What Is Steel Plate Welding?

Steel plate welding fuses individual steel plates by joining them with heat, pressure, or at times both. In industrial production, fusion welding utilizes the melting of both the base metal and filler metal to forge a permanent joint after the weld pool cools and solidifies.

Hence, you can use any method from the following:

• Shielded Metal Arc Welding (SMAW)
• Gas Metal Arc Welding (GMAW)
• Flux-Cored Arc Welding (FCAW)
• Submerged Arc Welding (SAW)
• Gas Tungsten Arc Welding (GTAW)

When welding thick steel plates, you’ll likely need to utilize additional welding passes to deposit more weld metal compared to thin plates. Hence, you can’t use one continuous pass. While appearance is important, a good weld needs adequate penetration, fusion, strength, toughness, and dimensional accuracy.

Hence, the welding procedure you select must be in accordance with the steel’s chemistry. It should suit the plate’s thickness, joint type, amount of joint restraint, filler metal, and level of heat input.

Common Steel Plate Welding Methods

There isn’t a single method for welding all steel plates that can be labelled as best. The best method for you depends on several factors, including plate thickness and quality, desired joint configuration, position and accessibility of welds, needed volume of welds, available equipment, and any specifications or standards. Now, let’s look at some of the common methods used for welding steel plates.

1. Shielded Metal Arc Welding (SMAW)

Shielded metal arc welding is commonly referred to as stick welding. SMAW utilizes an electrode that is coated in flux. In order to weld, an arc must be struck between the base metal and electrode. Once the electrode and base metal are molten, the flux is used to shield the weld pool from contamination. SMAW is used for:

• Structural steel welding
• Field welding
• Welding repairs
• Welding construction
• Heavy equipment welding
• Welding off-site where portability is required.

A major strength of the process is the flexibility. You can take SMAW equipment to places where a larger, more automated system would be impractical. SMAW is also useful for a variety of welding positions. SMAW has a lower deposition rate compared to FCAW and SAW. For welding thicker sections, this can increase the number of passes required to complete the weld.

For hydrogen-related cracking used in many structural applications, low-hydrogen electrodes are used. For this, the American Welding Society recommends filler-metal diffusible hydrogen be taken into account when determining appropriate preheat requirements.

2. Gas Metal Arc Welding (GMAW)

Gas metal arc welding (GMAW), also known as MIG or MAG welding, relies on continuously fed wire electrodes and shielding gas. Conventional shielded metal arc welding (SMAW) requires the welder to stop repeatedly to replace the electrode.

The GMAW technique is an improvement in that aspect since a wire electrode is continuously fed. So, you don’t have to stop again and again to replace electrodes. GMAW is more utilized in industries since it makes welding a more efficient process.

GMAW is utilized in:

• Steel fabrication
• Assembly of machine components
• Assembly of structural components
• Manufacturing
• Automated and semi-automated welding

The process produces a high level of productivity and leaves relatively less slag when compared to other welding techniques. This helps you get cleaner welds. However, GMAW can be sensitive to environmental conditions due to the frequent need for shielding gas. This is a bigger concern when welding outdoors.

3. Flux-Cored Arc Welding (FCAW)

Flux-cored arc welding (FCAW) uses a continuously fed tubular wire with flux. The wire decides whether FCAW can be self-shielded or requires an external shielding gas. High deposition rates and good penetration make FCAW an excellent choice for heavy fabrication. It is used in the fabrication of:

• Large steel structures
• Heavy equipment for construction
• Shipbuilding
• Industrial equipment
• Large steel components
• Fabrication of thick plate

For large steel components, FCAW offers a good balance of productivity and versatility. However, you also have to choose an appropriate wire classification and shielding arrangement according to your application.

4. Submerged Arc Welding (SAW)

Submerged arc welding is well suited for welding large quantities of thick steel plates. In SAW, an arc works under a layer of granular flux. It acts as a shield, protecting the arc and the weld pool from the atmosphere. You can easily utilise SAW with automated and mechanized welding. It is often used with the following:

• Heavy structural works
• Pressure vessels
• Heavy beams
• Shipbuilding
• Wind tower components
• Long seams
• Thick steel sheets

SAW’s primary advantage is its productivity. Since SAW uses a high-current welding process and can be used with a continuous wire feed, a large amount of weld metal can be quickly deposited.

For thick sections, you can use modern techniques as well. These combine SAW with narrow-gap or hybrid laser-arc welding processes. They can help reduce weld volume and heat input when compared to conventional SAW.

5. Gas Tungsten Arc Welding (GTAW)

GTAW, known as TIG welding, uses a non-consumable tungsten electrode. It results in better quality welds with high amounts of control. However, you might feel that it is a relatively slow process when compared to high-deposition welding processes.

