Field welding is a great way to weld metal pieces together in any location – either indoors or outdoors. This form of welding offers many advantages, including convenience and mobility – which can be especially important if you're working with something too large to transport inside easily.
However, some potential downsides come along with this type of welding. In this blog post, we’ll explore what field welding is, examine its pros and cons, discuss safety precautions when performing outdoor welds, and provide helpful tips on how best to ensure your work looks great.
What is a field weld?
Field welding is when a weld must be performed at the location of the final installation. This can be due to the size of the equipment being welded. This can be structural welds, and another example would be piping and pipelines.
In the oil field where I work, we aren't allowed to have flange sets as they're potential leak points. With environmental precautions in mind, all pipelines are welded. Stick welding is the most common welding process used for this.
Another example of field welding is structural steel fabrication. Structural steel fabricators often have to perform a field welding repair on location. It may be required for new construction as well. Stick welding is the welding process used for this application as well.
Most often, stick electrodes are used rather than a wire feeder. Flux-cored welding techniques could be used. However, the leads tend to be shorter and thus require the welders to be closer to the workpiece.
What is the purpose of field welding?
The purpose of field welding is to make welding repairs on equipment that can't be removed from their location due to size, time, and resource availability.
There are also times when even flanged piping can't be pre-welded due to the installation running between floors and walls of process facilities.
The other purpose of field welds could be during in-service piping weld repairs. This type of field repair is often welding sleeves in a corroded section of pipe.
What is the difference between shop weld and field weld?
Shop welding processes are performed in a controlled environment where MIG welding equipment can be used. The MIG welding operation gas prevents airborne contaminants from creating poor weld quality.
Field welding is often performed outside and therefore requires stick welding. The self-shielded processes are required as a MIG setup would lose all of its gas required to protect the weld joint.
Field weld inspections.
Field welds will have to be inspected. If it's piping, there will generally be an operational step to have non-destructive testing performed to verify weld quality. This is an accepted practice under API-570.
These inspections can be performed using high- and low-level x-ray and ultrasonic inspection techniques. However, the latter is generally used to verify enough base material metal to be welded before field work.
The x-ray technique requires coordination with operations and other crafts in the area to prevent accidental radiation exposure.
A quality control inspector and engineering groups will inspect structural steel welds.
Shop welding with a hydrostatic test.
I've seen hydro testing performed on the drill sites on highly long pieces of pipe where flange connections were available. It can be done, but with a ton of scrutiny and math due to fluctuations in outside temperature and windy conditions.
Performing shop welds better and hydro-testing the spool after welding is better than performing x-ray inspections in the field.
Reasons Shop welding is better Than Field Welding-
Components are at a constant temperature.
Fabricators are more comfortable in the position.
Easier inspection methods.
Removed from potential hydrocarbon-rich environments.
Better welded joint, in my opinion.
More choices for filler metal.
Plasma cutting availability.
Welding Processes Used
Typically, field welding is performed with the stick welding process, and in some cases, flux-cored welding techniques are used.
Shielded Metal Arc Welding (Stick welding process)
Stick welding uses electrodes that create protective gas as it's burned to protect the molten metal. Engine-driven stick welder will have longer leads than a wire feed setup and have plug-ins for other welding tools.
With pipe welding, there are many considerations with field welds that might not be required with welding structural steel. Scaffolders and insulators may be required to prepare the repair location. Operations staff may need to cut rates or energy isolate the pipe.
In-service pipe welding packages require a heat loss test performed. Heat input is added and then allowed to cool. Depending on the product temp flowing through the pipe and how fast the flow is will determine if the joint will cool off too fast or not.
If a heat loss test can't be passed, metal shavings are then collected to determine if the field welding repair can be made. Mag particle testing is quite often used.
If pipe sections have to be removed to perform the repair, it's possible to remove flammable material from the pipe. No longer are you allowed to cold cut the pipe and light a torch on one end to burn out the flammable material.
To safe out the line, it may require diesel flushing and steaming to get it cleaned. In some cases, welding plugs can be used with a nitrogen purge to keep the welders safe.
Field welding pros and cons.
Every welding process has its pros and cons. Field welding is no exception. Here we'll cover the pros and cons, so you better understand them.
Field welding pros-
No chance for a weld bust due to fitment in the field.
Saves time-consuming demolition and reinstallation.
Pipelines can be restarted faster for production. (Happy customer.)
Field welding cons-
Location can be undesirable.
Added costs and equipment. (Scaffolding, manlift, wind wall construction.)
Field inspections can be burdensome.
Premature failure due to ambient temperature issues.
Potential contamination and other defects.
Location can limit the welding processes that can be used.
Field welding adds other crafts. (Insulators, scaffolders, electricians if heat traced, energy isolation, potentially steaming to evacuate hydrocarbons.)
Final thoughts on field welding.
Field welds have their applications. Whether it is required for a structural steel project or running a pipeline, there are reasons to use the field weld. They can be faster and just as effective if performed correctly.
With all of the pros of a field welding repair, there are things to consider. Field welds have an even greater level of scrutiny than fabrication shop welds.
Environmental considerations should also be considered. Wind, temperature, weather, and welder safety must be considered. Additional PPE and work boots may be required if your welders work in an arctic environment.
Hydrocarbons and H2S in process facilities create a whole other hazard in itself.
The welding types need to be considered along with the types of filler metals required per the welding procedure.
Hopefully, this post has given you a better understanding of the field welding process and how it can have both pros and cons. We use it all the time in the oil patch where I work. If we can remove it and perform the welding in the shop, it's always the preferred option.