Search results

The stress corrosion properties of 3CR12 were evaluated in various media by means of potentiodynamic scanning and the slow strain rate techniques. In general 3CR12 shows good resistance to stress corrosion except in hot chloride solutions above 100°C.

Last month Dr. Parkins described the various types of pitting corrosion which may appear in steam boilers. In Part 2 corrosion associated with high concentrations of caustic soda (caustic cracking), corrosion fatigue and the deterioration due to local overheating are discussed.

Corrosion which take place in steam boilers is usually localised, leading to pitting or corrosion cracking rather than attack of a general nature, although this may be encountered in boilers due to the presence of acid conditions. For this reason Dr. Parkins confines his remarks to localised corrosion and in the following extensive article, specially written for Corrosion Technology, he discusses in Part I types of pitting corrosion. Next month corrosion associated with high concentrations of caustic soda viz. caustic cracking, corrosion fatigue and deterioration due to local overheating will be discussed.

To make clear that C‐steel can differ very much in corrosion resistance under practical conditions only because of differences in chemical composition of the steels.

In the electricity generating industry, “mild” (i.e. “plain carbon”) and low‐alloyed steels are used in huge quantities, for instance, in boilers, steam generators, heat recovery boilers and waste incineration boilers. The resistance to strain induced corrosion cracking (SICC) was determined by measuring the “repassivation” behaviour of the steels at freshly ground surfaces with an electrochemical technique. The corrosion current measured with time was used to calculate the cracking rates of a compact tension specimen.

A correlation was found between chemical composition, corrosion resistance to SICC and experiences under practical conditions. The results of early‐published papers on boiler corrosion (testing in FeCl₂ solutions), erosion corrosion (testing in wet steam at 20 bar), nitrate stress corrosion cracking (testing in NH₄NO₃ solutions) and SICC together with those originating from in‐service failures, were compiled into a reference database. This paper is a compilation of this work too.

The database and formulas presented make clear there is often a direct correlation between chemical composition of ordinary C‐steel and mentioned types of corrosion failures. The paper is of importance to designers, failure analysts and researchers.

Whilst it is generally agreed that the key determinant of the current money wage inflation is anticipated increases in prices, there remains a significant role for excess demand variables. Many of the studies on inflation which have appeared following the original expositions of the Phillips curve relationship have been concerned with producing efficient measures of excess demand variables. In the basic model developed by Phillips and Lipsey, the key determining variable of the rate of growth of money wages was taken to be the percentage rate of unemployment in the labour force. However, several recent contributors to the literature on this type of relationship have challenged the efficiency of the level of unemployment as a measure of excess demand for labour and specifically they have produced evidence which contradicts the central assumption of stability between unemployment and aggregate excess demand. In the U.K. it has been observed how since the end of 1966, Phillips type relationships between levels of unemployment and the rate of change of money wages appear to have broken down and apparent ‘discontinuities’ in the aggregate unemployment series have been noted. All these findings taken together with some earlier U.S. studies which found poor relationships between changes in wages and unemployment levels (see, for example, the discussion in) have concentrated attention on the search for superior measures of excess demand.

Introduction The ever increasing demands made on materials by advanced technology has led, in recent years, to a greater awareness of the importance of mechano‐chemical behaviour. These may be defined as the synergistic effect of mechanical forces and chemical reactions on the material. Although possibly interrelated, three classes of mechano‐chemical reactions have been identified as; stress‐corrosion (SCC), corrosion fatigue (CF) and hydrogen embrittlement. SCC has become one of the ‘in’ subjects of corrosion science during the last decade, while the importance of CF has emerged comparatively recently. In a review of the national corrosion and protection scene in 1970, it was revealed that 62 postgraduate research workers, representing 21% of the total effort in the corrosion and protection field, were involved in mechano‐chemical corrosion studies1. The bulk of these were working on SCC. This large research effort has not resulted in a standardisation of test methods nor, despite several attempts, in a unifying theory for SCC2. The newcomer to the field is faced with a bewildering variety of tests of varying complexity and validity. The supporters of each type of test tend to make exaggerated claims particularly when the test they are advocating is the only one which has caused a particular alloy‐environment system to exhibit SCC.

As part of an ongoing study developing and evaluating the use of programme budgeting (PB) and marginal analysis (MA) within purchasing organizations, conducts a survey of a health authorities’ requirements of a decision‐making tool based on PBMA. PB is a management decision‐making system. It provides a summary of resource use categorized according to the programme or end product to which it applies. This explicit description of current activities focuses attention on competition for resources among programmes and on the effectiveness of resource use within programmes. MA is an economist’s tool to evaluate options for changing the balance of resource use between or within programmes. Finds general support for PBMA techniques, although this waned with the higher functions of the tool. There was consensus that a health authority ought to know fundamentals like, for example, what proportion it spends on tackling coronary heart disease; and a majority view that PB will assist in revealing the key margins for service review

Although the wind of change is blowing strongly through the gas industry a substantial proportion of the gas, for some time to come, will be made by coal carbonisation and by carburetting water gas. Even these more conventional methods will be subject to change such as the choice of lower‐rank coals to produce reactive smokeless solid fuels and the use of light Hydrocarbon oils, such as primary flash distillate, in place of gas oil. This article deals with some of the corrosion problems that arise in these more established types of plant.