WELDING TECHNOLOGY

THE ARTHUR HALLET MEMORIAL LECTURES - No. 16 in the series March 1967

By R. A. MacKellar, A.M.S.A.I.M.M, M.S.A.I.W.

ABSTRACT

This lecture explains the need for an appreciation of knowledge in welding technology as an aid to all engineering operations in which welding is involved. It describes common electric welding processes in use and some of the problems encountered in their application. Quality and reliability requirements are discussed in terms of Specifications, Inspection, and Testing. The emphasis is upon the importance of welding technology in all its aspects as related to welding fabrication. 

INTRODUCTION

Welding technology is a reality that has not yet been fully recognized throughout South African engineering circles despite the widespread use of the practice of welding. Perhaps only when failure of a welded assembly has occurred, sometimes with devastating results, is the message driven home with shattering impact that behind this practice lies a technology of considerable importance.

Embracing the fields of engineering, metallurgy, physics, chemistry and corrosion and the infinite varieties of these sciences, welding technology is such a broad subject that no one person can be expected to be an expert in all its aspects. However, every welding engineer requires to have an appreciation of each, of these subjects, permitting him to fulfill his functions in a satisfactory manner. Behind him are the specialists, each capable of contributing specialized knowledge to the problems which continually beset the welding technologist.

As more nuclear reactors are built and larger, more efficient, power stations are designed, so do the responsibilities of the welding engineer increase. The erection of chemical plants, the introduction of new alloys and, the ever-increasing demands to operate at lower, or higher, temperatures bring to light new problems in the joining together of metals and their alloys.

Sub-miniaturization of components taxes the ingenuity of the technologist and the development engineer. And, all the time, the welding fabrication of hitherto straightforward assemblies becomes more difficult as new Specifications or Codes of Practice are introduced with a background of greater enlightenment in the effects of defects and design data.

The life of the engineer is becoming more and more complicated and wherever welding is being used, the need for an appreciation of welding technology is becoming essential. If a welding technologist is now available to provide assistance, it is the responsibility of the engineer in industry and in the design office or laboratory to recognize this need and to do something about it. If not, catastrophic failures could result in a possible loss of life or limb.

HISTORICAL DEVELOPMENT

There is not a great deal of published information about the historical development of welding, but from the following two sources1, 2, the following facts have been gleaned.

Native copper and gold were being collected in 5 000 B,C. but the earliest evidence of joining metals together dates from around 3 000 B,C. An example of lap welding is known to date from 1000 B.C. and it is interesting to note that an Iron headrest recovered from the tomb of Tutankhamen in Egypt manifested rudimentary knowledge of a welding technique,

In 1724, an experiment describing the joining together of two lead balls was described before the Royal Society and the ultimate tensile length of this joint was reported as being 2930 lb/m. But it was not until the early 19th Century that electric fusion welding was developed. Noteworthy in these developments were Sir Humphrey Davey, J. P. Joule, and Lord Kelvin, Early experiments in electric resistance welding were described by Professor Elihu Thompson in 1877 and these were an excellent example of serendipity. Towards the end of this momentous Century, foundrymen were relieved to learn that holes in castings could be repaired using a process developed by a Russian by the name of Bernados.

This was the advent of electric arc welding as we know it today.

After that, development was rapid and in 1907, Kjellberg was working on the use of coated electrodes, the importance of which was recognized during World War I.

As in most wars, the special impetus was given to technological development and the effect was evident after the war when, for example, Lloyds issued its first recognition of electric arc welding as applied to ship construction, not long after this, in 1920, the first all-welded ship was launched.

Having caught it breathe, welding development donned its three league boots and progressed at a phenomenal rate. The submerged-arc welding process was developed in 1937 and this was a major breakthrough in welding technology with tremendous repercussions throughout the engineering industry. The Russians claim to have introduced this process in 1941 but the Americans can justifiably be honoured. World War II saw the development of tungsten inertgas welding with particular reference to the aircraft industry and the post-war years have inundated us with sophisticated processes and techniques, each having its own fascinating range of applications.

As a result, laser welding, electron beam welding, ultrasonic welding, friction welding, and electro-slag welding are processes which are rapidly becoming commonplace, At the same time, the sphere of welding technology has had to expand in order to embrace the new problems in design and applications which have been presented to the engineers and scientists.

MODERN ELECTRIC WELDING PROCESSES

The processes in use in Southern Africa are many and are becoming more and more diverse. To describe them all in a paper of this nature is not possible but there is time to consider the main types without having to dwell upon the more common processes or explain in too great detail those of a more advanced nature.

Welding processes can be divided into two main types: (a) welding without pressure, and (b) welding with pressure. Welding without pressure is often referred to as fusion welding and the second method as pressure welding. For example, the common manual electric arc welding process is fusion welding and electric resistance welding falls into the second category.

The important welding processes are illustrated in Figure 1.

1. Electric arc welding

This process is the one with which most engineers are acquainted and is better described as shielded metal-arc welding as it involves an arc struck between two metallic elements - the electrode and the parent metal - shielded with a medium designed to improve the arc characteristics and protect the weld deposit. It acts in a similar manner to steelmaking with a reactive slag to remove undesirable constituents and the creation of a miniature casting of pure deposited metal possessing the desired chemical and physical properties.

