Investigations of sand–water induced erosive wear of AISI 304L stainless steel pipes by pilot-scale and laboratory-scale testing

Abstract

The repair costs of erosion damage caused by solid particle impingement from transporting slurries and other particle-laden liquids in pipes can be extremely high. In the absence of accurate predictive models, routine monitoring of the pipe wall thickness or the use of sacrificial coupons are required to warn of erosion damage or impending loss of containment. Apart from advantages for plant maintenance, the environmental, safety and production implications are enormous. Identification of critical pipe components susceptible to high levels of damage, and innovative ways to ameliorate the damage, has been an active topic of research for decades. Recent work at University of Nottingham and University of Southampton [Wear 250 (1–12) (2001) 771] has sought definitions of flow fields and particle dispersions and their relationship to erosive wear to facilitate the development of new designs and geometries for slurry handling equipment. This paper covers research that has been aimed at determining the distribution of erosion rates and the erosion mechanisms that occur over wetted surfaces within pilot-scale pipe systems handling water–sand mixtures at 10% by volume concentrations and at a mean fluid velocity of approximately 3 m/s. Experiments are presented which have been conducted on a test section consisting of an upstream straight pipe section followed by a bend (with a radius of curvature of 1.2 bore diameter) within a 78 mm diameter pipe test loop. The whole loop and test section was manufactured from AISI 304L stainless steel. The wall wear rates, obtained by gravimetric measurements, as a function of time are discussed. Circumferential erosion penetration and mechanisms at discrete locations have been measured by surface profilometry on replicas and scanning electron microscopy after cutting-up the pipe sections. The erosion rates and patterns are compared to those predicted by erosion models linked to computational models for the impact velocity and impact angle in bend and straight sections. Bend wear patterns are further compared to flow visualisation results from a transparent flow loop and electrical resistance tomography (ERT) to confirm the placement of particle burdens. The erosion rates, expressed as volume loss per impact (determined gravimetrically and via computer models) in bends are found to agree well with simple laboratory-scale water–sand jet impingement tests on planar stainless steel samples. The pipe loss data alone represents a significant resource for future erosion researchers to reference.