Steel structure

Steel structures may be exposed to a variety of corrosive elements  

A clear understanding of the corrosion process is essential to understand the steps to inhibit corrosion with protective coatings. 

Oxygen combines with iron, the major element in steel, to form rust. This electrochemical process returns the iron metal to the state that it existed in nature-iron oxide. The most common form of iron oxide or iron ore found in nature is hematite (FCjOj), which is equivalent to what we call rust. Iron in iron ore is separated from the oxide to yield usable forms of iron, steel and various other alloys through rigorous electrochemical reduction processes. 

The process of combining iron and oxygen, called oxidation, is accompanied by the production of a measurable quantity of electrical current, which is why this is called an electrochemical reaction. For the reaction to proceed, an anode, a cathode and an electrolyte must be present. This is termed a corrosion cell. In a corrosion cell, the anode is the negative electrode where corrosion occurs (oxidation), the cathode is the positive electrode end and the electrolyte is the medium through which an electrical current flows. 

Steel members deterioration may appear either in external corrosion, which would be visible upon inspection, or in undetected changes that reduce its strength. 

Tests to measure the bond which can be obtained with the concrete of the structure to be strengthened are best carried out on the structure itself. A possibility is to utilise a pull-off test as developed for the non-destructive testing of concrete(21). A circular steel probe is bonded to the concrete surface and specially designed portable apparatus is then used to pull off the probe, along with a bonded mass of concrete, by applying a direct tensile force. Any defects in bond would be revealed by the occurrence of failures at the adhesive-concrete interface. 

Studies into the use of adhesives in the fabrication of metal bridge parapets have been called for because it is difficult to obtain adequate welded connections between lengths of horizontal rail. The rails are generally rectangular hollow sections and for a welded joint different electrodes have to be used for the top and bottom 

For applications in new bridge construction a design life of 120 years is required(25). Although it may be possible to design out fatigue and creep by keeping working stresses low(26) the influence of the environment on adhesives over such a time span is very much 

In Chapter 8 two potential applications for the bonding of structural steelwork will be considered in some detail. These are bonded web stiffeners and tension splices or cover plates to girder flanges. 

Production platforms are coated only in exceptional cases or for the purposes of investigation because the life of the structure is greater than the life of the coating. Therefore in the design of the cathodic protection, only the protection potential Us of the steel need be considered. Steels with an ultimate tensile strength of up to 350 N mm are used for these structures, which are weldable even in thick sections, and the hardness of the welded material can be kept to 350 HV (see Section 2.3.4 [2,10]). Aluminum anodes with the same protection effect and life as zinc anodes have much less weight. This is a very important advantage for 

The anode mountings are welded to lap joints in the yard, and the anodes are installed at a minimum distance of 30 cm from the structure to achieve the most uniform current distribution [1-3]. Nonuniform potential distribution occurs even with this distance. 

Nodal points of the platform require special attention for corrosion protection. Therefore the anodes have to be installed in the vicinity of these points, as indicated in Fig. 16-4. The spacing must be sufficiently large that the welded joints of the nodes do not lie in the area of the lap joints. The effort for calculating the optimal distribution with the lowest weight of anodes is considerable and has led to computer programs by which the anode distribution can be estimated [11], 

The difficulties of such operations on the research platform Nordsee are described in Ref. 9. The Murchison platform was provided with a combination of impressed current protection and galvanic anodes because there was a limit to the load to be transported [12]. The anodes for platforms are installed and provided with cables at the yard. They are installed with redundancy and excess capacity so that no repairs are necessary if there is a breakdown. The lower part of the platform up to the splash zone is usually placed in position in the designated location at least 1 year before the erection of the deck structure so that impressed current protection cannot initially be put in operation. This requires cathodic protection with galvanic anodes for this period. This also means that the impressed current protection is more expensive than the galvanic anodes. 

New types of anodes have been developed and tested as shown in Fig. 16-5 to improve the possibility of maintenance and repair. They can be lifted onto a ship and repaired. The connecting cables are also replaceable. In shallow water, the anchorage must be accurately calculated because considerable dynamic stressing can occur in heavy seas. The ocean floor must be suitable for long-term anchorage. No supply ships must anchor in the area around the platform. This requirement alone often prevents the installation of impressed current anodes since the operator does not wish or is not able to restrict himself to these conditions. 

