Determine the Maximum Negative Operating and Collapse Pressure of Stocked Spiral Duct With and Without Corrugations

Abstract

Abstract This paper describes an experimental program to experimentally determine the extent to which incorporating corrugations in spiral ducts increased their strength, thus permitting operating and collapse pressures that were higher (more negative) than non-corrugated ducts of the same gauge. The presence of corrugations increased the apparent stiffness of the ducts, and therefore suppressed their tendency to deform under negative pressure. Relatively small diameter spiral seam ducts were more resistant to excessive deformations than larger diameter ducts, for a given wall thickness. At the smallest nominal duct diameters considered in this test program the negative internal gauge pressures where corrugated spiral seam ducts were likely to first exceed a prescribed deflection limit were as much as 6 to 9 times greater than the corresponding values for non-corrugated ducts of the same wall thickness. The ability to withstand the effects of negative internal gauge pressures diminished as the duct diameter increased. Little or no benefit to incorporating corrugations was observed at the largest duct diameters that were investigated. This research yielded a table of negative pressure capacity for several standard gauge spiral ducts, with and without corrugations, that will enable the estimation of maximum deflection of the ducts. This also provides guidance regarding potential collapse pressures.