What are the standard requirements for using stainless steel pipes in the Xizang region

At present, there are no comprehensive local standards specifically for stainless steel pipes in the Xizang region. However, there are some local standards related to the application of stainless steel pipes in certain specific engineering fields, such as DBJ540005-2018 "Construction and Acceptance Specifications for Civil Oxygen Supply Projects in Xizang Autonomous Region". 

This specification is applicable to the construction and acceptance of new, renovated and expanded civil oxygen supply projects with an oxygen supply design pressure not exceeding 1.0 MPa. The relevant requirements for stainless steel pipes are as follows: 

Pipe quality: For the elbows, tees, and reducers of stainless steel pipes, it is recommended to use manufactured pipe fittings. The quality of these fittings should comply with the relevant provisions of the current national standard "Code for Construction and Acceptance of Industrial Metal Pipelines" GB50235. 

Pipe welding: It shall be carried out in accordance with the relevant provisions of the current national standards "Code for Construction and Acceptance of Industrial Metal Pipelines" GB50235 and "Code for Construction and Acceptance of On-site Equipment and Industrial Pipeline Welding Engineering" GB50236. 

Welding environment: It should comply with the provisions of the current national standard "Code for Construction and Acceptance of Welding Works for On-site Equipment and Industrial Pipelines" GB50236. 

Welding seam appearance quality: It must not fall below the quality requirements of level III stipulated in the current national standard "Code for Construction and Acceptance of Welding Engineering for On-site Equipment and Industrial Pipelines" (GB50236). 

Chloride ion content: For austenitic stainless steel pipes, the chloride ion content in the test water must not exceed a certain standard.

 The details are as follows: 

Material Requirements 

Common materials: Depending on the usage scenario, 304 and 316 grades of stainless steel are commonly used. For instance, in some projects on the Xizang Autonomous Region Government Procurement Network, SUS316 stainless steel pipes were required to be used. 

Element content: Taking 304 stainless steel as an example, the chromium (Cr) content is usually between 18% and 20%, the nickel (Ni) content is between 8% and 10.5%, and the carbon (C) content does not exceed 0.08%. The precise ratio of each element ensures the corrosion resistance, strength and other properties of the pipe material. 

Dimension tolerance requirements 

Pipe diameter deviation: When the nominal outer diameter is less than or equal to 50mm, the allowable deviation is usually within ±0.5mm; when the nominal outer diameter is greater than 50mm, the allowable deviation is generally ±1%. 

Wall thickness tolerance: The tolerance range for thinner-walled pipe materials is more stringent, to ensure the applicability and safety of the pipe materials in various application scenarios. 

Performance Requirements 

Mechanical properties: Must comply with relevant national standards. For example, stainless steel seamless pipes for fluid transportation should meet the requirements of GB/T14976-2012, including having certain tensile strength, yield strength, and elongation, etc. 

Corrosion resistance: Stainless steel pipes usually need to undergo intergranular corrosion tests to evaluate their corrosion resistance in specific environments, ensuring that they can meet the lifespan and safety requirements in actual use.

Pressure resistance: A hydraulic test needs to be conducted to verify the pressure resistance of the pipe material. The test pressure and holding time must be carried out in accordance with standards. 

Process and Quality Requirements 

Welding process: Use appropriate welding methods, such as TIG (Tungsten Inert Gas) welding and PAW (Plasma Arc Welding), and strictly control parameters such as welding current, voltage, and welding speed to ensure that the weld seam is uniform, smooth, without pores, cracks, slag inclusions, etc., and at the same time ensure that the flow rate of the shielding gas meets the requirements to prevent the welding area from being oxidized. 

Surface quality: The surface of the stainless steel pipe should be smooth and shiny, without any obvious scratches, dents, deformations, etc. The surface roughness needs to reach a certain level of smoothness to meet the requirements of different usage scenarios. 

Hygiene requirements: For water pipes used for drinking water and domestic drinking water, the hygiene requirements after soaking should comply with the provisions of GB/T17219. 

Installation Requirements

When thin-walled stainless steel pipes are connected to pipes, fittings and accessories made of other materials, measures to prevent electrochemical corrosion should be taken. When thin-walled stainless steel pipes with different nominal diameters are connected to pipes made of other materials, corresponding special conversion connection components should be used according to the diameter size, such as threaded conversion connection components, flange conversion connection components, and groove-type pipe fittings, etc.