What should be the criteria for selecting the best filler material (or wire) for dissimilar weld?
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When selecting filler material for welding/joining two different alloys together, consider the following criteria:
Here are some general recommendations for welding materials for tanks, piping systems, pressure containing equipment, internals for pressure vessels and piping:
1. Filler metals should be specified in each WPS by AWS specification and classification. However, filler metals that do not conform to a standard AWS specification and classification, or which have special requirements, should be identified by manufacturer and type.
2. When joining similar metals, the deposited weld metal should match the chemistry and the mechanical properties of the base metal as closely as possible.
3. Whenever the minimum mechanical properties of the deposited weld metal fail to meet the minimum mechanical properties of the base metal, or whenever the nominal chemistry of the deposited weld metal differs from the nominal chemistry of the base metal, the weld metal recommendation should be submitted for review and approve prior to use.
4. A filler metal should be used only for the primary material and process applications recommended in the AWS filler metal specification or by its manufacturer (e.g., filler metals designed for "single pass welding" should not be used for multipass joints).
5. When joining two different ferritic steels, or when joining ferritic to martensitic steels, the filler metal should conform to the nominal chemistry of either base metal or an intermediate composition, except as follows:
6. For welding austenitic stainless steels, the following requirements should be met:
7. When joining austenitic stainless to ferritic steels, filler metal types should be selected as follows:
8. When the thickness of carbon or low alloy steel base metal exceeds 1/2 in. (13 mm), groove or fillet welds should be made with filler metals producing low hydrogen deposits. However, cellulose or rutile-type coated electrodes may be used for the root pass of a groove weld regardless of the base metal thickness.
9. Active submerged arc fluxes should not be used.
10. Alloyed SAW fluxes should not be used for welding low alloy steels.
11. Reprocessed flux or re-crushed slag should not be used for SAW of pressure-containing parts such as pressure vessels, piping and storage tanks.
12. WPS should be re-qualified whenever:
13. All-weld-metal tensile tests with any applicable production type PWHT to determine ultimate strength, yield strength, elongation, and reduction of area should be conducted whenever:
14. For SAW and ESW welding, the AWS electrode-flux classification and the flux manufacturer and trade name should be specified.
Offshore welded pipes should meet the requirements of the main body of the specification "Steel Line Pipe for Gas and …