As a result, GTAW is often not the preferred choice for filling large volumes of thick steel plates. This process is more commonly utilized to place root gaps or when you need to ensure high weld quality and precise control. GTAW is most suitable when compared with other high deposition processes in terms of weld quality and control.

However, you must remember that a high deposition process does not automatically become the best choice when the joint is hard to access or needs to be welded in different positions. Here is an outline of common welding methods you can use.

How to Weld Thick Steel Plates

Welding thick steel plates requires better preparation in comparison to welding thin plates. Hence, you should be able to control the entire welding process, from the initial preparation to the final inspection. Let’s discuss how you can weld thick steel plates.

1. Identify the Steel Grade

Your first step should be to determine what type of material you are working with. You must review the material certificate or specifications for:

• Grade of the Steel
• Thickness
• Yield strength
• Tensile strength
• Chemical composition
• Applicable standard
• Type of heat treatment

This information will assist you in selecting the appropriate welding procedure and filler metal. Just because you are welding two pieces of carbon steel does not necessarily mean you can use the same welding parameters for each material.

Cracking sensitivity and thermal control of high-strength and alloyed steels are generally greater compared to lower-strength steels.

2. Check the Plate Thickness

The next step is to measure the actual thickness of the plate and calculate the total thickness at the weld. Thickness tends to determine the heat input, joint preparation, the number of weld passes, the need for preheating, and the time required for the welding.

Even when you plan to preheat thicker plates, you can see how guidelines vary based on steel composition, thickness of the plate, filler-metal diffusible hydrogen, and joint restraint. This is essential for thick steel plates as their thermal behavior is quite different from that of thin plates.

3. Prepare the Joint Properly

Joint preparations directly impact the quality of your weld. Beveling a simple square butt joint may not be sufficient in thicker plates. In such a case, a groove may be needed. Where joint preparations are concerned, some common ones include:

• V groove
• Double V groove
• U groove
• Double U groove
• J groove
• Double J groove

The purpose of a good joint design is to provide access to the welding arc while allowing only a specific amount of weld metal to be deposited. A poorly designed joint often forces the welder to deposit more weld metal than what is necessary.

This excess of weld metal increases the welding time, heat input, cost, and distortion. For plates that are too thick, a well-designed groove may greatly reduce welding metal volume. However, it only works if an appropriate process and procedure are planned.

4. Clean the Steel

Prior to welding, the joint area must be thoroughly cleaned. Cleaning should remove:

• Oil
• Grease
• Moisture
• Rust
• Paint
• Mill scale
• Dirt
• Other contaminants

By keeping your surface clean, you can ensure that there are no contaminants present. This helps in establishing a stable arc and minimizes the chance of weld contamination. Consumables must also be considered.

For low-hydrogen electrodes, you should also pay attention to moisture. Appropriate electrode storage and handling also minimize moisture content. This helps in retaining the desired properties of the electrode.

5. Fit and Tack the Plates

Before doing the main welds, you must position the plates in the right place. You need to look for:

• Root gap
• Alignment
• Joint angle
• Plate squareness
• Size of tack welds
• Spacing of tack welds
• Restraint

Tacking involves more than just joining two pieces together. You must be careful because misalignment can cause gaps, which can adversely impact penetration as well as weld geometry.

Poor penetration can lead to greater restraint, which can increase stress levels during welding. The welding procedure specifications give the joint and welding parameters for a particular joint. Hence, you must follow them instead of relying on estimations.

7. Control Interpass Temperature

Controlling temperature during the welding process is more complicated than just preheating the welding area. The temperature of the weld prior to the deposition of the next weld pass is known as interpass temperature.

If you allow the metal to cool too much, the material may lose some or all of the benefit of the preheating. If you allow the metal to increase in temperature beyond the required range, it can completely disrupt the mechanical properties of the weld. For this reason, your welding procedure specifications must establish proper maximum and minimum interpass temperature limits.

8. Deposit the Root Pass

The root pass is arguably the most important part of the welding process. It forms the foundation of the remaining weld. Hence, you must ensure that it penetrates the base metal adequately, but doesn’t burn through. It must also be free from lack of fusion, slag inclusions, or any other defects.

Depending on the joint design and the welding process, you may choose a number of different processes including SMAW, GMAW, FCAW, GTAW, or any other qualified process for the root pass. The exact method of accomplishing the root pass should be in accordance with the welding procedure specifications.

9. Clean Between Passes

Before you put the next pass, make sure you have deposited the weld pass properly, removed slag, and inspected the weld thoroughly. This is especially essential for slag-producing processes. If slag gets trapped between passes, you can end up with inclusions. Between passes, you must look for obvious problems like:

• Cracks
• Undercut
• Porosity
• Lack of fusion
• Slag
• Poor bead profile

So, you must find the defect and continue to the next pass only after correcting the issue.

