**4. Challenges for engineers and technical managers**

One of the more difficult tasks for an equipment manager is signing off on the acceptance of repair work when the work falls within the domain of a specialist. Welding repairs certainly meet these criteria for most individuals. This section will examine weld defects and how to recognize them. It will cover the repair of defective welds and then go into detail about more extensive examination methods necessary to verify the quality of a critical weld.

### **4.1 Weld defects**

Defects in repair welds can have calamitous results. Therefore, it is necessary to identify defects and imperfections within a repair weld, before returning equipment to duty. Understanding the allowable variations in weld material's physical and mechanical structure will provide a reasonable basis for inspecting welds for imperfections. Pockets of impurities and variations in the weld that are within the acceptable tolerance range are called "discontinuities." Discontinuities that exceed the acceptable tolerance are called weld "defects" [16]. Defects must be ground away and repaired. Defects are generally caused by a poor welding technique, poor joint fit-up, or both. In the world of repair, poor joint fit-up is the most common cause of defective weldments. Repair jobs often consist of components that have separated and are no longer in their original position, making it difficult for the repairman to achieve the original geometry. This can be accomplished for many repairs, but sometimes it requires significant attention to detail and a bit of creativity to manipulate the original material into an acceptable repair position.

Defective welding techniques can cause impurities that affect the shape and size of the weldment, cause imperfections in the internal structure of the weld, and create other defects that adversely affect the weld's strength. The basic categories of weld defects are overlapping, undercutting, distortion and warpage, cracks, craters, porosity, and inclusions. Overlap is excess weld metal that reaches beyond the joint onto the base metal. The primary cause of overlap is an incorrect angle of the electrode with respect to the base material. If the electrode is not angled away from the weld pool on the leading edge, the arc will manipulate the weld pool, causing notches to form between the overlap and the base metal.

Undercutting defects occur when electrode travel speed is too fast, causing grooves or gaps on the toe of the weldment between the base metal and weld metal. The rapid travel speed does not allow enough time for the weld metal to fill in after penetration has occurred into the base metal. A thin or narrow weld bead also indicates excessive travel speeds. Good technique and weld speed will eliminate this problem.

The misconception that over-welding creates stronger joints was mentioned previously. Over-welding can also cause distortion and warpage of the base metal by the excessive application of heat. This occurs due to an improper joint design from the base metal thickness and dimensions. Applying a large amount of weldment in several passes can induce a large amount of heat, and it will also cause thin materials to flex and warp. This weld defect is extremely difficult to correct after the fact, due to the alteration of the base metal's natural shape. Heavy clamping in critical locations, before welding materials are likely to deform, is usually best. Once a piece has deformed into a complex shape, corrective choices become limited and generally involve minimizing further damage.

Cracks in the weld metal are often caused by other weld defects or excess stress induced at the joint. There are several classifications of cracks. Some cracks are internal and cannot be identified from the surface or at the throat of the weld. The stress-induced area at the toe of weldment is a common origination site for weld cracks [16]. Craters can form in the weld bead, causing a gap or hole in the weld metal due to the lack of filler metal deposited. Craters are easily corrected by revisiting the defect area after the weldment is complete. A new electrode should be used, beginning the tie-in 2.5 cm or so in front of the crater, allowing weld metal to melt and deposit into the crater, and extinguishing the arc after the proper amount of weld metal has filled the depression.

Porosity occurs when gas bubbles become trapped within the weld metal. This creates an uneven distribution of foamy weld metal. Porosity weakens the weld and can generally be identified at the surface of the weldment. Visible porosity is an indication that there is also porosity located below the throat of the weld. Inadequate weld preparation and contamination are the most common cause of weld porosity. The trapped gases are usually do not shield gases from the welding process, but gases from the oxidation and vaporization of the contaminates on the surface of the base metal [16].

Slag inclusions can result from trapped welding slag within the weld metal. This occurs only when using the SMAW/Stick/Arc welding process since GTAW/TIG and GMAW/MIG processes produce little slag peel. Slag inclusions can happen when an electrode has been consumed, and the welder ties into the old weldment with a new electrode, before removing the slag peel on the surface. Defects caused by improper welding techniques can be easily eliminated by following established welding procedures and maintaining the proper travel speed, arc length, and electrode angle recommended for the specific welding process.

