The words qualification and certification are probably the two most misunderstood words in the vocabulary of a welder. These two terms are erroneously used interchangeably. Often the person who speaks these words has in mind a meaning that is entirely different from what the person who hears them perceives. Generally, “certified” refers to the welder who has a certificate signed by somebody and certificates can be issued by almost anyone. A welder can get a certificate of welding proficiency on graduating from a vocational training course, high school course, community college or industrial training school. However, none of these will qualify the welder for doing code welding.

    Where welding codes are concerned, specific qualification tests are spelled out by the various codes.

    Often the statement, “I’m a certified pipe welder” leaves unanswered questions such as:

    (1) Qualified to what pipe welding code? There are several.

    (2) Qualified for what procedure? For what position; what type of electrode and base material; what thickness of base material?

    Another question is that of duration of the qualification. Some qualifications, such as AWS, are considered to remain in effect indefinitely unless the welder is not engaged in a given process of welding for a period of three months or more, or unless there is some specific reason to question the ability of the welder.

    Code Welding

    Every welding operation is intended to be carried out to assure operator performance at a stipulated level of quality for a given design, with certain built-in

    safety factors. These performance features may be required by shop standards, customer specifications, or rules and regulations of a specific code.

    A code is generally considered to be the most rigid of these requirements, since it carries the implication of law, and in some cases, actually is a law enacted by a government body. Standards are commonly included or referenced in the code in a municipal, state or federal government project to establish limits and controls over some features of the code. Some examples are a municipal building code, a state boiler and pressure vessel code, or a federal highway bridge code.

    A properly worded code does not include explanatory matter. Since the features outlined in the code must be enforceable as a law, the code is written in mandatory language, using the imperatives “shall” and “must,” or equivalent words. Explanatory matter is relegated to other documents or to appendices.

    The most frequently cited codes involving the welding industry are the ASME Boiler and Pressure Vessel Code and the AWS D1.l Structural Welding Code-Steel. Other codes and standards, such as API 1104 Standard for Welding Pipelines and Related Facilities, and ASME B31, Code for Pressure Piping, include specified qualification tests.

    There may be other instances when a welder may be qualified to a code, even though the work being done is not involved with such a code. This frequently happens when shop welding personnel are qualified to the Dl.l, D1.2, D1.3, and D1.4 series of the AWS Structural Welding Codes.

    Requalification- Some codes require requalification for every job. For example, even though a person may have qualified as an EXX18 welder (most qualifications are by type of electrode) on a certain building, that qualification may not be accepted at another building site, although it can be accepted at the option of the local building commission and the owners or architects. In most areas, even though a welder may still be working for the same contractor, the owners or architects of a new project will usually call for requalification of all welders involved. The same is true in most types of pressure vessel and pressure piping work. A welder will also be required to requalify when certain changes in the welding procedure are made. These changes are listed in the codes as Limitations of Welder Qualification.

    A welder is qualified after passing a particular qualification test. For example, a welder might b,e qualified under the requirements of Section IX of the ASME Boiler and Pressure Vessel Code. In general, an employer is responsible for assuring that welders are given the correct qualification tests before work begins, since the employer is responsible for the work of the welders.

    The welder who wants to be certified (not just qualified), should learn and practice the procedures described in AWS B2.1 latest edition, Standard for Welding Procedure and Performance Qualification Procedure, issued by the American Welding Society, as well as any particular requirements of the specific codes governing the type of work the welder wants to do.

    Qualification. There are two distinct steps toward qualification. The first is qualification of the welding procedure; the second is qualification of the welder.

    The procedure qualification is a common requirement of all codes and specifications governing welding. Its purpose is to test the capability of the procedure to produce a satisfactory welded joint, although this does not guarantee that all welds made under the procedure will be satisfactory. It merely serves to prove that satisfactory welds can be made by following the various steps of the procedure. Quality in welding depends on a great many interrelated factors, in which the procedure is the dominating control.

    The second qualification is a test of the welder’s ability to perform the work; this is a mandatory requirement in many codes. Again, passing this test is not a guarantee; it merely proves that the welder has the ability to make satisfactory welds under given circumstances.

    Procedure Qualification- Before taking the welding procedure qualification test, the welder will have to select a welding process, equipment, and materials, then design appropriate weld joints, and conduct trial welds. Each of these must be considered according to the metallurgical and mechanical properties of the materials involved, the degree of weld soundness or quality required, and cost. The step-by-step method which evolves is the welding procedure, and all codes require that it be in written form. The procedure may be expressed in broad, general terms, or it may be explicit in detail, depending on the class of work or type of product being welded, the ease or difficulty of

    reproducing satisfactory welds, and the knowledge, skill and integrity of the person doing the work. The welding procedure is a written specification covering the necessary steps to be taken to produce a satisfactory weld.

