TIP TIG Welding is always better quality than TIG and 100 to 500% faster with superior quality than TIG - MIG - FCAW.

General Weld Information For Nickel Alloy Welds.

 

Weld Note: Due to hardening potential and the formation of refractory oxides consideration is required for Precipitation Hardenable nickel steels.

TiP TiG is the logical process for these alloys. The primary weld differences between carbon steel welds and nickel alloy welds will be;

[1] The nickel welds will be much more sluggish, weld fusion is always a primary concern. Note the high weld energy and agitated weld pool with the TIP TIG mode does not have fusion concerns with sluggish alloys.

[2] The nickel welds are very sensitive to oxidation that can lead to extensive weld porosity. With MIG reactive gas mixes are required. Be concerned about the quality and reactive gas composition of the MIG gas mixes available at your local gas distributor.

Many cylinders used for argon mixes may have previously been used for argon 20 - 25% CO2 or argon Oxy mixes. The remains of the reactive components in the cylinders could influence oxidation. If you order 99% argon 1% CO2, ensure the cylinders used have dip tubes and that a certificate of gas composition is presented for each cylinder. Ensure you have adequate gas pre-flow and post-flow.

Note: With TIP TIG, you use argon so you should habe less oxidation concerns.

[3] The magentic influence on the arc is much more noticeable with nickel alloys, again this is a good reason to use Ed's MIG gas mix as the CO2 provides improved electron transfer and improved arc stability.

[4] The crack sensitivity is much greater with nickel alloy so use low to moderate weld parameters.

[5] The cleanliness in the weld areas is super critical when welding nickel alloys. Welding and post weld heating should only be carried out on nickel alloys that are clean and free of contaminates. Grinding and shot blasting are effective. With grinding use wheels that are dedicated only to the nickel welds. Wire brushing will typically not fully remove the surface oxides. If brushes or power brushes are utilized ensure they are made of stainless steels.

[6] Nickel alloys are sensitive to embattlement from phosphorous, and sulfur and these elements are found in many of the materials used in metal forming. Plasma or laser cutting oxides which will have higher melting temperature than the base metal should be removed from nickel alloy plate edges that will be part of the welds. The higher temp cutting oxides can act as a barrier against the sluggish nickel welds impeading weld fusion potential. The oxides from the cutting surfaces can also create internal weld porosity and cause a reduction in the nickel mechanical properties.

In contrast with carbon steels in which the oxides and inclusion typically rise at a fast pace to the weld surface, with the sluggish composition of nickel welds, the contaminates on the plate are more likely to become trapped in the weld. The sluggish nature of the nickel welds can also cause extensive lack of weld fusion especially on MIG welded parts > 4 mm. Lack of weld penetration can cause a point for stress concentration. When welding tube or pipe or butt welds with full penetration treat the weld like a stainless weld and ensure the backside of the root has an argon purge.

Note: With the higher weld - arc energy and unique weld agitation in a TIP TIG weld you will have much less internal weld defects than any other weld process.
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[7] Weld heat typically does not have a negative impact on the nickel alloys. A small amount of grain growth and annealing will occur in the welds HAZ.

[8] When you do a tensile test on a nickel welded sample, please keep in mind that the annealed part of the HAZ will be the first location to elongate. The plastic elongation will cause strain hardening which "actually increases the yield strength". The bottom line is the work hardening influence on the elongation is influenced by the size of the HAZ, and its important to remember that transverse tensile elongation or the noted transverse yield strength attained can be misleading.

[9] With multi-pass welds be aware of the weld heat input build up, especially when welding those oxidation sensitive, precipitation hardenable alloys which can leave an oxide surface on the weld that can impead multi-pass weld fusion potential. All Nickel welds subject to excess weld heat will be influenced by atmospheric contamination creating a severe oxide on the weld's surface. For mult-pass welds use interpass temperature controls (typically 300 to 350F) to minimize both the heat influence on the weld HAZ and oxidation potential.

Note: With TIP TIG the lowest weld heat should be produced with the cleanest possible welds.

[10] Pre-heat is typically not necessary for nickel alloys if the metals are at or above indoor shop temperature. If the metals have been stored outside or moisture is suspect to reduce the weld porosity potential, pre-heat the metals between 70 and 100F.

[11] Post heat treatment is usually not required for the common nickel alloys after welding to attain the desired corrosion resistance. However with nickel chrome 600 alloy, stress relief is required for fused-caustic service applications and also for alloy 400 applications as used in hydrofluoric acid service. Also note the nickel molybdenum and nickel silicon alloys HAZ can lower the corrosion resistance therefore these alloys may require a postweld solution-annealing treatment to restore the corrosion resistance of the HAZ.

Nickel Alloys and FILLER METAL SELECTION

 

Filler Metal Selection. As corrosion potential is the primary concern in the selection of nickel alloys the filler metal should have similar chemistry composition to the base metal to be welded. The 600 series nickel chrome and nickel- iron - chrome alloys can end up with that austenitic problem caused by carbide precipitation (CP) in the HAZ, see the stainless section. Its reported that the CP does in most cases not result in accelerated corrosion attacks. Like stainless weld consumables, additions of columbian or titanium are added to specific filler metals such as the popular Inconel 625 are used to help stabilize the welds and minimize the CP influence.

