A pipeline in the oil and gas industry transports oil, gas, and other substances under enormous heat and pressure-for weeks or months without pause. But it is not fixed in place and unyielding; the high heat expands the pipe as it moves, and pumps and compressors shake it constantly. This movement eventually creates stress, builds the pressure up enough, and gradually a weld breaks, a flange goes bad, or a whole section of pipe might simply blow out.
This is where a metallic expansion joint comes into play. It’s basically a flexible piece of metal that can be installed where two rigid pipes meet; its only purpose is to soak up the movement so that the rest of the system stays safe and sealed. In an industry like this, where a single failed pipe might cause a fire, a leak, or a complete loss of operation, there’s no question of whether expansion joints are a necessary commodity. They’re a must.
In this guide, we cover: what joints are, why they matter in the oil and gas industry, what they can be used for, the most common forms of a joint, why joints are advantageous, the problems associated with faulty joints, and how to correctly select and maintain your joint.
A metallic expansion joint is a special joint that is installed between two sections of rigid pipe or ductwork. These joints are installed to allow the expansion and contraction that can occur in pipe and ductwork because of increases in temperature, pressure, or vibration without putting excessive strain on the system and thus will still maintain a tight and leak-free joint.
The movable part is a pleated metal which is often called a bellows. As the pipeline expands, contracts, bends, or vibrates, the bellows accept and allow for the movement and transmits the load directly to the pipeline and equipment. A metal bellows is manufactured from several special metal alloys or, most of the time, stainless steel. Metal expansion joints operate very efficiently at high pressure and temperature, which is the case in the oil & gas industry.
Pipes in the oil and gas industry can face very demanding environments – probably the hardest of any. Here’s an explanation of the key forces that act upon these pipe systems and why a flexible joint is essential for handling them all.
The vast majority of oil and gas applications involve extreme temperatures. Whether you’re transporting hot oil, high-pressure steam, or hot process gas, a significant expansion can take place because metals tend to expand as they increase in temperature. This will put stress on existing pipeline stresses that, if left unchecked, can result in the weakening or failure of joints and supports. A Metallic expansion joint is designed to absorb this expansion and thermal expansion to compensate for heat.
Oil and gas pipeline fluid often moves under extreme pressure. This pressure exerts continuous stress on each component of the system, and that includes joint components. The joint selected for this application would need to not only withstand that pressure but also provide a range of motion to accommodate motion within the piping. That’s precisely the scenario for which metal bellows expansion joints and their robust style were intended.
Thermal expansion simply means the pipe becoming longer when the metal heats and contracting to become shorter when the metal cools down. On a long run of pipeline, the change in length can often be several centimeters throughout the whole run of the pipe; to accommodate this change without damaging the system, it’s for one of two purposes, and these occur most commonly on oil and gas lines and on many pipeworks.
Both pumps and air compressors work within every oil and gas plant and shake quite a lot while operating. Those vibrations can be transmitted through the pipeline and progressively wear out connecting parts or screw fittings. Metallic compensators take up a large part of the source vibrations transmitted. Those vibrations are attenuated at points of installation.
A pressure surge is an increase of the pressure caused by the instant closure of a valve or quick switch-on of a pump. The impact of this pressure surge will go deeply into the pipeline and damage non-pressure-resisting pipes and equipment. It is beneficial to install a joint that will cushion its effects and alleviate the pressure on the pipeline, and then prevent rapid failure.
Pipes are not perfectly fitted together; it is very common that the two pipes have a small offset at the ends or a small gap, which will induce stress in the pipe under installation or during operation. However, a metallic expansion joint has the capability to accommodate this small degree of misalignment during pipe installation. So the pipes can be correctly installed without imposing excessive and permanent strain.
Large pieces of equipment - things such as pumps, vessels or heat exchangers - can move a little over the years due to process equipment operating or the building settling down. The connected pipework then gets stressed. The flexible joint can accommodate that movement and relieve the stress from the pipework.
Learn More: Expansion Joint Installation Guide for Industrial Pipelines & Duct Systems
The majority of applications in the oil and gas industry include metallic expansion joints. The following sections outline the primary locations for their fitting and their respective functions within each.
Oil is converted into fuel and various other products by refineries, which also rely on operating equipment, at very hot and high pressures. Every bit of pipework here will tend to move- expand and contract. Metallicexpansion jointsare installed in every one of the pipe circuits in an oil refinery to compensate for these movements. They make for safer and leak-free installation for all the hot, high-pressure pipes.
They are designed to clean and prepare the natural gas to be put into use while also pumping the gas through long pipe sections using pressure. The challenge here is the changes in temperature and vibration experienced within these lines. Expansion joints absorb this motion and prevent damage at the connections, which ensures the gas continues flowing throughout the facility safely and effectively.