    Test Administration- Most codes are not specific on the point of who is to do the testing, but usually leave it to the option of the fabricator (or owner). In order to become certified under an AWS code, the welder must take the qualification test at an AWS accredited test

    facility. While the architect or owner may demand control over testing, in most cases they do not, leaving it up to the contractor. The latter, however, is responsible for every weld made during construction, so the contractor must document the qualification of each procedure used and of every welder working on the job.

    The qualification test record, or certification of procedure or welder, generally calls for the signature of the person conducting the test, as well as that of an individual who witnessed it. Whether they are employed by the weld fabricating company or by an independent testing laboratory, they are responsible for documenting the qualification.

    Preparation of the test specimen is a key factor in the success of the mechanical tests; improper preparation of a specimen may cause it to fail.

    There are five different types of codes which require weld qualification: (1) industrial (AWS, ASME, API, AWWA, and others); (2) military (NAV- SHIPS, MILSPEC; (3) governmental (local, state and federal); (4)consumer or customer specifications, and (5)manufacturers specifications on products for which weld quality is mandatory, but for which there are no existing specifications.

    In many product areas, the influence of the insurance companies affects the codes. The insurers, while not code-writing bodies in themselves, have been influential in having codes written since the beginning of welded fabrication. The insurance companies got involved in metal fabrication in the early days of this century with the introduction of pressure vessels of riveted construction. This culminated in 1915 in the publication, by the American Society for Mechanical Engineers, of the first Boiler and Pressure Vessel Code, which is updated as required and is considered the bible of the industry.

    Nuclear Systems Code

    ASME’s responsiveness to the needs of nuclear systems development and for public safety led to the first Nuclear Systems Code. This was accomplished through a close relationship with the Atomic Energy Commission, which requested that one organization accept responsibility for codifying the pressure boundary of the entire nuclear system. As a result, Section 111 of the Boiler and Pressure Vessel Code, initially published in May. 197 1, includes rules for design, fabrication and inspection of various classes of nuclear components such as piping, vessels, pumps, valves and metal containment vessels. Previous issues had included provisions for nuclear vessels.


    Procedure and performance qualification and testing standards for welding procedures, thermal spraying, brazing, testing and inspection are published by the American Welding Society.

    AWS C2.16, Guide for Thermal Spray Operator and Equipment Qualification provides for qualification of operators and equipment for applying thermal sprayed coatings. It recommends procedural guidelines for qualification testing. The criteria used to judge acceptability are determined by the certifying agent alone or together with the purchaser.

    AWS D10.9, Specification for Qualification of Welding Procedures and Welders for Piping and Tubing, covers circumferential groove and fillet welds but excludes welded longitudinal seams involved in pipe and tube manufacture. An organization may make this specification the governing document for qualifying welding procedures and welders by referencing it in the contract and by specifying one of the two levels of acceptance requirements. One level applies to systems that require a high degree of weld quality. Examples are lines in nuclear, chemical, cryogenic, gas, or steam systems. The other level applies to systems requiring an average degree of weld quality, such as low-pressure heating, air conditioning, sanitary, water, and some gas or chemical systems.

    MIL-STD-248, Welding and Brazing Procedure and Performance Qualification, and MIL-STD- 1595, Qualification of Aircrafi, Missile, and Aerospace Fusion Welders may be used when federal government or military requirements are involved.

    AWS B2.1, Standard for Welding Procedure and Performance Qualification, provides requirements for qualification of welding procedures, welders and welding operators. It may be referenced in a product code, specification, or contract documents. Applicable base metals are carbon and alloy steels, cast irons, aluminum, copper, nickel, and titanium alloys.

    AWS B2.2, Standard for Brazing Procedure and Performance Qualification, covers requirements for qualification of brazing procedures, brazers, and brazing operators for furnace, machine, and automatic brazing. It is to be used when required by other documents, such as codes, specifications, or contracts. Those documents must specify certain requirements applicable to the production brazement. Applicable base metals are carbon and alloy steels, cast iron, aluminum, copper, nickel, titanium, zirconium, magnesium, and cobalt alloys.

    ANSYAWS C3.2, Standard Method for Evaluating the Strength of Brazed Joints in Sheal; describes a test method used to determine shear strengths of brazed joints. For comparison purposes, specimen preparation, brazing practices and testing, procedure must be consistent. Production brazed joint strength may not be the same as test joint strength if the brazing practices are different. With furnace brazing, for example, the actual part temperature or time at temperature, or both, during production may vary from those used to determine joint strength.

    ANSIIAWS B4.0, Standard Methods for Mechanical Testing of Welds, describes the basic mechanical tests used for evaluation of welded joints, weldability, and hot cracking. The tests applicable to welded butt joints are tension, Charpy impact, drop-weight, dynamic-tear, and bend types. Tests of fillet welds are limited to break and shear tests.

