Fretting Corrosion Products of Aluminium Alloys

Abstract

An examination of a black powder produced by the fretting of aluminium alloy surfaces in a ship's hold has been carried out.

The fire risk associated with the accumulation of this type of material in confined spaces has been considered.     

Carburisation and creep phenomena in high‐alloy materials for ethylene pyrolysis furnaces

Summary

This paper reviews the various factors forming a basis for selecting high‐temperature (1100 °C) alloys for ethylene pyrolysis furnaces.

We discuss in particular the phenomenon of carburisation with carbon diffusion in the metal matrix and its resistance to viscous creep, particularly the phenomenon of secondary creep.

Both of these phenomena are discussed as a contribution to judicious selection of such alloys.     

Mechanical properties of joints welded in creep-resistant low-alloy T24 steel

Summary

During TIG welding of Zircaloy‐2 tubing in an atmosphere in which the air partial pressure P_AIR decreases as high‐purity inert gases are introduced into a chamber evacuated to various pressures, the arc voltages were measured, and the properties of the welds were examined.

The arc voltage increases with a decreasing P_AIR in the welding atmosphere.

The nitrogen content [N] in the weld metal varies in each circumferentially divided zone, with a linear relationship between √SRP_NZ and [N] being found.

The thickness of the surface oxide films after long‐term autoclave tests in water at high temperature and pressure was also measured and evaluated.     

The influence of bending on stress fields and fatigue strength of cruciform welds

Summary

This paper deals with stress fields in the vicinity of weld toes of cruciform non‐load carrying fillet welds.

An approach recently formulated for welded joints under remote tensile loading is extended to pure bending as well as to bending and shear conditions. The approach is based on two notch stress intensity factors that independently quantify Mode I and Mode II stress distributions.

The new method provides an analytical framework to a stress field criterion, already proposed by Atzori some years ago and more recently by Pluvinage and Verreman, to determine the fatigue strength of a welded joint.     

New technology of the arc welding

Summary

This paper describes the effect of evaporation during laser welding, especially its effect on keyhole formation. In order to investigate the evaporation, a numerical model of evaporation at the molten pool surface of laser welding was developed. The effect of evaporation during laser welding was numerically analysed by the model and the numerical result compared with experiments. This paper may be summarised as follows:

1. It is made clear by the numerical results that the molten pool geometry in laser welding is markedly affected by the evaporation process.

2. Numerical results show that evaporation of the molten pool surface produces a recoil pressure and a keyhole is formed as a result.

3. A calculated critical condition for keyhole formation has been compared with experiments and a satisfactory result has been obtained.

     

Fatigue design of offshore structures

Abstract

The paper describes problems relating to the fatigue analysis of offshore structures subject to cyclic wave loading.

The parameters having the greatest influence on the fatigue life of welded tubular nodes are discussed and a design procedure reflecting the latest trends in offshore engineering is presented.     

Fatigue strength of components with coatings made of self-fluxing alloys

Abstract

The influence of different types of buffer layer for type 308 austenitic stainless steel surface overlays with 19-21% chromium and 10-12% nickel contents was analysed.

The cladding passes were deposited on carbon steel test samples by the automatic submerged-arc welding process.

Experimental tests were conducted on buffer layers having seven different chemical compositions and the results obtained are reported and discussed in the article.

The experimental results allow the selection of the most suitable buffer layer to be deposited in order to obtain the required cladding performance in service.     

Hexamethylenetetramine Hydroiodide (HMTA-I) as a Corrosion Inhibitor for Steel in HCI Pickling Solutions

Abstract

The effect of hexamethy lenetetramine. hydroiodide (HMTA-I) as a corrosion inhibitor of steel in aqueous hydrochloric acid solutiOns has been investigated and its behaviourexamined as a function of HCI and inhibitor concentrations.

A comparison with the inhibitive efficiency of hexamethylenetetramine (HMTA) shows that HMTA-I iS more efficient than HMTA, espcially at lower acid concentrations.

