Weld Cladding

Weld cladding techniques were first developed at Strachan & Henshaw, Bristol, United Kingdom, for use on defence equipment, especially, for various parts of submarines. Through weld cladding, the composite structure is developed by the fusion welding process. All metals used as fillers may be used for weld cladding. Materials such as nickel and cobalt alloys, copper alloys, manganese alloys, alloy steels, and few composites are commonly used for weld cladding. Weld clad materials are widely used in various industries such as chemical, fertilizer, nuclear and steam power plants, food processing and petrochemical industries. Various industrial components whose base metals are weld-clad are steel pressure vessels, paper digesters, urea reactors, tube sheets and nuclear reactor containment vessels. Cladding using gas tungsten arc welding is widely used in aircraft engine components to maintain high quality. Weld cladding can be done by using various processes such as Submerged arc welding (SAW), Gas metal arc welding (GMAW), Gas tungsten arc welding (GTAW), Flux-cored arc welding (FCAW), Submerged arc strip cladding (SASC), Electro slag strip cladding (ESSC), Plasma arc welding (PAW), Explosive welding, etc. GTAW and PAW are widely used for the cladding operations, and they produce superior quality cladding because they generate high stable arc and spatter free metal transfer. Welding variables and inert gas shielding can be precisely controlled in both GTAW and PAW. Though GTAW and PAW cladding can produce excellent overlay with a variety of alloy materials, deposition rate is low compared to other processes which limit its application in industries. Submerged arc strip cladding (SASC) and Electro slag strip cladding (ESSC) is extensively used for cladding large surfaces of the heavy–wall pressure vessels. Three most important characteristics of SASC and ESSC are high deposition rate, low dilution and high deposition quality. Deposition rate in ESSC is much more than in SASC because of the absence of arc, whereas, dilution in ESSC is less compared to SASC because of the same reason. Weld cladding is widely done using flux-cored arc welding (FCAW) process due to various advantages. With properly established process parameters automation and robotization can be done easily in FCAW. Wear, corrosion and heat resistance of material surface is enhanced by plasma transferred arc (PTA) surfacing. PTA process is also considered as an advanced GTAW process used largely for overlay applications. Various advantages of PTA surfacing are very high deposition quality, high-energy concentration, narrow heat-affected zone, less weld distortion, etc. On the other side, demerits of PTA surfacing are low deposition rates, overspray, and very high equipment costs Cladding with the use of submerged arc welding (SAW) is applied for large areas, and its fusion efficiency is quite high. SAW can be easily automated and employed especially for heavy section work.

Piping Fundamentals

The piping system includes pipe, fittings, valves, and speciality components. All piping systems are
engineered to transport fluid or gas safely and reliably from one piece of equipment to another. Piping can be divided as • Small bore lines • Large bore lines As a general practice, those pipelines with nominal diameters 2” (50mm) are characterised as a small bore and preceding that as a large bore. Pipe sizes are on the basis of Diameter and Thickness. In some places, pipe size is designated by two non-dimensional numbers: Nominal Pipe Size (NPS) and schedule (SCH). Some major relationships:

• Nominal pipe size (NPS) is to describe a pipe by name only. Nominal pipe size (NPS) is generally related to the inside diameter (ID) for sizes 1/8” to 12”. For pipe sizes of 14” and beyond, the NPS is equal to the outside diameter (OD) in inches. Outside diameter (OD) and inside diameter (ID), as their names imply, refer to the pipe by their actual outside and inside measurements. The Outside diameter (OD) is the same for a given size irrespective of pipe thickness.

• The schedule belongs to the pipe wall thickness. As the number increases, the wall thickness
increases and the inside diameter (ID) is reduced.

• Nominal Bore (NB) with schedule (wall thickness) is used in British standards classification.
The main purpose of piping design is to configure and lay equipment, piping and other accessories
meeting relevant standards and statutory regulations. The piping design and engineering involve the following six (6) steps:

Selection of pipe materials according to the characteristics of the fluid and operating conditions including maximum pressures and temperatures.

• Finding economical pipe diameter and wall thickness.

• Selection of joints, fittings and components such as flanges, branch connections, extruded tees, nozzle branches etc.

• Developing piping layout and isometrics.

• Performing stress analysis as per the potential upset conditions and an allowance for those upset
conditions in the design of piping systems.

• Estimating material take-off (MTO) leading to material requisition.

