게시판 > 질답게시판 > 금속 부식 방지 원리 에 대해 궁금하여서 글 써보았습니다.

스테파노 Stefano

14-10-14 11:32

(1) 금속의 부식원리와 부식방지 원리는 아주 대단히 광범위한 주제입니다. 우선 이곳을 먼저 참고한 후 이해되지 않는 부분을 중점 질문해 주세요.

http://en.wikipedia.org/wiki/Corrosion

(2) 질문자의 경우 취급하는 물질이 수용성 열매체로 보이는데 우선 그 열매체를 공급하는 업체로부터 부식방지에 관한 자료를 요청하여 도움이 되는 자료를 구해보도록 하세요.

(3) 해당 열매체에 대해 시도해보았던 부식방지를 먼저 소개한 후 효과가 있지 않았던 부분을 중점질문하세요.
부식방지 막을 형성하도록 했었다면 그 막이 무엇이었는지 먼저 간략히 설명하고 효과가 사라진 이유를 먼저 생각해 본 후 질문하도록 하세요.

gojpw gojpw

14-10-14 17:38

짧은 제 소견을 말씀드리면,
- 부식이란 금속과 산소가 반응하는 과정이므로 산소를 제거할 수 있는 약품을 주입하는 방법이 있으며,
- 만약, 금속의 재질이 carbon steel 계열이라면 참고로 발전소의 경우, 일부러 산소를 과잉주입하여 금속 표면에 산화막을 형성시키는 방법도 적용하고 있습니다.
- 그외는 위에서 말씀하신 것 처럼 금속표면을 별도 약품 처리하는 것도 방법인 듯 합니다.

스테파노 Stefano

14-10-16 20:27

(1) gojpw님..
<금속의 재질이 carbon steel 계열이라면 참고로 발전소의 경우, 일부러 산소를 과잉주입하여 금속 표면에 산화막을 형성시키는 방법도 적용하고 있습니다. > 라고 설명하고 있는데 이는 정상운전시를 의미하는 것은 아닐것입니다.

왜냐하면..정상운전중이라면 보일러 용수나 응축수들은 항상 Deaerator를 거치면서 공기(산소)와 CO2를 제거하고 동시에 Boiler Feed Water에 Oxygen Scavenger를 투입하여 잔류산소를 없애주지 않으면 Boiler 드럼내에 곰보형태의 Corrosion이 생성되고 유속이 빠른 Steam이나 Condensate 관내의 산화철 피막은 부동태형태도 아니며 마모나 산소침투에도 취약해서 산소가 존재한다면 부식이 심각해지기 때문입니다.

(2) 산소를 과잉주입하여 산화막을 형성시기는 과정에 대해 구체적(적용시기, 적용방법, 주의사항등)으로 사용방법을 보충설명바랍니다.

gojpw gojpw

14-10-17 08:59

예전에는 보일러 급수내에 부식 방지를 위하여 Oxygen Scavenger를 투입하여 운전하는 것이 일반적인 방법이었으나 최근에는 Oxygen을 일부러 주입하여 산화피막을 형성하여 운전하는 방식이 적용되고 있습니다.
Oxygen Scavenger를 주입하는 방식을 AVT (전휘발처리)방식이라 하며, 산소를 주입하는 방식을 OT (산소주입처리) 방식이라 하여, 최초 준공 후 일정기간동안에는 AVT 운전을 하다가 일정 시간이 지나면 OT 운전으로 전환하는 방식을 최근 발전소에는 적용하고 있습니다.
이러한 이유는 AVT 운전을 하게 되면 아주 미량의 제거되지 않은 Oxygen이 배관 표면에서 Fe3O4 (magnetite)라는 피막 물질을 형성하게 되는데 이러한 피막형성은 더 이상의 산화반응이 일어나지 않게 하는 장점으로 작용하게 됩니다만, 문제는 Fe3O4의 형성 구조가 엉성하며 탈락이 잘 된다는 단점이 있습니다.
일정 기간 이후 OT 운전으로 전환하게 되면 엉성한 Fe3O4 피막 사이로 Fe2O3 (fematite)가 추가로 생성되는데 Fe2O3는 촘촘한 구조로 가지며, Fe3O4로 형성된 피막을 한층 더 튼튼하게 만들어주는 결과를 가져오게 됩니다.
장점으로는 Fe3O4 피막보다 Fe2O3 피막이 배관의 압력손실을 낮추어 주게되어 펌프 소비동력을 줄이게 되며, 산세정 주기도 약 2배정도 길어지게 되는 점도 있습니다.