The principles of the process are given in Figure 2. Shielded metal-arc welding is the most commonly used process and can be seen in operation in garages and nuclear power plants, to mention only two extremes in the application.

Many characteristics can be introduced into the electrodes used and because of this, a classification system has been developed for each type. This information is of considerable value to the engineer as it enables him to select the most suitable filler metal for each application. If only A.C. welding equipment is available, the best type of electrode can be chosen. However, if deep penetration characteristics are important, combined with positional welding requirements, such as are applicable to site welding of pipes, the best type of electrode requires a D.C. source. If deposition efficiency is a major factor to be considered, a reference to the classification system will assist in the selection, just as It will when higher tensile strengths are involved. The separation of electrode types into groups, will, for example, make it a relatively simple matter for the welding engineer to choose an electrode type suitable for the welding of the modern heat-treated alloy steels with yield points in the region of 100 000 lb/in.

It is not possible here to enumerate the various classification systems in use but in South Africa is usual to use the American, British and South African systems. The last system is directly related to the ISO system which might well be universally adopted, as it should, in the future.

Some idea of the diversity of the types and characteristics of the electrodes available is provided in Fig.3 which is reproduced from the handbook of the American Society of Metals.

In this table. the term " welder appeal" is used and this is one characteristic that often bedevils those who specify the use of one particular type of electrode for a given application. This characteristic is indefinable but is known to every welding engineer. It can be summed up by stating that unless the welder likes it, the use of the particular electrode can be a dismal flop.

As a result, " the tail may wag the dog" inasmuch as every conceivable scientific test can be negated by welders to whom the electrode selected has no "welder appeal". To his other attributes, the welding engineer may also have to add that of an understanding of psychology!

Indispensible as this process is, the drawbacks of the human element and relatively low production outputs for some applications are recognized and this has led to the development and introduction of other welding processes.

2. Submerged-arc welding

Much of the human element has been removed from this process as it is essentially automatic in nature: It is also capable of high productivity rates. There is, however, a great dependence upon the design and mechanical aspects which limits its use because complicated shapes of the assembly to be welded may preclude its use. This may be overcome but if the number of the assemblies to be fabricated is small expensive jigging and guiding assemblies are not warranted. Submerged-arc welding lends itself to repetitive work of a fairly simple nature. Pressure vessel and pipe welding are two fields in which it excels because of the repetitive nature of the work they need for weld deposits of controlled physical and chemical properties and the ability of the process to satisfy stringent Inspection requirements.

Apart from the advantage of being able to weld at a far greater speed - five feet per minute is not uncommon - it is also possible to alter physical and chemical properties to suit. By using one type of flux it is quite simple to weld carbon steel and stainless steel by simply altering the type of electrode wire used. Similarly, a wide range of physical properties can be achieved by using different combinations of fluxes and electrode wires. For example, with one type of electrode wire and two types of flux it is possible to achieve considerably different physical properties; alternatively, it is also possible to obtain the same effects with one type of flux and two different types of filler wire. Here then, is a versatile tool that can be used to great advantage by the welding engineer but in doing so care must be exercised. If, in an effort to satisfy the common cry for a " strong weld he may not meet the need for the designer "to have a ductile joint which is also an important characteristic. But by investigating the many combinations possible and by considering the importance of manganese, silicon, and molybdenum, the welding of low and high tensile steels can be achieved satisfactorily, when such other fa tors as cleanliness, edge preparation, notch ductility, corrosion, and strength are also to be considered.

It is in this field that the welding engineer's knowledge can be invaluable as his understanding of metallurgy and arc-transfer characteristics come to the fore.

The submerged-arc welding process possesses other distinct advantages as it can be used for processes other than joining together. As in the case of shielded metal-arc welding, it can be used to deposit an overlay of corrosion-resistant stainless steel on to a carbon steel substrate or to provide a skin of abrasion resisting alloy steel, covering a core of tough, ductile carbon steel. An example of the former application is shown in Fig. 4 in which cl recently developed a method using strip electrodes 2-3 inches wide has been used to provide a stainless steel layer on top of ordinary carbon steel.

The submerged-arc welding process can be used to weld stainless steel but owing to the limited production of welded assemblies in this material in South Africa, the benefits of this process have yet to be realized. Before embarking up in such programs, the local industry would be well advised to consult a welding engineer with a view to determining slag detachability characteristics and, more importantly, the possibility of a crack developing in welded joints. The presence of crack has been noted in welded assemblies supplied from overseas sources because of inferior welding procedures being used and this lesson could well be remembered when we commence such fabrication. The chemical composition of the weld metal not normally affects cracking of the weld but also affects resistance to corrosion.

