• SAFE PRACTICES

    Arc Welding

    (1) Protective clothing made of cotton or wool should be worn to shield all parts of the body from the rays of the arc and from metal spatter.

    (2) A helmet should be worn to protect eyes and face. See EYE PROTECTION.

    (3) The operator should be insulated from the work-piece when changing electrodes.

    (4)Noncombustible or fire-resistant screens should be provided to protect workers or other persons in the vicinity of the welding or cutting operation from the rays of the arc and weld spatter. Workers in the vicin- ity of the operations are required to wear eye and face protection, and protective clothing.

    (5) Hot metal should be marked to remind shop personnel not to touch it.

    (6) The frame or case of a welding machine should be connected to an earth ground. The workpiece lead connecting the work to the power supply should be made as short as possible.

    (7) Combustible material should not be used to support the workpieces.

    (8) Clear glass goggles should be worn to protect the eyes when removing slag or spatter.

    (9) Power lines to welding machines should be run overhead and out of reach of anyone standing on the ground.

    (10) Pipe lines, tanks or containers should not be welded until they have been properly cleaned. Specific procedures are contained in ANSI/AWS F4.1, Safe Practices for Preparation for Welding and Cutting of Containers and Piping.

    (11) A fire extinguisher should be available during any welding operation. See FIRE HAZARDS AND PROTECTION.

     

    Oxyfuel Gas Welding and Cutting

    Cylinder Safety- Compressed gas cylinders are safe for the purposes for which they are intended. Serious accidents connected with their handling, use and storage can often be traced to mishandling or abuse. Only cylinders designed and maintained in accordance with specifications of the U.S. Department of Transportation (DOT) may be used in the United States. Cylinders must not be filled except by the owner, or with the consent of the owner, and then only in accordance with the regulations of the U.S. Department of Transportation. It is illegal to remove or change the numbers or marks stamped into cylinders. Proper names for gases should always be used. Oxygen should not be referred to as “air,” or acetylene as “gas.” Several safety rules are specific to oxygen and acetylene.

    Oxygen- Oxygen is not flammable, but it supports combustion. Oil and grease should not be allowed to come in contact with oxygen cylinders, valves, regulators, gauges, or fittings. Oxygen cylinders or apparatus should not be handled with oily hands or gloves because spontaneous combustion may occur.

    Neither oxygen nor any gas should be used as a substitute for compressed air to power pneumatic tools or similar devices. It is dangerous to use oxygen to start a diesel engine, for imposing pressure in oil reservoirs, for paint spraying, or for blowing out pipelines. Pressure from an oxygen or gas supply should never be used to clear clogged oil lines.

    Acetylene- The cylinder valve should be fully open when the cylinder is in use. Acetylene should never be used at a gauge pressure in excess of 103 Kpa (15 psi). Acetylene cylinders should be used and stored in an upright position to avoid the possibility of drawing out acetone. The pressure in an acetylene cylinder does not accurately indicate the amount of gas contained in the cylinder. The amount is determined by weight.

     

    High-pressure and Fuel Gas Cylinders

    Gases used in oxyfuel gas welding, cutting, brazing, and heating operations are oxygen, acetylene, hydrogen, methylacetylene propadiene (MAPP), propylene, methane (natural gas), and propane.

    The two main categories of cylinders used in these operations are high-pressure cylinders and fuel gas cylinders. The following rules apply to both these categories:

     

    General Rules

    (1) Regulators, pressure gauges, hoses or other apparatus provided for use with a particular gas must not be used on cylinders containing a different gas.

    (2) Threads on regulators or other unions are designed to match those on cylinder valve outlets for specific gases. Connections that do not fit should not be forced.

    (3) Attempting to mix gases in a cylinder, or attempting to transfer any gas from one cylinder to another, is prohibited.

    (4) Never, under any circumstances, should the operator attempt to refill any cylinder.

    (5) Tampering with safety devices on cylinders or cylinder valves is prohibited. Repairing or altering cylinders or valves should never be attempted.

    (6) An open flame should never be used to detect combustible gas leaks. Soapy water should be used for this purpose.

    (7) Connections to piping, regulators, and other appliances should always be kept tight to prevent leakage.

    (8) Caps should be provided for valve protection; the caps should be kept on cylinders except when cylinders are in use.

     

    Operating Safety

    (1) Gases from cylinders should never be used without reducing the pressure through a suitable regulator attached directly to the cylinder.

    (2) After the valve cap is removed, the valve should be opened for an instant to clear the opening of particles of dust or dirt.

    (3) A pressure-reducing regulator should be attached to the cylinder valve before it is put in use.

