Cleaning and Flushing Methods
MECHANICAL CLEANING METHODS
The following is a summary of various mechanical methods used in cleaning piping and components:
Handwiping
• Cloths or rags should be lint-free
• Water or solvent is typically used in conjunction with the handwipe cleaning process.
Wire Brushing
• Either hand or power driven wire brushing is an effective method of cleaning small sections of piping
• Use corrosion resistant brush material on stainless steel components and do not use the same brushes on both stainless and carbon steel
Tube Cleaning Brushes
• Air, water, or electric powered expanding type power brushes that drive air or water through the brush provides a method of power flushing the interior surfaces of piping
• The water used to flush the interior surfaces of the piping must be compatible with the piping system cleanliness
• Do not use air driven brushes that require lubricated air if the motor air enters the pipe
• Do not use tube cleaning brushes through valves, strainers, flow orifices, or other sensitive components
• Avoid using tube cleaning brushes through socket welded or short radius fittings Grinding
• Grinding wheels and discs used for cleaning should only be vitrified or resinoid bonded aluminum oxide or silicon carbide
• Aluminum oxide flapper wheels and buffing discs provide effective mechanical cleaning on exterior surfaces
• Rotary files can be used for localized cleaning but should be faced with tungsten or titanium carbide
Shot or Grit Blasting
• Blasting is typically performed to the Steel Structures Painting Council (SSPC) standards
• Do not blast through sensitive components
• Only use iron-free grit for blasting stainless steel surfaces
• Sand grit may be used on carbon steel buttwelded piping
• Do not blast areas requiring liquid penetrant examinations
• For 2 inch and smaller piping, a radial type blast nozzle may be inserted into the pipe to blast the interior surface
Mechanical cleaning operations are usually followed by hand cleaning of accessible internal surfaces and by air blow or water rinse of inaccessible internal surfaces. Air blowing is preferred after a shot or grit blast.
VACUUM CLEANING
Vacuum cleaning can be used for the removal of metal chips and airborne foreign
materials while working or for local cleanup subsequent to work operations.
AIR BLOWING
Filtered, oil-free compressed air is used in the following applications to clean piping:
• Local cleanup of foreign material produced during erection or fabrication
• Drying of previously wetted systems
Care must be exercised to direct the air blow and particles away from internal
surfaces of the components being cleaned. Particles must also not be blown
through or at sensitive components.
SOLVENT CLEANING
The following solvents are typically used to clean piping:
• Alcohol
• Ethyl alcohol (Ethanol)
• Methyl alcohol (Methanol) anhydrous
• Isopropyl alcohol
• Acetone
• Toluene which is useful in removing silicone based lubricants
• Naphtha
• Distilled Petroleum Spirits or Mineral Spirits
For lined piping, solvents used for cleaning must be compatible with the lining
material. When bristle brushes are used in conjunction with solvent cleaning, they
must be non shedding.
WATER BLAST CLEANING
Water blast cleaning or hydrolasing consists of a high pressure , low volume water jetting of the internal surfaces of the piping system to remove rust, mill scale, oil, and other foreign materials.Radial type spray nozzles that drag the supply hose or push type cleaning nozzles should be used.
When cleaning carbon steel or alloy steel piping, 0.5% to 1% by weight of trisodium
phosphate should be used.
Water quality must be compatible for use on the piping system being cleaned. The water jet must not come in contact with valve seats, flow nozzles, or other sensitive components. After cleaning carbon steel and alloy steel systems, the pipe must be dried by air blowing or other methods.
SYSTEM FLUSHING METHODS
Several methods of system flushing are used to clean piping systems. In general,
the water used for flushing must be compatible with the system being cleaned. After
the completion of the flush, carbon steel and alloy steel systems must be air dried.
Recirculating Flush
This flushing method uses a single batch of water which is recirculated under
pressure through the piping system in a closed path at a prescribed velocity through
strainers, filters, or demineralizers to remove debris and water impurities.
