What type of cleaning methods can be considered for flushing and cleaning process lines and vessels during precommissioning?
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There are four different cleaning methods you can consider:
Cleaning with air
During the cleaning operation, the air velocity should be as follows:
Two main methods can be used:
Cleaning with Steam (for steam networks only)
Whenever steam is available, an excellent cleaning fluid is provided. Steam can be used, like air, for continuous blowing, and preferably, for intermittent blowing. The advantage of the latter is that between two blowings the pipes (and possibly vessels) cool and contract causing millscale and rust deposits to crack. These deposits are then easily removed in subsequent blowings. Steam blowing should be used only for steam networks.
Cleaning with water
Cleaning of piping by circulation of water: Line flushing uses water from the normal cooling or firewater systems. Water supply could conceivably be from other sources, i.e. City water lines, supply boat temporary pumps, etc., depending upon the ongoing situation. This type of flushing normally involves taking a section of piping and flushing it from a "startpoint" to an open end. A high velocity flow, in the order of 10-13 ft/s should be achieved in order to be effective. In some circumstances additional pumping capacity will be required. This method of cleaning is effective in removing loose debris from pipework but not particularly effective in removing rust and millscale from piping (or vessel) walls.
Fill and dump water flushing: Fill and dump flushing is often used for cleaning vessels. The method being quite simple, the adequately vented vessel is filled to the desired level with flush water and then dumped to grade, the flush water dislodges loose debris and rust and carries it out of the equipment. Note that some lines connected to the vessel can be flushed by dumping the water through them. One major problem with this method is the disposal of the large quantities of water involved which may overload the normal drain systems.
Cleaning of vessels or equipment by water spray or high pressure water: If there is only dust on the walls of a large vessel, a water spray from a hose pipe might be sufficient. High pressure water may be used to remove solid particles or foreign matter from inside walls or inside parts of vessel or equipment, in particular where access is a problem. Attention has to be given to the potential corrosiveness of water (chloride ions on stainless steel, seawater on carbon steel) and special water quality may be necessary (treated demineralized water or inhibited water).
Manual cleaning: When a system, or part of a system, can be entered, it may be possible to carry out pipewall or vessel wall cleaning manually using either rotary (i.e. air driven) or hand held steel wire brushes. Rust, scale, and dirt that are dislodged may be subsequently removed by the use of an industrial grade vacuum cleaner, by air blowing, or a combination of these two methods. Brushing should be avoided for vessels or piping fabricated from any grade of stainless steel. Carbon steel brushing may cause subsequent corrosion problems. In any event, stainless steel equipment is not likely to have significant deposits of surface dirt or oxide.
Line pigging: For equipment provided with pigging facilities, e.g. interplatform pipelines, platform-to-shore pipelines, etc., special brush pigs are available. These are pigs equipped with peripheral wire spike type brushes and it is often the case that such pigs are used to dislodge rust and scale from pipeline walls. However, deposits of rust and scale are not necessarily conveyed from a pipeline by the use of such a projectile. Such deposits are normally removed by sending a "scraper" or cupped pig through the line which pushes these loose deposits of it for subsequent removal at an "open end".
Your choice of the cleaning method should depend upon:
Well, some of the devices are not in the near vicinity but close by also need to be protected from damages. During flushing and blowing operations, large quantities of dirty water and dirty air are spread out in the units. This water or air generally contains sand, particles of rust, etc., and might damage other equipment (for example: breaking the glass of a pressure gauge). Additionally, the water itself may damage the insulation materials, the electrical motors, etc., accordingly, the following actions should be taken where necessary:
Consider protecting the devices within its network while performing cleaning. During the flushing or the blowing of a line, some particles such as sand, rust, etc. are carried away at high velocities and may either damage some devices when an impact occurs, or clog small diameter pipes. Accordingly, fragile devices have to be removed from the pipe before flushing/blowing.
The following are considered as fragile devices:
Here are some cleaning steps preparations that you can consider:
Whenever possible, the cleaning fluid should flow from top to bottom.
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