**2. Identification of engineering challenges in repairs**

There is a multitude of jobs and types of repairs requiring welding applications. Challenges can often be categorized by the location, component type, design criteria,

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

and the degree of critical quality needed in the repair. Repair location presents its own challenges from a logistical sense. Outdoor welding applications require mobilized welding equipment to access the repair. Mobilized welding equipment can require a fuel-based power source, due to a remote location or conditions. Due to the space constraint of certain repairs, it is common for mobile welding equipment to feature lengthy leads, which can also create unique circumstances. Outdoor welding repairs can present additional challenges derived from environmental factors, such as weather, terrain, and less than ideal base material circumstances. Not all welding processes are well-suited for this type of environment, limiting available repair options. These challenges call for strategic planning and an understanding of certain technical properties for repairs made in outdoor environments. There are fewer constraints for indoor welding repairs, where a variety of processes are available. Indoor welding environments found in machine shops, manufacturing facilities, prototype shops, and fabrication workshops are well equipped for operator comfort and process quality, without exposure to adverse environmental conditions.

### **2.1 Repair preparations**

Pipeline and structural welding are common examples of strictly outdoor welding applications. Professional welders of this category are highly skilled, due to the criticalness of their weldments and their ability to produce quality welds in difficult or uncomfortable body positions. This may consist of laying under a pipe in the mud to bevel, grind, mate, and weld pipe together, or it may mean being suspended hundreds of feet in the air, welding steel beams for structural applications. Critical preparation techniques are always used during the preliminary repair preparation process to ensure the quality of the weldment because, in many circumstances, time in the repair zone or position is limited.

Metal cleanliness and preparation are the most critical features for any field repair. Insufficient attention to base metal preparation will lead to unwanted imperfections in the repair. While certain welding processes are capable of penetrating through some surface rust, failing to clean the intended weld area of contaminants will always yield certain weld defects, such as slag inclusions, porosity, and craters. Weld defects lead to unwanted future cracks in the weldment, causing the component to lose structural integrity and have progressively weaker joint strength. Metal preparation is usually conducted using an electric angle grinder with a variety of disc attachments. Standard grinding discs are used to remove material quickly, and they perform well for removing large amounts of surface rust, paint, and other contaminates. Sanding disks, also referred to as "flap disks," are effective at removing mill-scale on the base material and polishing the metal surface.

Material fitment to maintain proper dimensions and alignment with other components during the welding process is nearly as vital as material preparation. Repairs due to a defect or flaw causing a component or related component to be displaced from their original state must be approached with caution. These conditions require the fitment of material to be returned to a near-original state prior to the repair process. However, the removal of old material often includes the removal of the original weldment or the removal of material near the damaged area. Taking measurements beforehand or using a secondary, mirrored part for dimensioning can be helpful for reestablishing the original location of a displaced component in need of repair. When proper material fit-up is completed, weld material can be added to the removed areas by making a series of weld passes to build up the filler material. Adding an amount of weld material more than what is necessary is generally recommended, so later grinding can remove the excess.

After achieving proper fitment of the base pieces, constructing a jig or welding additional structures to the member may be necessary to maintain the position of the pieces while welding. Welding induces rapid temperature changes with the heat concentrated in a small area. This thermal transfer of energy causes the metal to expand slightly, and under extreme conditions, it can cause warpage and deformation. High temperatures cause a crystalline structural rearrangement and reduction in tensile and yield strength in most metal materials [3]. Metal warpage is more likely to occur when applying a large amount of weld material to thinner materials with thicknesses of less than 30 mm. Part of the preparation process for the repairman is evaluating and mapping out the intended weldments in an effort to evenly distribute heat applied to the material during the repair. If the material movement cannot be avoided by distributing weld material and heat evenly, a temporarily fixed member can be welded in place to prevent movement from occurring. The temporary support can later be removed and grinded away.

### **2.2 Material analysis**

Welding repairs may be necessary on a variety of metal components that can be made from ferrous materials, such as carbon steel, stainless steel, and cast iron, as well as non-ferrous materials, such as aluminum and titanium alloys. Identification of the material is essential to executing a welding repair. Repairmen need to accurately be able to access which materials they are dealing with. All raw materials have specific properties associated with the type of material. Material properties are defined as measurable, quantifiable properties associated with the material. The material properties help categorize different materials and ease the process of material selection. Evaluating categories of mechanical properties of the material is an effective way to identify material for a field repair. Documentation is always best, but in the field, it seldom exists. When confronted with an unknown material, investigation should include at a minimum, a chemical test, and a hardness test. These two property indicators will help qualify the weldability of the material. Other properties can help narrow uncertainty in the base material. There are generally considered to be five categories of mechanical properties for common building materials [4], which are as follows:


Physical properties are perhaps the most easily identifiable material characteristics when conducting field repairs. These properties include the shape, size, color, texture, finish, porosity, and luster of the subject material [4]. Technological properties are also referred to as basic mechanical properties for the metal, and these include

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

hardness, malleability, machinability, weldability, and formability. It is recommended that the material's physical properties be evaluated first. This will allow an easier understanding and identification of mechanical properties, once known. In a repair situation, material identification is important for understanding the behavior of the component's base metal and how it is likely to react to different welding processes.