3. Electro-slag welding

In a discussion of modern welding processes, the electro-slag process is important. With this process, it is possible to weld together thick sections of metal in one pass at an extremely fast rate. Sections of electro-slag about three feet in thickness have been welded together and it is natural that such a process has excited considerable Interest amongst fabricators who are required to weld heavy sections together. Typical applications are to be found in the boiler and nuclear welding fields. Physical properties of the welded joint are excellent and the ever-present problem of notch-ductility can be overcome with ease. Figure 5 illustrates the process being used to weld together two 20 inch thick sections of steel.

4. Electro-gas welding

One disadvantage of the electro-slag welding process is that it cannot be used when thinner sections of steel have to be joined together. Electro-gas welding is a process which was developed to fill this breach and which retains the advantages of the former process. It is capable of high production rates-seventeen feet long joints can be welded in one inch thick sections in one hour - and deposition of welds of excellent quality.

A tubular electrode filled with flux is used and an additional shielding medium is provided in the form of carbon dioxide gas fed into the weld pool area through water-cooled copper shoes which contain the molten weld deposit in the seam. The type of flux used in the electrode wire provides alloying elements where required and deoxidizing elements to purify the weld metal. It is also of interest to note that the slag formed acts as a lubricant between the moving copper shoes and the weld and at the same time reduces the possibility of a copper pick-up on the surface of the weld deposit which can result in cracking.

Electro-gas welding is a process that has been tried and proved in South Africa, particularly in the construction of steel tanks. Another application, still to be used locally, is in the shipbuilding industry for the welding of hulls. This method is shown in Fig. 6.

5. Semi-Automatic welding

This most useful process for welding was introduced several years ago and. has found widespread application throughout all industries in which welding is used. Perhaps because of a conservative outlook in the. welded fabrication industry it has not been used to Its fullest extent but this may be overcome as a more progressive attitude is adopted in the face of competition,

Semi-automatic, or MIG, welding can be used to weld together carbon steels, alloy steels stainless steel and aluminum alloys. A continuous reel of consumable electrode wire provides the filler metal and a gaseous shield, the protection. A high rate of deposition in terms of pounds of weld metal deposited per arc hour can be attained and high duty cycles are also possible. This latter aspect is important when it is realized that the ordinary welder may only spend a third of this working hours in actually depositing weld metal. With higher pay for labour becoming the order of the day, increased efficiency is becoming more essential. Welds of excellent metallurgical properties are possible but to achieve this, attention must be given to the training of operators and development of optimum welding procedures and techniques.

If applied properly, this process can overcome many problems in fabrication practice such as poor fit-up, inadequate preparation and having to weld only from one side of the joint when high-quality welds are required.

6. Tungsten inert gas welding

The artistry of welding might be said to be embodied in this process which is in demand where high quality and careful control are essential. Developed in America in 1942, its immediate application was in the aircraft industry but since then it has been used in all spheres of industry. Without this process, it is claimed that the fabrication of components for the nuclear industry would not be so advanced. And in South Africa, it is anticipated that the rapid development of power stations will see its use becoming a normal occurrence for most of the tubular welding involved.

T.I.G. welding, as it is commonly referred to, depends upon the use of a non-consumable tungsten electrode generating an intense arc into which is fed a filler rod of suitable analysis for the metal being welded. Argon gas flowing around the electrode acts as an inert shield to prevent oxidation. As there is no shielding slag, the welder can study the weld puddle as it is formed and control his technique carefully. By this means and by the absence of foreign elements, welds of extremely high quality are obtainable even in aluminum alloys which are difficult to weld by any other normal process.

The welding engineer has introduced the T.I.G. welding process to solve some of his most difficult problems, a good example being the welding of titanium and zirconium.

 7. Other welding processes

Ultrasonic, friction, electron b am and high-frequency electric resistance welding are other modern processes recently introduced which are of considerable importance. As more exotic demands are made, they will assume advanced roles in welding science. Already they are proving to be invaluable, and any practicing engineer should be aware of their introduction. Lasers are much at the forefront of engineering technology and the application of this system to welding technology is already well advanced.

 WELDING FABRICATION

The term " welding fabrication" is almost as wide as the term "engineering" because it embraces design, methods of manufacture, welding procedures, and techniques employed, costing of assembly, inspection, and other factors.

Welding fabrication covers an industry on its own which has been developed because of its economy and convenience. If it did not have these two attributes, it could not have developed to its present stage.

The fabrication of assemblies and components has assisted the many industries with which it is assisted. The motor industry, foundries, light engineering, heavy engineering, electrical, electronic and pipeline are only a few fields in which it has found an important part to play - possibly even being indispensable to their continued development.

The costs of welding are low because of its convenience and adaptability. This situation is being continually bettered as processes, procedures, personnel, and techniques improved. The minimum preparation is required and a high degree of mechanization is possible, reducing expensive labour costs. Defective sections of weldments can be removed and repaired easily which is of importance when quality requirements are high.

Welded fabrications lend themselves to inspection systems because of the nature of faults present and perfection m the weld - if such is required - can be virtually guaranteed. If the present pace of research is continued, in a few year's time the welding engineer will also be able to determine accurately the effects of defects under given conditions and designers and inspectors will be able to issue specifications and certification of much greater practical significance than at present.