With MIG welding remember you will get greater current density (less sluggish welds) from smaller wire diameters. Welding under 6 mm thickness, I would recommend an 0.035 (1 mm) nickel MIG wire. Welding thicker than 6 mm, consider an 0.045 (1.2 mm) wire.



DON'T FORGET ED'S UNIQUE MIG GAS MIXES FOR NICKEL ALLOYS:
You can use straight argon for the Nickel MIG welds, however when using MIG spray transfer consider argon with 1% CO2, for applications 3 to 6 mm. For spray applications over 6 mm, to attain more weld energy try a three part mix containing argon - 40% helium - 1 % CO2. Use gas flow rates in the range of 40 to 60 cuft/hr. For those of you that are considering pulsed rather than spray, remember nickel welds are sluggish going from a pulsed peak to a low background weld current does not improve a sluggish weld in contrast to traditional spray. When TIG welding use the same filler metals as MIG with straight argon, treat the nickel welds as you would stainless welds.

 

 

 

 

[] When welding the 300 series of stainless to carbon steels the austenitic 309 filler metal and sometimes 310 are utilized. The 310 25% Cr - 20% Ni, can cause the austenitic welds to fail due to microfissuring which resulted in cracks in applications subject to thermal stresses. The weld failures were often a result of the differences of the coefficient of thermal expansion (CTE). The 309, 23% Cr - 13% Ni filler metal when used on stainless to carbon steels results in a weld with ferrite reducing the potential for mico-fissuring, however keep in mind depending on the application chemistry, thickness, weld process and parameters used, the dissimilar weld joints are still dilution sensitive. The 309 filler when used on stainless to steel welds still have large CTE differences therefore one should be concerned when the welds or parts are subject to temperatures over 600F in which high stresses or thermal fatigue effects the ferritic / austenitic weld interface.

[] Where the 309 and 310 have problems the weld solutions are frequently found with the 600 series Ni Alloy filler metals.

Ed developed this Inconel 625, pulsed MIG water wall clad
procedure, patented in 2007: Check the clad section.

 

[] The 600 series as many of you know are often called Inconel. These high Ni-alloy filler metals typically contain up to 72 nickel 15 % Chrome and 8% Fe. These filler metals have a much lower CTE than the 300 series austenitic alloys.When welding the lower CTE results in less weld thermal stresses. The Inconel alloys are also less sensitive to weld microfissuring or weld dilution concerns from dissimilar metals.

[] When parts are in service at temperatures >700 F, welds that contain high nickel to chrome ratios can be sensitive to sulfur corrosion. This risk is reduced with filler metals that have higher chrome / moly. Alloys 625 / 671. The 671 is AWS (ERNiCr-4 rod)

[] The 625filler, EniCrMo-3 rod , MIG and flux cored wire should be restricted to applications <1000F as weld embrittlement can occur.

[] For a story on how not to use Inco 625 for cladding boiler water wall tubes click.

 

WELDING, NINE PERCENT NICKEL CRYOGENIC APPLICATIONS.

A common application in which austenitic stainless and 9% nickel steels is in the construction of cryogenic, liquefied natural gas (LNG) containers. These containers can carry liquid argon, natural gas, helium, oxygen, nitrogen etc. These liquid gases are usually in an approximate temp range of -300 to -450F. Carbon steels and alloy steels have poor toughness and ductility at low temperatures. The alloy steels with nickel, austenitic steels typically 304 - 304L 316 - 316L - 347 and aluminum alloys all have excellent low temperature toughness.

Strict welding regulations are applied to welding cryogenic applications. The weld metal properties should contain low nitrogen, low ferrite, low carbon and high nickel. Filler metals such as Nickel Chrome Molybdenum, Nickel Chrome Iron or high alloy austenitic electrodes.The Nickel alloy consumables have a coefficient of thermal expansion that is close to the 9% nickel this reduces the risk of thermal fatigue in applications subject to thermal cycling. Typically the mechanical properties of nine percent nickel will be higher than those of the weld consumables utilized. This requires special consideration to weld qualification tests.

Note that with the 30X in centrast to the 30XL (low carbon grades). The higher the carbon the lower the impact toughness.Shop built stainless steel cryo vessels in the USA are built to ASME Boiler Pressure Vessel Code Section V111. Field erected vessels may use the API 620 Q. Austenitic stainless accounts for the majority of metals used for cryo applications. The rest of the applications use 5 to 9% nickel or aluminum. Where high strength is required nine nickel may be chosen instead of an austenitic steel. Its important to remember that nine percent nickel is an alloy that can rust.

PLEASE REMEMBER THE FIRST CONSIDERATION WITH WELDING COMPLEX ALLOYS IS THE WELD PROCESS: No other manual or automated weld / cladd process can produce the weld quality on nickel alloys that is attainind with the TIP TIG process can be used with either TIG -

 

• Welding Stainless Steels Safety Issues
  
  
• Stainless Steel Welding Consumables
  
  
• MIG Welding Stainless Steel Under 4mm
  
  
• MIG Welding Stainless Steel Over 4mm
  
  
• Welding Nickel Alloys