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The manifold is typically a tubular steel structure (similar to a template) which is host to a series of remotely operated valves and chokes. It is common for subsea tree control systems to be mounted on the manifold and not on the individual trees. A complex manifold will generally have its own set of dedicated subsea control modules (for controlling manifold valves and monitoring flowline sensors). 

The method has been utilized for stress investigation in bridges and other steel structures to determine production stresses or stresses originating from body weight, etc. [1 - 4]... 

Residual austenite is a steel structure which during cooling at martensite transformation temperature is not completely converted into martensite and remains unchanged at room temperature together with martensite. 

Application of Surface SH Wave s Detection Standard for the Ultrasonic Inspection of Weld Defects in Steel Structures, 3rd Revision, Architectural Institute of Japan, P27, (1996)... 

Table 2. Properties of Steel Structures for a Eutectoid Steel...

J. D. Keane and co-eds.. Good Painting Practice, 2nd ed.. Steel Structures Painting Council, Pittsburgh, Pa., 1982. 

C Steel structures and platforms (other than buildings)... 

A typical drive-in rack consists of a steel structure to support palletized goods at the pallet edge, with the center of the pallet unsupported. The space between pallet support members is sufficient to permit a lift truck to drive in to place or retrieve a load. These racks are usually made to accommodate 12 pallets, which are positioned from the seiwice aisle to the end of the rack. Because of the rack, each pallet position has the abihty to hold 6 to 8 pallets vertically. 

Copper is a galvanic metal and causes corrosion, in the presence of moisture, in nearby metals, such as cable sheathes, steel structure and water, gas or drain pipes, buried in its vicinity. With all such metafs. it forms a complete electrolytic circuit and corrodes them. Tinning may give protection against its galvanic effects but this is ati expensive proposition... 

Many steel structures - like bridges, storage tanks, and ships - are held together by welds. And when incidents arise from fast fractures or fatigue failures they can often be traced to weaknesses in the welds. The sinking of the Alexander Keilland oil platform in 1980 is an example. 

The toughness of wood is important in design for exactly the same reasons that that of steel is it determines whether a structure (a frame building, a pit prop, the mast of a yacht) will fail suddenly and unexpectedly by the propagation of a fast crack. In a steel structure the initial crack is that of a defective weld, or is formed by corrosion or fatigue in a wooden structure the initial defect may be a knot, or a saw cut, or cell damage caused by severe mishandling. 

The requirements (a) to (c) are obligatory for all types of coating and all objects to be protected for example, they are well known in the protection of steel structures. The objects discussed in this handbook are continuously in contact with electrolytes. For this reason in addition, requirement (d) is of great importance and is discussed in detail below. 

The railway lines on bridges are often electrically connected with steel or reinforced steel structures which usually have a very low grounding resistance. In new installations, an electrical separation of the rails from the bridge structure is required according to the grounding resistance of the structure and the type of rail bed. Independent of this, pipelines and metal sheathing of cables are always electrically separated from the structure in order to exclude direct transmission of stray current from the rails in these conductors. 

Nonuniform corrosion or pitting corrosion frequently occurs on steel structures in seawater and in soil. Nonuniform and pitting corrosion easily lead to damage in tanks, pipelines, water heaters, ships, buoys and pontoons, because these structures lose their functional efficiency when their walls are perforated (see Chapter 4). 

No one steel exceeds the tensile modulus of mild steel. Therefore, in applications in which rigidity is a limiting factor for design (e.g., for storage tanks and distillation columns), high-strength steels have no advantage over mild steel. Stress concentrations in mild steel structures are relieved by plastic flow and are not as critical in other, less-ductile steels. 

Organic coatings are applied mainly to mild steel structures and equipment. They are also used on aluminum, zinc-sprayed and galvanized steel, but to a lesser extent. The applications for organic coatings can be divided into three areas corrosion by atmospheric pollution, protection from splash by process liquors, and linings for immersion in process liquors [70-74]. 

Boyd, G. M., Brittle Fracture of Steel Structures (London Butterworths, 1970). 

