pH, 알칼리도와 염소이온이 동관의 부식에 미치는 영향 = Effect of pH, Alkalinity and Chloride on Corrosion in Copper Pipes

다국어 초록 (Multilingual Abstract)

It is of vital importance to provide consumers with safe drinking water The internal corrosion in distribution system is of concern partly because it can shorten the life of pipes by reducing wall thickness until there are leaks, partly because tubercles formed reduce the effective carrying capacity of pipes, and partly because it is often responsible for undesirable corrosion by-products such as lead, copper, iron etc. that deteriorate water quality, At present, the service pipeline for consumer's tap have being done with a wide variety of materials such as steel, copper, cast iron and stainless steel etc.
In these materials, copper pipes were chosen for this study because it is generally known that the corrosivity of copper pipe is very low, i.e. resistant to corrosion. That's true to some extent compared to uncoated steel pipes, but it is not true in real sense, somewhat fragile in case of pitting corrosion, according to the reports experienced in some advanced countries[Edwards, M., et at., 1996].
There are a bundle of factors affecting the corrosion of copper pipe. In order to alleviate the release of copper corrosion by-product, It is required to consider pH and alkalinity adjustments as key factors above all, To establish a relationship of cause-adverse effects in terms of alkalinity is of critical importance, that is to say, if the basic impacts of pH and alkalinity on copper corrosion are not clearly understood, utilities might run in the danger of unknowingly aggravating corrosion problems.
This research works hypothesized a priori that the three different factors as pH, alkalinity and chloride be of major factors in the corrosion of copper pipes, which are relevant to the release of corrosion by-products.
The results obtained in this research showed that for water samples at pH 7, 8, and 9, and at 10, 50, 100, 150 mg/L of alkalinity as CaCO_(3), higher PH levels led to lower concentrations of copper by-product to a certain extent.
At a given pH, higher alkalinity had a tendency to produce higher copper by-product. chlorides were similar to that of alkalinity in relation to copper by-product. This phenomenon might be due to the Nantokite(CuCl) formation on the inner walls of the copper pipe in time. 25 and 50 mg Cl^(-)/L were added to each sample adjusted with a given pH and alkalinity, respectively.
The average percent reduction of copper release was 45.7% at 25 mg C^(-)/L and 66.7% at 50 mg C^(-)/L. At pH and alkalinity changed in the tap water under stagnated state, it found that higher pH led to lower concentrations of copper by-product. At designed PH, higher alkalinity produced elevated concentrations of copper by-product. This showed that pH and alkalinity were the major factors of the corrosion of copper pipes. The analysis of both correlation and simple regression was done to evaluate the effects of pH, alkalinity, chloride and reaction time on the corrosion by-product release. In correlation analysis, it found that pH and alkalinity had significant effects on the concentration of copper by-product. From the regression coefficients computed by simple regression analysis, pH affected the total concentration of copper by-product more than alkalinity did. From the water samples at pH 7, 8, and 9 and at 10, 50, 100, 150 mg/L of alkalinity as CaCO_(3) in simulated distribution system, higher alkalinity at the same pH had the tendencies of increase in pitting(local corrosion). At 25 and 50 mg C^(-)/L, higher alkalinity had a tendency to increase in pitting corrosion. In the simulated distribution system with tap water, higher pH showed a tendency to decrease in pitting corrosion. At pH 7.5, 8.0 and 8.5, the pitting corrosion did not occur regardless of alkalinity.

목차 (Table of Contents)

• 목차 = ⅰ
• 표목차 = ⅲ
• 그림목차 = ⅳ
• ABSTRACT = ⅴ
• 1. 서론 = 1
• 2. 문헌연구 = 3
• 2.1 동관의 부식 = 3
• 2.1.1 부식에 영향을 주는 수질 인자 = 3
• 2.1.2 동관의 부식형태 = 9
• 2.1.3 동관에서의 스케일 형성 = 12
• 2.1.4 동관 부식에 대한 수질인자의 영향 = 14
• 2.1.5 인체 건강과 구리에 대한 국제 기준 = 16
• 2.2 부식속도 측정방법 = 17
• 2.2.1 시편 시험법(coupon techniques) = 17
• 2.2.2 전기ㆍ화학적 측정법 = 25
• 2.2.3 용출 시험법(Metal Release test: metal uptake test) = 28
• 3. 실험장치 및 방법 = 30
• 3.1 실험장치 = 30
• 3.1.1 시료 = 30
• 3.1.2 시편 세척 = 31
• 3.1.3 부식 부산물 용출 실험(pipe rig test) = 31
• 3.1.4 모의 급수관망 = 31
• 3.2 실험 및 분석방법 = 33
• 3.2.1 부식 부산물 용출 실험 = 33
• 3.2.2 모의 급수관망에서 전기ㆍ화학적인 부식속도 = 36
• 4. 결과 및 고찰 = 38
• 4.1 정체 상태에서 부식 부산물의 용출 = 38
• 4.1.1 pH 및 알칼리도에 따른 부식 부산물 용출 = 38
• 4.1.2 염소이온의 농도에 따른 부식 부산물 용출 = 46
• 4.1.3 영향인자들의 상호작용에 따른 부식 부산물 용출 = 49
• 4.1.4 수도물에 대한 부식 부산물 용출 = 54
• 4.2 모의 급수관망에서 영향인자가 동관의 부식속도에 미치는 영향 = 65
• 4.2.1 pH 및 알칼리도에 따른 부식속도 = 66
• 4.2.2 염소이온의 농도에 따른 부식속도 = 69
• 4.2.3 pH, 알칼리도와 염소이온의 상호작용에 따른 부식속도 = 71
• 4.2.4 수도물에 대한 부식속도 = 74
• 5. 결론 = 77
• 참고문헌 = 79