The Pipe Material Specification (PMS) is the major document for piping engineers. This document
describes the physical characteristics and specific material attributes of pipe, fittings and manual valves necessary for the needs of both design and procurement. These documents are contractual to the project and those contractors that work under them. A piping specification must contain those components and information that would typically be used from job to job. The following items below provide the primary component report and notes required for a typical piping system. − Pressure/Temperature limit of the Limiting factor for Pressure/Temperature − Pipe material − Fitting type, rating and material − The flange type, rating and material − Gasket type, rating and material − Bolt & nut type and material Manual valves grouped by type − Notes − Branch chart matrix with corrosion adjustment 1.14. DESIGN FACTORS The design factors that affect piping engineering include:

• Fluid Service Categories (Type)

• Flow rate

• Corrosion rate

• Operating Pressure and Temperature All this information is available in the Process Flow Diagrams (PFD’s), Piping and Instrumentation Drawings (P&ID’s) and Piping Material Specification (PMS).

What is Quantity Surveying?

 Quantity surveying refers to the cost management, procurement and contractual issues in the supply chain and marketplace. They usually advise on cost implications of the clients’ requirements and other stakeholders’ decisions. They monitor and update initial estimates and contractual obligations as the construction progress based on additional works and variations. The practices do provide services that are focused on buildings (the architectural elements), and civil engineering now provides services that include heavy engineering, oil and gas, and building engineering services. Although the engineering services are part of buildings, it would be out of place to claim that all quantity surveyors have the required skills and knowledge to provide expert advice on building engineering services as they do for other aspects of construction. Most of the quantity surveying practices consider building engineering services a specialised duty. Most of the building clients have become uncomfortable with the inability of quantity surveyors to provide conclusive and accurate estimates for their buildings arising from using lump sum approaches to price engineering services. Today, it is common to see or hear statements like ‘M&E Quantity Surveyors’ ostensibly to mean quantity surveyor that is ‘qualified’ to offer advice on building engineering service. Many of the universities now offer a degree in building services quantity surveying which aims at providing students with a sound understanding of the principles and practices involved in the building services quantity surveying specialism, up to degree level standard, and to help them in the progression to Masters the level should they so wish. A general question is if such degrees are required considering the knowledge and skills expected of quantity surveyors in the measurement of building works. Quantity surveyors have a background rich in the dynamics of costs of construction. Arguably, such degrees are not warranted. Several studies show that quantity surveyors have generally expanded on the nature and scope of services they now provide. In order to understand this, we evaluate the levels of involvement of quantity surveyors in the procurement of building services engineering. The study aims to provide fresh knowledge on the expertise of quantity surveyors with a focus on the procurement of building engineering services. This knowledge is valuable to academic institutions that offer quantity surveying programmes, practising quantity surveyors and other players in the construction industry. Quantity surveying is universal. However, it is carried out under different names. In a few countries, quantity surveying is very much related to cost engineering, while they are also referred to as cost economists or cost consultants in other places. However, quantity surveying is not just a simple thing. As such the phrase “quantity surveying” is a catch-up term that hides a multitude of meanings. The modern quantity surveyors perform various types of services that extend beyond the services traditional quantity surveyors provide and higher institutions offering quantity-surveying programs are responding accordingly by modifying and upgrading their course content. Quantity surveyors must provide advice on the strategic planning of a project. For the construction worker, this advice affects clients’ decisions on whether to construct or not and if the client decides to construct what effect does cost have on other criteria within the clients/users value systems including time and quality, function, satisfaction, comfort and aesthetics.

What is Submerged Arc Welding?

