Material And Surface Treatment Matching For One Closed Flat End Tubes

Meta: Material and surface treatment matching for one closed flat end tubes, comparing 304 and 316 stainless steel, polishing, passivation and forming compatibility.

1. Core Industry Pain Points

Wrong material and surface treatment selection for one closed flat end tubes causes premature corrosion and contamination. Many buyers choose SUS304 only for low cost, ignoring working medium and humidity. In coastal salt fog, weak acid or cold-chain environments, 304 stainless steel develops pitting corrosion within months. Corrosion products peel off and block the capillary lumen, triggering sensor failure. Surface treatment mistakes are common: powder coating applied on the inner wall sheds and clogs the bore; polishing without passivation leaves surface rust after welding. Material batches are sometimes mixed without marking, so 304 and 316 tubes are installed together, giving inconsistent corrosion resistance. Some suppliers ignore the difference between protective housing and capillary channel requirements, using unsuitable wall thickness.

2. Fundamental Working Principle

Material selection of one closed flat end tubes depends on corrosion load, temperature and fluid medium. SUS304 contains basic chromium-nickel passive film, suitable for dry indoor refrigeration sensors and neutral refrigerant systems. SUS316 adds molybdenum, greatly improving resistance to chloride and weak acid corrosion, fit for salt fog, cold chain and chemical scenes. Surface treatment changes surface characteristics: polishing reduces inner wall roughness and pollutant adhesion; passivation repairs the passive film; laser engraving provides batch traceability. The one closed end tube integrates protective function and capillary throttling, so material must balance corrosion resistance, ductility for bending and coiling, and cleanability.

3. Equipment and Category Classification

Main material series: Stainless Steel 304 and 316. Surface treatment equipment includes anodizing line, sandblasting cabinet, painting and powder coating booth, plating tank, brushing and polishing machine, and laser engraving machine. Forming equipment covers turning, grinding, milling, welding, bending, drilling, swaging, flaring, slot-cutting, stamping, deep-drawing and capping machines. Custom tube shapes include round, oval, square and rectangular flat closed tubes. Quality certification: ISO9001:2015 and SGS. Packaging can be standard carton or customer specified scheme.

4. Standard Operation Guide

Confirm four factors before material selection: working medium, ambient temperature, chloride exposure and service life. Select SUS304 for indoor neutral HVAC sensor assembly, with polishing or passivation for the capillary lumen. Select SUS316 for coastal, cold storage, chemical and high-humidity sensor housing. Choose surface treatment by function: polishing for capillary lumen; sandblasting plus powder coating for outer anti-corrosion shell; laser engraving for traceability. After forming, run three-stage cleaning: nitrogen purge, acid-alkali cleaning, pure water rinse, hot air drying and two-end sealing. For capillary use, inspect bore uniformity one by one for domestic material, and tune length according to the 1–1.2MPa high-pressure window.

5. On-Site Practical Experience

Many customers underestimate chloride erosion in cold chain and coastal projects. SUS304 only suits short cycles in such environment. Even SUS316 needs passivation after welding because welding heat destroys the passive film. Powder coating must not be applied to the capillary inner wall; coating shedding blocks the lumen. Laser marking should be on the outer non-bending area to avoid crack initiation. It is a common mistake to use thick-wall 316 tube for the capillary, harming heat exchange and bending. Keep material batch certificates and SGS reports for each shipment.

6. Conclusion and Value

Scientific material and surface treatment matching aligns corrosion resistance and mechanical performance with application scenarios for one closed flat end tubes. Distinguishing 304 and 316 and matching reasonable treatment balance cost and reliability. Cleanability and forming performance of the chosen material ensure smooth capillary cleaning, bending, coiling and brazing.

7. Industry Outlook and Suggestions

More low-carbon high-corrosion-resistant stainless steel grades will enter the market. Suppliers should provide a material selection checklist and mark medium limits clearly. Customers should add material composition verification in incoming inspection. For export refrigeration sensor products, prefer SUS316 and full passivation treatment.