Steel, roughness value commercial

The relative roughness is expressed as E D, where E = the surface roughness and D = the internal pipe diameter. Typical values of E D are 0.0015 for drawn tubing, 0.046 for commercial steel and 0.12 for asphalted cast iron. 

Thus, if we were to use the same pipe material (commercial steel) for the model as in the field, we would also have to use the same diameter (48 in.). This is obviously not practical, but a smaller diameter for the model would obviously require a much smoother material in the lab (because Dm -C Df requires em drawn tubing such as copper or stainless steel, all of which have equivalent roughness values of the order of 0.00006 in. (see Table 6-1). 

The actual size of the roughness elements on any surface will vary with the material, age and usage, deposits, dirt, scale, rust, etc. Typical values for various materials are given in Table 5.3. The most common pipe material—clean, new, commercial steel—has an effective roughness of about 0.0018 in. (0.045 mm). Other surfaces, such as concrete, may vary as much as several orders of magnitude, depending upon the nature of the surface finish. 

Commercially provided 25.4 mm diameter steel balls of two different roughness values were employed in this study. The balls have no preferential surface roughness pattern. The glass disc has 150 mm in diameter and its surface is optically smooth. The silicon dioxide spacer layer about 195 nm thick covers almost entire underside of the glass disc with the exception of a narrow radial strip where only chromium layer is deposited. Scanning probe microscopy examinations of silicon dioxide films shows that they are extremely smooth [14]. Material properties of the contact bodies are summarised in Table 1. The surface roughness parameters of steel balls measured by stylus technique are given in Table 2. 

Figure 6 was created in this manner for a series of decade values of He. It may be used in place of the Moody chart for standard pipeline design problems. Because of the manner in which the empirical correlation for B was determined, no correction for pipe relative roughness is needed when one is dealing with commercial grade-steel line pipe. 

It is well known that the friction factor and the convective heat transfer coefficient can be influenced by the relative roughness of the walls of a channel. For microchannels the relative roughness, defined as the ratio between the mean height of the surface asperities and the hydraulic diameter of the chaimel, can assume large values. Especially for stainless steel commercial microtubes the relative roughness can reach values equal to 2-8 %. 

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