#### **4.2 Repairing weld defects**

Welding defects must be repaired by the complete removal of the defect using either torch removal or grinding methods. Portable grinders with stone wheels are an excellent tool for the removal of weld defects. There is a selection of sizes in grinding wheels, and some wheels are designed to use the surface of the wheel, while others are designed to be used only on the edge. Grinding wheels designed for grinding with the outer edge of the wheel are a popular choice for removing joints, where a groove or bevel is present. Once the defect has been ground away completely, another welding attempt can be tried. For long stretches of removal, an oxygen-acetenyl torch may be used to gouge out the defect. This can be a more efficient method of removal in certain situations. Torch gouging may also be the only practical choice, if the joint is spaceconstrained, with little room to reach the defect area with a grinding wheel.

#### **4.3 Weld quality and examination**

It is important for field engineers and welders to evaluate the quality of their weldments. Each kind of defect displays unique characteristics, simplifying the identification and analysis process. Some defects are visually obvious, but a surprising number of repairmen do not thoroughly inspect their work after completion. Visually inspecting the weldment is vitally important to ensure the integrity of the repair, and it does not require significant effort. Cleaning the weldment and the area around the joint by removing slag with a wire brush is an easy process that results in improved visibility. The visual examination of a weld can usually be conducted with a flashlight, looking closely for the undesirable characteristics associated with the defects previously discussed.

The best practice for larger repairs and welding jobs is to have the inspection process functioning throughout the repair, conducted by a trained inspector at each step of the way. This preventative inspection protocol eliminates the continuance of defects during a repair [1]. However, an independent inspector for field repairs is not

## *Engineering Challenges Associated with Welding Field Repairs DOI: http://dx.doi.org/10.5772/intechopen.104263*

usually feasible. Therefore, it is vital for the welder to be capable of identifying defects as they occur. Quality control can be improved by having two or more qualified persons provide inspections. A fillet weld gauge is a handy tool for determining the size and quality of welded field repairs. This device is a measuring tool for checking the leg size and throat size of the weld [17].

In specialty applications where structural integrity is of utmost importance, inspections must be regular, and welds must meet the acceptable defect tolerance level. Specialty applications, such as underwater bridge welding, ship welding, and oil-rig applications must adhere to strict guidelines, codes, and are classified as a Class A weld. Welders in these fields must be licensed by passing a series of weld tests for joints configured in the 3F and 4F positions, administered and evaluated by AWS certified inspectors before beginning a new job, regardless of the prior experience of the welder. This requirement is due to the potential ramifications of a failed weldment [18].

### **4.4 Filling gaps and repairing cracked components**

Cracked components are common in the mechanical industry and are a regular failure mode for many pieces of equipment. These repairs are some of the toughest to execute, and this section will illustrate the overall process, so the equipment manager has an idea of the complexity of the operation. To repair a crack in carbon steel, a bevel directly on the crack must be ground to allow the weld metal to penetrate the base material, creating a tight joint at the crack. An electrode diameter size close to the width of the groove made by the grinder must be used. A standard size filler of 0.89 mm wire is generally sufficient if using a MIG welding process. Depending on the size and characteristics of the crack, an E6010 electrode and capped with a lowhydrogen E7018 electrode would be recommended to eliminate any undercut or hydrogen deposits created by the E6010 electrode, if using a GAW/Stick/Arc process. Finally, the weldment should be ground flush with the base metal to maintain its original appearance.

A field technician might encounter a situation where a gap needs to be bridged between two base pieces. A gap is when two materials should be welded together, but the pieces should not contact each other, as in **Figure 18**. The gap must be filled with weld metal, as in **Figure 19**. This technique should be considered the second stage in repairing a crack. A break that needs to be fixed by bridging a gap often originates from a hairline fracture or crack. When the material separates, it cannot always be drawn back together for repair. Filling gaps can be done in a variety of ways with different welding processes. Large gaps can be filled by using a backing strip. A

**Figure 18.** *Tack welds applied to establish a 0.3 cm gap between the separated pieces.*

#### **Figure 19.**

*Multiple large tack welds used to fill the gap between the separated pieces, where a continuous weld would likely blow through the gap.*

#### **Figure 20.**

*Welds ground-down to remove defects that occurred during the tack welding process joining the two separated pieces.*

#### **Figure 21.**

*A fine cap fillet pass used to finish joining two separated pieces, which may be ground flush for a solid appearance.*

backing strip is a section of material tack welded or stitch welded onto the base metal. This provides a surface for multiple welding passes without burning through. If a backing strip is used, it can later be grinded off and removed, or it can be left in place, depending on the criticality of the original dimensions. One simple technique to execute a gap fill is by making a series of tack welds along the joint, evenly spaced out. This allows the joint to be welded solid, while the tack welds provide enough weld metal to not blow through the joint. The fillet is typically ground flush after sufficient penetration and connection between the pieces has been established, as in **Figure 20**. Finally, a finish fillet can be applied to cap the weld, as in **Figure 21**.