    For welding materials and procedure qualifications, the most commonly used tests are round-tension; reduced-section tension; face-, root-, and side-bend; and Charpy V-notch impact. Fillet weld tests are employed to determine proper welding techniques and conditions, and the shear strength of welded joints for design purposes.

    AWS B 1.10, Guide for the Nondestructive Inspection of Welds, describes the common nondestructive methods for examining welds. The methods included are visual, penetrant, magnetic particle, radiography, ultrasonic and eddy current inspection.

    Qualification tests help determine the proficiency of welders to ensure that failures will not be caused by lack of skill. Also, the application of the welding processes in some fields is subject to regulation and inspection which, in some cases, is very rigid. Most welding codes require that individual operators pass a qualification test.

    The nature and the comprehensiveness of qualification tests varies with the work to be done. In general, the qualifying welds made by an operator will be made under conditions which duplicate, as nearly as practicable, the working conditions of the prospective job. For example, there would be a great deal of difference between the test required of a welder working on an aerospace application and those required for a welder who works wholly with structural steel.

    There is some difference of opinion as to the necessity of examining a welder on the theoretical knowledge of a process. Whether or not it is worthwhile to insist that an operator know something about the scientific background of the process would seem to depend on individual circumstances. There are many supervisors who think that if the foreman or head welder is well informed, satisfactory results can be obtained from welders who have demonstrated only their ability to manipulate the torch or the arc. It is certain, however, that knowledge of the process is no handicap.

    Before requiring welders to take qualification tests for any kind of work, it is advisable to prepare forms on which a record can be made of all the operating conditions, the observations made by the inspector, and a complete record of test results. These individual records should be carefully preserved for reference.

    A good deal of unnecessary expense can be circumvented if the qualification test is divided into two parts: first, observation of a preliminary break test, and second, a quantitative test.

    Preliminary Break Test

    A preliminary break test should be a made with a simple weld that can easily be broken through the weld itself. There are several methods of doing this:

    (1) using a plain butt weld and breaking it in a vise,

    (2)welding one plate to another in the form of a T on one Welding Encyclopedia

    side only and breaking by a sharp blow on the side of the plate opposite the weld and

    (3) making a lap fillet weld on one side only, then breaking through the weld by supporting the outside edges of the plates and hammering or pressing on the center of the weld;

    (4) making a butt weld and cutting nicks in both ends of the weld so that a sharp blow with a sledge hammer will result in a break directly through the weld metal.

    Other methods of designing an observation test can, of course, be used. It is always desirable to use a design which approximates the working conditions. The important thing is to complete a fracture through the weld so that the entire cross section of the inside of the weld can be examined for fusion, penetration, porosity, slag inclusions and grain structure.

    This test can be made with ordinary shop tools and involves a minimum of expense. It is obviously unnecessary to proceed to a more expensive laboratory test in the case of operators who do not show satisfactory proficiency at this point.

    Quantitative Test

    The quantitative test is for the purpose of determining how strong a weld the operator can make. If the welder is to be tested on butt welds only, the specimen plates are welded together and coupons are cut from these. The coupons are then tested for tensile strength and ductility in a laboratory. If the welder is to be tested on fillet welds, a double-strap lap joint is recommended. As a rule, it is difficult to make these test specimens with the welds in longitudinal shear.

    Hartford Test

    The Hartford Test refers to qualifying an employer's organization for an insurance company. The qualifying tests of the procedures and the welding which operators have completed are part of the requirements for qualifying the employer's organization. The welding operators can weld on code work only for the employer with whom the tests were performed.

    An insurance company engaged in shop inspection does not issue certificates of qualification to welding operators, since the certificates would be of no value to another shop.

    See TESTING for further reference to various qualification tests and testing methods. See also QUALIFICATION FOR CODE WORK, ASME BOLER CONSTRUCTION CODE; BOILER WELDING; BUILDING CONSTRUCTION



    The primary purpose of all the codes is to secure safe boilers, pressure vessels, and piping through minimum construction standards. Welding codes also provide means that will disclose inherent defects in methods of welding and lack of competency on the part of welding operators, since defective welds are almost invariably due to lack of control of the welding procedure.

    No two codes are exactly alike with respect to the provisions for qualifying welding operators. It is therefore necessary, when seeking detailed information as to the types of tests required, and the method of test supervision, to consult the specific code or specification governing the particular type of work to be done. 


    A crystalline form of silica (silicon dioxide SO2). Found abundantly in nature, quartz is the main constituent of granite, sandstone and other stones. In the welding industry it is used in powdered form in electrode coatings to prevent access of air to the hot weld metal. The quartz powder and other ingredients in the electrode coating form a protective slag on the weld bead. 


    An alloy containing four principal elements. An example of a quaternary alloy is a "chrome-moly steel," which contains the key elements of chromium, molybdenum, and carbon in iron. 

