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Recently acquired quantitative data on the initial corrosion rate of steel vs. the Ryznar index of natural waters are given as a basis of provision of overall service life of steel piping. In the light of the available fundamental knowledge of aqueous corrosion, the mechanism of high‐rate localised attack of coated steel piping from carbonated waters is outlined. A representative case history of multiple perforation of bitumen‐coated steel piping from localised corrosion is reported for a municipal potable water distribution system. Practical protective measures and corrosion monitoring techniques are considered in relation to the most aggressive waters.

Aqueous internal corrosion of steel Scuba tanks is critically considered as a cause of explosive accidents during charging, storage and use of air cylinders. More restrictive safety regulations are shown to be needed in relation to the extremely high corrosion rates induced by high oxygen pressures. Accidental sea water entries are particularly dangerous because of tubular type localized attacks occurring in the presence of chlorides. Consideration is given to possible protective measures by phosphate conversion treatments and coatings.

Electrochemical techniques are described of direct use to chemical processors for optimum material selection in designing and maintaining new plants as well as corrosion monitoring and control in operating existing plants. Reference is made to the three corrosion forms most responsible for failures in chemical equipment, i.e.: general corrosion, localised corrosion, and stress‐corrosion cracking. Practical examples are given of successful industrial application of electrochemical methods: 1) for controlling active corrosion of a stainless alloy in pressure reactors operated with hot sulphuric acid solution and 2) for preventing stress corrosion cracking of a low‐alloy steel in a pressure absorption tower operated with hot alkali carbonate solution.

Resistance to hydrogen embrittlement. Since cathodic protection is quite necessary and actually extensively applied for the electrochemical control of corrosion of immersed steel structures, adequate consideration must be given to the several deleterious effects of hydrogen (commonly included in the term ‘hydrogen embrittlement’) from overprotection.

The full development of marine technologies for the industrial exploitation of deep‐sea resources requires the availability of exhaustive engineering data on the degradation of constructional materials when immersed at great length in ocean environments. An overall review of behavioural figures from reliable sources allows to point out major weaknesses and uncertainties with candidate alloys and consequent demands for ameliorative and innovative investigation. Prominent objects of research can be envisaged, accordingly, in: (i) formulating low‐alloy steels whose surface is chemically convertible (by suitable pretreatments or free corrosion itself) so as to abate the rate of oxygen cathodic reduction i.e. the current density required for cathodic protection; (ii) singling out high‐strength steels whose resistance to corrosion‐fatigue and hydrogen embrittlement is in proportion to the strength level; (iii) developing cheaper alternatives to high‐molybdenum stainless alloys resistant to localised corrosion; (iii) combining (in optimal composites) the outstanding resistance of titanium to saltwater corrosion and the low‐cost good mechanical properties of steels.

Last month the author discussed platinum anodes using inert supports such as plastic and ceramic, common metal supports such as copper, and supports with passivating metal such as titanium or platinum. This concluding section discusses applications and operation. It is concluded that only two types of supported platinum electrode can be recommended at present—a platinum‐palladium foil anode with a plastic mount and platinised titanium.

Organic compounds containing sulphur, nitrogen and oxygen atoms are capable of retarding metallic corrosion. As the thiourea molecule contains one sulphur and two nitrogen atoms, thiourea and its derivatives are potential corrosion inhibitors. While extensive investigations have been carried out on inhibitor properties of thiourea, due attention has not yet been paid to a systematic study of inhibitor action of thiourea derivatives. However, several substituted thioureas have been investigated as corrosion inhibitors. The applications of thiourea and its derivatives as corrosion inhibitors reported in literature up to 1967 are narrated in this article.

Tests have been carried out to determine the stress corrosion susceptibility of Al‐4.4 a/o Xn alloy in the aged condition. Flat ribbon specimens were tested in aqueous solutions containing 3.5% NaCl at a constant stress of 5.76 kg/mm2 (32% of UTS). Polarisation studies carried out on the stressed and unstressed specimens reveal that the Tafel slopes have a much lower value in the stressed condition. The susceptibility to stress corrosion increases with the test temperature. An equation of the type Z=K. exp (—E/RT) with reciprocal life Z and test temperature T, is found to fit the data from which the value of the activation energy is found to be ca. 20 kcal.mol−1.