Submerged Arc Welding overview:

Submerged arc welding is a small different than most other forms of welding since the arc and the end of the electrode are not able to be seen to the operator. Both are kept below a pile of grainy flux. The majority ordinary use for this welding scheme is by machines, but there are semi automatic versions. The machine is used to start the arc and gives the electrode by feeding it to the weld region from approximately a spool. The flux is in a granule form and is dispersed in front of the weld pathway. The scheme is able to also be set up with two electrodes positioned vertically side by side, vertically one in frontage and one in backside, or in a v-shaped to speed the procedure up. Some of the flux is melted in the welding process which generates a slag that helps guard the weld from the surroundings and from cooling. A few joints up to 3" wide are able to be welded in one pass. This technique is regularly done in a flat position and is great for ships and bridges where extended welds are wanted.

The slag in this situation helps to generate a clean and strong weld. With the arc enclosed up, spatter and heat loss into the nearby surroundings is not a trouble. Alloy and metal powders are able to be added to the flux grains in order to assist fill the seam. Not a lot of smoke is created if any and no defense is wanted to shield from the light from an arc. The system is automatic simply and there is not a lot of talent wanted for the procedure. The slag generated limits submerged arc welding to simply to a flat position. The heat that is generated by the weld stays in the metal longer due to the flux covering which can boost distortion of the metals.

Residual Stress

Residual stress is a process-induced stress, frozen in a molded part. It can be either flow-induced or thermal-induced. Residual stresses affect a part similarly to externally applied stresses. If they are strong enough to overcome the structural integrity of the part, the part will warp upon ejection, or later crack, when external service load is applied. Residual stresses are the main cause of part shrinkage and warpage. The process conditions and design elements that reduce shear stress during cavity filling will help to reduce flow-induced residual stress. Likewise, those that promote sufficient packing and uniform mold cooling will reduce thermal-induced residual stress. For fiber-filled materials, those process conditions that promote uniform mechanical properties will reduce thermal-induced residual stress.

Flow-induced residual stress
Unstressed, long-chain polymer molecules tend to conform to a random-coil state of equilibrium at temperatures higher than the melt temperature (i.e., in a molten state). During processing the molecules orient in the direction of flow, as the polymer is sheared and elongated. If solidification occurs before the polymer molecules are fully relaxed to their state of equilibrium, molecular orientation is locked within the molded part. This type of frozen-in stressed state is often referred to as flow-induced residual stress. Because of the stretched molecular orientation in the direction of flow, it introduces anisotropic, non-uniform shrinkage and mechanical properties in the directions parallel and perpendicular to the direction of flow.

Reducing flow-induced residual stress
Process conditions that reduce the shear stress in the melt will reduce the level of flow-induced residual stresses. In general, flow-induced residual stress is one order of magnitude smaller than the thermal-induced residual stress.

• higher melt temperature


• higher mold-wall temperature


• longer fill time (lower melt velocity)


• decreased packing pressure


• shorter flow path.

Rule Of Thumb Fillet Weld Sizes

Cutting Machine Conditions

1. Cutting and welding are done by authorized personnel in designated cutting and welding areas to the greatest extend practical.
2. Adequate ventilation is provided for all cutting and welding work.
3. Torches, regulators, pressure reducing valves, and manifolds are Underwriters Laboratory listed or Factory Mutual approved.
4. Oxygen fuel gas systems (e.g., oxygen/acetylene welders) are equipped with listed and/or approved backflow valves and pressure relief devices.
5. Eye protection and protective clothing are worn by all cutters and welders, helpers, and fire watches, as appropriate. Workers adjacent to arc welding areas are protected from the rays by screens or shields.
6. When cutting and welding are done outside of designated areas, the following actions are performed.
7. Permit is completed for each shift.
8. continuous fire watch is maintained, when designated by permit, by trained employees (see employee training, Fire Watch). A fire is attacked only when obviously within the capability of the portable extinguisher.
9. A member of supervision (i.e., craft supervisor) inspects the job site at lest once before the start of each job and at least once every 24 hours until the completion of the job.

1. A craft supervisor determines the best location (s) for the fire watch and verifies that automatic fire protection is in service, that precautions taken are adequate, and that information on the Permit is correct.
2. Combustible materials, equipment, or building surfaces within 20 feet of the work or below the work must be either covered with fire-resistant welding blankets, moved, or wetted down. Openings in ducts, tanks, or other confined spaces within 20 feet of the work are also covered or plugged. Fire-resistant welding blankets are used for electric arc operations instead of wetting the work down.
3. Cutting or welding is prohibited in the following situations.
4. In sprinklered areas while sprinkler protection is out of service.
5. In explosive atmospheres of gases, vapors, or dusts or where explosive atmospheres could develop from residues or accumulations in confined spaces (see item 8).
6. On metal walls, ceilings, or roofs built of combustible sandwich type panel construction or having combustible covering.
7. Confined spaces such as tanks are tested to ensure that the atmosphere is not in excess of 10% of the lower flammable limit prior to cutting or welding in or on the tank. Tests are repeated as conditions warrant, once each shift as a minimum. Mechanical ventilation is continuous when cutting or welding in or on a confined space.
8. When cutting or welding must be done on small tanks, piping, or containers that cannot be entered, they are cleaned, purged, and tested prior to starting the work. For work on combustible liquid or gas piping or tanks, intermittent testing is done during the work and a Job Safety Analysis is provided with the assistance of Fire Protection Engineering.
   

Welder and Welding Methods

Welding has been used in thousands of manufacturing activities and is the most common means of permanently joining metal parts. Welders construct or repair metal products by sealing parts using different welding methods.

How Welding Works:

• Craig House, a First Class boilermaker welder and workshop manager, says that among the various welding methods used, manual metal arc welding or stick welding as it's known in the industry is a commonly used method.

• Arc welding involves two large metal alligator clips carrying a strong electrical current. One clip is attached to any part of the work piece metal part being welded while the second clip is attached to a thin welding rod. When the rod touches the metal part, a powerful electrical circuit is created.

Turn Up The Heat:

• The intense heat created by the electrical current causes the metal part and steel core of the rod to melt together.

• This cools quickly and results in a solid bond. During welding, the flux (welding wire) that surrounds the rod's core vaporises, forming a gas that serves to protect the weld from atmospheric elements that might weaken it.

Craig House unravels the process:

• Pressure vessels are round cyclinders which are to be welded longitudinally. The vessel will already have been tack welded by a boilermaker and after it is set up on rollers, run-off tabs are put on.

• These enable welders to continue welding past the end of the joint. It gets welded from the inside first, rotated and then welded from the outside.'

• Welders also join beams used in the constructing of buildings and bridges, and join pipes in pipelines, power plants and refineries.