Polarisation mesaurements show that the chemisorption of iodide anions and organic cations increases the overpotential for both hydrogen-ion discharge and metal ionisation.

The adsorption oforganic cations, which in the case of HMTA is appreciable only at high HCI concentrations, iS enhanced in the case of HMTA-I by iodide adsorption at anodic areas.

The surface coverage in 2M HCl has been calculated and the semi-empirical isotherm of Freundlich has been found to fit the results over the entire range of inhibitor concentration studied (up to 10^–2M ).     

Nature of the Oxide Film Present on Iron after Inhibition in 0·05 M Chromate Solutions

Abstract

Chemical and microprobe analyses have been used to study the composition of the oxide films formed on iron by 0·05 M potassium chromate, pH 4–8.

Chemical analyses have shown that the air-formed oxide film was thinned and evenly reinforced with a normal iron chromium spinel having a composition in the range Fe²⁺ (Fe³⁺_0·5 Cr³⁺_1·5)O₄ — Fe³⁺ Cr³⁺ O₃

Microprobe analyses indicated enrichment of chromium at scratch lines, but the effect was small compared with the overall thickening of the films.     

Tests on joints between steel and graphite

Abstract

Under a research programme devoted to the study of metalceramic joints, which are of considerable importance in the field of advanced technology, various tests were performed on joining carbon steel to graphite by brazing with different filler metals.

The results of each test are reported, with particular emphasis on the quality of the welded joint. The structural stability of the joints was also verified by long term annealing treatments at high temperature (850°C).     

The Influence of Surface Preparation on The Kinetics of Film Growth on Mild Steel in Chromate Solutions

Abstract

Film growth on mild steel in chromate solutions was found to be logarithmic with respect to time for all types of surface preparation tested; these included polished, abraded, pickled and grit-blasted surfaces. Growth constants, and also the monolayer uptake of‘labelled’ chromium, Cr^*, before logarithmic film growth started, varied in a similar fashion as different types of surface preparation were used.

Relative values of surface roughness factor (S.R.F.) calculated from relative values ofgrowth constants agreed with published values of S.R.F. for comparable suffaces, where these were available.

It is suggested that measurements of Cr^* uptake with respect to time made instandardised conditions could be used as a method of determining relative S.R.F.     

Thermal elastic‐plastic stress‐strain analysis considering temperature rise due to plastic deformation under dynamic loading in undermatched joints study of dynamic deformation and fracture properties of welded joints with strength heterogeneity (Report 1)

Summary

This paper describes an automatic welding system that can simultaneously control the bead height and back bead shape during one‐sided MAG welding with a backing plate. The system uses a high‐speed rotating arc welding process together with an arc sensing technique for seam tracking and torch height control.

The arc sensing technique is also used to detect variations in the groove shape. The detection mechanism is described in detail in this paper.

The system further uses a newly developed welding parameter control method in which only the wire feedrate and welding voltage are adaptively controlled, the other welding conditions being kept constant. This method is able to keep the bead height constant and retain the back bead shape even if the groove shape changes.

Initial welding experimental results have shown the system to be effective and satisfactory for controlling the weld bead shape in one‐sided GMAW (MIG/MAG) with a backing plate.     

The exfoliating corrosion of cupro-nickel feed-water heater tubes

Abstract

The exfoliating corrosion which occurs on the steam side of cupro-nickel feed-water heater tubes is described, together with a laboratory investigation designed to study the effect of operational variables such as condensaiion, temperature, pressure, thermal cycling and oxygen admission on the corrosion of cupro-nickel alloys.

Corrosion similar to that occurring on feed-heater tubes could be reproduced only in high-pressure steam containing oxygen. An explanaiion is given of the incidence and mechanism of corrosion and practical remedies are suggested.     

