production batch (not exceeding 30 tons). Conduct a quality re-examination. When the two-layer polyethylene anti-corrosion layer is made of hot-melt adhesive, the appropriate technical performance should be determined according to the engineering requirements. index. Table

4 Adhesive performance indicators Project performance index test method density g/cm3 0.920~

0.950 GB/T 4472 Melt flow rate (190 ° C,

2.16 kg) g/10min >=

0.7 GB/T 3682 Vicat softening point (A50, 9.8N) >=90 GB/T 1633 Embrittlement temperature <=-50 GB/T 5470 Oxidation induction period (200 ° C) Min >=

20 Circumference MPa >=

20 Deviation b <=15 GB/T 1040.2 Fracture nominal strain a >=600 GB/T 1040.2 Indentation hardness Mm (23 ° C) (60 ° C or 80 ° C) c <=0.2 <=0.3

Appendix B

Note. The test temperature for the gelation time and curing time of the epoxy powder coating is the coating temperature specified in the product specification. Normal temperature coating powder test when not specified The test temperature is.200 ° C, and the low temperature coated powder test temperature is lower than.200 ° C. Table

3 Performance indicators of sintered epoxy coating Project performance index test method Adhesion

Appendix H

Chemical resistant corrosion c (soaked 7d) 10% HCl 10% NaOH 10% NaCl >=85 >=85 >=

85 Appendix I UV resistant aging c (336h) >=

80 Appendix J a Stretching speed 50mm/min. b Normal temperature type, test condition is 60 °C; high temperature type, test condition is 80 °C. c Resistance to chemical media and UV aging is the tensile strength after the test and the retention of the nominal strain at break.