Welding standards are documents that govern and guide welding activities. Standards describe technical requirements for a material, process, product, system or service.

They give also information on equipment, methods, procedures and tests used to demonstrate that the requirements are being met.

"Welding standards" is a comprehensive term that includes codes, specifications, recommended practices, classifications, methods and guides. Differences appear in them as a consequence of different purposes pursued by their writers. Therefore the various documents, although similar in content, are not interchangeable.

Codes, usually applicable to processes, explicitly indicate mandatory actions. Specifications provide requirements, generally for products.

The voluntary character of Welding standards becomes mandatory when so established by procurement documents, or when specified by governmental authorities having jurisdiction, for public safety, upon that type of regulated subject.

The larger scope of "standardization", that includes of course Welding standards, is to promote compatibility and competition of products and services, to improve quality and reliability at a reasonable price, and to simplify products for greater usability and ease of maintenance.

With the progress of globalization and international supplies of goods and services all over the world, Welding standards are required to be increasingly understood and applicable everywhere. Therefore there is an ongoing effort to obtain the largest available consensus on truly international Welding standards, issued by ISO (International Standardization Organization). However not all international standards are written in English.

Although we cannot cover every single document that may be required, we present hereafter a list of most popular Welding standards hoping to do a service to our readers who may look for particular answers to their problems. Reading and learning Welding standards is also a recommended self-improvement habit that can contribute noticeably to personal growing and professionalism.

The Southern African Institute of Welding (SAIW) conducted its first ISO 3834 certification process in September this year, in accordance with the International Institute of Welding and the European Federation for Welding certification system, awarding local manufacturer Stainless Fabricators with the first ISO 3834 certification in the country. The SAIW reports that end-users such as Sasol, Eskom, and Mittal Steel, have supported the implementation of the scheme since inception.

Stainless Fabricators MD Peter Viljoen says previous dealings with end-users such as Sasol entailed rigorous auditing, since the ISO 9000 system did not incorporate welding fabrication-specific issues. 'The emphasis of the ISO 3834 system is on quality management systems specifically in the welding systems, and covers all facets of welding.'

Viljoen adds that in the past, end-users were expected to cover the expenses incurred during duplication work, which resulted from a lack of a standard specification. He says the ISO 9000 system lacked the depth to deal with sophisticated projects, and often manufacturers were unable to deliver to end-user specification.

'With the implementation of the ISO 3834, there is a standard and norm for welding, and end-users are realising that there is really no need for duplication work, and the cost that implies. 'Welding is considered a special process because the final result may not be capable of being verified by routine testing.'

Viljoen says the quality of the weld has to be manufactured into the product, and not inspected; this means that welding normally requires continuous control and that specified procedures be followed. The ISO 3834 standard concerning quality requirements in welding has been specifically prepared to identify the controls and procedures required to produce welds of a quality level acceptable to the end- user of the product.

'It should be noted that it is not a quality system standard replacing ISO 9001: 2000, but it can form a useful tool when ISO 9001 is applied by manufacturers. However, ISO 3834 can be used independ- ently of ISO 9001: 2000.'

The main advantages for a fabricator choosing to implement the International Welding Fabricator Certification Scheme, through the ISO 3834 standard, includes the welding process-specific quality tool, which can stand alone, or be used with ISO 9001: 2000.

The welding process quality management tool is audited by welding industry experts so that true value is added for the fabricator's benefit. This avoids the system being relegated to a 'paper exercise'. Large end-users of fabricated equipment have already realised the potential value in this standard and are considering requesting fabricator compliance for future work.

The anticipated revised Occu-pational Health and Safety Act may include the certification of Pressure Vessel Fabricators and this ISO standard could be adopted to also align our industry with Europe's. Export opportunities are becoming more attractive and the alignment of our fabrication industry to Europe will create more business.

SAIW executive director Jim Guild says the larger end-users want to have confidence in the technical capabilities of their supplier organisations, and that the ISO standard will be invaluable in accomplishing this. He adds that, further, the potential changes to regulations in the Factory Act, which is likely to happen this year, makes it advisable for pressure vessel and boiler manufacturers to have their systems certified by an independent third party.

'Customers and end-users will want to be completely assured that the quality standards laid down by the Act have been adhered to,' says Guild.

He says that welding is a unique process in that the final result cannot be verified by testing only, but that the quality of the finished product is incorporated in the entire process thorough a continuously monitored control system, which follows specific procedures.

