Smooth Like Butter: Why Surface Finishing Matters For Tubes

Smooth Like Butter: Why Surface Finishing Matters For Tubes

Size and material are some key considerations that people make when selecting tubes, pipes, and fittings for industrial usage. However, one should not overlook the importance of surface finishing, which includes the smoothness of the tube.

For the transport of media, we are generally interested in talking about the inner surface of a tube. Most of the time, smoother surfaces are ideal because they facilitate a better flow of fluids through the channel. Rougher surfaces tend to trap particles, including debris and contaminants like bacteria. Substances can also collect on uneven surfaces and contribute to wastage over time.

From a durability point of view, rougher surfaces also usually erode and wear out faster. In the long run, using tubing with unsuitable surface smoothness can result in the need to replace parts more often, jacking up maintenance costs. As such, smoother surfaces are generally preferred for most uses.


How to measure smoothness

Smoothness can be measured and described in a few ways, one of them being the roughness average, or the Ra-value.

Roughness average is a measure indicating the average height of all the peaks and valleys of a surface. Different industrial standards have gradings for materials that tell users about the roughness average of a material. For example, according to the ASME BPE standard, SF1 means the stainless steel has a maximum Ra of 0.51 μm, while SF4 means a max Ra of 0.38 μm.

Generally, a smaller Ra-value indicates a smoother surface – however, we will also see that the type of surface finish also affects smoothness independently of the Ra-value.


Types of surface finishing

Two materials with the same Ra-value may not have the same level of ‘smoothness’. That’s because the roughness average only tells you the average heights of the peaks and valleys but not the density or regularity of these peaks and valleys.

Take a cold-rolled and pickled surface versus a polished surface. The former typically has more irregular peaks and valleys, with a higher deviation. The polished surface has more regular and tightly packed peaks and valleys, with a smaller deviation.

All these affect the flow and functionality of the tubing and should be considered when selecting the right tubing for a specific purpose.



In conclusion, surface finishing plays a critical role in the functionality and longevity of tubes and fittings. A high-quality surface finish provides protection against corrosion and enhances durability, which is particularly important in the transport of hazardous materials. Additionally, the choice of surface finishing optimises efficiency and reduces wastage.

At Pharmchem Engineering, we provide customised industrial solutions for companies with the aim of improving performance and achieving customer satisfaction. We also supply comprehensive parts like fabric expansion joints, dry disconnect couplings, and Teflon hoses for your specific system needs. Speak to us to understand more about how we can help with your industrial piping needs, including tubing installations and valves.