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most common types of offline cleaning equipment are pressure-driven systems (water lances and
air/water systems (brushes, pigs, scrapers, air/water)) andmechanical systems (scrapers, cutters,
rotating brushes). The method for each site depends on the rate of corrosion and biofouling;
physical characteristics and corrosion resistance of the pipe material; type of foulant; length of
unit outage; and cleaning frequency (Rice et al. 1993).
Offline systems cost less than online and require little maintenance or monitoring. All offline
systems require an operator or technician to operate. The condenser or section of the condenser
must be taken out of service to access pipes, and the piping systemmust be shut down.When the
offline cleaning is completed, the system is put back in service and the cleaning components are
stored.
Offline systems are typically only used when the foulant has built up enough to warrant
shutdown. A heavily fouled area may be challenging to clean. Brushes are only effective at
cleaning soft foulants, scrapers are too slow to use for routine cleaning, and pigging can damage
pipewalls and/or become jammed (Stone andWebster EngineeringCorp. 1992).
6.2.1. PressureDrivenSystems
6.2.1.1. Flushing/water lances
Flushing requires forcing water through the pipes at high speeds to carry away particles. This
method requires a large volume of water that is pumped through a flexible hose or metal shaft
with a stainless steel head attached at the end. The head has several holes drilled into it to define
a particular spray pattern and self-propel water through the pipe. Water pressure of about 8,000
to 10,000 psi is used, so operators need to use extreme caution. The high pressure can collapse
pipe ends and inserts and damage the pipe coatings. Equipment being cleanedmust be taken out
of service in order to operate the lance. The lances can damage and gouge the pipes if used
aggressively or incorrectly (Rice et al. 1993).
6.2.1.2. Air/water systems
One of the simplest systems uses a cleaning brush that is blasted into the pipe using compressed
air, pressurizedwater (approx. 200-400 psi), or both. Debris is flushed out with propellant as the
brushmoves along the pipe and into the outlet waterbox. Scrapersmust be usedwhen the foulant
cannot be removed by the brushes (Rice et al. 1993). Scrapers are described inSection 6.2.2.
Pigging requires forcing an object (pig) through the pipe to push or wipe away loose material.
This method requires building launch stations and receiving stations. Inline valves, meters, or
other structures in the flow path may block the pig. The devices do not require special
maintenance or monitoring; however there is immediate performance degradation after cleaning.
Pigs are typically cheaper than online alternatives, but the labor costs are higher because they
require an operator or technician to operate. Pigs have been designed to be self-propelled for use
in longer runs of piping and for areas with 90-degree bends. Pigs are able to use terminal points
(e.g., valves) to activate a reverse mechanism to change travel direction. Pigs can also take
advantage of oncoming velocity head to propel themselves upstream (Stone and Webster
EngineeringCorp. 1992).