    (4)After attaching the regulator and before the cylinder valve is opened, the adjusting screw of the regulator must be released.

    (5) The cylinder valve should be opened slowly, using only tools or wrenches provided or approved by the gas manufacturer. The gas should never be permitted to enter the regulator suddenly.

    (6) Before a regulator is removed from a cylinder, the cylinder valve should be closed and all gas released from the regulator.

    (7) The operator should not use the regulatorsattached to cylinders as brackets to hang torches.
    (8) Sparks and flames from the welding or cutting torch should be kept away from cylinders.

    (9) Hot slag should not be allowed to fall on combustible materials or on the cylinders.

    (10) When cylinders are not in use, valves should be kept tightly closed.

     

    Cylinder Storage

    (1) Do not store cylinders near flammable material, especially oil, gasoline, grease, or any substance likely to cause or accelerate fire.

    (2) Do not store reserve stocks of cylinders containing combustible gases with oxygen or other gases; they should be grouped separately.

    (3) Store all cylinders in a well-ventilated place.

    (4)All cylinders should be protected against excessive rise of temperature. Cylinders may be stored in the open, but in such cases, should be protected against extremes of weather. During winter, cylinders stored outdoors should be protected against accumulations of ice or snow. In summer, cylinders stored outdoors should be screened against continuous direct rays of the sun.

    (5)Cylinders should not be exposed to continuous dampness.

    (6) Full cylinders should not be stored near elevators or gangways, or in locations where heavy moving objects may strike or fall on them.

    (7) Full and empty cylinders should be stored separately to avoid confusion.

     

    Safe Handling

    (1) Cylinders should never be dropped or permitted to strike each other violently.

    (2) A lifting magnet, or a sling rope or chain should not be used when handling cylinders. A crane may be used when a safe cradle or platform is provided to hold the cylinders.

    (3) Cylinders should never be used as rollers, supports, or for any purpose other than to carry gas.

    (4)When empty cylinders are returned, cylinder valves should be closed before shipment. Protective caps and nuts for valve outlets should be in place before shipping empties. 

  • SAFETY EQUIPMENT

    Various items, including clothing, eye wear, head gear, hand wear, foot wear, instruments, tools, and devices used to protect workers from injury or death when working with potentially hazardous chemicals, materials, articles, equipment, processes or systems associated with welding. See EYE PROTECTION, ARC WELDING, OXYACETYLENE WELDING, WELDING FUMES, and SAFE PRACTICES. 

  • SAFETY VALVE

    A pressure-release device installed in pressure vessels and pipe systems which is designed to blow out when the pressure rises above a predetermined point. 

  • SALT BATH

    Immersion of steel and other metals in a salt solution for tempering or heat treating.  Salt baths may be classified in three general types: neutral, reducing or oxidizing.

    Neutral Baths

    (1) Low-temperature baths which are operated at 150to 595°C (300 to 1100°F) may be used for tempering or for low-temperature heat treatments such as the solution treatment or aging of aluminum alloys.

    (2) Medium temperature baths, operated at 675 to 900°C (1250 to 1650°F) are used principally for heating steel before quenching. High-temperature baths, higher than 925°C (1700°F), are used primarily for heat treatment of high-speed steel (tool steel alloys), but may also be used for copper brazing.

    Among the precautions to be observed in using various types of salt bath: it is important to avoid contamination of neutral baths with cyanide salts. Another precaution is to avoid overheating the bath.

    Reducing Baths

    Reducing salt baths are used for carburizing or nitriding. A sufficient concentration of cyanide must be maintained in reducing salt baths for satisfactory results. A carbonaceous blanket on top of a bath of this type not only cuts down heat loss, but also helps to reduce the breakdown of cyanides in the bath.

    Oxidizing Baths

    Oxidizing baths are used for coloring steels or other metals and may also be used for annealing noble metals. Fused salt baths of this type may be used at 5 10°C (950°F) for blackening steel, and an aqueous solution of this type may be used at 150°C (300°F) for the same purpose.

    The surface hardness of heat-treated tool steel alloys may be increased by nitriding them in a “high-speed case” salt bath at approximately 550°C (1025°F) for a relatively short period of time. The tendency of sharp edges of tools treated in this manner to chip can be reduced by a subsequent tempering operation at 540 to 565°C (1000to 1050°F). 

  • SALT-BATH DIP BRAZING

    A dip brazing process variation.

  • SAND HOLES

    Craters or porous holes in castings. 