If the disadvantages of welding fabrication are to be discussed, two are worth mentioning. One is that it is so easy that unskilled personnel may design or weld a structure which subsequently fails in service. This can so easily occur in garages, for example, with the result that life is endangered. The other disadvantage, if it is on when all the advantages are considered, is the cost of weld metal. In order to obtain a welded joint of similar chemical and physical properties, anything between R400 and R1 000 may have to be spent per ton of weld metal deposited, whereas the cost of the parent metal may only be in the region of R80 per ton.

Because of these factors, care should be exercised at the design stage that a welded assembly suitable for the service conditions anticipated is designed and that only the required amount of weld metal is deposited to ensure reliability at an economic cost. Adequately trained operating and supervisory personnel should also be fully used to control the application of such an expensive metal

DIFFICULT METALS

This is a term commonly used by engineers whenever something out of the ordinary run of welding is discussed. It is granted that there are difficult metals to weld because of their properties and other factors such as being in a heat-treated condition prior to fabrication.

Many of the so-called "difficult metals" are relatively easy to weld either together or to some other metal. What is not recognized generally is that ordinary low carbon steels may prove to be more difficult to weld together when high standards of quality apply than when stainless steel has to be joined with carbon steel, and ordinary standards of quality are applicable.

The major problems are often involved in the fabrication of welded assemblies and not in the welding per se. An example of this may be taken from a recent problem encountered by a local welding fabricator who had to manufacture aluminum alloy storage vessels of extremely high quality. The parent metal as received from overseas sources could not be rolled into a cylindrical shape because of its being in a heat-treated condition and consequently of low ductility. The material, therefore, had to be re-heat-treated to render it soft and ductile. Because of corrosion conditions in service, a particular type of filler metal was specified which would not be susceptible to the aggressive attack anticipated. This immediately presented a problem to the fabricator as the filler alloy used was prone to hot-cracking in the welds and only another filler metal of different composition, but more susceptible to corrosion could obviate this. Fabrication of the vessels proceeded but the extremely high standard of inspection and acceptance soon presented another difficulty. The type of filler metal used not only cracked but it was also prone to porosity. Each repair made generally became progressively worse and a vessel had to be scrapped which had been subjected to weld repairs. The welding of this" difficult metal" was relatively easy compared to the fabrication problems encountered and the problems presented by the service to which the vessels were to be exposed.

Many other examples could be given of the ease in which many metals and alloys can be welded but which present difficulties in other respects.

Difficulties in welded fabrication can often be avoided by overcoming ignorance. Knowledge in welding technology can be the greatest asset to any engineer or fabricator called upon to supply assembles of complexity in design, quality, and material. It is suggested that those who refer to the welding of certain materials as "difficult" are either lazy or ignorant; lazy because they are not prepared to develop methods of overcoming the problems encountered, and ignorant because they are unaware that ways and means are available to join together the metals or alloys in question. Welding science has developed to such a degree and has collected such an armament of weapons in its war against the problems presented that virtually any metallic and, often, non-metallic material can be welded.

The term" difficult metal" then has become relative to economic undertones. Costs of overcoming the problems may be high as has been found in the nuclear and space satellite industries but advantages in progress have been reaped. On a high level, therefore, the industry must invest in welding technology to make it easier and more economic to weld these " difficult" metals and, on a more mundane level, the engineer must dispose of his fear through ignorance that some materials are unweldable.

Perhaps by paying more attention to aptitude, selection of materials, basic engineering and metal-lurgical facts, design, and development programs, he might realize that the metal is not so difficult after all. And as welding is not the panacea to all joining problems, the engineer always has recourse to other methods such as riveting and the use of advanced cementing materials that are not to be scorned as any welding engineer will truthfully relate.

COMMON MISTAKES

It is not intended to catalog the numerous common mistakes encountered in practice. Two mistakes are commonly made. The first is that the welder, fully competent to undertake the work, is given work by a supervisor who is incompetent of knowing whether the standard demanded is acceptable in service. The second is that the designer often makes no allowance for the idiosyncracies of welded fabrication or that welds often contain faults.

In the first instance, the welder is too often recognized as a person who could not quite make the grade as, say, a motor. mechanic and that is why he is a welder. Sometimes, regrettably, this is true but, still, no effort is made to improve him and his knowledge. After an inadequate apprenticeship, in some cases, the welder is often required to deposit welds under varying circumstances. Sometimes a weld of poor quality is all that is necessary and no harm is done, but there are occasions when he must perform a task of a high standard and is incapable of doing so. The supervisor, in turn, may be at fault because not only is he responsible for the training of his personnel best also for the instructions given. If the Incorrect Instructions are given because of ignorance, untold harm can result, and this is of extreme importance in modern welding fabrications where advanced performance is becoming commonplace. A great onus is placed upon the supervisor, therefore, to ensure that his operating staff is adequately trained and competent to undertake the work allotted to them. He must also recognize that, pertaining to each job undertaken, other factors apply. The service conditions to be encountered, the degree of inspection applied and, above all, the economic factors must be understood. Perfection is desirable but a supervisor who demands this at all times can ruin a fabrication organization; equally, a supervisor who scoffs at perfection or a predetermined standard of quality can be just as dangerous. The ideal, of course, IS to have a supervisor who fully realizes that quality is, after all, fitness for purpose.