  • QUENCH TIME, Resistance Welding

    The time from the end of the weld, weld interval, or downslope time to the beginning of the temper time, during which no current flows through the workpieces and the weld is rapidly cooled by the electrodes. See Figure I-1. 


    The sudden cooling of heated metal by immersion in oil, water, or some other liquid medium (e.g., glycol or liquid nitrogen), a molten salt, or by spraying with a jet of water or compressed air. The purpose of quenching is to produce desired weld strength properties in hardenable steel.

    Ferrous alloys (e.g., especially, plain carbon, high-strength low-alloy, and tool steels) which can undergo transformation hardening, or non-ferrous alloys which can be precipitation hardened, are generally quenched to either produce or retain a particular microstructure.

    In non-ferrous alloys (for example age-hardenable aluminum alloys with copper, magnesium-silicon, lithium, or other additions) quenching is usually applied after the alloy is rendered single-phase by heating, i.e., is solution-treated or solutionized, in order to retain that single phase in a supersaturated state relative to a key solute element. Heating under controlled temperature-time cycles allows a second-phase to precipitate and induce hardening in what is called aging.

    The rate of cooling through the critical range determines the form in which the steel will be retained. In annealing, the heated steel may be furnace-cooled to about 595°C (1100"F), then it may be air cooled to room temperature. Slow cooling to 595°C (1000°F), which is below the critical range, provides sufficient time for complete transition from austenite to pearlite, which is the stabilized condition of steel at atmospheric temperature. In normalizing, the heated steel is removed from the furnace and allowed to cool slowly in the air. Such cooling is more rapid than in annealing and complete transition to pearlite is not obtained. In this instance, air cooling is a mild form of quenching.

    To harden steels it is necessary to use a more rapid quenching medium. The three common mediums used are brine, water, and oil. Brine produces the fastest temperature change; water is next, while oil produces the least drastic change. Although oil does not cool the heated steel through the critical range as rapidly as water or brine, it cools the steel rapidly enough to develop sufficient hardness for practical purposes.

    A drastic quench is required for relatively low-carbon steels in order to develop the required hardness. However, this type of quench is likely to cause the steel to warp and crack, and may set up internal stresses. When the structure changes from austenite to martensite, the volume of the steel is increased. If the change is too sudden cracking will occur. Cracking occurs particularly in the lower temperature ranges, when the steel is no longer plastic enough to adjust itself to expansion and contraction.

    The shape and thickness of the workpiece influences warping and cracking. Thin flanges on heavy sections are especially susceptible to warping. When tubular parts are quenched they should be immersed with the long axis vertical to reduce warping. Because of the less drastic action of the oil quench, many of these difficulties are avoided, and for this reason oil is preferred over brine or water if sufficient hardness can be obtained.

    The quenching medium is normally maintained at about 20°C (70°F), and provision should be incorporated to prevent temperature change of more than +/-10°C (+/- 20°F). This involves a large reservoir of liquid and a method of providing circulation and cooling. It is important to note that the rate of cooling throughout the critical range is governed by the temperature maintained in the quenching medium. Since a slight variation in the temperature of the quenching medium will have an appreciable effect on the rate of cooling, the quenching medium temperature must be held within narrow limits to obtain consistent results.  After steel is reheated and prepared for tempering, it is quenched in either air or oil. Chrome-nickel steels, because of their tendency toward temper brittleness, should always be quenched in oil. 


    There are various quenching media such as water, oil, brine, molten salts, molten metal, still air or blasted air. Water and brine are the most drastic quenching mediums. To satisfactorily harden steel, water should be kept below 25°C (80°F) and continu- ally agitated during the quenching operation. Agitation of the cooling medium insures a more uniform and faster cooling action. Brine is faster, is more uniform, and is less affected by increases in temperature. Oil is used as a quenching medium in hardening operations. Molten salts or molten metals are high-temperature quench baths and are frequently used with interrupted or timed quenching. Air provides the mildest type of quench. 


    Interrupted quenching is used to modify the rate of cooling of an alloy in heat treatment. An example of interrupted quenching is found in the treatment of an axle after repair by welding. A specific time in oil will cool the surface rapidly enough to suppress the transformation to a given depth below the surface. In interrupted quenching, if immersion time is sufficiently short, there will be enough heat in the interior of the axle to raise the temperature of the exterior layer, effecting a tempering treatment. Subsequent  tempering is unnecessary, and the highly stressed condition caused by full quenching is avoided.


    (Chemical symbol: CaO). Quicklime, or calcium oxide, is unslaked lime. When quicklime is added to coke and heated in an electric furnace, the resulting products are calcium carbide and carbon monoxide. Calcium carbide is used in the process of generating acetylene. 


    Common name for mercury; used in instruments, vapor lamps and batteries.