Electron beam hardening for the regeneration of turbine blades

Abstract

Wear-resistant protective zones, restricted to pre-set areas on the rotor blades of turbines and made from heat-treatable steels alloyed with chrome, can be produced efficiently by electron beam (EB) hardening. The EB plant of type ESA 150-MR is suitable for carrying out hardening processes on small numbers of blades in combination with a component-specific positioning device.

The method and instruments described here were used to make a fairly large number of turbine blades fit for use again by reconstruction after destruction by erosion.     

Flux cored arc welding — the state of the art and current applications

Abstract

The advantages and potential applications of flux cored welding are reported, together with a review of process developments and the situation internationally.     

Welding characteristics of heavy-gauge plates for nuclear vessels

Abstract

The results are given of the characterisation of a weld made on a plate of A533B C1 1 steel, used in the construction of BWR nuclear vessels.

The work was carried out under an ENEL-CRTN research programme conducted at the CISE for the study of the structural integrity problems of the primary circuit components of BWR nuclear plants, and focused in particular on the application of fracture mechanics techniques.

The weld was made transversely by automatic submerged-arc welding on a 136mm thickness plate.

The parent metal, the weld and the HAZ were characterised from both the microstructural and the mechanical points of view; in particular, the fracture toughness properties up to 300°C were determined, under both static and dynamic conditions.

The fatigue crack propagation was also studied in an environment simulating the plant operating conditions.     

Influence of Surface Condition on the Corrosion of Aluminium Brass

Abstract

The corrosion behaviour of aluminium brass, with four different surface treatments (highly and lightly oxidised, pickled and sandblasted), was studied in natural sea water, both stagnant (aerated) and flowing.

Electrochemical measurements and weight loss determinations showed that the oxide film produced during industrial annealing had little effect on the corrosion rate as compared with a pickled surface, in both stagnant and flowing conditions. Sandblasted surfaces were inferior.

Measurements of currents flowing in galvanic couples formed between oxidised and stripped metal were small and decreased with time, but the oxidised surfaces appeared to be slightly more vulnerable than the pickled ones to localised corrosion. Some further work is needed here.     

The corrosion of aluminium in solutions of sodium fluoride and sodium chloride

Abstract

The corrosion of 99·997% aluminium by 0·1 N-sodium fluoride and chloride has been examined in the presence of air over the pH range 2—13. When a solution of either salt was saturated with aluminium oxide, corrosion was arrested.

Under anaerobic conditions, 0·1 N-sodium fluoride attacked the air-formed oxide film and corrosion was rapid, in contrast no corrosion was observed in 0·1 N-sodium chloride solution.     

Interfacial Corrosion of Brazed Stainless Steel Joints in Domestic Tap Water. II. Metallographic aspects

Abstract

Previous work has indicated that interfacial corrosion of brazed stainless steel joints in domestic tap water is probably associated with a selective dissolution of one component of a lamellar eutectic structure, which thereby provides easy access to the interface for the aqueous environment.

The metallographic features of the phenomenon have now been explored in more detail in order to characterise the structural changes taking place. A tentative mechanism is proposed to explain the changes observed at the interface where copper is found to be deposited.     

Optimisation of the composition of KH20N45M3B welding wire

Summary

The main aim of this research is to investigate the suitability of ‘tailored blanks’, fabricated with laser welding technology, prior to forming. It is also a review of their fatigue and corrosion behaviour.

During the experiments, laser-welded joints were performed using different steel/thickness combinations, most commonly used in today's automobile industry. Joints were assessed by metallographic examination, as well as by pressing, fatigue and corrosion tests.

In order to evaluate the suitability of ‘tailored blank’ technology on an actual automotive component, a suspension mounting was produced by joining, using both laser and roller resistance welding, two FePO4 bare steel sheets of different thickness (1.5 and 2 mm).

Fatigue strength of the lighter component has generally produced comparable results to the standard component made in a single thickness (2 mm). This confirms the suitability of ‘tailored blank’ technology to save body weight and optimise material utilisation.