Technical FAQs

Pipe welding is often more challenging than other types of welding and requires a higher level of welder skill. This can be due to the working conditions as well as factors such as the travel angle of the weld, the pipe position and the diameter of the pipe. The difficulty increases as the position changes from 1G to 6G (see ‘Pipe Welding Positions’ above).

Pipe welding can be dangerous if the correct precautions are not taken. Welding can expose welders to fumes, dust and other airborne particles, as well as heat and dangerous levels of light that can be harmful without the correct safety equipment. The hazards are increased due to the conditions that pipe welders may be required to operate in, making pipe welding potentially dangerous.

Pipe welding uses arc welding techniques, including shielded metal arc welding (SMAW), gas metal arc welding (GMAW) – including both MIG and MAG welding, flux-cored arc welding (FCAW), submerged arc welding, and tungsten inert gas (TIG) welding.

The amount of time taken to weld a pipe depends on factors such as the size of the pipe, the working conditions and the welder’s level of skill. In addition, the amount of passes required can change for different jobs and the different welding techniques have different rates of deposition (MIG is generally faster than TIG, for example). However, as a rule of thumb, the average welder can complete 140 inches of weld per hour. By checking this hourly speed against the diameter of the pipe, you can get an idea of how long a pipe will take to weld.

5G pipe welding relates to the position in which the pipe is welded. In 5G welding, the pipes are placed horizontally in a fixed position and the welder moves around the pipes, welding in a vertical direction.

6G pipe welding relates to the position in which the pipe is welded. In this position, the pipe is placed at an angle so that it slopes at around 45° from the horizontal (X) axis or vertical (Y) axis. The pipe is fixed and the welder moves around the pipe to perform the weld. This is the most advanced pipe welding position.

Downhill pipe welding is when the welding is carried out with a downward progression, as opposed to uphill pipe welding, where the welding is carried out with an upward progression. Although uphill welding is considered stronger and is better for thicker materials, it takes longer to perform and has a greater potential for burn through than with downhill welding. On thinner pipe walls, downhill welding lets the welder run ‘hot and fast,’ improving productivity where heat penetration is not such an issue.

Pipe welders, as opposed to pipeline welders, are also sometimes called pipefitters, steamfitters or simply just ‘fitters.’ They are responsible for the assembly, installation, maintenance and repair of piping systems and fixtures.

A question that many people ask is: What is the difference between a Pipeline Welder and a Pipe Welder?

A Pipe Welder tends to construct piping systems that are contained within an industrial environment such as an oil refinery, chemical plant, computer chip factory or other factory. It typically deals with many different sizes of piping and potentially many different materials. The pipe spools that are made up all tend to have unique shapes, so they are pretty much custom made on a one-off basis.

A Pipeline Welder works on “transmission” pipelines that can span many kilometres. In some parts of the world is not uncommon for these pipelines to span hundreds of kilometres. These pipelines typically transport oil from oil fields to refinery or production facilities, or transport gas from gas processing facilities to end user markets etc.

When constructing these long pipelines, the welds tend to be very similar in nature, and the highly repetitive nature of the welding work tends to favour the use of highly productive welding processes and techniques. Some welding techniques such as the use of cellulosic welding consumables are allowed on pipeline welding, when they would be prohibited for most other pressure containing applications, due to the specific productivity advantages that they provide. This means that Pipeline Welders need to have these skills in their arsenal, which would not be required by the process Pipe Welder.

It is important to note that pipelines are designed and built to different codes than process plant piping. To take account of the fact that transmission pipelines are more material intensive and are often installed in such a way that they are isolated from humans, they tend to be made to higher stressed designs than is the case for process piping.

An Industrial Pipefitter designs, instals and maintains piping systems on construction sites or commercial fabrication facilities.

The Pipefitter is a vital construction role, working within strictly defined processes and procedures to exacting standards. This often involves working on major infrastructure projects for example power stations and oil and gas facilities both in the UK and overseas Engineering Construction Industry.

The Pipefitter can work in hazardous environments which can include working at height, over water and in confined spaces.

The Pipefitter role encompasses the positioning, assembly, fabrication, maintenance, repair and decommissioning of piping systems within Engineering Construction, both on construction sites or at commercial fabrication facilities. This can include working in environments with systems that may carry water, steam, food, pharmaceutical, chemicals, gas, hydrocarbons or fuel which may be used in cooling, heating, lubricating and other processes.

 The Pipefitter works with various pipe materials such as ferrous and non-ferrous metals, plastics and composites. These materials can vary from 15 mm to 1200 in diameter and from 5 mm up to 75 mm in thickness dependent upon the content of the pipes and the operating pressures of the systems.

The role requires the knowledge and skills to implement the specified method of jointing required within often complex piping systems.