Oil and gas production happens on offshore platforms. Conditions are harsh: salty, hot, and tight space. There is a need for pipework capable of withstanding high heat and pressures and the vibrations it entails, as well as coping with air corrosion to the steel. Metallic expansion joints in a corrosion-resistant form are commonly seen in the harsh conditions on these platforms to meet these demands.
LNG plants cool gas into a liquid state to permit its transport and storage; it does so at exceptionally low temperature conditions. Metals shrink when hot and expand in the cold, so these systems experience a lot of movement; an expansion joint used in LNG applications must be able to handle these extreme temperatures and provide adequate protection for these systems against its temperature driven movements.
When oil & gas are converted to chemical & plastic compounds inside petrochemical plants, fluids under intense heat conditions & chemical reaction processes pose an extraordinary challenge to pipework in many ways. The combined forces of heat, pressure & abrasive media will severely test conventional piping systems. Metallic expansion joints made from the right materials can effectively withstand the corrosive medium.
These long pipelines carrying oil and gas travel over long distances. Throughout such extended stretches of pipeline, there are forces exerted on it due to thermal expansion and earth displacement. To prevent the pipeline from rupturing, expansion joints have been incorporated throughout. These keep the pipeline intact for the entire length of its construction.
Compressor stations increase the gas pressure to help push it through the pipes and tubes of gas distribution networks. This compressor creates intense vibration while working with gas at an elevated pressure. A metal expansion joint in the pipe alleviates this vibration and handles the elevated gas pressure.
Pump stations use the force from high-power pumps to propel fluids through the pipeline. Similar to compressors, these pumps can transmit vibration and pressure fluctuations to the existing pipeline structure. The expansion joints provide support for these vibration and pressure changes to the line immediately exiting the pump.
Large quantities of oil and gas, amongst other products, are stored on site in vessels and tanks. This network of pipework between tanks expands, contracts, and moves as products enter, exit the tanks, and through variations in temperature. Metallic expansion joints accommodate this movement in the joints.
Not every problem is going to require the same type of joint. To sort it out, here are the most common expansion joint metal configurations you'll come across on oilfield jobs and what each one works best at.
Axial Metallic Expansion Joint: This is by far the simplest and most commonly encountered style of expansion joint, and absorbs linear or axial movement along the line of its pipe. It works perfectly well on a simple straight run where heat expansion is the dominant movement.
Universal Metallic Expansion Joint: In this style, the bellows units are joined together with a section of central pipe which permits additional side-to-side displacement. Such a design is appropriate for long, complex pipework installations involving displacement between sections that require higher degrees of expansion capability than can be attained by a single element.
Hinged Metallic Expansion Joint: This is a hinged joint because it features hinges that make sure it is only capable of bending in one direction, exactly the same way that a door opens on its hinge. This joint controls angular movement because it refers to angular motion; bending at a set location, eg., an elbow. The hinges also help to provide controlled pressure along the line.
Gimbal Metallic Expansion Joint: The gimbal joint permits bending in multiple directions at the same time, so it applies to pipes that need flexibility in many directions. In many cases, the application of the gimbal joint goes to offshore operations and sophisticated process piping systems.
Pressure Balanced Expansion Joint: The pressure within can create a pushing force - "pressure thrust"- that can be quite damaging to connected equipment. To compensate for this force so that it is not imparted on sensitive equipment and to absorb movement, pressure-balanced joints are employed on pumps, turbines, etc.
Elbow Pressure-Balanced Expansion Joint: This is a pressure-balanced joint integrally cast into the bend, where the change in direction in the piping occurs. The joints nullify the pressure thrust and will accommodate movement at the elbow location itself. Given that a bend would anyway form a natural point of stress in such systems, this offers a solution where both the bend and thrust control are required together.
In-Line Pressure Balanced Expansion Joint: This version is only for a straight run of pipe and not for bends. It cancels the pressure thrust and accommodates axial expansion within the line. This is typically used with an on-line straight section where thrust control is necessary.
Externally Pressurized Expansion Joint: Here the pressure is supplied on the outside of the bellows rather than the inside. As the bellows is protected from over-expansion, it can accommodate very long axial movements without becoming unstable. This type is also suitable for handling significant amounts of movement in a confined area.
Learn More: Different Types of Piping Joints: A Complete Industry Guide
Not only will the correct joint attach two pipes, but joints also have a purpose to benefit a system in ways shown:
Metallic expansion joints are built to control the elongation and contraction of the pipes when there is fluctuation in the temperature. It is designed in a manner to make absorb this axial compression as the pipe swells with hot fluid, so as not to exert pressure against the support structures.