  • SANDBERG (In Situ) RAIL HARDENING PROCESS

    The Sandberg process is an application of the oxy-acetylene flame to harden rails. In this process, rails already in service are heated with the torch, then quenched with water. In one experiment, rails treated by this process remained unaffected after 360 000 cars had passed over them, although adjoining lengths of untreated rails corrugated when subjected to the same test. See also FLAME HARDENING. 

  • SANDBLAST

    A method of discharging fine sand at high velocity to remove rust, dirt and scale from a surface before welding, painting, or finishing.

    When welding, if more than one layer of metal is to be deposited, the oxide and scale should be: removed from each layer before the next layer is applied. Sand-blasting is probably the fastest and most efficient method of producing a thorough cleaning job.

    A portable sandblaster consists of a sheet metal tank provided with a filling hole and a pipe T-outlet for an air-operated siphon. The siphon consists of a pipe from the vertical of the T to the bottom of the tank; the horizontal outlets of the T are fitted with a sand nozzle and an air control valve. The sand nozzle tip should be replaceable because it will wear quite rapidly. A sandblaster of this type will operate well with an air pressure of about 620 kPa (90 psi).

    Care should be exercised when sandblasting to avoid entrapping sand in crevices or embedding sand in the surfaces of soft metals and alloys. Particles of sand can result in contamination of subsequent weld passes, and can lead to other problems in the weldment. 

  • SAWS, MANUFACTURE AND REPAIR BY WELDING

    Welding is used in the manufacture of saw blades for band saws, power hacksaws, and circular saws. A hard strip (or ring) containing the teeth is welded to a softer, tougher strip (or disc) to provide for safe operation of the saw blade. Processes include resistance seam and “mash” welding, high-frequency (resistance) welding, and laser-beam and electron-beam welding. Brazing is also used to manufacture saw blades.

    Repairs- Cracks in band saw and circular saw blades can be repaired by welding. A section with broken teeth can be cut away, and replaced with a usable section cut from an old blade and welded in place. However, a special technique is necessary; special jigs and anvils are required, and specific welding rods must be used.

    Band saw steel is made of nickel-, chrome-, or molybdenum-steel, or another alloyed steel. The car- bon content often is about 0.70%.Welding rods, therefore, should approximate this alloy, and an excellent choice is a chrome-vanadium steel rod containing approximately 0.80 to 1.10% chromium, 0.15 to 0.18% vanadium and 0.40 to 0.50

  • SCALE

    A term sometimes applied to a surface coating of oxide on molten iron or steel. 

  • SCALING POWDER

    A flux used to dissolve the oxide that forms in cast iron welds. 

  • SCARF

    The chamfered surface of a joint. 

  • SCARF GROOVE

    A weld groove in a butt joint consisting of members having single-bevel edge shapes. The groove faces are parallel. See Figure S-1. 

  • SCARF JOINT

    A nonstandard term for SCARF GROOVE. 

  • SCARFING

    A process for removing defects and checks which develop in the rolling of steel billets. Scarfing is accomplished with a low-velocity oxygen deseaming torch, a specially designed torch with an unusually large oxygen orifice. The steel is preheated locally to a cherry red, and the oxygen, under low pressure and velocity, is projected against the red-hot surface. The steel around the defect is consumed and the defect is entirely burned away.

    Alternatively, the term scafing is used to refer to the process of preparing a scarf groove. 

  • SCHAEFFLER DIAGRAM

    A diagram proposed by A. E. Schaeffler in 1956 to predict the ferrite number (FN)of a stainless steel weld deposit. The user calculated the chromium and nickel equivalents of the deposit, based on weld chemistry, and was able to plot the ferrite number. The Schaeffler Diagram was followed by the DeLong diagram (proposed by W. T. DeLong in 1974), the Espy Diagram (proposed by R. H. Espey in 1982), and the WRC-1992 Diagram (developed by a Welding Research Council Sub-committee in 1992 and described in WRC Bulletin 342. See DELONG DIAGRAM, WRC-1988 DIAGRAM, and ANSI/AWS A5.4, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding. 

  • SCREEN

    A device usually constructed of a fine wire mesh filter designed to prevent foreign matter from entering the regulator or torch. Also, the wire mesh used as a gas “lens” in gas tungsten arc welding torches to pro- vide laminar flow of the shielding gas.

     

  • SCREENS, PROTECTIVE

    A moveable, often portable, protective barrier or partition used around welders (especially in arc welding) to protect others in the vicinity from sparks, spatter, and arc flash. Screens may be constructed from translucent material that blocks ultraviolet radiation, or an opaque material. See also EYE PROTECTION and PROTECTION FOR WELDERS. 

