+2 votes
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Filler material or wire for dissimilar weld

asked Aug 12, 2014 in Material by ChemKB (8,210 points)
What should be the criteria for selecting the best filler material (or wire) for dissimilar weld?

3 Answers

+3 votes
answered Aug 12, 2014 by TPham (5,010 points) | selected Aug 12, 2014 by ChemKB
 
Best answer

When selecting filler material for welding/joining two different alloys together, consider the following criteria:

  • When welding dissimilar steels, the welding criterion is often determined by the steel with the higher Carbon value.
  • When welding high-alloy steels to low-alloy steels, it is typically a good practice to preheat the low-alloy steels to more than 300 degree Fahrenheit to migrate the Hydrogen out of the weld site to reduce the stress cracking potential.
  • When welding dissimilar stainless steels, ensure the filler material has similar corrosion resistance and mechanical properties of the higher alloy. An example of that is when you weld 316L to 304L, a 316L filler material should be used.
  • Select a filler metal that has high temperature strength, oxidation resistance as well as maintaining ductility in the weld and avoiding hot cracking.
  • Consider annealing or slow cooling the welding process to reduce the corrosion cracking.
  • The higher the strength of the alloys, the less weld-ability between them.
commented Aug 13, 2014 by ChemKB (8,210 points)
Thanks Tadd for answering my question.
+1 vote
answered Aug 13, 2014 by sabdullayev (5,290 points)

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:

  • For attaching non-pressure parts to pressure parts, the filler metal chemistry should match the nominal chemical composition of the pressure part.
  • For welding Type 405 or 410S hexmesh, anchors, etc., to carbon and low alloy steel, the filler metal should be:
    • Inconel Class ERNiCrFe-6, provided the welds are not exposed to sulfur above 700°F (370°C), or
    • Type 309 (25 Cr-12 Ni), for design temperatures not exceeding 600°F (316°C).
    • For service conditions exceeding the limits stated in 2 conditions above, the filler metal selection should be reviewed and approved prior to use.

6.      For welding austenitic stainless steels, the following requirements should be met:

  • When joining ASME P-8, Group 1 austenitic stainless steels, the filler metal must contain at least 1 FN (Ferrite Number) or 1 percent ferrite.  However, 347 electrodes should contain at least 4 FN.
  • When joining two different austenitic stainless steels, the filler metal may match either.
  • When joining 310 or 330 stainless steels and for cryogenic and special corrosive service, 0 FN filler metal may be used.

7.      When joining austenitic stainless to ferritic steels, filler metal types should be selected as follows:

  • Inconel Class ERNiCrFe-6, provided the welds are not exposed to sulfur above 700°F (370°C).
  • Type 309 (25 Cr-12 Ni) for design temperatures not exceeding 600°F (316°C).
  • Type 310 (25 Cr-20 Ni) stainless steel should not be used.
  • For service conditions exceeding the limits stated in 2 conditions (ERNiCrFe-6 and 309) above, the filler metal selection should be reviewed and approved prior to use.

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:

  • Wire chemistry for ferritic steels is changed from one AWS classification to any other classification or to a chemical composition not covered by the AWS filler metal specifications.
  • Filler metal is changed from one specific make and type designated under AWS Classification "G" to any other manufacturer or manufacturer's designation.
  • Submerged arc welding flux is changed from one manufacturer to another or from one manufacturer's grade to another grade (equivalency on the basis of AWS A5.17/A5.17M or AWS A5.23/A5.23M is not acceptable).  The manufacturer and the manufacturer's grade of flux should be stated in both the WPS and the PQR.
  • Flux cored electrodes are changed from one AWS classification to another, electrodes are not classified by AWS, or electrodes are specified with supplementary requirements.  Requalification is not required for a change in the position designator from EX0T-X to EX1T-X and vice versa.
  • The chemical composition of the weld deposit is changed from one A-Number to any other A-Number in QW-442 of ASME Code Section IX, including a change from A-1 to A-2 and vice versa.

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:

  • The deposited filler metal does not fall within any of the AWS filler metal specifications, A5.XX Series.
  • Satisfactory mill test reports or other supplier certifications are not available.

14.  For SAW and ESW welding, the AWS electrode-flux classification and the flux manufacturer and trade name should be specified.

+1 vote
answered Aug 19, 2014 by lulopez (2,220 points)
  • Filler metals should be selected in accordance with the characteristics of the base metal.
  • The filler metals should be low hydrogen type.
  • The filler metal used should have a nickel content below 1.0%

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