'These procedures are laid down in the ISO 3834 quality standard, and the basic reason for having a company certification scheme is to make sure that the manufacturers and fabricators are constantly and consistently working to the standards set by ISO 3834,' says Guild.

Although the need for such a standard was identified many years ago, Viljoen says it was not until recently, when the European Federation for Welding developed the standard, owing to competitiveness and unification with Europe, that the local industry responded to the need. Since January this year, the system has been available to members of the International Institute of Welding, says Viljoen. With the accreditation of Stainless Fabricators, the SAIW also received its international accreditation from the International Institute of Welding.

Guild says that with the the acquisition of an international accreditation, the large end-users will not be the only benefactors, but that the system will be a great help to exporters as the quality of product will now be recognised internationally.

This is a description of welding of rail joints using Thermit welding. In this process, the highly exothermic reaction between aluminium and iron oxides results in the production of molten steel which is poured into a mould around the gap to be welded. The superheated molten metal causes the rails to melt at the edges of the gap to be welded, and it is also the filler metal, so that the material from the rails coalesces with and joins the added molten steel as it solidifies to form a weld. Thermit is the trade name for one of the granular mixtures of aluminium metal and powdered ferric oxide. Ignition of the Thermit is usually carried out by lighting a magnesium ribbon or sparkler.

Procedures for Thermit welding:

• The rails are cut square and the gap to be welded is prepared within prescribed limits. (If the rail ends are cut skewed, the gap will be non-uniform and the fusion of the rails will be asymmetric.)
• The cut faces are cleaned with kerosene oil and a wire brush to remove rust, dust, or greasy material, etc. (Otherwise, this material may get fused with the weld material and this may render the weld defective.)
• A 1m-long steel straightedge is used to align the running edge of the rail head. The rail ends are 'peaked' to accommodate contraction during solidification and cooling of the 'Thermit' steel. If 'rising' of the rails is not done, the joint will sag due to differential cooling of the rail head (where more material is available and hence the cooling is slower) and rail foot after cooling. A sagged joint gives bad riding and becomes a maintenance problem. Such a joint will be subject to larger stresses due to the dynamic augment. For lateral and vertical alignment, wedges are used.
• Stands for crucible and torch are fixed on the railhead, at appropriate locations, on opposite sides of the welding gap and position and the height of the torch stand is checked and adjusted by placing the preheating burner or welding torch on it which is then removed and set aside for later use.
• A set of prefabricated moulds of the appropriate rail section is selected and examined for suitability. The rail profile of the mould is checked by placing the mould against the side of the rail to be welded. If required, small adjustments to the mould profile are made by rubbing the mould gently against the sides of the rail. Then the moulds are placed in the mould shoe (i.e., clamp), seating it properly using luting sand. The placement of the mould should be central over the gap as otherwise while pouring the molten metal, one rail end will get more heat than the other and the fusion of the metal at the other rail end may not be complete. The recess, if any, between the mould and the rail profile is sealed with luting sand. A slag bowl is attached to the mould shoe to collect the overflowing slag and molten metal during the pouring.
• The magnesite lines crucible is housed at the correct height and alignment on the swiveling crucible stand. A closing pin is placed at the bottom over the opening. This pin's head is covered by about 5g of asbestos powder, so that it does not melt in contact with the molten metal and 'auto tapping' takes place.
• The crucible is swung away from the rail and the 'portion' (self-igniting mixture which yields the molten metal) is poured into the crucible, heaped in a conical shape.
• Using LPG (commercial use cylinders) and oxygen (or petrol and compressed air, an older technique, but still in use), the preheating burner or welding torch is lit and the flame is tuned. This torch is placed in its stand which is fixed over the gap, and the flame is directed into the mould through the central opening. The flame heats the rail ends and this is done for a specified time for each rail section and the pre-heating gases employed.
• As the preheating is completed, the Thermit reaction is initiated by igniting a sparkler and putting it into the crucible. The reaction is allowed a specified time and the slag is allowed to be separated from the molten metal. Thereafter, the closing pin is tapped from the outside, thus discharging the metal into the top central cavity of the mould. Thereafter, the crucible and torch stands are removed.
• The excess Thermit steel over the head of the rail (head riser) is removed after solidification (but when the metal is still red hot) by either manual chiseling or using hydraulic weld trimmers.
• The remaining refractory material is removed and the steel vent risers attached to the collar of the foot of the weld are snapped off.
• The wedges, etc., are removed, any fastenings that were removed, are re-fixed and the railhead is ground manually or using grinding machines.