Industrial Statistics with Minitab

12.6 Pores

In a process of steel plates welding some pores appear in the weld. These pores are mainly due to the protective coating (to prevent oxidation) of the bearing plates. When burning the paint some gases are generated and are trapped in the weld; this creates some small bubbles that form pores.

Three different types of paint can be used. Each type of paint provides the same protection, but they are probably different in creating pores. Therefore, a test is performed. The test consists in welding five pairs of plates, each with one type of paint. As unpainted metal also produces pores when welded (due to soiling or other factors), only half of the plates are painted. Later, the porosity in the weld corresponding to the painted and the unpainted area are measured.

Is one type of paint better than the others?

The interesting outcome is the difference between the porosity in the painted and the unpainted areas, as this is the value of porosity due to the painting. These differences are calculated in the datasheet:

By analysis of variance: Stat > ANOVA > One-Way (Unstacked)

The difference is statistically significant (p-value = 0.003). Paint B produces less ...