The Pipefitter must be able to work autonomously and as part of a team ensuring compliance with health, safety and environmental, processes and procedures. The Pipefitter must also work with other Engineering Construction occupations such as welders.

Orbital welding is a technique whereby the welding tool is rotated through 360° (or 180° in double up welding) around a static workpiece. Originally developed to solve the problem of operator error in Tungsten Inert Gas (TIG) welding (also known as Gas Tungsten Arc Welding (GTAW)) and allow for a uniform weld around pipes and tubes, which can be difficult to achieve with manual welding processes.

The orbital welding process can create high quality repeatable welds with the use of a computer, meaning that there is little need for intervention from a welding operator. The process is used for two main applications: tube-to-tube / pipe-to-pipe joining and tube-to-tubesheet joining.

The process was originally developed by the aerospace industry in 1960 by Roderick Rohrberg of North American Aviation to address fuel and hydraulic fluid leakages in the X-15 rocket research plane. In the 1980s, improvements in control systems, portability and power supplies meant that orbital welding machines could be transported between construction sites.

Hot tapping, also known as pressure tapping, is a method of connecting (either by drilling or cutting) to a pressurised system, such as a pipeline or pressure vessel, without removing the pipe or tank from service. This prevents costly and potentially dangerous environmental hazards while allowing for continued operation.

Hot tapping strictly refers to the installation of connections to pipelines while they remain in service. In the welding context, it is commonly used for any welding onto in-service equipment. Hot tapping is frequently used to repair areas that have undergone mechanical damage or corrosion, or to add branches for system modifications. There are distinct economic and environmental advantages to performing this welding without removing a pipe from service and possibly venting quantities of greenhouse gases, such as methane.

Problems can occur with hot tapping when the risk of burn-through, unstable decomposition of the flowing product and the risk of hydrogen cracking are not considered adequately.

Burn-through occurs when welding onto a pressurised pipe if the un-melted area beneath the weld pool is not strong enough to contain the internal pressure of the pipe. The greater the wall thickness of the pipe, the less the risk of burn-through. Unstable decomposition of the flowing product can cause violent reactions when heated under pressure; this is prevented by taking special precautions to prevent the internal wall temperature exceeding a critical temperature. This critical temperature is dependent on the nature of the flowing product.

The risk of hydrogen cracking is increased for hot tapping in comparison to other welding situations, due to the flowing product increasing the rate of heat flow from the weld region. This leads to shorter cooling times, with an associated increased risk of forming hard microstructures and thus greater susceptibility to hydrogen cracking. The cracking risk can be reduced using low-hydrogen electrodes, and through careful selection of heat input.

Preheat control is sometimes possible, but the cooling capacity of the flowing contents can make this an inefficient approach. Temper bead deposition sequences can be used to control hardness.

In welding, and manufacturing in general, automation refers to some or all the steps in an operation being performed in sequence by some mechanical or electronic means.

Certain functions may be performed manually (partial or semi-automation); or all of the functions may be performed without adjustment by the operator (total automation). Automation can be applied to many different processes.

Equipment may accommodate a single assembly/family of assemblies (fixed automation) or may be flexible enough to be quickly modified to perform similar operations on different components and assemblies (flexible automation).

Regardless of the degree of automation, its objective is to reduce manufacturing costs by increasing productivity and improving quality and reliability. However, it can fail as well as succeed depending on the application.

Successful application requires careful planning, and the product, plant and equipment costs should be analysed to determine if it is feasible.

The extent to which automation should be employed is governed by several factors:

• Product quality – better process control, product improvement and scrap reduction are all possible.
•  Production level – higher output and improved inventory turn-over may be the most significant advantages.
•  Manpower – automation may allow the welder to work outside a hazardous environment, and it may be possible to use cheaper semi-skilled labour; however, education and training of personnel will be required to make optimal use of an automated system.
•  Investment – savings and costs resulting from an automated system must be identified, including availability/cost of capital.

The importance of the factors will vary with the type of industry and application, and each should be considered.

The primary role of the welding procedure specification (WPS) is to provide guidance to the Welder out in the field. It shows the welder what joints are covered by the welding procedure, and what welding parameters are to be used when performing the welding. 

The WPS is also the document that is used by the welding engineer and other people on the design side, to communicate the necessary technical and code requirements to the Welder, the welding supervisor, and the welding inspector.

We will consider where WPS’s come from, what types of information they typically contain, and how to read and apply them.

Arc welding is a type of welding process using an electric arc to create heat to melt and join metals. A power supply creates an electric arc between a consumable or non-consumable electrode and the base material using either direct (DC) or alternating (AC) currents.

Metal Inert Gas (MIG) welding and Metal Active Gas (MAG) welding, process numbers 131 and 135 respectively in accordance with ISO 4063, are both variations of the Gas Metal Arc Welding (GMAW) process, which they are more commonly referred to as in USA and some other countries.