A system with no expansion joint transfers the flow and power at every position directly to valves, pumps, and vessels. This puts constant pressure on those components and the pipes in the system. Expansion joints use metal to prevent excessive force from traveling along the pipe and reaching your equipment.
Pumps and compressors set off constant vibrations which can spread through the pipe system. In the long term, this loosening causes vibrations to wear parts and loosen joints. Many vibrations will therefore be absorbed at the site of emission by the joint itself.
There can be minute differences in pipeline alignment on initial installation or during system growth due to thermal cycles or material fatigue. A metallic expansion joint accommodates this pipe-to-pipe offset-caused strain in a permanent, leak-free manner.
Almost all pipeline breaks start because the stress has no escape and it grows into cracks and leaks. By providing room to handle movement, pressure swings, and vibration, the connection can relieve much of that stress before it builds to something serious.
Because movement and vibration are then absorbed by the joint, there is a much reduced amount of wear in the equipment connected. Pumps, valves, and pipes get considerably better lifespans. This inevitably reduces the need for equipment and thus saves you money long-term.
An under-stressed system requires less maintenance and fewer repairs, which means the joint reduces the frequency of call-outs and replacements. Planned maintenance and repairs also become cheaper.
In an Oil & Gas application, a failure could result in a leak, a fire, and worse. Safety comes first; this joint helps prevent potential failure by ensuring that the system remains sealed and stationary. This helps ensure not only the integrity of the plant, but the lives of everyone associated.
In most oil and gas operations, you will get both extreme heat and extreme pressure all at once – conditions in which very few parts will survive. Metallic expansion joints are created out of robust materials and design concepts capable of withstanding such environmental demands.
Learn More: Benefits of Expansion Joints in Industrial Piping Systems
If a poor joint has been picked, or has sustained damage over time, it could also have several devastating consequences. Read on for explanations and key warning signs to look for:
In a worn or stressed joint, the 'seal' breaks, allowing fluid loss within the system. In the oil and gas industry, even the slightest leak can be the cause of significant damage, safety issues, and costs.
The bellows are continuously moving. The folds slowly get weary from this frequent movement, so they start to form tiny cracks. If the bellows crack open, proper pressure retention is no longer possible.
When a joint is deteriorated/improperly selected, it loses some ability to soak up vibration. Vibration is sent into the pipework and machinery, reducing the lifespan of components and connections to joints.
When the stresses are no longer being taken up by the joint, they are transmitted to the welds and flanges. Repeated movements eventually can fatigue weld joints and fail the flange connections. The problems identified can represent serious failures.
If the material used to construct the joint is not suited for the given environment, the material can suffer from corrosion, and therefore it can become weak. Corrosion digs into the material of the joint until it reaches the point that it can no longer withstand the pressure.
Failure of a joint can cause a moving part and its connection pipes to go out of line. These movements put irregular stress on the connection, which increases the rate of wear and increases the chances of failure.
Pressure thrust is the force developed by internal pipeline pressure; it may apply substantial forces on any adjoining equipment if the correct fitting is not selected and installed properly.
In case of a sudden joint failure, the entire production line might have to be halted. These kinds of unforeseen shutdowns are expensive and bothersome, since they rarely occur at a moment like downtime but during full operation.
Heat loss and system pressure drop can occur from any joint or hose when it starts to leak or become excessively worn over time. As a result, the pumps and compressors have to work harder, creating high running costs due to increased energy use.
There are some good clues that a joint is under stress and should be looked at more closely. This will help prevent a problem down the line. Some clues include drips or signs of leakage, cracked bellows, noise (a ringing or a shudder) in the joints, corrosion or scale, and out-of-alignment pipe segments.
Learn More: Top 7 Signs Your Expansion Joints Need Replacement in Industrial Piping Systems
Making the right choice of joint is an engineering decision and not just a choice from a catalogue. There are a number of checks before specifying a joint for your system. These are listed below.
Operating temperature: You have to know the extremes to which the joint will be exposed and also whether it tends to be hot all or sometimes only to have an idea about which material to select and not have it change. For that, you'll need to pick the correct temperature material.
Working pressure: Figure out what pressure the joint is designed to withstand, not just running, but also the spike pressure on startups. And the joint's rating must also meet that pressure level without going bad while flexing.
Media type: The type of substance the pipeline carries - whether oil, natural gas, steam, a corrosive chemical - dictates material demands on the joint. The fluid material would call for the selection of the proper welding alloy to be used in joint design and fabrication.
Pipe size: The joint needs to correspond to the same diameter as the rest of the pipe in which it will be used. No matter how good the joint in every other aspect may be, if it will not install into the other joint properly, it will not function.
Movement requirements: Think about how the pipe is going to move during its normal operating cycle. Is this axial, lateral, angular, or a combination? A joint must be engineered to only see specific movements. A joint designed for axial motion will not survive lateral movement.
