飲用水配水管線中鉛和不鏽鋼之電化腐蝕反應

Abstract

臺灣自1979年開始禁止使用鉛管作為飲用水管，而為了改善飲用水的品質，自來水公司開始使用進行管線的汰換工程，不鏽鋼管為近十年選用的新管材。由於考慮到汰換管線的成本和住家的隱私問題，因此汰換工程主要選擇在公共給水管線中進行，家用鉛管則繼續殘留在住戶中，而造成部分汰換的狀況產生。由於鉛和不鏽鋼之間具有標準電位差，因此當鉛和不鏽鋼連接送水時會產生電化腐蝕反應。 此研究的目的是要了解在不同的操作條件下，如：pH值、[氯離子濃度mg/L]/[硫酸根離子濃度mg/L] 或CSMR 和在相同CSMR=2時改變氯離子和硫酸根離子濃度，鉛和不鏽鋼之間的電化腐蝕反應對於鉛溶出的影響，此外評估使用正磷酸作為腐蝕抑制劑控制鉛溶出的效果。實驗結果顯示，當鉛和不鏽鋼的電化腐蝕反應產生時，水中的鉛濃度會提高，且當pH降低或CSMR提高時，鉛溶出的影狀況會更明顯。此外，在自水中加入正磷酸鹽可以減緩鉛溶出的情況，但是當電化腐蝕反應發生時，仍需注意CSMR，因為即使在飲用水中含有正磷酸鹽的情況下，CSMR越高飲用水中的鉛濃度仍然越高。

Lead pipe has been banned for distributing drinking water in Taiwan since 1979. In order to improve drinking water quality, partial replacement of lead pipes, in which lead pipes in the public area were replaced by stainless steel pipes while those in the private premises remained intact, was commonly practiced in Taiwan due to the high cost and difficulties to access private properties. Due to the different potentials of lead and stainless steel, galvanic corrosion may take place if they are electronically connected in water. The objectives of this research are to characterize the effects of galvanic connection between lead and stainless steel on lead release and the effects of pH, chloride and sulfate concentration on this process. The experiments were conducted by connecting aged lead pipes and stainless steel fittings under different pH, chloride to sulfate mass ratio or CSMR and different chloride and sulfate concentration under a fixed CSMR of 2. Orthophosphate was evaluated as a corrosion inhibitor to control lead release. The results demonstrated that lead release increased when lead and stainless steel were galvanically connected and the rate of lead release accelerated with the decreasing pH and increasing CSMR. Orthophosphate could effectively reduce lead release but CSMR needs to be considered since water with a higher CSMR still caused more lead release when galvanic corrosion took place.