If so, are you aware of your obligations to the end client, the job contract, the drawings and specifications? This is a greatly misunderstood area and we would love to help you manage it. What does this mean for you the fabricator or the site welder? Well these standards are created to make sure all parties have a foundation, a level playing field, to work on as an absolute minimum guarantee of a certain level of quality. It lays out the requirements for design, as in weld size, length and placement, for the minimum training level required, do you need a full tradesman or not, for the testing required, x-ray or crack testing, and for the documentation that you are required to produce to satisfy the job requirements. This is usually carnival equipment or structures like the Southern Star Observation Wheel in Melbourne.
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The standard is an effective way to get the finish you want or need on stainless steel structures. This guide should help you to nominate the quality of weld to the standard. What is this standard? This standard is for welding any non-pressure stainless steel equipment and when it was first drafted in , its structure followed that of Part 1 dealing with carbon steel. A major revision in removed redundant text, expanded the good workmanship guidelines and brought the weld assessment and finishing processing up-to-date, while including guidance on precautions to minimise risk of failure from vibration.
The assessment section includes mandatory limits to weld defects and now includes optional features such as level of heat tint and surface roughness that may be specified by the principal or owner.
In particular, the post-weld treatment provides a number of possible processes and results, and specifying the option desired will minimise cost and frustration and deliver the result required. As an example of mandatory requirements, there are strict requirements for personnel qualifications, which are difficult to address retrospectively.
The raw product of welded fabrication Figure 1 refer to banner image above is typical of a routine TIG butt weld of two thin stainless steel sheets and displays a rainbow of colours on the surface.
The colours are caused by optical interference of reflections from the front and back of the heat formed oxide layer - just like reflections in an oil film on water. They must be removed along with a small amount of steel underneath them, where the chromium has been depleted during welding.
Specifying their removal is covered later in this article. Classification of welds Welds are classified as Category 1 structural or Category 2 non-structural. Category 1 welds have a subset Fatigue Applications FA , where vibration and fatigue failures may be an issue. The main difference is that Category 1 and Category FA welds require external visual inspection plus sub-surface inspection by radiography or ultrasonics.
The permitted levels of sub-surface defects are listed in Tables 6. However, all of the Categories 1, 2 and FA are assessed against three levels of surface defects revealed by visual and liquid penetrant inspection. The permitted defect sizes are set out in Table 6. The temptation is to specify Level A for everything, but this may raise costs unnecessarily without adding to durability. Often Level B is very satisfactory. Category FA welds require compliance to Level A assessment of surface defects plus restrictions on the angle between fillet weld tangents and the adjoining stainless steel surface.
This restriction supplements the 1 in 4 slope in section thickness changes set out elsewhere in the standard.
Table 6. It applies only for FA requirements. Post-weld surface finishing The standard also provides options for post-weld and surface finishing. Welds may be treated mechanically with abrasives, or chemically or electrochemically. Any of these finishes can be called up for Condition I and Condition II, but the defining feature of Condition I is that the weld bead must be ground flush. This strip polishing is common in tank fabrication for the food and beverage industries. It removes the heat tint and the chrome depleted layer beneath it without using pickling acids, but it also improves cleanability by removing the weld bead with its inherent unevenness.
In vibrating applications, the mechanical removal also decreases the risk of stress concentration along the stiffening line of a weld bead.
These options are included in Condition III. Amongst other variables, the grit size will determine the roughness Ra and Rmax and hence the as-abraded corrosion resistance and cleanability. Condition III does not have acceptance criteria. Tables 1 and 2 below are a guide to the use of category, class and condition used both for treatments applied and assessment results and relate them to post-weld processes. Other treatments While mechanical abrasion will remove heat tint and the chrome depleted layer, it will expose manganese sulphide inclusions which are points for corrosion initiation.
It may also leave metal flakes on the surface, which provide crevice corrosion sites. Pickling [Section 6. Pickling a non-abraded weld area will not significantly change the surface roughness, but will give similar corrosion resistance to an abraded and pickled surface. If the use of hydrofluoric acid is difficult, then a nitric acid passivation process of an abraded surface will improve the passive film, remove the inclusions, but not any metal flakes.
A passivation treatment will strengthen the passive film even of a pickled surface. A nitric-only treatment is not effective on a heat tinted surface. Other modifications of Conditions I and II include electropolishing [6.
Both apply a current which dissolves the surface either in a bath electropolishing or on site electrocleaning. Electrocleaning is a manual process, and while it can produce a very strong passive film, its results depend on the expertise of the operator. The longitudinal weld in the pipe refer to Figure 3 below still has weld reinforcement, but is chemically clean.
The black lines parallel to the weld have not been affected by the acid pickling and are probably due to cracked oils not removed by solvents prior to welding. Post-pickling passivation is also included in this Condition II suite of treatments. The mechanical treatment of heat tint by stainless steel brushing [6.
Abrasive polishing, linishing, grinding [6. In addition, the surface may be too rough for good cleanability or smooth appearance. Under Condition II, one treatment to provide oxide-free welds for pipes and tubes is the use of inert gas purging with low tens of ppm oxygen levels.
Apart from the weld inspection, Section 5 of the standard has multiple recommendations for excellent fabrication including heat input, interpass temperatures, avoidance of arc strikes and welding under adverse weather conditions, to name a few.
Conclusion The specification of weld quality requires an understanding of mechanical and chemical processes used to produce a smooth and clean surface suitable for the specific application. The standard provides a shopping list to accurately specify exactly what you want. Respecting that intent will lead to the greatest productivity in delivering the structure.
Section 1 Scope and General
This standard sets out requirements for materials of construction, prequalified weld preparations, methods for the qualification of welding procedures and welding personnel, together with workmanship and inspection requirements for the welding of reinforcing steel in concrete structures designed and constructed in accordance with AS and AS It is intended for the welding of reinforcing steel complying with AS , AS and AS , but applies also to the welding of steel connection devices, inserts, anchors and anchor details, including prefabricated assemblies required in reinforced concrete and precast concrete constructions, in the fabrication shop and in the field. NOTE: Appendix A gives a li st of matters of a contr actual nature which might need to be finalized between the pri ncipal and the contr actor. This standard applies primarily to the welding of reinforcing steel and other steel devices intended for use in reinforced concrete construction complying with AS and AS
Sectors Our standards development activities are divided into industry sectors. These sectors are supported by Stakeholder Engagement Managers who are available to advise and assist stakeholders. We co-ordinate the attendance of Australian experts at international meetings and participate in the preparation of a wide range of International Standards. We are extremely active within the international standardisation movement and a number of our senior management team members hold important voluntary offices on international standards bodies.
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