GB/T 5135.20 Coated anti-corrosion steel pipes

Scope and Definition of Standard Application

GB/T 5135.20-2010 "Automatic Sprinkler Fire Extinguishing Systems Part 20: Coated Steel Pipes" specifies the technical requirements, test methods, and inspection rules for coated steel pipes in automatic sprinkler fire extinguishing systems. It is applicable to coated steel pipes with a nominal diameter not exceeding 300mm and an internal coating of epoxy resin. This standard defines coated steel pipes as composite pipes with steel pipes as the base pipe and plastic layers or other anti-corrosion materials coated on the inner and outer surfaces, divided into two types: inner coating and inner and outer coating.

Material and structural requirements

The base pipe shall comply with GB/T 3091 (welded steel pipe) or GB/T 8163 (seamless steel pipe) standards, and the coating material shall be epoxy resin powder. The thickness shall be divided into 0.30mm (DN<80) and 0.35mm (DN ≥ 80) according to the pipe diameter. The outer surface is usually red and should be clearly labeled with product model, base pipe specifications, execution standards, and other information. The connection forms include threaded, flange, and groove types, which must meet the requirements of GB/T 7306.2, GB/T 9119, and GB 5135.11.

Performance and Test Methods

The coating needs to pass multiple performance tests:

Pinhole test: Use an electric spark leak detector to check the integrity of the coating, and select a voltage of 1500V or 2000V according to the thickness. If there is no electric spark, it is considered qualified.

Adhesion test: According to CJ/T 120-2008 standard, the adhesion level should reach level 1-3.

Environmental adaptability: including high temperature (300 ℃ constant temperature for 1 hour), low temperature (-10 ℃), pressure cycling (0.4-2.5MPa alternating) and other tests, the coating must not peel off or crack.

Mechanical performance: After bending test (DN ≤ 50mm) and flattening test (DN>50mm), the coating is undamaged.

Manufacturing process and construction requirements

The coated steel pipe adopts electrostatic spraying or hot-dip technology, and the base pipe needs to be shot blasted to Sa2.5 level, preheated to 40 ℃~60 ℃, and then coated with epoxy resin. During construction, it is necessary to control the uniformity of the coating. Electromagnetic thickness gauges are used for thickness detection, and 100mm uncoated areas are reserved at both ends for welding. If the external anti-corrosion layer is hot-dip galvanized or other materials, it must comply with the corresponding standards.

Application Fields and Quality Control

This steel pipe is widely used in fields such as fire sprinklers, water supply and drainage, and petroleum and gas transportation, combining the strength of the steel pipe with the anti-corrosion properties of plastics. Production enterprises need to pass the national fixed fire extinguishing system quality inspection and UL certification, implement CJ/T 120-2008 and GB/T 23257-2009 standards, and ensure the hygiene performance of coatings (in accordance with GB/T 17219) and long-term stability of use (for more than 50 years).

Quality Inspection and Marking

Before leaving the factory, a visual inspection, electrical discharge testing, thickness measurement, and adhesion testing are required. Each batch of products must provide a certificate of conformity and a testing report. The logo content includes production date, company name, product model, etc., for easy traceability.