스테파노 Stefano

14-10-17 16:02

감사합니다. 설명한 내용을 아래의 IAEA Site에서 재확인할 수 있었습니다.
(i) https://inis.iaea.org/search/search.aspx?orig_q=RN:17040491
(ii) https://inis.iaea.org/search/search.aspx?orig_q=RN:8313252

<인용(i)시작/>
Purpose: To enable oxygen injection controlled to a proper density in any of operation modes of a nuclear power plant. Method: Oxygen injection point is disposed each by one at the upstream and the downstream of a condensate filter and desalter. Oxygen is injected while adjusting the opening degree of an injection valve using a flow rate measured by a condensate flowmeter as a parameter. Upon plant starting, oxygen is injected at a density of about 100 - 200 ppb at the oxygen injection point on the downstream in order to form a protective oxide membranes on the surface of feedwater and condensate pipeways. Then, after the plant enters into the rated operation, oxygen is injected both on the upstream and downstream, in which the oxygen density in the feedwater is adjusted to 20 ppb at the upstream and about 30 ppb at the downstream, that is, about 50 ppb in total. This enables to protect the equipments and pipeways of feedwater systems against oxygen corrosion, as well as apply firm oxide protection membrane treatment to the surface of the pipeways. (Seki, T.)
</인용끝>

<인용(ii)시작/>
In BWR plants, the metallic components brought into the core lower heat conductivity as scale, and increases radiation dose. Therefore metallic components are removed from condensate with filters and desalters, and the elution of metals in feed water system is inhibited. In order to lessen the metal elution in feed water system, it seemed that dissolved oxygen must be as low as possible, but in actual operation, the elution of iron was unexpectedly large, and the measures to inhibit it were required. It has been reported that the corrosion of iron was inhibited remarkably when the dissolved oxygen in neutral water was more than 15-30 ppb. Accordingly experiment was carried out to confirm the corrosion-prevention effect of oxygen. The results are summarized as follows. When oxygen was injected in the feed water for BWR, the elution of iron was inhibited. The concentration of dissolved oxygen at the exit of condensate desalters should be at least 20 ppb, and once the elution of iron is inhibited, the concentration may be lowered to 10 ppb. The total iron content in feed water began to decrease with the start of oxygen injection, and after about one day, it turned out to be almost constant. When the oxygen injection was stopped, total iron content began to increase after about a half day. The elution of iron was inhibited by oxygen injection because the passive state film of Fe3O4 and γ-Fe2O3 was formed on carbon steel surface. (Kako, I.)
</인용끝>

*BWR=Boiling Water (Nuclear) Reactor

<인용(i)시작/>
Purpose: To enable oxygen injection controlled to a proper density in any of operation modes of a nuclear power plant. Method: Oxygen injection point is disposed each by one at the upstream and the downstream of a condensate filter and desalter. Oxygen is injected while adjusting the opening degree of an injection valve using a flow rate measured by a condensate flowmeter as a parameter. Upon plant starting, oxygen is injected at a density of about 100 - 200 ppb at the oxygen injection point on the downstream in order to form a protective oxide membranes on the surface of feedwater and condensate pipeways. Then, after the plant enters into the rated operation, oxygen is injected both on the upstream and downstream, in which the oxygen density in the feedwater is adjusted to 20 ppb at the upstream and about 30 ppb at the downstream, that is, about 50 ppb in total. This enables to protect the equipments and pipeways of feedwater systems against oxygen corrosion, as well as apply firm oxide protection membrane treatment to the surface of the pipeways. (Seki, T.)
</인용끝>

<인용(ii)시작/>
In BWR plants, the metallic components brought into the core lower heat conductivity as scale, and increases radiation dose. Therefore metallic components are removed from condensate with filters and desalters, and the elution of metals in feed water system is inhibited. In order to lessen the metal elution in feed water system, it seemed that dissolved oxygen must be as low as possible, but in actual operation, the elution of iron was unexpectedly large, and the measures to inhibit it were required. It has been reported that the corrosion of iron was inhibited remarkably when the dissolved oxygen in neutral water was more than 15-30 ppb. Accordingly experiment was carried out to confirm the corrosion-prevention effect of oxygen. The results are summarized as follows. When oxygen was injected in the feed water for BWR, the elution of iron was inhibited. The concentration of dissolved oxygen at the exit of condensate desalters should be at least 20 ppb, and once the elution of iron is inhibited, the concentration may be lowered to 10 ppb. The total iron content in feed water began to decrease with the start of oxygen injection, and after about one day, it turned out to be almost constant. When the oxygen injection was stopped, total iron content began to increase after about a half day. The elution of iron was inhibited by oxygen injection because the passive state film of Fe3O4 and γ-Fe2O3 was formed on carbon steel surface. (Kako, I.)
</인용끝>

*BWR=Boiling Water (Nuclear) Reactor