Velocity Flush
A cleaning technique that utilizes the ability of the rapidly flowing liquid or air to scrub, sweep, and scour foreign material from internal walls of the system. Particles picked up in the flush are sent out as waste or trapped and collected on mesh screens or filters. The effective velocity should exceed the design flow rate by two times through the system to perform as desired.
Soaking Method
This process is used when it is not possible to achieve flow by the recirculating method due to the inlet connections or tube shapes for vessels. The disadvantage of this method is that it requires a stronger solution to perform the cleaning and sampling is not as accurate.
Acid Cleaning
This process cleans the internal surfaces of water touched pressure parts to remove
mill scale and rust. The acid solution reacts with iron scale and forms ferric oxide.
Chemical Cleaning
This process uses the circulation of a hot alkaline water or citric acid solution through
the pipe systems to remove oil, grease, fitting lacquers, preservatives, inhibitors, and
possible siliceous materials from carbon steel piping and equipment. The hot alkaline water is followed by an acid solution flush to remove iron oxide and mill scale. The acid solution flush liquid is neutralized and flushed out of the piping system.
CLEANING ADDITIVES
Wetting Additives
Wetting agents are used to improve the contact of a cleaning solution with the pipe
and equipment. The additives reduce the surface tension of the cleaning solution
and thereby enhance the cleaning of the metal. Because they are detergent based,
the wetting agents tend to foam which may not be acceptable in all applications.
Anti-Foam Agent
These agents are sometimes used when detergents are added to chemical cleaning
solutions. Their use maintains a low foaming level during cleaning and discharging
of the solution to the waste collection system or tank.
Acid Inhibitors
When added to the cleaning solutions, these inhibitors allow higher cleaning
temperatures and slow the reaction between the cleaning solution and the piping or
equipment base metal.
Chemical Cleaning Set-up
Temporary equipment is usually required to perform any on-site cleaning. A P&ID should be marked up and reviewed showing:
• Scope of the cleaning
• Desired flow path
• All temporary piping and instruments
• Heating source for the operation
• Strainer and filter locations
All temporary pipe should adhere to the following:
• Pipe should be Schedule 40 minimum
• Welded joints should be used to prevent leaks
• Check gaskets to ensure they are compatible with the heat and chemicals being used
• Monitor the system to prevent over pressurization
Temporary Instruments
• Make sure temporary glass site gauges installed
• Provide differential pressure gauges across strainers to indicate fouling or flow reduction
• Install temperature indicators to monitor flushing temperatures
Solution Heating Equipment
There are two methods for heating chemical cleaning solutions.
• Direct contact method
• Steam supply heat exchanger
Flushing Safety
Safety measures such as warning signs, barriers, or temporary personnel insulation
should be considered. Review all chemical flushing with the Site Safety Representative before starting the flush. .
Chemical Cleaning Set-up
Mechanical cleaning (line-pig) can be used to knock loose dirt and sand particles
and remove oil and grease from the interior piping walls. Filtered well water, plant
water, or city water is normally used for line-pigging of the system. The drums and
coolers required for the cleaning are normally prepared by the vendors prior to the
equipment arriving at the site.
Following the mechanical cleaning and field assembly of required temporary piping,
the acid solution is applied to remove scaling. Whenever possible, agitate the piping
to shake any loose materials free. After the acid cleaning, rinse the system with
fresh water. When using citric acid, a fresh water rinse is not normally performed.
The descaled pipe is then passivated to prevent further corrosion by applying a
phosphate coating. Any of three different solutions are typically used:
• Monosodium phosphate
• Disodium phosphate
• Sodium nitrate
After being passivated, the system is dried using dry nitrogen or filtered, dry
compressed air. Do not flush the passivated system with water. After drying,
inspect the piping to be sure it is free of rust, mill scale, or other foreign material and
restore and close the system tightly. Blanket the system with inert gas, apply a rust
preventative, or fill the system with oil to minimize rusting in the system.
