Cladding the inside of a pipes and valve seats with an abrasive and/or corrosion resistant material onto a cheaper substrate in one or two layers is common in the oil and gas industry as pipe networks made of dissimilar materials have longer life and are more economical. The process is ideal for welding automation as the torch or component movement is generally very simple (e.g. helical or stepped rotation). An overview of simple and more complex clad products is shown in the following slides.
The automated machines used to internally clad pipes and the like generally employ one or two GTAW torches and hot-wire system(s). These torches are able to clad the substrate with high integrity layers at increased deposition rates and reduced dilution compared to cold-wire systems (more info here and here). Plasma transferred arc and laser may also be used as a heat source with hotwire or powder feed systems. OEM machine builders offering GTAW with hotwire include Polysoude, Arc Specialties, Jetline, Amet, Welding Alloys, Fronius, Arc Machines, Redman Controls (please suggest missing companies below).
Automatic spiral cladding with laser by Rofin (with powder)
It’s obviously rather difficult to see and control the torch and wire feed when they are embedded far up a pipe. As such, welding cameras are commonly employed to monitor the process. As cladding consumes a lot of wire, the wire spool is changed often. Unless endless wire systems are employed (click here for a short review), cameras are also particularly important for checking that the weld torch and wire are correctly positioned before restarting the cladding process. The three important features for such a welding camera are the ability to visualize both when the arc is on and when the arc is off, water-cooling due to space constraints and small camera size. The following video shows a two torch process developed by Arc Specialties for KladArc.
The Hobart dabber TIG was developed for building up worn down knife-edges on turbine seals and blades with reduced heat affected zones. Jetline Engineering and Liburdi are the two companies (that I know of) to currently offer this equipment.
In a dabber TIG process, the wire and current are both pulsed. First, the current is pulsed, transferring heat to create a weld-pool on the build-up edge. The wire pulse is synchronized to ‘dab’ into the weld-pool after it is formed (i.e. the weld-pool is created, the wire is fed in and then the wire is retracted). When the dabbing motion is well proportioned to the current, the wire acts as a heat sink, cooling the puddle and limiting the overall heat transfer to the knife edge and therefore the heat affected zone. These conditions can be used to build-up a delicate edge in a stable and defect-free manner.
In the following video, the dabber TIG process is monitored using a welding camera with a spot filter. After 45 seconds (and for the next 4 minutes), the dabbing wire is switched on.
The MeltView MIRA camera is suitable for precision applications such as dabber TIG and micro plasma. MeltTools offers the camera with an appropriate zoom lens to provide magnified views of the process, facilitating faster and more accurate set-up and greater weld-quality.
Narrow gap welding refers the welding of deep groove joint penetrations using GTAW / GMAW / SAW. The two key benefits of narrow gap welding are the ability to weld thick sections more economically due to reduced joint preparation and reduced distortion as the welds are parallel sided.
Whichever process is employed to fill in the gap, adequate fusion and wetting of the side walls is required. In the following video this is achieved for a GTAW based system with a specialist oscillating tungsten electrode.
Commonly the narrow gap welding using the GTAW process is monitored and controlled by way of a welding camera as shown in the following video. In this video four weld heads simultaneously fill up the joint gap. An operator makes fine adjustments to the welding processes remotely. The cameras provide close-up images of a weld-pool that is otherwise difficult to see due to the narrow preparation. Furthermore, the management of the process is significantly improved as a single operator can simultaneously control and coordinate the four torches from the console.
For such equipment, if the torch position can be remotely controlled or has suitable sensors to maintain the correct torch height (e.g. Automatic Voltage Control – AVC) and the correct position of the electrode relative to the joint seam (seam tracking using mechanical (tactile), inductive, optical, laser sensors), then the operator can be positioned at the control console. For both remotely controlled and automatic welding operations, an operator is required to monitor the whole operation, especially when welding more expensive stainless steel alloys that are commonly seam welded.
Without a remote control for mechanized seam welding applications, the operator crawls along the sheet with his head near the arc to monitor the welding operation. The job is awkward, monotonous and risky as exposure to fumes, heat and arc increases operator fatigue and contributes to ill-health.
It is generally acknowledged that ~80% of the weld cost comes from the direct labor cost. The application of a viewing system can effectively improve working conditions, immediately resulting in reduced fatigue and absenteeism and improved operator concentration and weld quality. An affordable welding camera thus gives a very quick return on investment.