Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking Sep23

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking...

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking Arc welding is a process by which steels are joined by coalescence. Normally the process uses a compatible filler material. Before a well-bonded joint is produced, the joint surface is to be heated above the melting temperature in order to completely fuse with the weld metal. Though the metallurgical reactions which involve melting, solidification, and solid-state transformation are not unusual, the temperatures and cooling rates observed are severe. Active gases also are present and can dissolve in the fused steel. Fluxes are introduced to alloy with and protect the weld metal. Generally, joints are rigid and restrain dimensional changes caused by shrinkage and solid-state transformations, producing residual stresses of yield-strength (YS) magnitude. Since the metallurgical changes do not occur under equilibrium conditions, and since the stresses are high, many of the reactions can take place in either or both the weld metal and the heat affected zone (HAZ) of the steel and can produce defects that weaken their soundness. Because of the tremendous variability of the welding processes, it is difficult to provide much detail about the exact mechanisms involved or the corrections that can be made. Furthermore, many corrective measures are obvious once most defects are explained. One problem, which relates to hydrogen (H2), is not simple. Since this problem is becoming more relevant as more high-strength, low-alloy (HSLA) steels are being welded, the subject of hydrogen-induced cracking (HIC) is very important. Carbon (C) and low alloy steels are welded since they have widespread application and good weldability. This usefulness is mainly due to the metallurgical characteristics of the iron (Fe) base system. The characteristic includes the ability to undergo allotropic (microstructural) transformation which allows the opportunity for hardening and strengthening through...

Pipe and Tubular Products of Steel...

Pipe and Tubular Products of Steel The term pipe and tubular product of steel is the used to cover all hollow products of steel. These products are normally produced in cylindrical shape. However, they are frequently altered by different processing methods to produce square, oval, rectangular, and other symmetrical forms. Pipe and tubular products have a large number of applications, but they are most commonly used for conveying of fluids and as structural members. Steel pipe and tubular products are normally produced from wrought carbon (C) or alloy constructional steels and are usually designated by the terms pipe, specialty tubing, and oil country tubular goods (OCTG) etc. Pipes and tubular products have an outside dimension, an inside dimension and the wall thickness as shown in Fig 1. Fig 1 Dimensions of pipe and tubular products The steel pipe and tubular products are usually classified broadly as (i) pipe, and (ii) tube. The application of the terms pipe and tube is not always consistent. The term pipe is normally used to describe cylindrical products made to standard combinations of outside diameter and wall thickness. The main difference between a pipe and a tube is the way the diameter of the pipe or tube is designated. Pipe is normally designated by a “Nominal Pipe Size” based upon the ID (inside diameter) of the most common wall thickness while the tube is designated by the measured OD (outside diameter). As an example a 20 mm steel pipe with 4 mm thickness has an OD of 28 mm while a 20 mm steel tube has an OD of 20mm.  The two broad classifications of steel pipe and tubular products are subdivided into several named use groups. As an example, the term tube covers three such groups namely (i)...