Lube Oil Flushing
Prior to any lube oil flushing operation, it is important to check supplier, engineering,
and client requirements for the flushing operation to ensure that the criteria for the
conduct and acceptance of the flush is clearly understood. It is best to have a specific procedure or instruction defining the flushing operation approved by all parties prior to the start of the work. The first step in lube oil flushing is to chemically clean and passivate all associated piping, heat exchangers and vessels.
The following are the normal steps used in a lube oil flush:
• Prepare jumpers around seals and bearing housings as close as possible to the
bearings.
• Charge the system with the specified oil. The fill amount should give an operating level near that for which the system was designed.
• Install 100 mesh screen in the return line to the reservoir.
• Circulate the flushing oil for a minimum of 4 hours at the maximum recommended temperature while hammering the piping, switching valves, and cycling bearing and seal oil rundown tanks (if so equipped).
• When clean, remove all temporary jumpers, and reconnect all permanent piping.
Install 100 mesh screens at the inlet to each bearing. Install blinds in the seal oil
system, if so equipped, so as not to flush through the seals.
• Unless otherwise specified by the supplier, continue to circulate the flushing oil in
4 hour increments until all screens are clean.
• When clean, remove temporary jumpers, reconnect all permanent piping,
remove screens, replace filters and clean filter housings. Check pump inlet
screens and clean if needed.
• Circulate oil for a minimum of 8 hours.
• Discard filters and clean the filter housings. The client may want to see the
discarded screens to verify the adequacy of the lube oil flush.
Plant Steam Start-up
The set-up to perform plant steam starting begins when the system is being placed
in service. Begin with a walkdown of the system looking for any discrepancies,
checking the hydrotesting restoration. The following steps represent one method to
start-up for plant steam and are done with concurrence and direction of Startup
and/or Client representative:
• Check gaskets and valve line ups.
• Tag-out the system as needed
• Open drain valves
• Close all steam trap inlets to prevent clogging
• Start Boiler and open isolation valves
• As the system heats up let the condensate and steam run freely out the open drains. After the condensate has slowed to a steady rate begin opening steam trap branches and closing the drains.
• Replace or repair any steam trap not functioning properly.
MAINTAINING CLEANLINESS DURING CONSTRUCTION
The following guidelines should be followed to maintain system cleanliness during
fabrication, installation, and rework operations:
• To keep a system clean, start with clean materials. During work operations,
keep the materials in a clean condition.
• Apply rust preventatives to the internal surfaces of carbon steel components.
Preventatives must normally be removed prior to turnover.
• Keep openings into components sealed when work is not actually in progress.
• Perform localized cleanup after completing work operations and prior to reclosing
the system.
• Protect clean systems in the vicinity of foreign matter or dirt producing work
operations. This can be done by establishing clean areas and by using internal
dams or external encapsulation when systems are opened.
• Establish a foreign object and access control procedures for clean areas.
• Immediately remove all visible metal particles or chips after cutting.
• Do not use flame cutting in areas where slag may blow into inaccessible
surfaces.
• Do not cut pipe in a vertical position if there is a possibility of cutting chips falling
into inaccessible areas.
• Clean grinding dust from a ground out area prior to breaking through the wall or
root pass to prevent the dust from entering the clean system.
• Use magnetic drill bits to drill holes in carbon or alloy steel pipe to minimize the
entry of metal particles. Frequently clean holes during the drill operation.
• Use hole saws when cutting chips cannot be easily removed form internal
surfaces. Holes should be cleaned just prior to breaking through and the plug
should be immediately be removed.
• Clean the ends of threaded pipe to remove lubricant and metal chips at the
completion of threading.
• Provide an oil-free air blow of all field fabricated piping assemblies, including
valves, to remove loose foreign material.
• Seal the openings in completed field fabricated piping assemblies until installed.
Provide desiccant on the inside of the completed pipe assembly if required by the
project specifications.
• Prior to fitting or bolting up flanged or other mechanical joints, clean flange faces
of mill varnish or other preservatives.
• Cover tack welded pipe joints to prevent the entry of dust until the joint is to be
welded out.
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