In designing a welded assembly, the designer has to layout a three-dimensional structure on a two-dimensional plan. This is a big enough problem but to introduce what might be loosely termed a fourth dimension is a prodigious task. That extra dimension is practicality and it covers an immense variety of factors such as the adequacy of the specification used, if any, the practicability of fabricating it and the provisions for inspecting it as stipulated. Too often, the designer makes the mistake that the inspectors are midgets or have extraordinary facilities for examining welds in locations in which welders with exceptionally long necks and arms are capable of depositing. The designer may also accept welds literally at face value and stipulate visual examination of joints only. In doing so, he accepts a cosmetic value of no importance and neglects the fact that the most serious faults can be present below a weld of flawless surface appearance. In the event of him realizing that other methods of inspection exist such as magnetic particle inspection, radiographic examination, and ultrasonic testing, to name only a few, the other extreme may be introduced of either inadequate non-destructive testing or over-testing. To equate, as some designers do, magnetic particle inspection with ultrasonic testing is dangerous to both clients and. manufacturer. But to stipulate anyone's method without also defining acceptance standards is inadmissible. The designer must, therefore, now not only calculate stress levels but also ensure that the minimum levels are guaranteed by the optimum method or system of inspection. The responsibility is considerable but must be accepted if progress is to be made. As emphasised earlier, knowledge is the only preventive.

If these two basic problems are realised and acted upon, the other mistakes in welding fabrication fall into place. Errors in the design and specifying offices will be minimized and faults on the shop floor will cease to a large extent.

The common mistakes of incorrect electrode selection, poor fabrication procedures, and bad welding techniques will disappear in the light of knowledge and the all too common excuse of increased costs will prove to be specious as improved efficiency and decreased cost of rectification become evident.

TRAINING AND TESTING

Resulting from the foregoing, the practical engineer may well ask if it is possible to satisfy the demands made upon him and his personnel. The answer is in the affirmative provided certain basic rules are obeyed. These are:

With modern procedures and techniques, trailing has become essential if full benefits are to be derived from them. The purpose of training is twofold; it assists the inexperienced to make maximum use of the equipment and it helps to adjust the experienced welder who has picked up incorrect techniques which might be detrimental in new and advanced applications. At every stage, if possible, the welder should be instructed not only in how of his activities but also in the why. Such people are, at the same time, being assisted to fit into supervisory posts at a later stage in their development.

A great fetish is being made nowadays of testing in the welding fabrication industry. The advantages of this are indisputable but an appreciation of its value must be maintained. A large number of competency tests for welders have been devised as an aid to establishing whether a welder is capable of conducting certain types of welding. This is admirable but It must be recognized that what happens under test conditions does not necessarily occur in practice. Human fa tors intervene and a welder who proves himself competent under test conditions sometimes reveals himself to be the opposite in practice; conversely, the welder who fails a test may be completely acceptable on the job. This is recognized by experienced supervisory staff but they also must obey the rules and regulations of specifications which stipulate a minimum standard of approved workmanship.

Control, therefore, becomes an important, if not indispensable, a requirement in practice. It is of no use training and testing welders or operators of welding equipment only to establish that their end product is unacceptable. The necessary rectification may prove to be costly and awkward, to the detriment of all. Control during fabrication and welding assumes considerable importance in modern practice and this, in conjunction with training and testing, cannot be neglected if success is to be assured.

Training of welders is to be encouraged, testing is to be applied, but in-process control is mandatory if the full benefits of the first two procedures are to be gained.

 QUALITY CONTROL

Present demands in the industry make quality control imperative and it has become so closely associated with welding technology that it must be considered to be part of it. In the near future, it is anticipated that here in South Africa a tremendous impetus will be provided for the development and application of quality control techniques and systems when the new power stations are erected. New specifications and quality requirements will challenge the welding engineer to do his utmost to satisfy the increased demands made.

At present, quality control is still in an emerging state with attendant difficulties due to lack of appreciation of its value, shortage of trained personnel and there is a great deal of ignorance concerning the significance of defects. As time passes the appreciation of the n ed for quality control is increasing rapidly but this, regrettably, is often only because of failures highlighting the absence of such control. Facilities for the training of personnel have also improved and a cadre of highly experienced specialists has developed over the years. The last aspect is the one in which the most exciting and useful developments are taking place. The effects of defects are being subjected to intense study throughout the world, the British Welding Research Association being outstanding in this field. All of this knowledge is freely made available to the International Institute of Welding which has the task of collating what is becoming an avalanche of information and disseminating it to all interested bodies. South Africa was a founder member of the Institute and accredited members on each Commission receive each report published.

The work of the I.I.W. is reflected in the activities of the International Standards Organization which introduces specifications based upon the advanced knowledge available.

