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Advances in welding technology continue to create efficiencies for the businesses who adopt them. Applying best practices help ensure weld quality and efficiency.

Welding Stainless Steel – Hints and Guidelines

15 January, 19 9:42 am · Leave a comment · Colin Brown
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Welding of Stainless Steel

Stainless steel contains a minimum of 10.5% chromium which imparts it corrosion resistance by forming an oxide layer on the surface. The most common stainless steel is the austenitic type (300 series) which contains chromium and nickel as alloying elements. Other types include ferritic, martensitic and duplex stainless steels. Most stainless steels are considered to have good weldability characteristics. Most common processes used for welding stainless steel are TIG (GTAW) and MIG (GMAW). But, stick welding (SMAW) is also utilized.

Differences in Properties:

The properties of stainless steel differ from mild steel, and these differences need consideration when welding as below:

  • Higher coefficient of expansion, 50% more for austenitic – this results in more distortion
  • Lower coefficient of heat transfer – welding requires lower heat input as it is conducted away slowly
  • Lower electrical conductivity – using the correct and consistent stick-out distance is more critical when using MIG/TIG, higher wire speed for the same current is required when MIG welding

Why segregated work area?

Welding of stainless steel is carried out in a work area segregated from carbon steels. Moreover, tools dedicated for use with stainless steel must not be used to work on carbon steels. These tools include brushes, hammers, clamps, grinders etc. The segregation of work area and tools safeguard the contamination from carbon steels, which may cause welding defects and corrosion (rust) on stainless steel. You must also wear gloves when working with stainless steel as this will prevent oil from the hands passed onto the stainless steel.

Preparation is key!

With stainless steel, it is important that the joint surfaces are thoroughly cleaned before welding to remove any dirt, grease, oil etc. The filler wire also needs to be completely clean.

Additionally, the joint design including the joint gap must cater to the higher expansion rate of stainless steels.

Filler Material Selection:

Filler materials used generally are the same as the base metal. Special considerations are required to select a filler material if welding dissimilar stainless steels or stainless steels where no identical filler material exists. Furthermore, filler materials are selected to reduce the risk of intergranular corrosion and hot cracking.

Welding Considerations:

It is essential to protect the weld during welding using a mainly inert gas. Additionally, the weld root needs to be purged using a pure inert gas.

When welding austenitic stainless steels, it is important to restrict the heat input to a level which is just sufficient to ensure a good weld. The interpass temperature is limited to 350 F. Preheating is not carried out on austenitic stainless steels. Very low carbon grades (suffixed with L e.g. 304L, 316L) are used to prevent the formation of chromium carbides in the heat affected zones which causes intergranular corrosion.

Martensitic stainless steels are generally used as wear resistant materials in overlaying applications. To avoid cracking, accurate preheat needs to be applied and a minimum interpass temperature maintained.

Ferritic stainless steels are used mostly in automotive applications. The heat input in these steels during welding needs to be limited, and a maximum interpass temperature of 300 F is recommended. This will ensure that the grain growth in the material is controlled and the strength is maintained.

With duplex stainless steels, the heat input also needs to be restricted.

Cleaning and Passivation:

Stainless steel welds must be cleaned and passivated after completion to ensure corrosion resistance and good appearance. This is performed manually by mechanical (brushing, grinding, blasting), chemical (applying pickling agents and other chemicals) or electrochemical means.

Red-D-Arc has a wide range of equipment suitable for stainless steel welding for rent including the following:

Multi process welders capable of stick, TIG, MIG, submerged arc, air carbon arc cutting, flux core, up to 1500 A

MIG welding units up to 750 A

TIG welding units up to 750 A

Stick welding units – up to 625A

Also 4 and 6 Paks of welders available

Orbital welders – suitable for stainless steel pipe/tube welding

Various brands including Miller, Lincoln, Red-D-Arc

Have a look at our complete range of welding products.

Axxair Orbital System Makes Welding Small Pipes Easy

18 October, 18 3:12 pm · Leave a comment · reddarc
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multi pipe welded array
Welding small diameter tubing can be difficult.  The tight radii often require expert welders to deliver precise torch manipulation with finesse.  If the welder is not skilled enough, the out of position areas are at risk of poor quality due to gravity affecting the weld pool and ineffective torch angles.  If out of position welds cannot be completed satisfactorily, the part must be rotated.  However, some assemblies can’t be rotated because of size constraints or they might rotate off of center.  If a mechanized welding solution is desired for small diameter components, look no further than our Axxair Orbital Fusion Closed Welding Head Systems.


