B. Hou

Effect of alloy elements on the anticorrosion properties of low alloy steel

Effect of alloy elements on corrosion of low alloy steel was studied under simulated offshore conditions. The results showed that the elements Cu, P, Mo, W, V had evident effect on corrosion resistance in the atmosphere zone; Cu, P, V, Mo in the splash zone and Cr, Al, Mo in the submerged zone.

Corrosion of C-Mn steel in simulated tidal and immersion zones

Abstract Experiments to simulate the corrosion of a mild steel (designated A3) in the open sea have been conducted to explain observed differences between the behaviour of suspended specimens that were electrically connected together on the one hand and unconnected on the other. Reasons for differences between the corrosion behaviour of individually suspended specimens in the laboratory and that of steel in a marine service environment have also been investigated. The effect on corrosion of the ratio of water depth in the tidal zone to that in the immersion zone has also been studied.

Chromate passivation of hot dipped Zn25Al alloy coatings

Abstract A low concentration chromate passivation treatment has been successfully applied to a new type of hot dipped Zn2 5Al alloy coating, and the corrosion resistance of the chromate passive film has been assessed using the copper accelerated acetic salt spray (CASS) test, electrochemical measurements, and sea water immersion testing. The results showed that the corrosion resistance of the Zn2 5Al alloy coating was significantly better after the chromate passivation treatment. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses showed that the composition (at.-%) of the low concentration chromate passive film was: 5·5S–3·4Na–11·8C–7·9Ti–41·6O–1 3·7Cr–16·0Zn. Aluminium was not found in the film, which is attributed to the dissolution behaviour of the Zn2 5Al alloy coating in acidic chromate solution.

Corrosion of mild steel in sea mud containing sulphate reducing bacteria

Abstract In this work, the corrosion behaviour of a mild steel was studied in a sea mud extracted solution in the absence and presence of sulphate reducing bacteria (SRB) by electrochemical impedance spectroscope measurements and scanning electron microscope characterisation. The presence of SRB in the sea mud extracted solution affects corrosion of steel remarkably. In the absence of SRB, the steel corrosion is somewhat inhibited by the formed corrosion product layer. However, the addition of SRB enhances corrosion of the steel due to its metabolism activity. It is speculated that the formed sulphide product may experience transformation decreasing the protectiveness of the product layer. Dans ce travail, on a étudié le comportement à la corrosion d’un acier doux dans une solution extraite de la boue marine, avec ou sans la présence de bactéries sulfatoréductrices (SRB), au moyen de mesures au spectroscope de l’impédance électrochimique et de la caractérisation au microscope électronique à balayage. La présence de SRB dans la solution extraite de la boue marine affecte la corrosion de l’acier de façon remarquable. En absence de SRB, la corrosion de l’acier est quelque peu inhibée par la couche formée par le produit de la corrosion. Cependant, l’addition de SRB augmente la corrosion de l’acier à cause de l’activité de son métabolisme. L’hypothèse est que le produit sulfuré formé peut se transformer, diminuant ainsi l’effet protecteur de la couche produite.

Study on growth factors of intermetallic layer within hot-dipped 25% Al-Zn alloy coating on steel

Abstract25% A1-Zn alloy coating performs better than hot dip galvanized coating and 55% A1-Zn-Si coating with regard to general seawater corrosion protection. This study deals with the interfacial intermetallic layer’s growth, which affects considerably the corrosion resistance and mechanical properties of 25%A1-Zn alloy coatings, by means of three-factor quadratic regressive orthogonal experiments. The regression equation shows that the intermetallic layer thickness decreases rapidly with increasing content of Si added to the Zn-Al alloy bath, increases with rise in bath temperature and prolonging dip time. The most effective factor that determined the thickness of intermetallic layer was the amount of Si added to Zn-Al alloy bath, while the effect of bath temperature and dip time on the thickness of intermetallic layer were not very obvious.

Study on steel corrosion in different seabed sediments

A series of simulation experiments on carbon steel (A3 steel) and low alloy steel (16 Mn steel) in marine atmosphere (MA), seawater (SW) and seabed sediment (SBS) including rough sea sand, fine sea sand and seabed mud were carried out indoors for a year or so by means of individually hanging plates (IHP) and electrically connected hanging plates (ECHP). The corrosion of steels in SBS was mainly due to the macrogalvanic cell effect. The steel plates at the bottom of SBS, as the anode of a macrogalvanic cell, showed the heaviest corrosion with a corrosion rate of up to 0·12 mm/a, approximately equal to that of steel plates in marine atmosphere.The test results showed that the corrosion rates of A3 and 16 Mn steel in marine environment were in the order: MA>SW>SBS by the IHP method; and MA>SBS>SW by the ECHP method. The corrosion rates of steels in the water/sediment interface were directly proportional to the grain size of the SBS by the ECHP method, but those of steels in the water/sediment interface did not vary with the grain size of SBS by the IHP method. The corrosion rate of low-alloy steel was a little higher than that of carbon steel. The results of this study have important applications for design of offshore steel structures such as oil platform, pier, and port.