Steam traps are an essential component of any steam system, but often tend to go neglected in my experience. In most cases this is because the impacts of steam trap malfunctions on system efficiency and performance are poorly understood. Poorly functioning steam traps can lead to significant energy losses and also have a significant impact of heat transfer, potentially compromising product quality and throughput. It therefore makes sense to invest in a steam trap management programme to ensure that all steam traps are functioning as designed.
Condensate forms when energy is removed from saturated steam, causing the steam to give up its latent heat. Steam traps are designed to trap steam inside the steam system and release this condensate, which can then be collected and returned to the boiler for incorporation into boiler feed water. By trapping the steam it is forced to condense, maximising its heating potential. Steam traps are typically found downstream of heating applications and on steam distribution headers. There are a wide range of trap designs available, and hence the failure modes associated with steam traps can be diverse. It is therefore important that the condition monitoring systems implemented with regards to steam traps take individual trap design and mode of operation into account. Steam traps fail in two fundamental ways – they can either pass steam or fail to pass condensate. The precise reasons for these failures are a function of the trap design and these failures can also occur across a continuum e.g. blockages can be minor or severe, and also change in severity over time.
A trap that fails to pass condensate is generally more of a process problem than an energy efficiency problem. Condensate tends to back up in the steam system, heat exchange surfaces become covered and heat transfer is compromised. As a result, heating rates decrease and throughput may be reduced, particularly where the process concerned is a constraint. A further potential impact of this failure could be water hammer in the steam system as accumulated condensate finds its way into steam distribution headers.
A trap that passes steam can be both a process problem and an energy efficiency problem. From a process point of view, some of the steam will not condense, and since not all of its latent heat is transferred, heating rates may become a problem. From an energy efficiency perspective, the quantum of the loss depends on the specifics of the condensate recovery system. In systems open to the atmosphere, the steam would pass into condensate recovery vessels and cause flashing to occur, with losses from vents in the system. In principle, passing traps are akin to steam leaks in these circumstances, and there are a number of analytical approaches that can be used to quantify the losses involved. It is important in systems like these to regularly inspect vents for excessive steam losses, which could be indicative of trap failures. The problem is less severe in closed condensate recovery systems e.g. systems equipped with flash vessels or with vent condensers, though process heating problems may still be evident.
Blocked or passing traps can be detected with temperature checks (e.g. infra red spot checks or photographs) and ultrasound. In general, a number of approaches used in combination is best. In extensive steam systems the number of steam traps can be enormous, and since trap failures are inevitable, if management systems are not in place the consequences can be significant. Many companies I visit carry out annual steam trap audits using third parties, and while this is better than doing nothing at all, it is inadequate. It is better in my view to include individual steam traps in the plant’s maintenance programme, and to schedule inspections for every trap such that this activity is carried out throughout the year. This avoids the situation of having a trap fail a month after an annual inspection, and this failure only being detected some eleven months later when the cumulative costs have already been severe. It is also best in my view to integrate steam trap maintenance into other plant maintenance activities, which implies incorporating inspection into the tasks carried out by maintenance staff. This could mean the purchase of some basic condition monitoring equipment, but the benefits would typically outweigh the costs, particularly for large sites. Artisans would generally need training in steam trap maintenance, and this can be carried out by OEM’s.
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