Closed-Head Pipe Welders

Axxair Orbital Fusion Closed Welding Systems are comprised of two main parts: the
Axxair Orbital Fusion Closed Welding Head
and the Axxair Orbital Inverter Power Supply.  The Orbital Fusion Closed Welding Head fully encompasses the assembly being welded.  This means that an inert gas environment can be created around the part, preventing it from the risk of oxidation that it might be exposed to during a welding operation that relies solely on a gas nozzle.  The Orbital Fusion Closed Welding Head also has a ring drive that enables full 360 degree motion around the weld joint, all the while keeping a consistent torch angle.  Furthermore, it is capable of going over 360 degrees for when slope-in and slope-out parameters are needed.
Closed Welding Heads

“The Orbital Fusion Closed Welding Head also has a ring drive that enables full 360 degree motion around the weld joint, all the while keeping a consistent torch angle.”

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What Do American Welding Society Wire Filler Metal Designations Mean?

07 September, 18 2:58 pm · Leave a comment · reddarc
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Selecting Welding Wire

coil of welding wire
When selecting a wire electrode for welding, one will most likely run into an American Welding Society (AWS) filler metal classification. A purchaser who isn’t familiar with the AWS classification system might select the wrong type of wire. If the purchaser is only familiar with gas metal arc welding (GMAW) wire and is attempting to purchase self-shielded flux-cored wire (FCAW-S), confusion may arise about the differences between the two classifications. This too could result in selecting the wrong wire electrode. To help prevent this from happening, we’ve created this welding wire reference guide to remind welders exactly what the different AWS classifications designations mean. We’ve included references for solid wire electrodes, metal-cored wire electrodes, gas-shielded flux-cored electrodes, and self-shielded flux-cored electrodes.

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Strengthening Metal Parts with Hardfacing

27 April, 18 2:42 pm · Leave a comment · reddarc
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Metallic parts sometimes fail their intended use at a lower stress than they are designated for.
Various forms of wear such as abrasion, impact, metal to metal contact, heat, and corrosion can compromise the strength of metal pieces. This is where hardfacing comes in. Hardfacing is a technique which can be applied to minimize the damage from these types of wear, helping to prolong the life of metal pieces.

What is hardfacing?

Hardfacing —often called hardsurfacing— is the covering of the metallic part with a wear resistant metal by welding. Alloys which commonly need to be hardfaced include carbon alloy and low alloy steels whose carbon content is lower than 1 %. These include stainless steels, manganese steels, cast iron as well as nickel and copper-based alloys.

Metallic parts sometimes fail their intended use at a lower stress than they are designated for.

Techniques, Materials and Costs

The particular hardfacing technique for a job depends on the geometry of the part and relative cost of the hardfacing method. Costs can vary with the deposition rate of the material.

These cost variations can be summarized as follows:

  • Flux cored arc welding (FCAW) 8 to 25 lb/hr
  • Shielded Metal Arc Welding (SMAW) 3 to 5 lb/hr
  • Gas Metal Arc Welding (GMAW), including both gas-shielded and open arc welding 5 to 12 lb/hr
  • Oxyfuel Welding (OFW) 5 to 10 lb/hr

 

Applied materials commonly include cobalt based alloys such as STELITE, and nickel based materials like chromium carbide alloys. More advanced materials such as complex carbides containing columbium, molybdenum, tungsten, or vanadium can also be used and provide more overall abrasion resistance. They also have a very low friction factor, which can be used in situations involving severe abrasion.

Hardfacing can be applied to both newly manufactured pieces, in order to prevent deterioration, or to strengthen and extend the life of worn pieces currently in use.

Red-D-Arc provides welding machines suitable for hardfacing using techniques including SMAW, FCAW and GMAW.

Is Gas Welding Really Cheaper?

13 April, 18 4:54 pm · Leave a comment · reddarc
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Oxy acetylene welding torch

The answer is often no, and here’s why…

Gas (oxy-acetylene) welders used to be the rock stars of welding. From shipbuilding to automotive manufacturing to steel forging, but that was then. Arc welding is a modern welding method that outmatches gas welding in almost every respect.

Weld finishing:

Arc welders use electric current generated by a transformer or a generator to produce a uniform, clean welds that almost never require finishing. This is not the case with gas welding. Gas welding operates using the heat generated by the ignition of a gas mixture (oxygen and acetylene) to melt the welding material or to simply fuse two parts together. This process often results in a bad surface finish. Gas welding can require additional work involving hours of grinding and polishing the welds.
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AirGas Logo

Airgas, an Air Liquide company, is the nation's leading single-source supplier of gases, welding and safety products. Known locally nationwide, our distribution network serves more than one million customers of all sizes with a broad offering of top-quality products and unmatched expertise.