British Standard Code of Practice CP2008 Protection of Iron and Steel Structures from Corrosion, 69. ... 

MKI The Mark I containment consists of two separate structures (volumes) connected by a series of l.irae pipes One volume, the dry well, houses the reactor vessel and primary system components. The other i oUmic is a torus, called the wetwell, containing a large amount of water used for pressure suppression and as, i heai sink. The Brunswick units use a reinforced concrete structure with a steel liner. All other M,uk 1 cnni.un ments are free-standing steel structures, The Mark I containments are inerted during plant oper.mon i. prevent hydrogen combustion. 

Sprinkler and water spray installations-Many process and storage area buildings should be protected by automatic sprinkler systems. The size and arrangement for water supply are dependent upon the nature of the hazard and the degree of protection desired. Water spray installations are particularly adapted for cooling uninsulated steel structures, elevated pipe lines, vessels, spheres, and similar plant installations. 

No. 1 Pictorial Surface Preparation Standards for Paindng Steel Structures... 

The API Standard 4F, First Edition, May 1, 1985, API Specifications for Drilling and Well Servicing Structures, was written to provide suitable steel structures for drilling and well servicing operations and to provide a uniform method of rating the structures for the petroleum industry. API Standard 4F supersedes API Standards 4A, 4D, and 4E thus, many structures in service today may not satisfy all of the requirements of API Standard 4F [2-5]. 

AISC specifications for the design fabrication and erection of structural steel for buildings shall govern the design of these steel structures (for AISC specifications, see the current edition of Steel Construction Manual of the American Institute of Steel Construction). Only Part I of the AISC manual, the portion commonly referred to as elastic design, shall be used in determining allowable unit stresses use of Part II, which is commonly referred to as plastic... 

Structural Steels. Structures shall conform to sections of the AISC Specifications for the Design, Fabrication and Erection of Structural Steel Buildings."... 

Galvanized wire guy strand shall conform to ASTM A-475 Zinc-Coated Steel Wire Strand. Aluminized wire guy strand shall conform to ASTM A-474 Aluminum Coated Steel Wire Strand. Galvanized structural strand shall conform to ASTM A-586 Zinc-Coated Steel Structural Strand. Galvanized structural rope shall conform to ASTM A-603 Zinc-Coated Steel Structural Wire Rope. ... 

Asphalt Asphalt is a natural occurring mineral or as the residue from the distillation of asphaltic petroleum. It is less brittle and has better resistance to sunlight and temperature changes than coal tar enamel. Its water resistance is good but less than for coal tar enamel. It is not resistant to solvents or oils. It may crack at low temperatures and age at elevated ones. Like coal tar enamels, it is primarily black in color and difficult to overcoat with other materials. Its main use is for the in-situ coating of roofs or aboveground steel structures. 

British Standards Institution, BS 5493 1977, Code of Practice for protective coatings of iron and steel structures against corrosion. 

Chandler, K. A. and Bayliss, D. A. Corrosion Protection of Steel Structures, Elsevier Applied Science, Barking (1985). Department of Trade and Industry, Committee on Corrosion Guides... 

No. 16 Engineering coatings - their applications and properties. Durability of steel structures, CONSTRADO. 

Other inspection services available include the examination of steel structures (new and existing), electrical wiring installations, containers (to meet Statutory Instm-ment No. 1890), dangerous substances (carriage by road in road tankers or tank containers) to meet Statutory Instmment No. 1059, examination of second-hand plant prior to purchase, plant undergoing repair or modification, the Control of Industrial Major Accident Hazard Regulations (CIMAH) Statutory Instmment No. 1902 and Control of Substances Hazardous to Health (COSHH) and Pressure Systems Regulations. 

Galvanic corrosion is the enhanced corrosion of one metal by contact with a more noble metal. The two metals require only being in electrical contact with each other and exposing to the same electrolyte environment. By virtue of the potential difference that exists between the two metals, a current flows between them, as in the case of copper and zinc in a Daniell cell. This current dissolves the more reactive metal (zinc in this case), simultaneously reducing the corrosion rate of the less reactive metal. This principle is exploited in the cathodic protection (Section 53.7.2) of steel structures by the sacrificial loss of aluminum or zinc anodes. 

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