These use heat created from an electric arc between a consumable metal electrode and a workpiece, creating a weld pool and fusing them together, forming a joint. The arc and weld pool are protected from the environment and contaminants by a shielding gas.

MIG/MAG is similar to other arc welding processes, e.g., MMA, in that heat for welding is produced by forming an arc between a consumable metal electrode and the workpiece; the electrode melts to form the weld bead. The main difference is that the metal electrode is a small diameter wire fed continuously through the contact tip of the welding torch from a wire spool, while a shielding gas is fed through the welding torch. As the wire is continuously fed, the manual process is sometimes referred to as semi-automatic welding. MIG and MAG welding both use a gas supply to provide arc shielding, unlike MMA where the flux on the electrode is melted to provide arc shielding.

Manual metal arc welding (MMA or MMAW), also known as shielded metal arc welding (SMAW), flux shielded arc welding or stick welding, is a process where the arc is struck between an electrode flux coated metal rod and the work piece. Both the rod and the surface of the work piece melt to create a weld.

Flux cored arc welding (FCAW), also know as dual shield welding, is a semi-automatic arc welding process that is similar to metal active gas (MAG) welding. FCAW uses a continuous wire fed electrode, a constant-voltage welding power supply, and similar equipment to MAG welding.

Tungsten Inert Gas (TIG) welding, also known as Gas Tungsten Arc Welding (GTAW) is an arc welding process that produces the weld with a non-consumable tungsten electrode.

When sourcing welding equipment for a project, with a time scale measured in months, then buying the required equipment is not always the best choice. Renting equipment for the duration of the project might be more feasible.

Get the latest equipment

Why make do with whatever equipment you happen to have lying around? A policy of ‘make do and mend’ is fine up to a point; all contractors do it. But, have the full on-costs of operating older equipment been considered? Machine down time, increased maintenance, labour down time, lower productivity, missed deadlines, project overruns, penalty clauses and so on? Why not select the equipment that best meets the needs of the current welding project?

Renting does not increase your fixed costs

The purchase of equipment can represent a significant increase to a contractor’s fixed costs. By renting equipment instead, the fixed costs of ownership are transformed into a variable cost. Variable costs are dependent on how much the asset is used. If your welding project has a definite time frame, the known costs of rental stop once the project is completed – a rental ‘off switch’ can be pressed. If the equipment is purchased the fixed costs of ownership continue – they cannot be easily turned off. In addition to the cost of the initial purchase, there are several other ongoing costs of ownership – such as insurance, maintenance, in-service inspection, repair, and storage. The total costs of ownership tend to increase over the life of the equipment and are only marginally related to actual use. The rent or buy choice can have a direct impact on bottom line profitability and the underlying financial strength of the contractor’s business.

Renting can reduce your financial risk

For many contractors, finance is not a limitless resource – it needs to be managed. Purchasing equipment will use up the financial resource available, including valuable working capital if a down payment is required. With no upfront cash outlay to find, renting equipment can help to keep valuable working capital intact. Financial resource can instead be channelled into core business activity, rather than into machinery.

Cope with peak workloads

It is not always desirable for contractors to keep a large equipment fleet – equipment might just possibly be needed to cope with a sudden upswing in trade, but somehow it spends most of the time sitting in the yard. Minimising your owned equipment fleet and supplementing your needs with rented equipment – brought in when activity levels dictate – seems to make more economic sense. Use the kit you need, where and when you need it. Just press the rental ‘on switch’.

Keep to budget

Rental costs are known from the outset and for the duration of the rental period. For contractors quoting for or running a particular project, the rental cost can easily be assessed and built into the project quotation or operational cost. Because the costs are known in advance, keeping within budget is relatively straightforward. Giant cranes, for instance may not be needed

Taking opportunities

Although market conditions get ever more challenging every day, smart contractors still survive and flourish. They are prepared to take opportunities and to even create their own opportunities. With in-built on and off switches, renting offers contractors a lower risk way of obtaining quality equipment when prevailing market conditions are uncertain, or the available financial resource is limited. Rental enables a contractor to enter new markets or sectors without an onerous, upfront investment in expensive machinery. Rental allows a contractor to try out new, more productive equipment first, before buying. Renting can therefore help keep contractors current, able to adapt to the latest kit and to make and take opportunities, as and when they present themselves.

Focus

Renting equipment leaves contractors free to focus on running their core business. No need to worry about residual values, depreciation rates, asset economic life, business taxation etc. Although tax rules vary from country to country, it is usual for equipment rental charges to be an allowable deduction for tax purposes. On the other hand, the full capital cost for purchased equipment is not normally allowable in year one. However, some governments may have tax incentives to encourage investment in equipment.