Question

Explain the following observations, using diagrams to illustrate your answer wherever possible:

(a) Steel nails used to hold copper roofing sheet in position failed rapidly by wet corrosion.

(b) The corrosion of an underground steel pipeline was greatly reduced when the pipeline was connected to a buried bar of magnesium alloy.

(c) Mild-steel radiators in a central heating system were found to have undergone little corrosion after several years' service.
(d) A reaction vessel for a chemical plant was fabricated by welding together stainless steel plates containing 18% chromium, 8% nickel and 0.1% carbon. During service, it was observed that the vessel corroded badly near the welds.

Answer 1

ANSWER:

(A). Steel bars used to hold copper material sheet in position flopped quickly by wet erosion. at rooftop because of dampness noticeable all around or because of downpours, the oxygen present in test sum in decreased by the accompanying response.

O+2HO + 4e ------ >4OH

also, the metal corroding response an

Fe ---- >Fe +2e-

these two particles from hydrated iron oxides which later reason disappointment of steel nails used to hold the copper.

(B). the corrosion of an underground steel pipeline was extraordinarily decreased when the pipeline was associated with a covered bar of magnesium compound. the component happens in light of the fact that magnesium has a more negative erosion voltage and the magnesium combination and steel pipeline couples to frame an electrolyte cell. the more electromagnetic magnesium composite turns into the anode and pipe moves toward becoming cathode. the anode disintegrates and the cathode is ensured. the alloys are forestall to arrangement of oxide layer and convert to a cathode.

(C). metal-steel radiators in focal mending framework are found to have experienced. here for the most part the focal recuperating framework are closed to have an oxygen free climate and because of absence of oxygen in the framework corrosion does not happen as oxidation of mild steel does not happen.

(D). tempered steel plates by and large consume severely close welds if welding is done on it. the close by zone of a weld is called heat effected zone where the metal got hold however didn't dissolve. carbon is available in steel to enhance quality and this carbon takes up chromium carbide. because of arrangement of chromium carbide (Cr2O3), the chromium of close by zone is lost and consequently there is no longest assurance from chromium and thus they consume gravely.