In Submerged Arc Welding (SAW) process, the arc and the molten weld metal are covered by an envelope of molten flux and a layer of unfused granular flux particles. The arc is literally submerged in flux, as such the process is relatively free of intense radiation of heat and light. In most typical open arc welding processes the resulting welds are very clean. Like Gas Metal Arc Welding (GMAW) process, SAW process makes use of a solid wire electrode that is consumed to produce filler metal. The arc currents are usually considered to be very high (500A to 2000A). The efficiency of transfer of energy from electrode source to the workpiece is very high (usually over 90%), since losses from radiation, convection and spatter are minimal. The deposition rate along with the weld reliability is good. A reduction in Cost and improved productivity in welding operations can, therefore, generate a considerable impact on the competitiveness of various manufacturing industries. At the time of welding, joint preparation and arc efficiency are the most important factors dominating the cost and productivity of the weld. The desired amount of weld penetration must be achieved in a single pass the welding speed will be the major factor that determines the welding time. The efficiency of the arc is determined by proper penetration as well as the productivity of quality welds. The filler material is an uncoated, continuous wire electrode, that is applied to the joint along with a flow of fine-grained flux, which is supplied from a flux hopper via a tube. The electrical resistance of the electrode should be as low as possible to facilitate welding at high current and so the welding current Is supplied to the electrode through contacts very close to the arc and immediately above it. The arc burns in a cavity, which it is filled with gas and metal vapour. The top of the cavity is formed by molten flux. The solidified weld and the solidified flux covers the weld in a thin layer and which must subsequently be removed. The excess flux can be reused again. It also has a thermal insulating effect that reduces heat losses from the arc. As a result, more of the input energy is there for the process of welding. There are greater thermal efficiency and a faster rate of welding. It has been found that there is greater thermal efficiency in submerged arc welding that shields metal arc. The thickness of the part is considered important in developing the desired penetration. The procedure for welding stainless does not show much difference in stool steel does not differ greatly from that of welding mild steel. The material being used is expensive and necessary conditions of service are usually required necessitating extra precautions and attention to detail. Stainless steel can be welded using either A C or DC with as short an Arc as possible in order to overcome any possibility of alloy loss across the arc. When using AC, slightly higher current and setting may be required. While welding in the flat position, stringer beads should be used and, if weaving is required, this should be limited to two times the electrode diameter. The heat input, which affects the corrosion resistance and leads to excessive distortion, should be limited by using the correct electrode diameter to give the required bead profile and properties at the maximum travel speed.

Refining of Crude Oil

The main aim of refining is to convert crude oils of several origins and different compositions into valuable products and fuels having the qualities and quantities demanded by the market. The different types of refining processes, such as separation, conversion, finishing, and environmental protection, are done and briefly discussed. The everchanging demand and quality of fuels, as well as environmental concerns and the hurdles facing the refining industry, are also highlighted. Environmental laws have played a vital role in the advancement of the refining industry and may even change the competition between petroleum and other alternative energy sources. Refining is regarded as the processing of crude oil into a number of valuable hydrocarbon products. Processing utilizes chemicals, catalysts, heat, and pressure to separate and combine the different types of hydrocarbon molecules commonly found in crude oil into groups of like molecules. The refining process also rearranges their structures and bonding models into different hydrocarbon molecules and compounds. Therefore, it can be said that it is the type of hydrocarbon (paraffinic, naphthenic, or aromatic) and its demand that affects the refining industry. Petroleum refining has evolved continuously in response to changing demands for better and different products. The change in the demand has also been conducted by continuous advancement in product quality, such as octane number for gasoline and cetane number for diesel. The initial requirement was to generate kerosene for household use, followed by the development of the internal combustion engine and the production of transportation fuels (gasoline, diesel, and fuels). Refineries produce a variety of products including those used as feedstocks for the petrochemical industry. In the initial stages, refining consisted of mere fractionation of crude oil followed by the progress in the 1920's of the thermal cracking methods, such as visbreaking and coking. The processes crack heavy fuels into more useful and desirable products by applying pressure and heat Modern refineries incorporate fractionation, conversion, treatment, and blending operations and may also include petrochemical processing. Most light distillates are more turned into more useful outcomes by adjusting the size and arrangement of the hydrocarbon molecules through cracking, reforming, and other conversion processes. In general, the refining industry has always been considered as a high-volume, low-profit-margin industry. World refining stays to be challenged by the ambiguity of supply, challenging market circumstances, government regulation, availability of capital, and slow growth. Although shipping of refined products has been rising over the years, a close bond remains between domestic markets and domestic production. This explains the large differences in refinery schemes from one country to another and from one region to another.

What are the defects in welding?

