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不鏽鋼管材對配水系統自來水水質之影響

為了解決1 in pipe fittings的問題，作者Saroj Adhikari 這樣論述：

Stainless steel (SS) has gained popularity for use in drinking water distribution systems over the last decade owing to unique properties, including strong resistance to corrosion and ease of fabrication. In Taiwan, replacement of lead (Pb) service pipe with stainless steel pipe was implemented in

2003 to address water loss due to pipe leakage in 2002. The large-scale use of SS was unprecedented and could have unintentionally altered the drinking water quality. However, studies on the use of SS materials in distribution systems are rare because these materials are generally assumed to be iner

t with water. Recent studies have shown that galvanic corrosion between Pb and SS can occur during partial replacement, resulting in accelerated Pb release. Since SS was introduced mainly to address water leakage, the impact on drinking water quality is less understood, which needs to be scientifica

lly investigated. For example, concentrations of chromium (Cr) and nickel (Ni), major components of SS, are expected to increase in drinking water over time with the use of such materials. This can potentially create health issues unknown to the public and can pose challenges to existing regulatory

measures.A series of well-controlled short-term batch experiments were designed using SS materials to investigate the activation of SS and its effect on galvanic corrosion. Similarly, a long-term pilot study involving a recirculating SS system was setup in the laboratory to examine the impact of SS

plumbing materials on drinking water quality. Following the pilot study, a Ni contamination survey in elementary schools in Taichung was conducted. The objectives of this study are to (1) investigate the effects of acids on the activation of SS and examine the mechanisms of galvanic corrosion using

‘active’ and ‘passive’ SS wires and pure Pb wires, (2) examine the effects of flow rates and water corrosivity on drinking water quality in a recirculating stainless steel system and (3) assess nickel contamination in drinking water samples of elementary schools in Taichung by employing an intensive

sampling survey.Firstly, the effects of various concentrations (0.5, 1, and 2 M) of three strong acids (HCl, H2SO4 and HNO3) on the activation of SS surface was investigated. HCl and H2SO4 activated the surface, whereas HNO3 was found to enhance passivation. The effects of HCl were observed in term

s of pits and crevices penetrating to the deeper layers while H2SO4 affected only the outer surface layer and did not result in deeper pits. Although the protective surface layer is assumed to self-heal, the ability to do so was found to be less effective with HCl than with H2SO4. Furthermore, the p

henomenon of galvanic corrosion that occurs between Pb and SS activated with acids was also examined for the first time in this study. Findings illustrated that conventional anodic and cathodic processes reported to occur between Pb and passive stainless steel do not occur when the latter is activat

ed. In galvanic contacts involving Pb and activated SS, reverse galvanic corrosion was observed, which caused SS to corrode instead of Pb, as evidenced by higher concentrations of soluble and total Fe compared to Pb, unlike in the general galvanic corrosion. Corrosion of activated SS increased with

decreasing pH and increasing the concentrations of chloride and sulfate under a fixed CSMR.Secondly, the effects of the physical parameter (flow rates) and water corrosivity on SS plumbing materials were investigated using a recirculating SS system. All three metal constituents (Cr, Fe, and Ni) were

released at low, medium, and high flow rates. While only trace amounts of Cr were recorded (below 50 µg/L), Fe and Ni levels were exceedingly high. When the flow rate was increased from low to medium, Fe and Ni were released at a maximum 229 µg/L and 121 µg/L, respectively. High flow rates, however

, resulted in lower metal concentrations. Metal release reduction with increasing experimental time at high flow rates indicates that flow rate affects SS materials through passive leaching. In a separate recirculating system involving a more corrosive environment with a high flow rate and low pH (6

.5), high chloride (250 mg/L), and TOC (1 mg/L as C), corrosion of SS was observed, which increased as a combined effect of the parameters considered. The maximum concentrations of Cr, Fe, and Ni reached 3.9 µg/L, 68.7 µg/L, and 274 µg/L, respectively, during the most corrosive phase of the experime

nt (combined pH, chloride, and TOC), as opposed to only 1.2 µg/L, 49.4 µg/L, and 158 µg/L, respectively, at the initial phase maintained at low pH alone. The corrosion effect of water corrosivity was supported by the rise in Cr concentrations, indicating damage to the protective passive film on the

surface layer of SS.Lastly, recognizing the potential health impacts and limited information about Ni in drinking water, one of the key constituents of SS material, an intensive sampling survey of drinking water was conducted in elementary schools of Taichung as a part of a first-of-its-kind investi

gation into possible Ni contamination from such sources. Ni concentrations in drinking water were sporadic with total concentration exceeding the Taiwan EPA standard (20 μg/L) in 4 schools. The concentrations varied with the season, water usage, and age and size of the schools. Samples collected on

weekends and in the summer were more likely to exceed the standard. Similarly, a higher tendency of exceedance was observed in schools with a larger student population (≥ 500) and schools over 50 years of age. Nickel-containing fittings and plumbing materials are commonly used in Taiwan, and finding

s of this study indicate the possibilities of Ni contamination in drinking water from such materials.