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Early this year (CORROSION TECHNOLOGY, March issue) we published the first part of a paper presented before the American Petroleum Institute's Refining Division and also the National Institute of Corrosion Engineers, describing the different forms of hydrogen damage and the prevention steps that were taken at the new fluid catalytic cracking unit of the Richfield Oil Corporation. At that time we announced that we hoped to publish more of this interesting paper, brought up to date. This, then, completes the work of Messrs. Neumaier and Schillmoller and describes protective steps that have been taken at the fluid unit gas plant, the evaluation of these steps, monitoring and the use of organic inhibitors.

Sulphides, in particular hydrogen sulphide, not only possess an unpleasant odour and are toxic, but also cause acute corrosion damage to municipal sewage systems and plants. The hydrogen peroxide waste water deodorization system introduced by Degussa AG of Frankfurt am Main, Federal Republic of Germany, oxidizes hydrogen sulphide and other sulphides to counteract odours and corrosion, the residual oxygen also preventing the renewed formation of hydrogen sulphide. If temporary oxygen deficiency should occur during biological treatment, more oxygen can be added simply and rapidly in the form of hydrogen peroxide. These processes are easily controlled, involve little investment and offer the advantage that pure water and oxygen are the only product remaining from reactions involving hydrogen peroxide.

Catalytic reforming has grown rapidly during the past six years, reaching over a million barrels daily. This acceptance is largely due to the effectiveness of catalytic reforming as a source of low‐sulphur, high‐octane motor fuels; aromatics for petro‐chemicals and low‐cost hydrogen are valuable by‐products. Some ten competitive processes are available to the refiners. Of the processes available, those using a platinum‐type catalyst have found the widest acceptance. Of the nearly 200 units in operation or under construction, over 90% use a platinum‐containing catalyst.

High‐temperature corrosion by H2S is a new problem in refinery technology. It is associated with catalytic reforming and desulphurisation processes which were introduced during the last 5–7 years.

U.S.S.R. Oxygen and nitrogen in metallised surfaces. One of the most important considerations in the matter of extending the life of units or components under rolling friction conditions or corrosion is the use of different pseudo‐alloys on a steel base, and the chemical composition and nature of these ‘alloys,’ especially in the matter of oxygen and nitrogen content. Electro‐metallising is briefly described. The micro‐structure of a steel metallised pseudo‐alloy is shown and discussed. Characteristic features are porosity and heterogeneity, the former amounting to 10 to 15%. Methods of analysis, especially for oxygen and nitrogen, include anodic solution and separation of non‐metallic inclusions (including oxides) in powder form. Nitrogen content averaged 0.13% and oxygen 2.7% (without manganous oxide). An x‐ray study was made of the phase constitution of non‐metallic inclusions, with tabulated results and x‐ray photographs. Analyses of the pseudo‐alloys for carbon manganese, sulphur, phosphorus and silicon are also tabulated. —(L. V. Krasnichenko et al., Zh. prikl. Khim. (J. Appl. Chem.), 1958, (8), 1170–1174.)

Although under many conditions a carefully made weld should introduce no special corrosion risk, the fact remains that welding raises special corrosion problems. The reasons are discussed by Dr. Evans in the first part of his article. He then considers in particular the corrosion of welded stainless steel and aluminium alloys, corrosion fatigue, and hydrogen blistering and cracking.

This paper aims to use an imidazole-based n-ionic Gemini surfactant derived from palm oil to inhibit the sulfide stress corrosion cracking of a supermartensitic stainless steel.

The slow strain rate testing technique, hydrogen permeation tests and potentiodynamic polarization curves have been used.

Addition of the inhibitor below the critical micelle concentration (CMC) decreased the corrosion current density (i_corr), but not enough to avoid embrittlement due to the entry of hydrogen into the steel. Instead, the addition of the inhibitor close to the CMC decreased the i_corr, suppressed the entry of hydrogen and inhibited the sulfide stress cracking of steel. Finally, the addition of inhibitor above the CMC led to a slight increase of i_corr and promoted localized corrosion, however, the sulfide stress cracking of steel was inhibited.

A green sulfide stress corrosion cracking inhibitor of a supermartensitic stainless steel has been obtained.

GERMANY Stress corrosion in highly‐stressed steels. A description is given of the appearance of cracks of a predominantly transcrystalline character in ordinary and alloyed heat‐treated steels used in condensation units of high‐pressure plants, and experiments made to get these appearances under laboratory conditions. These cracks may be caused by the hydrogen resulting from very slight corrosion on the surface of the steel when in the presence of certain specific active substances, especially hydrogen sulphide. The hydrogen penetrates the metal, where, as a result of recombination, it creates very high local pressures. Extensive research has been undertaken in the U.S.A. in connection with similar phenomena appearing in the mineral oil industry.

The increasing incidence of corrosion induced failures query the efficiency of corrosion prevention measures and/or their monitoring techniques. Of concern too, is the phenomenon of twelve o'clock corrosion and the subsequent rupture. This indicated that the inhibitor was not protecting the upper surface of the pipe wall which could be possibly averted by batching a slug of inhibitor solution ahead of a pig or between pigs on regular (e.g. monthly) basis.

Thiourea, allyl thiourea and phenyl thiourea have been investigated as corrosion inhibitors for copper in nitric acid. All the substances are predominantly cathodic inhibitors. The present article reports the use of thiourea, allyl thiourea and phenyl thiourea as inhibitors of the corrosion of copper in nitric acid.