问题 问答题 简答题

试述凝汽器汽侧腐蚀的种类及原因?

答案

参考答案:

凝汽器铜管汽侧腐蚀种类有:①氨腐蚀。②冲击腐蚀。③铜管泄漏时的二氧化碳和氧腐蚀。④腐蚀疲劳。⑤应力腐蚀。引起上述腐蚀的原因有:.

(1)氨腐蚀:在凝汽器铜管汽侧的蒸汽及凝结水中均含有微量氧,一般小于30ppb此时这些氧气首先和铜管发生氧化还原反应,生成Cu20或CuO。当凝结水中的含氨量小于200ppm时,Cu20和CuO能均匀的覆盖在铜管表面,形成保护膜,阻止了氧气与铜的反应,即使金属阳极发生极化,但是当凝结水中含氨量一旦超过200ppm时,氨则与氧化铜及氧化亚铜发生络合反应,生成水溶性较强的铜一氨络离子,从而破坏了铜管表面的保护膜,而当铜管裸露于凝结水时,使得水中溶解氧又与铜发生反应。而反应生成物再次被络合。如此往复循环的反应,使铜管遭到严重腐蚀。

(2)冲击腐蚀:当除盐水直接送入凝汽器中作补给水时,如果布水装置不合理,除盐水直接冲击铜管表面使铜管表面保护膜遭到破坏,而且此时除盐水含饱和氧,导至铜与氧发生氧化还原反应,而反应生成的氧化亚铜保护膜不断地被冲击,又使氧与铜的反应不断进行。故此,引起了铜管的冲击腐蚀。

(3)铜管泄漏时的二氧化碳和氧腐蚀:当铜管泄漏时,冷却水可直接进入铜管汽侧,由于冷却水中含有大量碳酸盐及饱和氧,而碳酸盐分解后使水呈微酸性,由于微酸性的水在氧的参与下可直接溶解铜管表面保护膜,而保护膜破裂后氧与铜管接触又生成保护膜,然后保护膜又被溶解,如此反复进行,最终铜管被腐蚀,。

(4)应力腐蚀:当铜管在制造、安装、运行中产生应力时,由于铜管汽侧含氨量很高,故容易发生应力腐蚀。

(5)腐蚀疲劳:因为铜管受交变应力时,又直接接触氧及氨等侵蚀性介质后铜管产生断裂。

判断题
单项选择题

Deflation is an economic theory relating changes in the price levels to changes in the quantity of money. In its developed (1) , it constitutes an analysis of the (2) underlying inflation and deflation. As (3) by the English philosopher John Locke in the 17th century, the Scottish (4) David Hume in the 18th century, and (5) , it was a weapon (6) the mercantilists, who were thought to equate wealth with money. If the (7) of money by a nation merely raised (8) , argued the quantity theorists, then a "favourable" balance of trade, (9) desired by mercantilists, would increase the supply of money but would not in-crease (10) . In the 19th century the quantity theory (11) to the ascendancy of free trade over protectionism. In the 19th and 20th centuries it played a part in the (12) of business cycles and in the theory of foreign (13) rates.

The (14) theory came under attack during the 1930s, (15) monetary expansion seemed ineffective in combating deflation. Economists argued that the levels of investment and government spending were more important than the money supply in determining economic activity.

The tide of opinion (16) again in the 1960s, when experience (17) post-World WarⅡ inflation and new empirical (18) of money and prices— (19) A Monetary History of the United States (1963) by Milton Friedman and Anna Schwartz—restored much of the quantity theory’ s lost prestige. One implication of this theory is that the size of the stock of money must be considered when shaping governmental policies (20) to control prices and maintain full employment.

16()

A.reversed

B.occurred

C.emerged

D.finished