To the engineer, the work of the abovementioned bodies may appear to be academic and complaints may be made that the practical significance of then deliberations takes a long time in filtering through to the shop floor or construction site level. This is not so, as amendments to existing specifications based upon decisions made by the I.I.W. and I.S.0. are published regularly.

It would not be fully correct to state that inspectors became necessary as the number of craftsmen diminished they became essential in a highly industrialized economy as higher productivity was achieved and mechanization utilizing unskilled operators became an everyday practice.

Inspection thus became quality control and a specialized field independent of production. It now embraces many types of specialists from the man with the micrometer to the scientist with a complex array of elaborate electronic equipment. The specialist in non-destructive testing has, in many respects, become the most important type of inspector m welding fabrication because his services are accepted as a matter of course. His findings and his decisions can result in the acceptance or rejection of assemblies varying from the small to the massive. But it is not to be forgotten that the reliability of a minute component can profoundly affect that of a total assembly worth thousands, if not millions, of Rand.

Any engineer involved in the design construction or use of equipment or structures on which some form of quality control is exercised must, in his own interests ensure that control is conducted properly with skilled and, where necessary, qualified staff. Engineers are professional people and their responsibilities and reputations must not be endangered by the judgments of those who are incompetent, integrity, responsibility, the ability to act in a fiduciary capacity and knowledge are the attributes sought in an inspector. Such people are becoming increasingly difficult to find but they are available if the engineer is prepared to seek them and employ them under mutually acceptable terms. The claim is often made that quality control increases costs and results in commercial mayhem. This may be true but a closer investigation of the situation should be made to determine if it is not really a case of ineffective supervision, ineffective equipment, deficiencies in procedures and the wrong attitude to quality resulting in defective assemblies which are proved to be so by inspection. The increased costs may, in reality, not be due to inspection but to rectification of effects. If the correct systems are introduced and controlled, quality should provide a quantity.

 SPECIFICATIONS

Every engineer deals with specifications and codes of practice, and soon develops an appreciation for their advantages and disadvantages, then soundness or their weaknesses. Some engineers prefer to have only the barest skeleton and others demand voluminous documents leaving nothing to the imagination. Some compel the supplier to obey every clause without deviation while others may be amenable to compromise. It would be wrong to say who is correct. It would be unfair to suggest that the ignorant require the specification with innumerable clauses and appendices which they force the fabricator to obey implicitly, there are too many factors involved.

A specification should be a " detailed description of the particulars of some projected work in building, engineering or the like, giving the dimensions, materials, quantities, etc., of the work, together with directions to be followed by the builder or constructor". In some instances, it has also been found that it is for the guidance of a wise man and the obedience of a fool.

The technical world is flooded with such documents and engineers are often perplexed over which one to use. Sometimes they do not know and their procedure of selection develops into a guessing game; others who consider that the acceptance standards are too lax, arbitrarily alter these standards to what they consider is required. In doing so, particularly in welding fabrication, this can be nonsensical. It is often assumed that the smaller the size of a defect or the lesser the number of discontinuities the safer the structure will be. Welding research has shown that this is not so and that gross faults will not be serious if the item is under static loading. Dynamic loading, however, can cause failure to be initiated from a defect of macroscopic proportions. The nature of the fault, the metallurgical characteristics of the weld and parent metal, the location and the plane in which it lies are of major importance when assessing the significance of such imperfections.

The confusion associated with the use of specifications does not occur only because engineers and others are dealing with subjects of which they possess scant knowledge. International specifications are desirable; national pride makes it a matter of prestige for each country to maintain a body to publish specifications under the name of that country and organizations, who consider both types of documents do not satisfy their particular needs, also issue specifications, Many benefits result but amidst this plethora of documentation, confusion is inevitable. Rationalization of standards has become essential and an excellent plea has been made by Dr. Week of the B.W.R.A. for this.'

 It is hoped that engineers will assist in this process or simplifying matters by accepting that welding specification and codes have -been compiled by specialists acting on the latest available information. They should, therefore, not presume to be sufficiently omniscient to alter these published specifications unless they have good reasons or know that what they are doing will provide real benefits and not imagined ones. If, on the other hand, the engineer is desirous of having a specification to suit some particular aspect of welding fabrication, the assistance of specialist welding and inspection authorities should be obtained.

 INSPECTION AND TESTING

In modern welding technology, inspection and testing of welds and assemblies have assumed major importance because it is by these means that the efforts of welding engineers to improve the science and practice of the craft are largely proved. Initial examination by one method or another can indicate whether faulty welds are present and similar methods can reveal incipient failure. Should a failure occur, the same methods may pinpoint the cause of failure with future benefits to all. Inspection and testing can be varied to suit anticipated service conditions and if this is applied properly, inestimable benefits can be obtained. The degree of inspection applied is important but this must be left to the discretion of those who are aware of the limitations of each method and the value of the information obtained.

Not all the methods of inspection and testing currently in use will be discussed; some of these may be well known or obvious to the practicing engineer and the remainder would require detailed treatment in order to apprise him of their principles and applications. For those interested in more information, the many sources of information should be consulted.

