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.
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.
Inspection, Surface Prep and Non-destructive Testing
Are you in the oil & gas industry? Are you involved in non-destructive testing, inspection, or surface preparation? How about maintenance of pipelines, heat exchangers, or pressure vessels? If you deal with these or similar operations, proper cleaning of surfaces might well be a process you regularly undertake.
Cleaning Delicate Equipment Safely
What is the best way to clean surfaces of such equipment? While there is no one best way for every circumstance, dry ice cleaning is a state-of-the-art method that can save time and money. It uses recycled CO2 in the form of solid dry ice particles as the cleaning media. Dry ice is soft and non-abrasive to most surfaces and can thus be used around delicate components, including electronics, that would be damaged by water or solvents. As the blasting equipment is portable it can be used in place, thus minimizing disassembly and other preparation time. Lastly, dry ice turns to a gas after contact with the surface being cleaned — cleanup time is rock bottom minimum, there is nothing to dispose of, contamination of moving parts is not an issue.
To begin, let’s establish what exactly we’re talking about when we say “biodiesel.” ASTM (American Society for Testing and Materials) has published a standard, D6751-07b, that defines what biodiesel is. We’re not talking about used cooking grease, or even commercially produced biodiesel, if it doesn’t meet this standard.
Also, the word “biodiesel” is often used to describe what is actually a blend of biodiesel and diesel fuel. (The diesel fuel sold for on-road use in the U.S. is Ultra Low Sulfur Diesel fuel, or ULSD.) The term “BX” designates the blend ratio, where “X” stands for the percentage of biodiesel in the blend. So B100 means 100%, or pure, biodiesel, while B20 means 20% biodiesel mixed with 80% ULSD.
Additionally, this article doesn’t address OEM recommendations or warranty limitations. We’re simply looking at the question from a mechanical standpoint.
So now, with all that out of the way, what’s the bottom line?
Here are a couple of snags that can show up in any diesel engine when using biodiesel:
Fuel filters may initially clog:
This applies to engines that have burned petroleum diesel for years before switching to biodiesel. Over time, petroleum diesel leaves small carbon and tar deposits in a fuel system. B100, a mild solvent, will “clean out” the fuel system, dislodging these deposits. This is a good thing, but it’s inconvenient when a fuel filter clogs with these deposits. Once the fuel system is clean (usually after burning 1-2 tanks of B100), this issue goes away. B20 and lesser blends do not have this cleaning effect.
Biodiesel begins to gel at a higher temperature than ULSD. As a general rule of thumb, the greater the percentage of biodiesel present in a blend, the higher the temperature at which it will start to form wax crystals too large to pass through the fuel filter. In extreme cold, without a fuel preheating system, all but the most dilute biodiesel blends may be impractical.
Now, let’s discuss changes in diesel engine technology.
Pre-common rail diesel engines (mostly pre-2000)
These engines work very well with B100 (as well as with lesser blends). In fact, biodiesel is often a superior fuel for these engines. It is a far better lubricant than ULSD, sharply reducing injection pump wear. Unlike ULSD, which is made up solely of hydrocarbon chains, biodiesel molecules also contain oxygen. This oxygen contributes to better combustion. Thus, even though biodiesel has a lower energy content than ULSD, some engines may actually see a slight increase in power output, with minimal loss of fuel economy when using biodiesel.
Common rail diesel engines
Rule of thumb:
Any biodiesel blend works great.
Diesel engines with common rail injection systems started showing up in the early 2000s. These systems burn ULSD more efficiently than older systems, so biodiesel’s oxygen content no longer offers any real efficiency advantage, and its lower energy content manifests itself in a slight reduction in fuel economy and power. Further, high precision common rail injection systems are “tuned” to fuel of a given viscosity, and the viscosity of B100 differs significantly from that of ULSD. This may, for example, change the spray pattern of fuel into the combustion chamber, and the end result can be an increase in soot and carbon buildup.
Engines with diesel particulate filters
Rule of thumb:
While B100 works, these engines work best with lower blends, like B20.
In 2008, the EPA started phasing in its Tier IV diesel emissions standard, which required an immediate 90% reduction in particulate matter. Diesel particulate filters, or DPFs, are exactly what they sound like – a filter in the exhaust system that captures particulate matter, such as soot. To regenerate, or clean, the filter, atomized ULSD is injected into the exhaust. When it reaches the DPF, it ignites and burns off the particulates that have collected there. To accomplish this, many engines periodically inject ULSD into the cylinder during the exhaust stroke. This ULSD vaporizes and flows through the exhaust system with the other exhaust gases. Biodiesel, however, is less volatile than ULSD. When it is injected into the cylinder during the exhaust stroke, rather than flowing out through the exhaust valve as a vapor, some of it condenses on the cylinder walls as a liquid and runs down through the crankcase. Over time, this biodiesel accumulates and dilutes the engine oil. Thus, for engines equipped with this style of DPF regeneration, biodiesel blends generally should not exceed B20.
Some DPF systems are able to eliminate this problem by using an extra injector located in the exhaust system to handle regeneration. Such configurations don’t cause engine oil dilution and so are compatible with B100, but they are also less common.
Rule of thumb:
B20 works with DPF-equipped diesel engines. Higher blends work with some engines with specific configurations for DPF regeneration.
Complications associated with using B100 may vary from negligible to major, depending on the engine configuration and the operating environment. B20 and lower blends, on the other hand, present minimal complications when used in any modern diesel engine and in all but the coldest operating environments.
Diesel Generator Rentals
Red-D-Arc carries diesel, LPG and natural gas generators in a range of sizes.
D&D Power provides full service oilfield generator rentals including generator paralleling.
We also provide diesel air compressors for rent.
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.
“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.”
We are pleased to announce the launch of a new product in our weld automation category. Red-D-Arc now offers adjustable pipe stands with a carrying capacity of up to 4 tons, in both low and high profile versions. Combined with our turning rolls and positioners, these stands offer an effective solution for supporting pipes during the welding process for both manual and automated applications.
“Pipe stands with a carrying capacity up to 4 tons… low and high profile versions available.”
Our pipe stands feature polyurethane rollers and have been fully UL and CE tested. All of Red-D-Arc’s weld automation equipment has had its weight capacity UL verified to ensure safety and quality. This is a first in the weld automation industry.
2 Ton Adjustable Height Pipe Stands
4 Ton Adjustable Height Pipe Rollers