Useful information about welding
Weldability is the property of steel and certain metals to join together when they are brought to the fusion temperature. Because it allows the joining of parts without discontinuities, welding is an ideal way of assembly. Precise execution conditions are essential for obtaining good results.
Welding activities must be carried out in accordance with EN ISO 3834
Specification of quality requirements for welding procedures, as follows:
EN ISO 3834-1: 2006 Quality requirements for fusion welding of metallic materials.
Part 1: Criteria for selecting the appropriate level of quality requirements.
EN ISO 3834-2: 2006 Quality requirements for fusion welding of metallic materials.
Part 2: Complete quality requirements.
EN ISO 3834-3: 2006 Quality requirements for fusion welding of metallic materials.
Part 3: Normal quality requirements.
EN ISO 3834-4: 2006 Quality requirements for fusion welding of metallic materials.
Part 4: Basic quality requirements.
ISO 3834 specifies quality requirements suitable for fusion welding processes of metallic materials. The requirements contained in this international standard can also be adopted for other welding processes. The requirements refer only to those aspects of product quality that can be influenced by fusion welding, without being assigned to a specific product group.
The qualification and attestation of specialized technical personnel is necessary. Also, the Welding Technical Manager (RTS) in accordance with EN ISO 14731.
In metallurgy, the welding of steel parts represents a particular problem. In order for the welded joints to be strong, the steel must be weldable.
The quality classes, which differentiate the steels within the same brands, highlight, on the one hand, good welding behavior, and on the other hand, the safety of welds and welded parts, by ensuring toughness and avoiding brittle breaks.
The way steel behaves during and after the welding process is dependent on both the material and the dimensions/shapes. As well as the manufacturing and operating conditions of the part to be welded.
Thus, the factors that influence the weldability of steel can be of the following nature:
– metallurgical determined by:
1. Chemical composition – carbon is the main element in steel that influences the weldability of steel. That is why it is necessary to limit the carbon content (usually below 0.20 – 0.22%);
As a result of welding carbon and low-alloy steels with low carbon content, where higher heating-cooling speeds are well supported and no overheating or hardening structures are formed, tighter joints in I,Y,X can be foreseen , K, which can be welded by processes with strong heat sources without risk of cracking or deformation-tension.
Alloy steels have greater rigidity, are easily tempered, so the weld pool must be formed more of the filler metal, the penetration of the weld must be lower, and the heating-cooling speeds reduced, being the adoption of V, U joints is advisable , 1/22U which is welded with less intense regimes.
2. The steel production process. It is necessary for weldable steels to be quenched so that all impurities and inclusions of gases and oxides are removed;
3. The filler material and the metallurgical processes that take place during welding. For steels with a higher carbon content, electrodes with a basic coating (with a low hydrogen content) are recommended; coated electrodes which after melting form a low alloy steel deposit.
– constructive determined by the thickness of the welding metal, the shape and location of the seam that influence the production of internal stresses, etc.;
– technological determined by the welding process, the order of execution of the welds, the speed of welding and cooling, the intensity of heating, combating internal tensions, etc.
The way of operating the welded construction also has a great influence on the factors listed above and implicitly, on the weldability.
1. With electricity:
a. with electric arc;
b. with plasma;
c. with electron beam;
d. by electrical resistance;
e. with high frequency currents;
d. with laser.
2. With chemical energy:
a. with the oxy-acetylene flame;
b. alumino-thermal;
c. in the forge fire;
d. by explosion.
3. With mechanical energy:
a. by friction;
b. by percussion;
c. with ultrasound;
d. by cold pressing.
Starting from July 1, 2014, companies that produce welded steel or aluminum structures must be certified according to the EN 1090 standard. Only construction steel and aluminum products that have the appropriate CE mark can be sold or put into circulation in Europe.
EN 1090-1: Requirements for conformity assessment of structural elements. (CE Marking)
EN 1090-2: Technical requirements for the execution of steel structures
EN 1090-3: Technical requirements for the execution of aluminum structures.
The EN 1090 standard defines the following four execution classes:
Execution class 1 includes structural elements made of steel with resistance class up to S275 and structural elements made of aluminum alloys. These include buildings with up to 2 floors (4 floors if they are detached), bent beams up to 5 m long, cantilever beams up to 2 m long and balustrades for stairs in residential buildings. It is also valid for agricultural buildings, for example barns.
Execution class 2
Includes all structural elements made of steel with resistance class up to S700 and structural elements made of aluminum alloys. Normally, this class includes buildings with between 2 and 15 floors. It is the most frequently encountered class.
Execution class 3 refers to supporting structures made of steel with resistance class up to S700 and structural elements made of aluminum alloys. Examples include buildings with more than 15 stories, road and rail bridges, pedestrian and bicycle bridges, and crane taxiways.
Execution class 4 includes all structural elements that present extreme risks for people and/or the environment in the event of failure. This refers, for example, to railway and road bridges over densely populated residential areas or potentially dangerous industrial enterprises such as safety tanks in nuclear power plants.
These execution classes are applied either to the structure as a whole, or to a part of the structure or specific details.
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