  • SEAL WELD

    Any weld designed primarily to provide a specific degree of tightness against fluid leakage. 

  • SEAM

    A nonstandard term when used for a welded, brazed, or soldered joint. 

  • SEAM WELD

    A continuous weld made between or upon overlapping members, in which coalescence may start and occur on the faring surfaces, or may have proceeded from the outer surface of one membel: The continuous weld may consist of a single weld bead or a series of overlapping spot welds. See Figure S-2. See also ARC SEAM WELD and RESISTANCE SEAM WELDING.

    Seam welds are made with resistance welding equipment in high-production manufacturing. Seam welds are typically used to produce continuous gas- or liquid-tight joints in sheet metal assemblies, such as automotive gasoline tanks. This process is also used to weld longitudinal seams in structural tubular sections that do not require leak-tight seams. A resistance seam weld is made on overlapping workpieces and is a continuous weld formed by overlapping weld nuggets, by a continuous weld nugget, or by forging the joint as it is heated to the welding temperature by its resistance to the welding current. 

    In most applications, two wheel electrodes, or one translating wheel and a stationary mandrel, are used to provide the current and pressure for resistance seam welding. Seam welds can also be produced using spot welding electrodes; this requires the purposeful overlapping of the spot welds in order to obtain a leak-tight seam weld. Two variations of this process are lap seam welding, using two wheel electrodes (or one wheel and a mandrel) and mash seam welding, which makes a lap joint primarily by high-temperature plastic forming and diffusion, as opposed to melting and solidification.

    In mash seam welding, overlap is maintained by clamping or tack welding the pieces. The electrode wire seam welding process uses an intermediate wire electrode between each wheel electrode and the workpiece. This process is used almost exclusively for welding tin mill products to fabricate cans.

    Butt joint seam welding is done with the edges of the sheets forming a butt joint. A thin, narrow strip of metal fed between the workpieces and the wheel electrode is welded to one or both sides of the joint. The metal strip bridges the gap between the workpieces, distributes the welding current to both sheet edges, adds electrical resistance, and contains the molten weld nugget as the nugget forms. The strip serves as a filler metal, and produces a flush or slightly reinforced weld joint.

    Two seam welds can be made in series, using two weld heads. The two heads may be mounted side by side or in tandem. Two seams can be welded with the same welding current, and power demand will be only slightly greater than for a single weld.

    A tandem wheel arrangement can reduce welding time by 50%, since both halves of a joint can be welded simultaneously. Thus, for a joint 182 cm (72 in.) long, two welding heads can be placed 91 cm (36 in.) apart, with the welding current path through the work from one wheel electrode to the other. A third continuous electrode is used on the other side of the joint. The full length of the joint can be welded with only 91 cm (36 in.) of travel. See RESISTANCEWELDING (RW) and TUBEMANUFACTURE. 

  • SEAM WELD SIZE

    The width of the weld metal in the plane of the faying surfaces. See Figure S-3.

  • SEGREGATION

    The tendency for alloy constituents to freeze at different temperatures during (real, non-equilibrium) solidification so that there is an uneven distribution of these elements in the alloy. Such segregation can occur on either a microscopic scale, as the natural result of solute redistribution (due to the distribution coefficient), or on a macroscopic scale as the result of improper (incomplete) mixing of dissimilar metals or alloys or due to gravity effects in alloys. See METALLURGY. 

  • SELECTIVE BLOCK SEQUENCE

    A block sequence in which successive blocks are completed in an order selected to control residual stresses and distortion. 

  • SELENIUM RECTIFIER

    Selenium rectifiers were used in d-c welding power supplies until the development of silicon, or solid state, rectifiers. Selenium rectifiers provided a convenient means of changing alternating current to direct current. This ability was based on the characteristic of permitting the current to pass freely in one direction, while blocking, or greatly limiting, its passage in the opposite direction.

    If the rectifier cell readily passes current in a forward direction, it indicates that the resistance to current flow in this direction is low. The resulting forward voltage drop across the cell thus must also be low. Conversely, if the current flow in the opposite direction is blocked, or held to a minimum value, the reverse resistance must be high. Consequently, the voltage drop across the cell in the reverse direction must also be high. The minimum value of the reverse voltage drop is limited by the breakdown potential of the barrier layer of the rectifier cell.

    Selenium rectifiers had the advantage of being able to accept high-voltage surges without breaking down. Cooling was easily achieved, because selenium rectifiers were usually made up of a number of plates. This also made it easy to add more rectifying surface if required for a specific application. The disadvantage of the selenium rectifier was that it required more physical space in the power source. It was an important stepping stone in the development of solid state rectifiers.