Surface preparation steel constructions

Surface Preparation. Steel hot rolled at 800-900 °C acquires a tenacious oxide layer (mill scale) that is cathodic with respect to the steel to the extent of about 300 mV. In the presence of an electrolyte (seawater containing 3.5% salts, mainly sodium chloride) the steel would corrode and pit and roughen severely. The first process in new construction and refurbishment is therefore the complete removal of mill scale. A small amount of very light-gauge steel is prepared by acid pickling, but most steel for ship and off-shore construction is centrifugally or pneumatically blasted with steel shot that can be recycled or with expendable abrasive grit. Freedom from scale and soluble salt contamination are the main requirements, texture and profile are less important [11.13],... 

In the practice of adhesive bonding for applications in construction, surface pretreatment is likely to be the most difficult process to control. The choice of treatments must be tempered by the scale of operations, the nature of the adherends, the required durability, the adhesive to be used, and the cost. The performance of joints constructed with cold-cure epoxies is likely to be critically dependent upon surface preparation, as exemplified by the experience of the Scottish Irvine Development Corporation. In 1978 they elected to use vertical externally-bonded steel plate reinforcement to strengthen the abutment walls of three pedestrian underpasses. A year later, the plates were reported to be falling off, accompanied by extensive interfacial corrosion the steel surfaces had been abraded by hand, and the concrete surfaces chemically etched. 

Only heavy abrasives can be used in preparing steel surfaces for painting. Lighter abrasive media, such as apricot kernels, plastic particles, glass beads or particles, and walnut shells, are unsuitable for heavy steel constructions. Because of their low densities, they cannot provide the amounts of kinetic energy that must be expended upon the steel s surface to perform useful work. In order to be conunerdally feasible, an abrasive should be ... 

Hydrogen is the principal gas released by dense metals. The surface preparation of stainless steel, commonly used in the construction of vacuum vessels, determines the surface composition/chemistry, desorption, and outgassing properties of the material. Aluminum is also used in the vacuum environment and the outgassing properties of this material have been studied. Glasses may outgas water and other gases at very high temperatures. 

Requirements of the adhesive. A full compliance spectrum for steel/concrete bonding has been published by the authors(18) and is reproduced as an Appendix at the end of the book. The purpose of the adhesive is to produce a continuous bond between steel and concrete to ensure that full composite action is developed by the transfer of shear stress across the thickness of the adhesive layer. Experience has shown that the best chance of success is likely to be achieved by using cold-cure epoxy based adhesives which have been specially developed for use in the construction industry. Provided that the surfaces have been prepared properly, these bond well to both steel and concrete and do not suffer shrinkage and cracking problems such as may occur with other systems like polyesters. For these purposes a cold-cure adhesive is defined as one which is capable of curing to the required strength between the... 

To prevent galvanic corrosion, the CFRP is constructed on GFRP applied to steel surface. The procedure used for preparation of termination detail must avoid damage to the steel cylinder. Any damage, including gouges and punctures, needs to be repaired prior to CFRP system installation. 

Larger membrane modules having surface area about 700 - 800 cm were also prepared and tested. These modules were constructed using about 80 -100 PEI hollow fibers of 35 cm length. These fibers were potted at both ends using epoxy resin into 11/4 inches diameter steel tube having an outlet on the side. The module was sealed at both ends by means of steel end caps fitted with 0-rings. Fiber lumens were open at both ends. 

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