Weldability of Steels...

Weldability of Steels There are several factors which control the weldability of carbon (C) and low alloy steels in electric arc welding. A good understanding of the chemical and physical phenomena which occurs in the weldments is necessary for the proper welding of the different steels. Operational parameters, thermal cycles, and metallurgical factors affecting the weld metal transformations and the susceptibility to hot and cold cracking are some of the factors which have marked influence on the weldability of steels. There are also some common tests which determine the weldability of steel. The C and low alloy steels represents a large number of steels which differ in chemical composition, strength, heat treatment, corrosion resistance, and weldability. These steels can be categorized as (i) plain C steels, (ii) high strength low alloy (HSLA) steels, (iii) quenched and tempered (QT) steels, (iv) heat treatable low alloy (HTLA) steels, and (v) pre-coated steels. To understand weldability of steels, it is necessary to have knowledge about the various weld regions. Characteristic features of welds Single pass weldments In the case of a single pass bead, the weldment is generally divided into two main regions namely (i) the fusion zone, or weld metal, and (ii) the heat affected zone (HAZ) as shown in Fig 1. Within the fusion zone, the peak temperature exceeds the melting point of the base steel, and the chemical composition of the weld metal depends on the choice of welding consumables, the base steel dilution ratio, and the operating conditions. Under conditions of rapid cooling and solidification of the weld metal, alloying and impurity elements segregate extensively to the centre of the inter-dendritic or inter-cellular regions and to the centre parts of the weld, resulting in significant local chemical in-homogeneities. Therefore, the transformation behaviour of...

Contingency Planning

Contingency Planning Unforeseen threats never knock on the door before their arrival. They just arrive and destroy everything that comes in their path. Contingency planning provides protection against these unforeseen threats. In the case of an organization, contingency planning covers failures of critical systems, equipment, automated processes, energy, communications, suppliers, personnel, and natural calamities. It consists of the actions taken by the organization to prepare the organization for an impending emergency. It is a management tool used to analyze the impact of potential crises so that adequate and appropriate arrangements are made in advance. It is general enough that it confers different ideas to different disaster managers and emergency personnel, depending on their circumstance and area of concern. The cost to implement and activate a contingency plan can be high, but the impact of its absence is prohibitive. Further if a small contingency is not curtailed in time then it can create a snowball effect and rapidly generate a greater crisis. In the organization, it is essential to have mechanisms that ensure constant operation. When there is an unexpected disruption, an appropriate contingency plan can make a huge difference. The definition of an optimal contingency plan is a complex problem involving diverse resources such as systems, equipment, spare parts, services, and specialized manpower etc. The contingency solution involves alternative processes and recovery strategies so that in the case of a contingency, all the necessary resources are available in order to bring the system back to normal operation using the minimum resources and in the least possible time. Chinese general Sun Tzu has said, “Plan for what is difficult while it is easy, do what is great while it is small. The difficult things in this world must be done while they are easy; the...

Importance of Hearth, Dead man and Tapping in Blast Furnace Operation Apr13

Importance of Hearth, Dead man and Tapping in Blast Furnace Operation...

Importance of Hearth, Dead man and Tapping in Blast Furnace Operation  A trend of deterioration in ore quality is seen these days with the increasing demand for iron ore. The deterioration in ore quality is accompanied with higher quantities of slag which in turn affects burden descent and liquid flow through the hearth. These conditions provide a catalyst for lining wear mechanism with bosh, stack and hearth linings coming under additional stress. Tapping in the blast furnace is adversely affected and trough and runners in the cast house get under strain due to higher slag volume. All these put increased pressure on blast furnace operations. The poor quality of iron ore affects the operation of the blast furnace in the following way. Slag volume – Poor quality of iron ores bring into the furnace higher quantities of impurities resulting into increase in the slag volumes. Heat load – The furnace thermal condition undergoes changes since a large quantity of heat is required to melt the additional slag as well as to keep it in proper fluid state for its drainage. This introduces higher heat loads inside the blast furnace. Coke rate and productivity – Increasing slag volumes needs a higher fuel input into the furnace, and where pulverized coal injection rates are already running at optimum, this results into a higher coke rate. Higher coke means introduction of higher amount of ash in the furnace resulting into further increase in the slag volume. This has got a deteriorating effect on the productivity of the furnace. Process stability – The deterioration in the ore quality affects the process stability adversely and has an unfavourable effect on the smooth running of the blast furnace. Due to the above factors, the production process in the blast furnace...