Surface Finish of Sanitary Seamless Pipes

What are the surface finish standards for sanitary seamless pipes?

The surface finish standard for sanitary seamless pipes typically requires a surface roughness Ra value of less than 0.8 μm. For applications requiring high hygiene, the Ra value may even need to be less than 0.4 μm. These standards ensure the smoothness of the pipe's inner surface to meet the needs of industries such as food and pharmaceuticals for sanitary seamless pipes.

Sanitary seamless pipes are widely used in the food, pharmaceutical, and cosmetic industries, and their surface finish is an important indicator of pipe quality. So, what is surface finish? And how is it evaluated?

Surface finish is an older term; the formal term in current standards is surface roughness. Surface roughness is a key parameter used to evaluate the quality of the inner surface of a pipe. It reflects the microscopic geometric errors of the pipe's inner surface, i.e., the microscopic unevenness of the surface.

Surface roughness is primarily assessed by measuring the microscopic contours of the pipe surface and calculating the arithmetic mean deviation of the contour. This average value is the surface roughness Ra value (unit: μm). A smaller Ra value indicates a smoother surface.

The approximate correspondence between the surface finish grade ▽ and surface roughness Ra in the old standard is as follows:
▽8 ≈ Ra 0.4μm,
▽7 ≈ Ra 0.8μm,
▽6 ≈ Ra 1.6μm.

Surface Finish Standards for Sanitary Seamless Pipes:

1. Surface roughness Ra value requirements

The surface finish standards for sanitary seamless pipes vary depending on the application. Generally, for applications requiring high hygiene, such as food processing and pharmaceuticals, the surface finish requirements for the inner surface are very high, typically requiring an Ra value less than 0.4μm to ensure product safety and hygiene. In applications with general hygiene requirements, an Ra value less than 0.8μm is sufficient. The industry generally adheres to international standards such as ASME BPE or ISO 2037.

2. Surface Cleanliness Requirements
In addition to surface roughness, the surface of sanitary seamless pipes must be clean, free of any impurities and contaminants. Pipes are easily contaminated by particulate matter and dust during processing, transportation, and installation, therefore timely cleaning is essential to ensure their effectiveness.

Importance of Surface Finish Standards:
The surface finish standards of sanitary seamless pipes are crucial for ensuring product safety and hygiene. In industries such as food and pharmaceuticals, pipes are vital channels for material transport, and the surface finish of their inner surfaces directly affects product quality and hygiene. If the inner surface roughness is too high, bacteria can easily grow and form biofilms in the microscopic pits, potentially contaminating materials and threatening consumer health. Furthermore, rough surfaces are difficult to thoroughly clean with CIP (clean-in-place) and SIP (sterilize-in-place) processes. Therefore, strictly adhering to surface finish standards is key to ensuring product quality and consumer safety.

Roughness Comparison of Different Surface Treatment Processes:
AP Tube: Pickling and passivation, surface roughness Ra ≤ 2.5 μm
BA Tube: Bright annealing, surface roughness Ra ≤ 0.8 μm (up to 0.4 μm)
EP Tube: Electropolishing, surface roughness Ra ≤ 0.4 μm (up to 0.15-0.2 μm)

Conclusion: 

The surface finish standard for sanitary seamless tubing is determined based on the actual application. In highly hygienic environments, a higher surface finish standard (Ra ≤ 0.4 μm) is required to ensure product safety and hygiene. It is recommended to clearly specify the Ra value, applicable standards (such as ASME BPE), and testing methods in the technical agreement during procurement.

Read more: Seamless Steel Pipe Surface Roughness Standard