10. Use Multiple Passes

Thick sections require you to lay multiple passes. So, you don’t just fill the entire joint with one huge weld pass. You have to progressively build the weld using individual passes. Depending on the joint, weld sequences may include:

• Stringer beads
• Controlled weaving
• Alternating sequences
• Back-step sequences
• Balanced welding
• Skip welding

The weld sequence you use should be able to control heat distribution and distortion. The aim is to achieve the needed weld size and penetration without going beyond the qualified range of heat input.

11. Control Heat Input

Heat input is a very important factor in welding. It depends on welding current, voltage, speed, and your welding technique’s thermal efficiency. Using too little heat can lead to poor fusion or cooling that is not optimum.

Using too much heat can cause excessive distortion. This can also affect the microstructure and mechanical properties of the joint. Therefore, your goal shouldn’t be to maximize the available amperage, but rather to achieve a consistent, controlled level of heat input.

12. Manage Distortion

Thick steel does not eliminate the problem of distortion. During the welding process, steel is heated and cooled. It expands and contracts, creating stresses in the weld and surrounding metal. You can manage distortion by using:

• Proper joint design
• Appropriate welding sequence
• Well-balanced weld positioning
• Controlled heat input
• Using tack welds
• Proper fixturing
• Back-step or skip sequences where appropriate
• Symmetrical welding where possible

Your goal should be to control distortion during the fabrication process rather than trying to straighten the completed structure.

13. Allow Controlled Cooling

Once you are done with the welding process, you must allow the component to cool down according to the welding procedure specifications. Do not automatically quench a welded thick steel component unless your procedure specifies it.

Rapid, uncontrolled cooling can lead to harmful microstructures and cracking in susceptible steels. Hence, for critical applications, the required cooling, post-weld heat treatment, or hydrogen control procedure should be in correspondence with proper specifications.

When welding thick steel plates, you need more than just the right machine. You need repeatable parameters. Here are some parameters you need to consider when welding thick steel plates.

Welding Equipment for Steel Plate Welding

Your equipment must match the plate, welding process, production volume, and environment. Here is the essential equipment you must have in order to weld steel plates smoothly.

● Welding Power Source

Your choice of power source depends on the welding process. Fabrication shops working on heavy-duty projects may need more powerful equipment for FCAW, GMAW, or SAW.

For field welding, SMAW may require an emphasis on ruggedness and portability. For automated welding, you may require a travel system that is properly mechanised or a welding carriage.

● Wire Feeders

When considering GMAW or FCAW, a wire feeder must ensure uniform wire delivery. A stable wire feed contributes to consistent arc characteristics as well as uniform deposition. For thick plate applications, you must choose a feeder and torch system that can accommodate wires of larger diameters and be able to withstand the duty cycle.

● SAW Equipment

SAW consists of a power source, wire feeder, welding head, flux delivery system, and travel mechanism. For long repetitive welds, where productivity is important and consistency is key, mechanized SAW may be your best choice. Control of wire feeding and travel speed may be easier to implement with mechanized SAW. This helps you enhance the consistency of welding.

● Preheating Equipment

You must ensure a consistent way to heat a plate when preheating is necessary. Under the given circumstances, this can include:

• Gas burners
• Heating resistance
• Induction heating
• Heating blankets
• Other controlled heating systems

The important thing is not to just heat steel. You also need to check whether the temperature specified is achieved and sustained.

● Temperature Measurement

You can use appropriate temperature measuring equipment to verify preheat and interpass temperatures. Depending on your process and specifications, these may include:

1. Temperature crayons
2. Contact thermometers
3. Infrared thermometers
4. Thermocouples
5. Temperature measuring and controlling systems

For more critical fabrication, temperature measuring and controlling systems must be as per the applicable requirements and procedures.

● Welding Positioners

You can make your thick steel plate welding process easier with a welding positioner. It has the ability to rotate and position your workpiece so that you don’t have to move around it again and again to access the joint.

If you are able to keep your weld in a favourable working position, you can ensure increased productivity and consistency while lowering operator fatigue. Positioners are especially useful in repetitive industrial fabrication projects.

● Fume Extraction and Safety Equipment

Welding generates fumes, heat, ultraviolet radiation, sparks, and other hazards that are considered dangerous. Hence, you must install a good local exhaust ventilation system or ensure sufficient general ventilation in your welding area. You must also have:

1. Welding helmet
2. Protective clothing
3. Welding gloves
4. Safety shoes
5. Eye protection
6. Hearing protection if required
7. Respiratory protection if required
8. Fire prevention equipment

You must follow all the necessary safety requirements applicable to your workplace as well as your welding process.

Conclusion

Frequently Asked Questions

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