8 422 AU : IPRM 2007 : SectIon 8 : conSUMAbleS WARnInG Welding can give rise to electric shock, excessive noise, eye and skin burns due to the arc rays, and a potential health hazard if you breathe in the emitted fumes and. SFLC STANDARD SPECIFICATION 07 1 0740 WELDING AND ALLIED PROCESSES 1. This standard specification and appendices describe the general requirements for welding, fabrication, brazing, inspection, and. Welding-steel, welding low carbon and low alloy steels by all processes. Know the Weldability of steels and iron base alloys. What makes a material easy or hard to weld. Brittle heat affected zone. Naval grade high strength low alloy (HSLA) steels can be easily welded by all types of fusion welding processes. However, fusion welding of these steels leads t. ![]() Welding methods and processes - Road to Success. Introduction. Welding is the primary connecting process in pipeline construction. Several different welding processes can be deployed during the construction phase of the pipeline. Each process has its advantages and limitations when being implemented in girth welding activities. The specific welding process used must be considered based on its overall ease of implementation in the particular welding activity, criticality of the service environment and techno- economic impact. Welding of pipelines and related components comprise of mainline welds (i. Even with the emergence of new technology, arc welding remains the most common welding type used in pipeline construction. Arc- welding activities can be classified into two typical categories such as mechanized/automated welding, and manual welding. Adaptive control welding is also an advanced form of automatic welding, which is welding with a process control system that automatically determines any changes in welding conditions and directs the equipment to take appropriate action. This shall be classified as automatic welding for the purpose of this discussion. This classification is in accordance with the degree of operator involvement in the performance of the welding activity. Topics Covered: Background. Gas Tungsten-Arc (GTA) and Gas Metal-Arc (GMA) Welding. WELDING PROCESSES CODE OF PRACTICE 3 1. Introduction 1.1 What is welding? Welding is the process of permanently joining two or more materials together, usually metals, by heat or pressure or both. When heated, the material. Welding is the primary connecting process in pipeline construction. Several different welding processes can be deployed during the construction phase of the pipeline. Each process has its advantages and limitations when being. The following is a breakdown of welding processes involved and considered for each portion of pipeline construction and related components, discussing the advantages and limitations of each process. The table below gives a comparison of the pro and cons of the different welding processes. The comparison shows the criteria used for the selection of the welding method. It is usually recommended to weld high- strength steel with low hydrogen electrodes for all passes. However, past experience has shown that high- strength steel pipe can be successfully welded using a cellulosic root and hot pass with proper preheat and filling the remainder of the joint with low hydrogen electrodes. Matching strength. Matching strength is not formally defined, and sometimes it causes the wrong interpretation when using it either to refer to the joint strength, or to the welding consumable specified minimum strength. These two variables are completely different. The former refers to the strength of a welding joint with respect to the pipe base metal, while the other refers to the standardized way to measure the strength of the weld metal of a given welding consumable in certain conditions. Joint strength is very important in pipeline construction. The welding consumable should be selected in order that the welding joint strength matches (or overmatches) the strength of the pipe. In other words in a match or overmatch joint, the joint strength has to be equal to or greater than that of the base metal respectively. In order to clarify these concepts, it is necessary to explain that most of the material designations refer to the yield strength (. For example, API 5. L Grade X7. 0 has associated a minimum . Looking at those numbers, it seems that electrode will produce an under- match joint. However, the final strength of a joint will depend on a number of variables, in which can be included the following variables: base material chemistry, dilution, oscillation, travel speed, and others. Consequently, it is impossible to perfectly predict the final strength of a welded joint. Most of the welding consumable standards specify the minimum mechanical requirements based on a particular welding procedure, which is completely different to a typical welding procedure for pipeline. Consequently the results obtained in those tests are just reference values, and they cannot be related directly to the final strength of a joint. Furthermore, the actual yield strength . Matching can be used for most applications, but in some cases, it may not be the most economical or conservative choice. Under- match welding consumables might be used when the hardness of the root pass is a concern, even if other higher strength consumables are to be used to fill and cap the weld. The two most popular methods of manufacturing large diameter steel line pipe are longitudinal seam submerged arc welding and spiral (or helical) seam submerged arc welding. These two types of line pipe can be discerned by locating the pipe weld seam reinforcement and determining if it runs longitudinally or helically relative