[Haichuan Chemical Valve Management] Series Posts – The “pitfalls” in boiler valve installation – Lessons learned by experienced professionals through trial and error

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Proper management of valves is the foundation for stable operation. Everyone is welcome to engage in discussions and share their thoughts in this series of posts: [Haichuan Chemical Valve Management] https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=5719309 ---------------------------------------------------------------- Disclaimer: The contents of this article are intended solely for technical exchange and reference purposes. They do not constitute any form of professional engineering advice, design basis, or operational guidelines. -----------------------------------------------------------------------------------Those who handle equipment maintenance all share one consensus: three parts product quality and seven parts installation. This is especially true for valves. No matter how good a valve is, if there are mistakes during installation, it will lead to endless problems later on. The veteran workers who’ve worked in boiler rooms all have plenty of “bitter lessons” regarding valve installation etched in their memories. Today, I’ve organized these experiences in hopes that they’ll help others avoid falling into the same pitfalls. First pitfall: Improper pairing of gaskets and flanges. Most connections between valves and pipes are made using flanges, with gaskets in between. The material and type of gasket to be used should be determined based on the temperature, pressure, and corrosiveness of the medium. In actual practice, however, people often just grab a rubber pad from the warehouse and install it. The temperature and pressure in the boiler steam pipes are simply too much for rubber gaskets to withstand; they may age, harden, leak, or even crack in a short period of time. Generally, metal wound gaskets or metal-graphite composite gaskets must be used on steam pipes. Additionally, if the gaskets aren’t placed correctly during installation, or if the bolts aren’t tightened symmetrically—or if the torque applied is insufficient or uneven—this can result in uneven stress on the flange surfaces. Consequently, leaks occur after thermal expansion and contraction during operation. These are all details, but when it comes to steam leakage, there’s no room for ambiguity. The second pitfall: The installation direction of the valve was reversed. For valves with flow direction requirements, arrows are cast on the valve body or the flow direction is indicated thereon. But there are always people who don’t pay attention to the arrows, or think it doesn’t matter which direction they install it in. It was not until operation began that the problem was discovered: the check valve had been installed in the wrong direction, allowing the medium to flow back unimpeded and completely losing its function of providing one-way flow control ； The stop valve was installed in the wrong direction; the stem packing is always on the high-pressure side, which leads to leakage and poor sealing ； If the pressure relief valve is installed backwards, it may not function at all. Therefore, before installing the valve, it is essential to confirm the flow direction of the medium and the allowed installation direction of the valve, and to make a mark; check these again during installation. Third pitfall: Welding heat effects cause damage to the valve internals. Some valves have their ends welded to the pipes. The high temperature generated by welding can be transmitted to the interior through the valve body; if there are non-metallic seals (such as PTFE) between the valve stem and the valve seat, or if there is a tightly fitted gap, the high temperature can cause the seals to deform or become damaged, or it can result in the valve stem getting stuck. Therefore, valves that require welding connections, those with non-metallic components inside, usually need to have their valve body welded to the pipeline first; after cooling, the internal components of the valve are then installed ； Or, measures such as wrapping a wet cloth around the middle of the valve body to reduce temperature can be taken during welding. If this process requirement is not followed, internal damage will become apparent during the valve’s power-on testing. Fourth pitfall: No “piping inspection” and “purging” were carried out after installation. During pipeline construction, it is inevitable that debris such as welding slag, iron shavings, and stones will enter the pipes. If the pipeline is not purged and flushed in a timely manner after the valve is installed, these debris may accumulate inside the valve chamber. Especially in safety valves and control valves, foreign objects stuck on the sealing surfaces can cause leakage or sticking, and in severe cases, they can even damage the sealing surfaces. Therefore, before pressure testing and flushing new piping systems, important valves such as control valves and safety valves are often replaced with temporary short pipes to prevent damage. Put it back in after it has passed the flushing test. Fifth pitfall: Insufficient consideration for operational space. Valve handwheels, pneumatic actuators, and electric actuators require space for maintenance and operation. In some large-diameter gate valves, the lift travel of the valve stem is quite large; if one fails to take into account the presence of beams or pipes above during installation, it becomes impossible to fully open the valve. Some exhaust valves are installed under the ceiling, close to the wall, making it impossible for operators to reach the handwheel to operate them. Some control valves are installed in locations that are too narrow, making it impossible to insert a wrench for maintenance. These oversights during the planning phase will cause long-term problems in operation and maintenance. The sixth pitfall: the issue of sampling pipes for safety valves, pressure gauges, etc. The pipeline at the inlet of the safety valve should be short and straight, with an inner diameter that is not smaller than the diameter of the safety valve inlet; otherwise, it will affect the discharge capacity. The pressure tapping tubes for pressure gauges and pressure switches must not be led from areas with eddies or high flow velocities; otherwise, the measurement values will be low and unstable, leading to incorrect operations. Many specifications provide clear guidelines regarding these installation details, but laziness or a desire to cut corners on site can easily lead to hidden problems. The seventh pitfall: the valve is not in the correct position during pressure testing. During the hydraulic testing of the system, some valves need to be in the open position while others need to be in the closed position in order to test their strength or tightness. Making a mistake not only renders the test ineffective but may also damage the sealing surface. When performing a overpressure test on a safety valve, it must be locked or removed; it cannot be pressurized with the spring still in place, as this will inevitably damage the spring. These regulations are standard procedural requirements that must be followed. Having talked so much about the pitfalls associated with installation, the purpose is not to scare anyone, but rather to remind us that valve installation is a process that requires care, precision, and adherence to standards; one should not become careless just because the valves themselves are of good quality. By referring to standards, relying on experience, and conducting thorough inspections, the valve can be kept in good condition from the first day of installation. The experience of the veteran craftsmen is the result of years of exploration and reflection by them. Passing on these experiences to future generations to avoid repeating the same mistakes is the cornerstone for ensuring the long-term and stable operation of boiler systems.