The lack of training to the operator or careless application of welding technologies causes discontinuities in welding. Infusion welding, defects such as porosity, slag inclusion, solidification cracks etc., deteriorates the weld quality and joint properties. Common weld defects found in welded joints:

These mistakes may result in sudden crashes which are unexpected as they give rise to stress intensities. The common weld defects include:-

i. Porosity 

ii. Lack of fusion 

iii. Inclusions 

iv. Cracking 

v. Undercut 

vi.Lamellar tearing 

i. Porosity

Porosity takes place when the solidifying weld metal has gases trapped in it. The presence of porosity in most off the welded joints is due to dirt on the surface of the metal to be welded or damp consumables.

ii. Lack of Fusion

Due to very little input or slow traverse of the welding torch, lack of fusion arises. A better weld can be obtained by increasing the temperature, by properly cleaning the weld surface before welding and by choosing the proper joint design and electrodes, a better. On extending the fusion zone to the thickness of the joints fully, a great quality joint can be achieved.

iii. Inclusions

Due to the trapping of the oxides, fluxes and electrode coating materials in the weld zone, the inclusions have occurred. Inclusions are caused while joining the thick plates in several runs using flux cored or flux coated rods and the slag covering a run is not completely removed after each run and before the next run starts. By maintaining a clean surface before the run is started, providing sufficient space for the molten weld metal between the pieces to be joined, the inclusions can be prevented.

iv. Cracking

Due to the strain at the time of phase change, cracks may occur in various directions and in various locations in the weld area. Due to poor design and improper procedure of joining high residual stresses, cracking is seen. A stage-wise pre-heating process and stage-wise slow cooling will prevent such type of cracks.

v. The undercut

The undercut is caused due to incorrect settings or using improper procedure. Undercutting can be detected by a naked eye and the excess penetration can be visually detected.

vi. Lamellar Tearing

Due to non-metallic inclusions, the lamellar tearing occurs through the thickness direction. This is more evidently found in rolled plates. As the fusion boundary is parallel to the rolling plane in T and corner joints, the lamellar tearing occurs. By redesigning the joint and by covering the weld area with ductile material, the lamellar tearing can be minimized.

Visual Inspection

The structure of the visual inspection process is one of the most important features that influence its

effectiveness. From the work process perspective visual inspection consists of several stages:

• visual “screening”/search for potential defects

• finding a defect (“detection”)

• defect classification

• a decision

that classifies a component, product or service. Each of the stages has an impact on the effectiveness of inspection. The first stage, when an object is visually examined by a man, requires vigilance, heightened the sense of sight to detect potential errors. In the first and second stage of inspection, when the level of inspector’s perception is of particular significance, appropriate working conditions and inspector’s knowledge about potential defects are absolutely required. In the third stage, based on his knowledge about the defects and classification criteria, the inspector makes the decision on the type of defect detected in the product. In the final part of the inspection process, the inspector decides if the product may be forwarded to further steps of the process, or if it should be separated from good quality products. Two of the four stages mentioned above (searching for defects and decision-making) seem to be of particular importance from the point of view of visual control. It turns out that they are most exposed to decision variability of the operators. In the inspection process, they may make two types of errors classify a good quality product as defective (FALS) and classify a defective product as good The likelihood of committing these two types of errors and the fraction of products that do not conform with requirements after the inspection process are the key indicators of inspection efficiency. There are many factors that affect the efficiency of visual inspection. Making the decision concerning the quality of inspected products requires not only specific knowledge of the industry but often also an individual approach to every inspected product and high sensitivity to defects. Relevant research shows that the efficiency of visual inspection is affected by independent factors and factors related to and dependent on man. These two main groups of factors can be divided into five categories, Technical factors are associated with the physical execution of visual inspection in the production process. They include, for example, factors related to the actual quality level, product features subject to inspection (their accessibility for visual inspection), to the standards, based on which the product is controlled, the availability of tools used during the inspection, etc. Psychophysical factors are associated with mental and physical conditions of inspectors. These include age, sex, intelligence, temperament, health condition etc. Research in this area aims at identifying the characteristics comprising the profile of the ideal inspector. The next group of factors affecting the effectiveness of visual inspection are organizational factors. These include support in decision-making during the inspection, acquiring inspector skills, number and type of inspections, information on efficiency and accuracy of conducted inspections, as well as stress factors influencing the inspector, such as time, consequences of incorrect assessment (no bonus, loss of company image, etc.). Workplace environment conditions are associated with the workplace, where the inspection takes place. Light, noise, temperature, as well as the organization of the workstation itself,  come under this The last group is related to the social environment, where inspectors work. The work often involves pressure from people, whose interest is contrary to the inspector’s work. For example, production staff (often colleagues) exert pressure expecting approval of their work (which is related to the payment of salaries, bonuses). In turn, employees of the management board may exert pressure to minimize reinspections of products with an unambiguous assessment.