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.
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.
Since 1996, the EPA’s regulations for non-road diesel engines emissions have been phased in through four progressively more stringent tiers. Different tiers went into effect at different dates for different engines, but since 2015, all new non-road diesel engines, including stationary engines, but comply with the EPA’s Tier IV (Final) standard.
Today’s Tier IV compliant diesel engines are far more complex, efficient, and expensive than their unregulated ancestors from the early 1990’s.
How does Tier 4 compare with the previous generation (Tier III)?
For Tier III, the standard focused on reducing NOx (nitrous oxides) and NMHC (all hydrocarbons except methane) emissions to levels on par with federal requirements for on-road diesel engines. Since these non-road emissions were unregulated prior to the Tier Emissions Standards, we have no basis for a hard comparison, but the EPA estimates that since 2010, Tier III has been reducing NOx emissions by about 1 million tons per year. This is the amount of NOx produced annually by about 35 million cars.
Conspicuously absent from Tier III was any limit on PM (particulate matter), although the Tier II limit still applied to Tier III motors.
To comply with Tier III, most engine manufacturers relied on the following technologies:
- Improved airflow through the engine (more responsive turbochargers, improved combustion chamber design, and variable valve timing) – This reduces NMHC and PM.
- Precise control of injection (electronically controlled, common-rail injection systems) – A series of small fuel injections during the combustion cycle, instead of on single injection “blast” reduces both PM and NOx.
- EGR (Exhaust Gas Recirculation: a portion of the exhaust is routed back into the intake air) – This dilutes the intake air with inert gases and absorbs heat, reducing NOx.
Tier IV had a long phase-in period, from 2008 until 2015. For most engines, it was broken into an “Interim” and “Final” phase. Tier IV (Interim) addressed particulate matter, calling for a further 90% reduction over Tier II. In addition, it required a further 45% reduction in NOx over Tier III. Tier IV (Final) now requires yet another 80% reduction in NOx over Tier IV (Interim), as well as some more modest additional PM reductions for some engine classes.
To comply with Tier IV, engine manufacturers have employed these additional technologies, among others:
- DPF (Diesel Particulate Filter) – This reduces PM.
- CCV (Closed Crankcase Ventilation: Blow-by gases that get into the crankcase are recirculated back into the engine instead of vented to the atmosphere) – This reduces NMHC and PM.
- SCR (Selective Catalytic Reduction: A reduction reaction converts NOx to nitrogen, water, and CO2.) – This drastically reduces NOx.
These past two decades of Tiered Emissions Standards have driven a rapid evolution in diesel engine technology. Today’s Tier IV compliant diesel engines are far more complex, efficient, and expensive than their unregulated ancestors from the early 1990’s. Even more drastic, though, has been the reduction in emissions during this time: a 99% drop in both NOx and PM as well as a 95% decrease in tailpipe emissions overall.
It’s a great day in Tulsa
It’s a beautiful day in Tulsa Oklahoma. – April 4, 2018
Drop by booth #507 and check out our Orbital Tig and Induction Heating systems. We’ve got a beautifully reconditioned 300 amp Red-D-Arc Diesel welder for sale with special show pricing!!
Don’t forget to scan your badge for PennWell Drone Draw!!
www.pipelineenergyexpo.com – April 3-5, 2018
By guest blogger David H.
Having worked in shipyards for seven years, I’m familiar with how dirty this type of job site can be. Ship repair worksites and welding surfaces are often filthy with rust, dust and other contaminants. Even in shops and yards where fabrication is ongoing, cleanliness is often lacking. If fabricated or refurbished pieces are being installed onboard, the surface to which the piece will be welded could be rusty, coated with scale, or have other types of corrosion.
It is hard to overstate the importance of having a clean surface when welding. Welds made on unclean surfaces can become contaminated and fail; this is especially true with certain metals, such as aluminum, and certain types of welding, such as TIG, but for all welds at least some level of cleanliness is important.
Methods and Equipment
There are numerous methods available for cleaning surfaces. The most basic are simple wire brushes and scrapers; these are ineffective beyond removing common dirt and simple surface contamination. Some hand-held tools, such as grinders and reciprocating needles are slightly more effective.
A surface that is properly prepared by blast cleaning can help you ensure fewer problems with weld quality.
Deeper cleaning processes can help to ensure high-quality welds. This is particularly important where a failed weld could be costly or create shipboard dangers for the crew. For corroded or contaminated surfaces something stronger is required. Some of the best systems available are blast cleaners. Red-D-Arc has a number of blast cleaning rental options. Dry-ice systems are environmentally sustainable, non-destructive, and use inexpensive, readily available dry-ice pellets. Recycled glass systems, which reduce dust by as much as 95% compared to dry-blasting, are available too.
Take a look at our selection of rental blast cleaners which can powerfully clean up the dirtiest weld surface. A surface that is properly prepared by blast cleaning can help you ensure fewer problems with weld quality.
Importance of Preheating in Welding – Equipment Options
Preheating reduces the risk of cracking in weld metal and heat-affected zone (HAZ) by:
- Lowering the cooling rate of the weld – prevents formation of brittle weld metal/HAZ, allows more time for hydrogen to escape the molten weld.
- Removing moisture (hydrogen source) from the part.
- Reducing shrinkage by lowering the temperature differential.
Preheat or not?
The requirement and level of preheating for steel is determined by the relevant welding code and is dependent on the weld heat input, chemical composition of steel (carbon equivalent), thicknesses, diffusible hydrogen etc. Non-ferrous materials generally require preheat because of their high thermal conductivity.