Mechanical properties are critical to understanding structural repair applications, particularly when there are critical zones of stress and strength maintenance requirements. Material properties commonly found in engineering material references are as follows [3]:


Tensile strength for different types of material is experimentally determined by a standard testing method, conducted using a tensile test machine. The selected material is marked at two locations, 50.8 mm apart. Once the selected material is placed on the machine, an axial load is applied by pulling the material in opposite directions at a constant rate. As the test progresses, the load divided by the original cross-sectional area of the material within the marked area represents the resistance that the material has to the tensile load being applied [1].

The stress (σ) unit is in force per area, while the strain (*ϵ*) unit is formally dimensionless, it is expressed as displacement in length per original length. The maximum load applied before failure of the material, divided by the static crosssectional area of the material being tested is equal to the ultimate tensile strength (σ) of the material. From stress and strain values, the modulus of elasticity of a material can be calculated as [1]:

$$\text{Modulus of Elasticity } (E) = \frac{\text{Stress } (\sigma)}{\text{Strain } (\sigma)} \tag{1}$$

Modulus of elasticity (E) is a way to quantify the springiness of a material or the stress value of a given material as it is deformed by a force in one direction. It is also commonly referred to as Young's Modulus, after English physicist, Thomas Young. The AISC states that the standard for all low-carbon steel is a modulus of elasticity of 200,000 mPa [5]. Section area is an important metric, used when calculating the stress and strength of materials with loads applied in compression, tension, and shear configurations. If the member is not symmetric throughout the length of the applied load, then the section at which the material or structure will induce the most stress is used in the calculation. Once the desired cross section is found, the neutral axis must be located. The neutral axis of a section represents the plane of zero strain and zero stress, and it can be a good place to locate a spot weld during the fitment process [1].

Material hardness is a well-correlated property with many other physical properties, and it is determined using a Brinell hardness test. The test is conducted by applying a known load to the surface of the material using a hardened steel ball. The diameter of the impression that the ball leaves on the tested material is the measured result of the test. The diameter of the impression can be converted to the Brinell number as follows [6]:

$$\text{BHN} = \frac{2P}{\left(\pi D \left(D - \left(D^2 - d^2\right)^{0.50}\right)\right)}\tag{2}$$

where *BHN* = Brinell Hardness Number;

*P* = Load on indenting tool (kg);

*D* = Diameter of hardened steel ball (mm); and.

*d* = measured diameter at the rim of the impression (mm).

Fortunately, the Brinell Hardness Number does not typically need to be calculated. For most materials, the number can be found using various Brinell charts. One might be exposed to materials with a high Brinell hardness utilized in high wear environments, as in abrasive situations, due to contact with other moving components. The Brinell hardness can be increased using a thermodynamic hardening process. There are various methods of hardening materials, but in the simplest form, hardening is achieved by increasing the temperature of the material to a modest degree and then rapidly cooling it by quenching the material. The quick change from a high temperature to a cold temperature hardens the material by locking-in elevated temperature crystal structures.

Tool steel used for drill bits, mill cutters, and hand tools is typically hardened, along with other critical mechanical components, such as shafts, bearings, and gears. Hardened materials can be a challenge for welding repairs, due to their impenetrable nature of the material. The heat applied to the material during the welding process, along with the rapid cooling typically present in welding, can make the hardened steel base material brittle and cause cracking along the joint. Heating the material slowly and evenly with an oxygen-acetylene torch, while monitoring the temperature of the joint before welding, will soften the material and allow the weld process to penetrate deeper. After the weld is complete, cooling the material around the joint slowly will maintain the material's hardness, but make the material less brittle. This softening process is also referred to as annealing [7].

The ASTM is an organization established to produce standards for material properties of all sorts. For nearly 120 years, ASTM has written technical standards for materials, products, and other systems [8]. Physical properties are defined by characteristics, such as corrosive resistance, hardness, density, and thermal conductivity, to name a few. When choosing metal material or evaluating an existing component for repair, corrosive resistance is an important factor to consider. Understanding the environment that the material is exposed to aids the welder in selecting preparation requirements and the welding process. In general, the welder should determine the following material properties before starting a repair:


• whether is it outside or inside the application.

It is commonly known that mild steel is corrosive, but when painted, the structural life of the steel is lengthened significantly. The corrosion rate is simply measured by the millimeters of corrosive penetration into the material per year. A common alternative to painting is the plating of the metal. Materials can be plated with a variety of different plating materials. Zinc-plated bolts are a common example of a component that receives plating for increased durability. It might be best to use stainless steel for structures exposed to salt water or high moisture atmospheric environments. Stainless steel is highly resistant to oxidation and a popular choice to use for marine structures, along with many industrial food processing applications having health code precautions. Materials with any of these anti-corrosion features must be treated specially, and repair welders must take these elements into account when planning repairs. Additionally, a repair technician should almost always consult a specialist, if they spot a highly stressed area, find corrosion or hydrogen embrittlement, or have a hightemperature operational environment [9]. Finally, if chemical information about the base material is available, levels of carbon and other alloying materials provide critical information to the repair technician. Certain stainless steels cannot be effectively welded, and in general, a 0.35% carbon level is typically considered the upper limit for welding. Material chemistry mainly identifies what cannot be welded or where extreme caution should be applied when making repairs. There are now test kits available that can determine a metal's chemical content within a matter of hours [10]. There is simply no excuse for not knowing what material you are dealing with anymore.