Pressure thrust: Pressure thrust refers to the thrusting force exerted by fluid pressure within the pipe. With some layouts, it is necessary to contain these forces so that equipment does not become stressed; pressure-balanced joints might be required to accommodate them.
Installation space: Check where there will be sufficient space for the joint and any fittings required. Some models require significantly more space than others to function properly. Where space is restricted, a tight-fitting design using an externally pressured system is possibly the appropriate choice.
Corrosion resistance: The joint will need corrosion resistance to be able to perform in harsh or salty conditions, which is quite common offshore as well as in the chemical industry; for instance, the materials selection is critical to keep the joint working in those applications.
Fatigue life: Fatigue life is defined as the number of movement cycles before bellows joints fail or wear out. If a system contains lots of motion or frequent movement, a high fatigue life of a joint will be required to ensure it withstands countless cycles of movement.
Design standards: You must design and construct your joint according to relevant design standards. These design standards ensure joint integrity. Design to a specific design standard may be mandatory as an industry requirement.
Maintenance accessibility: Think about whether the joint is in a place where it can be easily inspected for repair. A joint that is in a place difficult to access will need more attention. Think about where the joint placement will be best to maintain.
Learn More: How to Select the Right Metallic Expansion Joint for Industrial Applications
Even an excellent joint will need occasional maintenance in order for it to achieve its full service life. The following points outline the fundamental principles involved with the ongoing upkeep of a joint.
Develop a regular schedule and check each joint periodically. During inspection, you should look for corrosion, leaks, breaks, and other damage on each connection. Catching the issue when it's minor keeps it from escalating.
Pay close attention to any signs of fluid leaking outside of the seal. The tiniest bit of leakage suggests that your seal is degrading and needs repair soon, ideally before a little leak becomes a massive failure. For anyone operating in the oil and gas sectors, this practice couldn’t be more critical.
As the bellows is the most susceptible part, it must be thoroughly inspected. Examine the bellows for minor cracks, creases, and any irregularity in folds that suggests developing stress-corrosion; creases are very liable to cause collapse of the joint.
Note the vibration levels that the joint and components are undergoing. An increase in vibration may indicate the development of a potential problem. The components around the joint will be damaged over time by severe, repeated shaking.
Ensure the anchors and pipe supports are firmly installed. The weight of the pipes must not be borne by a failed anchor or support, or it will be put onto the joint, and it might have to cope with stresses that it's not able to cope with.
After a long period of time, the constant vibration in the joint will result in loosening of bolts. So tightening up these nuts or bolts from time to time to the proper level on your equipment is what is required while servicing your particular gear equipment. If not properly tightened, they’ll be a likely culprit for the gear not functioning properly and leaking from the junction.
Dirt, dust, and deposits can settle on and around the joint. This holds moisture, which may enhance corrosion, and the defect becomes harder to detect during the annual inspection. The joint is easy to clean in this way to give it a longer lifespan.
Don’t let the old joint fail – replace it before it’s too late. Planning for replacement during an upcoming scheduled shutdown is a far more reasonable – and far cheaper – option to consider rather than to wait for an impending joint to fail suddenly.
Maintain a record of each joint check and each action taken. This helps you monitor the status of your joints over time and observe trends. It will also notify you when you should consider replacement.
The first part of the challenge is to select the right joint, but the success is determined largely by the maker that is chosen. We work with manufacturers with a real understanding of conditions, and it is here that we excel, with Flexibel.
Flexibel designs and manufactures metallic expansion bellows and joints for a diverse range of sectors, requiring precise attention to detail. We custom manufacture each joint, ensuring the configuration works perfectly for your service. Flexibel works with industry giants in the oil & gas, petrochemical, marine, power, and processing industries, utilising some of the very finest materials suitable for hostile applications.
Flexibel can also offer you technical engineering support for advising on the right joint. With rapid delivery throughout the UAE and around the wider GCC, and dependable after-sales service, Flexibel is your partner in pipework systems. This is one of the reasons that makes Flexibel one of the trusted metallic expansion joint manufacturers in the region.
Although metallic expansion joints are so small, they have a vital job in the oil and gas sector. These items work to absorb the heat, stress, vibration, and movement that would otherwise destroy the pipelines, tanks, and general machinery, and as such, help to ensure that pipelines and systems remain tight and secure.
Selecting the correct joint for each connection will ensure your pipelines are protected and your fittings will last, which helps to reduce the number of failures and outages that cost the most.
When safety, efficiency, and uptime are supreme, finding the proper joint is not a choice but a requirement. If you require customised metal expansion joints that perfectly meet your operational conditions, let the team at Flexibel be your partner for effective results.
