Welding Stainless Steel In Shipbuilding
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In shipbuilding, the most common procedure is the electrical arc welding course. The regions in shipyards are usually open and exposed to the ambient air setting. Although, in some shipyards, these regions may be in large covered areas and isolated from the weather. Welding operations in these regions tend to be largely high-performance GMAW (Gas Metal Arc Welding), FCAW (Flux-cored Arc Welding), and SMAW (Shielded Metal Arc Welding). Rarely other welding procedures are performed in these production regions.
Materials utilized in this area are various grades of steel, aluminum, stainless steel, and other piping materials. Some shipyards have particular areas where stainless steel and aluminum are welded and processed. In comparison, other shipyards have fewer volume operations at locations where space is accessible.
An inert industrial gas with high thermal conductivity, helium (He) shields the molten weld pool and prevents oxidation when increased heat input is desired during the welding of metals like aluminum, stainless steel, copper and some magnesium alloys.
Hydrogen (H2) is the lightest of all the gases. Used to enhance plasma welding and cutting operations, it is commonly mixed with argon for welding stainless steel because of its oxide reducing characteristics.
The welding of dissimilar materials is common in certain power generation facilities such aspetrochemical refineries, as well as in many mining and mineral processing facilities. The corrosion resistance provided by stainless steel is often necessary for equipment in those facilities. When the environment or service conditions permit, however, the material can be welded to less expensive carbon steel. In these applications, carbon steel, which includes mild and low alloys, serves the important role of reducing costs in constructing and operating these manufacturing plants.
As with any welding application, attaining success when welding dissimilar steels requires the careful selection of filler metals and the proper welding procedures. This holds true regardless of which process the welding application uses.
Note, the topic of joining dissimilar metal spans an enormous number of materials and fabrication processes. The advice and suggestions offered in this article apply to a range of stainless steel and carbon steel, including the commonly used 304L austenitic stainless steel and mild steel combination, as well as mentions of duplex and other such stainless steel grades. Welding operators who are uncertain about an application should always consult with a welding distributor or a filler metal manufacturer for specific welding and filler metal recommendations.
Three factors to rememberWhen welding stainless steel to carbon steel, it is critical to pay attention to chemistry, mechanical properties and corrosion resistance to avoid potential trouble. For all three factors, choosing the right filler metal can help reduce concerns.
As an example, when joining 304L stainless steel to mild steel, the most commonly recommended filler metal is 309L. During the welding process, the weld becomes diluted with some of the stainless steel from one side of the joint and some of the mild steel from the other side, mixing in material from each side of the weld. The goal is to create a final weld deposit whose chemistry is compatible with each side of the weld joint. Using 309L filler metal achieves this goal when joining 304L stainless steel to mild steel.
Matching the mechanical properties of each type of material is important, as well. Attaining a mechanical match is a function of having the correct chemistry, and also a reflection of the heat created by the welding procedure. As a general rule, when welding any type of stainless steel to carbon steel, the filler metal should match or slightly exceed the mechanical properties of the weaker of the two materials.
Heat input is important To address the factors of chemistry, mechanical properties and corrosion resistance, it is important to follow a suitable welding procedure that limits the heat input to the weld and stainless base material. Limiting the heat input reduces dilution of the weld deposit with the mild steel portion of the weld joint. This in turn helps maintain the alloy content of the weld deposit and its desired corrosion resistance.
Other stainless steel grades may form undesirable phases that result in brittleness or poor corrosion resistance if held too long at a high temperature. Sigma phase (a brittle, intermetallic phase with high hardness) can form in some stainless grades at elevated temperatures and can seriously compromise mechanical and corrosion resistance properties. In duplex stainless steels, for example, the heat input is responsible for the balance between ferrite and austenite in the final weld and heat-affected zone (HAZ). The proper level of heat input can help to maintain the desired amount of each phase in the finished weld and base metal HAZ.
Pitfalls to avoid: warping, cracking and oxidationStainless steel has a high coefficient of thermal expansion, a measure that refers to the rate at which a material expands with changes in temperature. In short, stainless steel expands and contracts more with temperature changes in comparison to carbon steel.