to the pipe axis. While longitudinal seam submerged arc welded pipe is the most common type of steel line pipe used for cross- country pipelines, spiral seam submerged arc welded pipe has been rapidly gaining popularity. It is often lower cost than longitudinal welded pipe and can be supplied in longer lengths, which lowers overall pipe laying time and costs. If not properly controlled, this offset results in difficulties welding the root pass and possible inadequate penetration. The internal line- up clamping pressure can be increased to reduce out of roundness, but this increases the risk of stress cracks, especially when using cellulosic electrodes. Facing this scenario characterized by poor fit- up, more robust welding processes and welding techniques are needed. Pulsed gas metal arc welding (GMAW- P) usually accommodates the effects of poor fit- up, producing a thick root pass with low diffusive hydrogen. Consequently, cracking probability is lower and penetration tends to be better than shielded metal arc welding (SMAW). Pipeline diameter and wall thickness. Pipe diameter plays a major role in how long it will take to weld a root pass. Larger diameter pipe, such as 1. Thus, larger pipe diameter results in slower pipe laying speeds. To offset this, the number of welders (or arcs) may be increased, or a faster welding process may be selected. Increasing pipe wall thickness usually results in higher weld zone hardness, which increases the tendency of weld cracking at the root pass. This is due primarily to the following factors: Thicker wall pipe tends to have more alloys and a higher carbon equivalent than thinner wall pipe to obtain the same strength. This results in harder weld and weld zone, and consequently, lower weldability. The greater mass of steel cools the weld faster, which increases the weld zone hardness. Thicker pipe is more rigid, resulting in higher residual stress. It is more difficult for hydrogen to diffuse from the weld zone due to faster cooling and the increased distance it need to travel to the surface. Therefore, it should not be assumed that a root pass method that worked successfully on thin wall pipe would perform as well on thicker wall. Higher preheat temperatures, lower hydrogen welding electrodes, or a different welding procedure may be needed. Also, heavy wall thickness pipes often require toughness evaluation at the root. In this case, the selection of the root pass procedure shall take into account a robust welding technique that can accommodate base metal dilution and keep toughness properties. When wall thickness is heavy, some codes and standard require post heat treatment of the weld. This will have a strong impact on productivity and weld final properties. Toughness, in particular, could be negatively affected. Heat input has to be carefully selected, as does welding technique in terms of welding consumable and parameters. Pipeline terrain and environmental conditions. Pipeline laying speed is highly dependent on the terrain and environmental conditions. Fast laying speeds are usually obtained on flat, dry plains. Pipe laying speed is slowed by conditions such as rocky, hilly or wet terrain, bad weather, as well as river and road crossings. If conditions are present for slow laying speeds, there may be limited benefits by selecting a fast root pass method if the root pass welding crew is frequently slowed down waiting for the right- of- way to be cleared. Extreme weather conditions like those in deserts or cold regions may affect the performance of welding equipment and welding variables such as preheat and inter- pass temperature. In particular in cold weathers, low temperatures and fast welding process (low heat input) may present a tendency to create welding defects such as lack of fusion; preheat temperature and particularly inter pass temperature should be carefully monitored. Other conditions such as altitude may affect some welding processes, not only reducing productivity but also increasing the tendency to produce welding defects. Additionally, this fact is increased by the drop in efficiency due to the negative effect of altitude on welder. On small projects, the high initial capital costs incurred may not be recovered. Rental of the equipment might be more appropriate; however project delays may then induce significant additional costs. Inspection. Increasing the root pass welding speeds necessitates faster weld inspection speeds. The results of the traditional method of radiography inspection follow production welding by approximately half to one day. This is due primarily to the health and safety precautions that must be taken when working with a radioactive material or a radiation source. This inspection delay may be satisfactory at traditional root pass laying rates of 4. However, automatic welding systems can lay pipe in excess of 2. This requires a faster inspection method to keep up and follow closer to the production welders. Automatic ultrasonic testing (AUT) is the preferred method for inspecting automatic pipeline girth welds. Radiation hazards are eliminated. AUT inspection crews can work in close vicinity to others, including the welding and pipe coating crews. It is also fast, with the inspection data automatically processed by computer. Radiography can have a difficult time detecting non- volumetric planar flaws, like lack- of- fusion, which is more common with mechanized/automatic GMAW processes. AUT does an excellent job in detecting these flaws. Also, recent advances in AUT . With faster inspection speeds and results, the time to bury the pipe into the ground is reduced, lowering spreads costs.
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