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Pipe Joint Maintenance Challenges
Pankaj Soni, Country Manager - India, Victaulic. There are many problems faced by engineers , operators and owners in the maintenance and refurbishment of pipe joints. This article specifically discusses the types of joining solutions, their advantages and disadvantages, and explains how the right choice of pipe joining method can significantly cut operating costs.

Most plant room structures will require some degree of piping system maintenance. For example, strainers are regularly changed out; turbulence and clogs in strainers, which can lead to floating debris in the system, may cause heavy wear on pumps and reduce the efficiency and life of the equipment. Bearings and impellers also suffer from erosion over time and may need to be replaced. In addition, lines of pipe may become corrupt and require maintenance or replacement.

Unscheduled repair is the most pressing and time-sensitive type of maintenance because of its unplanned nature and, in most cases, immediate necessity. It can include the repair of erosion and corrosion, cracks, leaks, weld failure - such as pinholes or incomplete fusion, material failure - such as defects in a pipe, and equipment malfunction.

Initial piping system assembly costs are therefore only a part of the total system costs. How much the system might cost to run and maintain throughout its lifetime is frequently overlooked at an early stage of installation and little consideration is given to joint performance over a long period. Long-term factors, including erosion, creep and fatigue, may be significant in the maintenance of a plant, but there are other factors to be considered as well.

Access Issues
Systems will inevitably require access over their lifetime, whether it is for routine scheduled work, expansion or unscheduled repair, designers and those maintaining systems should at the earliest possible stage plan for easy access, future maintenance and change outs at joints. Where a system needs to be completely drained or a plant needs to be shut-down to allow access for maintenance, the cost in lost productivity may be especially significant. The most important objective is to eliminate the need for shutdown or reduce it so that the plant can return to full operating capacity as quickly as possible.

Older plants may present structural constraints with limited access, and designs that do not incorporate adequate spaces for modern system expansion. Physical changes or expansions to the piping system, made to adjust existing installations, replace old piping or alter the existing system by adding to it, can be extremely difficult under these circumstances. A piping method that keeps pipe-runs and fittings to a minimum and optimises available space for plant and pipe fitters to operate will increase efficiency.

JOINT ANATOMY
Flange Joint

A flange joint uses an external or internal ridge or rim for attachment to another object, such as the end of a pipe or pump. All pieces that connect in the system have flanges that allow the parts to be bolted together. No flame is required for assembly whilst ease of assembly and disassembly is variable depending on the number of bolts.

Mechanical Joint
A mechanical joint is a joining method comprising of four elements: the pipe groove, the gasket, coupling housings, and the nuts and bolts. The pipe groove is formed by cold forming or machining a groove into the end of a pipe. The key section of the coupling housing engages the groove and within the housings is a resilient, pressure-responsive, C-shaped elastomer gasket that provides a triple seal. The coupling housing fully encloses the gasket, reinforcing it and securing it in position.

Welded Joint
A welded joint joins together materials of the same type or class through application of a combination of heat and pressure. Welding offers good joint integrity, a choice of processes, approaches and automation, but involves high operating costs, skilled labour and an intensive naked flame that can be a worksite hazard.

Pipe-Joining Choices
A full range of pipe-joining solutions can be found in plants across India - including welding, flanging and mechanical grooved systems. Whilst the age of techniques vary considerably - the Romans employed flanging, whilst mechanical pipe joining is a relatively recent twentieth century development. Pipe joining remains a critical area where choice of method can have a great impact on system maintainability. Skill levels, ease and speed of operations are key factors that determine not only installation costs but also maintenance costs over time. A traditional welded system requires highly skilled workers and is labour intensive. To repair welded piping systems, workers have to cut out a damaged pipe section, which is time consuming, can cause operational In a traditional flanged system, multiple bolts are needed to create a joint and removing these bolts is a time-consuming process, as they need to be manually removed and there must be space around the joint for this operation to take place. For example, a 12-inch flange joint requires 12 bolts to be removed before gaining access to the system. This becomes lengthy and complicated in systems requiring regular routine maintenance when nuts and bolts of flanges require regular removal or even cutting off.

With mechanical pipe joints, only two bolts need to be removed to access the system, allowing more time-efficient maintenance procedures. Additionally, unlike a flanged joint, a two-bolt coupling can be ¬free floated  around the pipe for quick alignment adjustment and easy access. Mechanical pipe joining systems also require fewer man-hours than traditional methods: welding, for example, takes up to 45 per cent more man-hours.

Safety First
Not only is welding a time-consuming process but its many associated dangers can make it a less attractive joining method. The additional preparation needed to make the job site safe during maintenance increases man-hours, down time and costs. Fire watches are essential during and after the work because of the risk of sparks and there are additional health and safety risks for welders and other workers. Welding equipment s leads and compressed gases can cause hazards and toxic fumes can expose workers to serious health problems.

Welding frequently requires that an entire system is drained and dried prior to performing maintenance work on joints, since pipe could burst when flame comes in contact with liquid. Also, if a welder accidentally opens the wrong pipe or if the system is not fully drained, the worker can suffer from molten metal splatter.

In all facilities, but particularly in high-risk structures, handling potentially flammable or hazardous chemicals and materials, a flame-free pipe-joining method offers obvious safety advantages. It eliminates the risk of fire and the need for special fire safety precautions and protective wear and minimises potential disruption to normal plant operations. Use of flame-free pipe joining methods also significantly decreases insurance liability.

Durability
Workers pressurising and depressurising a system repeatedly for many years, which fatigues the rubber components in the pipes, often inflict system damage. In a traditional flanged system, the torque on the bolts employs a high compressive load on the internal gasket, which makes it stick to one or both of the flanges. When the multiple bolts are removed and the flanged joint is disassembled, often the gasket will tear, causing it to fail upon reinstallation.

With a mechanical coupling the compressive loads on its gasket are different from those on a flange. The gasket has a C-shaped cross- section seal that is durable and can handle significant compressive and cyclical loading. Traditional welded or flanged piping systems have rubber bellows or braided flexible hose to accommodate vibrations; however these materials tend to wear out during the lifetime of the system, requiring periodic repair or replacement which can be costly and time consuming. Failure of such items can be sudden and unpredictable, causing serious health and safety risks if, for example, rubber splits in a heating system and hot water escapes. Rubber compensators can be eliminated by using the grooved-end mechanical pipe-joining method, and placing three flexible couplings either side of a pump or other source of vibration.

Flexible couplings are specifically designed to allow pipe expansion, contraction and deflection and allow the pipe to vibrate within the coupling, therefore localising vibrations generated by equipment and reducing the amount of noise transmitted down pipes. The design of the mechanical joint allows for this movement without wearing out the gasket, effectively reducing noise and vibration with little maintenance throughout the life of the system.

Conclusion
There are several different methods of pipe joining, each with its own unique set of advantages and disadvantages. Those involved with the design and maintenance of systems should think carefully about the type of system they employ, as it may have much wider consequences for the running of the whole plant, impacting future site safety, productivity and profitability.