Differences in the coefficient of thermal expansion and the thermal conductivity can cause some difficulty when welding dissimilar materials. Stainless steel will naturally want to expand and contract more as a result of the high heat seen during welding. Conversely, carbon steel (particularly mild steel) is a good conductor of heat and therefore will cool more rapidly and shrink faster as the joint cools. These differences add to the stress on the joint, created as both sides expand with heat and contract with cooling. This can cause warping or misalignment of a dissimilar metal weld. It can also cause cracking if the stresses created by differences in thermal expansion and contraction exceed the strength of either material.
To address these two issues when welding stainless steel to carbon steel, avoid highly restrained joints that create high stresses as the joint is heated and cools down. If a highly restrained joint configuration is required, use modest heat input and some pre-heating to delay cooling of the joint after welding is completed. Insulating the weld joint after the last weld pass also will slow cooling and help prevent thermal stresses from cracking a joint.
When it comes to protecting the material from oxidation, these dissimilar metal welds should be treated just as a stainless weld would. Open root joints should be shielded from the atmosphere on the backside of the weld (back purging). The practice of back purging, most frequently used when TIG welding, helps prevent contamination of the weld from behind the joint. Otherwise, the weld joint and stainless steel side of the weld can be damaged by oxidation, which is the result of a reaction with oxygen and nitrogen in the atmosphere. Oxidation will damage the corrosion resistance of the weld and stainless steel HAZ. To prevent this from occurring, purge the back of the joint with an inert gas such as argon, or use one of the commercially available coatings that can be applied to the back of a weld joint prior to welding.
Preparation for stainless steel to carbon steel weldingProper cleaning and preparation are vital steps to help ensure successful welding of dissimilar materials. Grind the mill scale or coatings back by at least 1/2 inch on each side of the joint. Follow this task by cleaning the area with a solvent such as alcohol or acetone. These steps help get rid of grease and oil, which tend to carry the phosphorous and sulfur that are the primary causes of hot cracking.
FCAW is among the most popular welding processes because of its flexibility and versatility. Metals like cast iron, stainless steel, carbon steel, high-nickel alloys, and low-alloy steels can be easily welded using the flexible FCAW process.
The flux-cored arc welding process finds its use in industries like construction, heavy equipment repair, structural steel erection, shipbuilding, etc. The primary reason for this is that, unlike most other welding processes, FCAW works on all kinds of materials even if contaminated (except for dealing with contaminants like oils, water, and paint).
SMAW finds its use both indoors and outdoors for welding low-alloy and high-alloy steels, nickel alloys, carbon steel, and cast iron (like FCAW). Just like flux-cored arc welding, SMAW, too, creates a layer that you can chip off later.
Flux-cored arc welding (FCAW) is primarily used for welding thick materials and metals. These include cast iron, carbon steel, stainless steel, high-nickel alloys, and low-alloy steels for activities such as shipbuilding, bridge construction, structural steel erection, and heavy equipment repair across a wide range of heavy industries, including construction.
Some examples of stud welding users include; metal working industries, shipbuilding, aerospace, offshore drilling platforms, petrochemical industries, insulation installation, construction and anywhere metal fastening is required.
Some examples of stud welding users include; metal working industries, shipbuilding, aerospace, offshore drilling platforms, petrochemical industries, insulation installation, construction and anywhere metal fastening is required.\" } }, { \"@type\": \"Question\", \"name\": \"What are the benefits of stud welding\", \"acceptedAnswer\": { \"@type\": \"Answer\", \"text\": \"Stud Welding is a major improvement over other methods and the benefits are many!
All Types of Metals - practically any metal can be adapted to stud welding. Aluminum, mild steel, stainless steel, copper, and brass are the most common. Exotic metals such as titanium and Inconel can also be used.
Steel, a term that actually describes an entire family of metal alloys, is a versatile and common type of metal with a wide variety of applications and uses. There are many grades but most types of steel fall into two broad categories, carbon steels and stainless steels. Though they have the same basic composition of iron and carbon, steel types tend to have a variety of alloying elements. Carbon steel tends to have under 10.5% chromium content, but steel must be at least 10.5% chromium to be considered stainless. These differences give each type of steel its respective properties. 59ce067264
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