Dimensional and visual examinations of welded assemblies are simple to perform and are considered to be of basic importance. On a more advanced level, proof testing using hydrostatic, pneumatic or tensile methods is often used to prove the integrity of a fabrication. Useful as they may be, it should be recognized that undetected defects may be present which affect the validity of such a test. Having satisfactorily passed inspection methods such as visual, dimensional and proof testing, there are many types of welded assemblies that will provide unblemished service for many years. However, in this sophisticated era, such methods are now often unacceptable because it is known that defects may be present which are not detected by the above methods.

A greater degree of inspection then becomes necessary and this may involve a large variety of more specialized tests requiring more advanced interpretation of results.

The first step may be to conduct a destructive test of the weld and adjacent metal to determine the physical properties of importance to the metallurgist. Yield and ultimate tensile strengths are characteristics of value; ductility and notch-ductility properties can also provide essential information. Brittle failure of welds has assumed importance in modern engineering technology which may seem to be over-emphasized but which certainly cannot be neglected.

The chemical composition of the weld metal sometimes has to be confirmed because it can indicate the possible behaviour of the assembly in service. For example, the metallurgist who discovers that an ordinary type of stainless steel assembly has been welded with a fully austenitic filler metal may wish to confirm that cracks are not present in the joint. In another case, the composition of the weld deposit may affect its resistance to corrosion such as is experienced in sulfate digesters and galvanizing baths.

The metallurgical structure of the weld often requires assessment because this can also indicate proneness to corrosion such as is experienced in a pump column at a mine. The examination of a welded joint under the microscope or magnifying lens can provide information to a specialist which is of considerable significance. Apart from verifying the causes of failure, it can also prevent them.

In a sphere of its own lies the field of non-destructive testing which is often contentious in practice and has resulted in numerous arguments over its advantages. Radiography is, in the mind of many engineers the panacea to all inspection problems and, to them, a radiographically acceptable weld is consequently a perfect, weld. This is the trap into which many otherwise sound people fall because it is outside their already extensive knowledge that faults can exist which are not detected by radiographic methods. To a specialist, a radiograph provides vital information but, other important information can affect his decision, such as how the radiograph was exposed, what type of film was used and which technique was used. These are only some of the factors to be considered,

Equally, with other methods of non-destructive testing, the specialist will realize that limitations exist that are not appreciated by the engineer who is unaware of the details, As a result, the engineer may be be wild red by the variety of tests conducted and may even express his exasperation. What the engineer must realize is that one method of test can complement another one so that the final decision made as to the integrity of a weld is based upon a careful and knowledgeable scientific system.

When the engineer happens to be introduced to the ultrasonic examination of welds, the great difficulty may be encountered. The conviction that ultrasonic examination is infallibly is just as bad as rejecting it out-of-hand because of its apparent duplicity in results. This method requires a skilled operation and careful interpretation of the results. The human factor is important and the utmost integrity on the part of the operator is demanded. Even the technique used can affect the information obtained and an understanding that certain defects in welds are undetectable by ultrasonic examination should be considered by any engineer who accepts or specifies this particular system.

The foregoing comments may be confusing but they are not intended to be so. They are intended to outline, the advantages to be derived from intelligent inspection and to emphasize that each method possesses disadvantages. No universally applicable method of inspection has been devised which will reveal all defects and, certainly, no system has been developed which will assess automatically the significance of any fault revealed. Attempts are being made to do this on a computer-like basis but, so far, human judgment is still the most satisfactory in service.

It has been found that during a four-year graduate course in engineering, only forty-five minutes are devoted to welding. Nobody has calculated the time, if any, spent in appraising an engineer of the methods and advantages of inspection and testing. Time may be spent in stress-analysis but, useful as it may be, this is insufficient. The engineer, if he has not already been introduced to it, will find that welded fabrications will enter into his professional activities, no matter in which field they may be. Inspection and testing will also assume importance as greater demands are made upon his ingenuity and resources.

Every engineer should be cognizant of this and prepare himself for these future requirements. To do this he will either have to improve his own knowledge of welding technology or be prepared to acknowledge the specialized knowledge brought to him by the welding engineer and the welding inspector.

 THE FUTURE OF WELDING

Is there a future in welding? The answer is most decidedly in the affirmative. As advances are made in every engineering field, it is remarkable how welding is called upon to make its contribution. Power stations of increased output and efficiency could not be developed without the advantages of welding and the alloys used. In aeronautical engineering, welding fabrication of exotic metals and alloys is indispensable to future development. The bolting together of sections in nuclear reactors could not be countenanced and welding has become the only answer to many problems. Costs are important in the shipbuilding industry and only by replacing riveting with welded fabrication have costs been reduced.

In each of the above fields, conventional welding processes have been proved but the introduction of unconventional processes has still to be experienced in common practice. Friction welding, laser welding, ultrasonic welding, and electron-beam welding are presently being used but when introduced on a largescale commercial basis, their impact will be considerable.

As each advancement is made and introduced in the engineering field, the demands made upon the engineer will increase. Therefore, it is essential that those who are in any way involved maintaining an appreciation of the problems as they arise and devise ways and means of overcoming them. The increased specialization will become essential and the engineer will find himself becoming increasingly dependent upon specialists who are active in what are becoming narrower fields of interest as knowledge in them accumulates.

WELDING INFORMATION

Somebody once claimed that each day enough technical journals and reports are published to keep the average engineer, reading at a normal rate, occupied for 1200 years. This problem also besets those who wish to keep abreast of developments in welding technology. Many publications and reports are available from America, Britain, and Russia. Germany, France, and Poland also publish much information.

For the engineer who is deeply interested in obtaining more information than that available in publications available from the abovementioned countries, he would be well advised to establish contact with the International Institute of Welding and the British Welding Research Association. From these two organizations, he will be able to obtain the best information about welding technology.

There are also numerous textbooks published from which valuable basic information can be obtained. A list of these is given in the Bibliography.

Assistance and information can be obtained from the South African Institute of Welding who deeply recognize the need for improved knowledge in welding technology. This Institute periodically organizes schools of welding technology in which the various aspects of welding science, art and practice are discussed. The Founding, Welding and Production Journal publishes papers and thus disseminates much knowledge in South Africa welding technology.

CONCLUSION

It has become essential for the engineer to be aware of the role of welding technology in industrial practice and development in order that full use may be made of the craft, art, and science of welding. Only some of the more important aspects of the subject have been highlighted and no attempt has been made to describe or explain the more practical features. Such information is available from many sources and engineers and students are encouraged to make full use of these facilities.

South Africa has experienced the dawn of nuclear research and is expected to develop rapidly in this field with consequent effects upon the local fabrication industry which will, in any event, be expanding along many other lines. The challenge has been given and it can be met with confidence but unless welding technology is appreciated and utilized, the costs of such development are in danger of being needlessly increased because of what might be termed the factor of ignorance.

Acknowledgments

The author thanks the Council of the South African Institute of Welding and the Directors of Hall, Longmore and Co. Ltd for permission to deliver this lecture. The assistance provided by the following Companies who made samples and other illustrative matter freely available is acknowledged:

African Oxygen Limited,

Rockweld Corporation (Pty.) Ltd.

Thermal Welding Products Ltd.

 REFERENCES

1. Encyclopaedia Britannica.

2. S. DITCHFIELD. A history of welding, F.W.P. Journal, 1966, Vol. VI, No. II.

3. DR R WECK A rational approach to standards for welded construction. B. W.R.A. Bulletin, 1966, Vol. 7, February, March and April.

 BIBLIOGRAPHY

The following publications are recommended as sources for further reference:-

Welding design. School of Welding Technology, S.A. Institute of Welding, 1963.

Welding metallurgy. School of Welding Technology. S.A. Institute of Welding, 1964.

Welding course for works supervisory staff. School of Welding Technology. S.A. Institute of Welding.

New horizons in welding. South African Institute of Welding, 1965.

Founding welding, production engineering journal. Published jointly by: Institution of Production Engineers (S.A. Council), South African Institute. of Foundrymen and South African Institute of Welding, P.O. Box 9092, Johannesburg.

Welding handbook. Section 1-5. American Welding Society.

The science and practice of welding. A. C. DAVIES. Cambridge University Press, 1963.

Welding practice. Vol. 1: Welding methods and tests. Vol. 2: Welding of ferrous metals. Vol. 3: Welding of non-ferrous metals. Edited by E. Fuchs and H. Bradley. Butterworths Scientific Publications and I.C.I. Ltd., 1951-1952.

The welding encyclopedia, 15th Edition. MORTON GROVE, Illinois, U.S.A., 1964.

Welding technology. F. KOENIGSBERGER. Cleaver-Hume Press Ltd., 1953.

High productivity in heavy engineering. A. G. THOMPSON. Iliffe & Sons. 1960.

Arc welding. F. J. BAKKER and A. J. HOVESTREIJDT (Edit9rs). N. V. Philips Gloeilampenfabricken, 1964.

CO2 shielded consumable electrode arc. Welding. A. A. SMITH British Welding Research ASSOCIATION, 1965.

Electroslag welding. B. E. PATON (Editor). American

Welding Society, 1962 (Translated from the Russian publication).

Memorandum on non-destructive methods for the Examination of welds. British Welding Research Association, 1964.

Non-destructive testing. J. F. HINSLEY. MacDonald & Evans Ltd., 1959.

Ultrasonic non-destructive testing of material. Dr. J.v.H.

KRAUTKRAMER. Salus-Schall Ltd., 1961.

Design of weldments. O. W. BLODGETT. James F. Lincoln Arc Welding Foundation, 1963.

Design for welding in mechanical engineering. F. KOENIGS-BERGER. Longmans, Green & C0., 1948.

New concepts in steel design and engineering. United States Steel Corporation, 1961.

The metallurgy of welding. D. SEFERIAN (Translated by E. E. Bishop) Chapman and Hall, 1962.

Weldability of steels, R. D. STOUT and W. D. DOTY.

American Welding Research Council, 1953.

Welding for engineers. H. UDIN, E. R. FUNK, and J. WULFF.

Chapman and Hall, 1954.