1. General requirements for flushing
1.1. Reach and maintain a satisfactory initial cleanliness level
a. Chemical cleaning and treatment system internal surfaces (components, steel pipes and hoses).
b. Perform a hot oil rinse to reach the target cleanliness of the system.
c. Check and assess whether the cleanliness meets the requirements.
d. Follow the steps below to disassemble the flushing circuit to prevent contaminants from entering the cleaned system.
Seal all component joints and flanges.
e. Implement daily maintenance to ensure that the cleanliness is within the control target range.
1.2. Maintain cleanliness after rinsing
a. Prevent new contaminants from entering the system.
b. Select the appropriate system filter. New oil must be filtered before it can be added to the tank.
All new components and / or valve blocks connected to the system must meet the previous requirements. More in the component
After replacement, disassembly, or similar operations, new cleaning and hot oil flushing must be performed.
1.3. Flushing points a. Connect flushing circuits in sequence.
b. Those components that will be damaged by high flow rate, moisture, particles or chemical flushing must be taken
Short-circuit (not connected to the flushing circuit) and clean it separately.
c. The flow regulating element will increase the pressure drop of the system.
Clean alone.
d. Blocks, valve blocks, pumping stations, motors, fuel tanks, and assemblies should follow specific procedures
rinse.
1.4. Cleanliness requirements of hydraulic components
Some components and assemblies will be connected to the main system after cleaning. The cleanliness of these components should be at least better than the cleanliness requirements of the system. The supplier of hydraulic components shall provide proof of cleanliness of the components. If the component cleanliness certificate cannot be obtained from the component supplier, the system installation unit must clean these components according to a specific procedure. However, if the supplier's cleaning does not meet the requirements, the cleanliness certificate cannot be regarded as effective.
Note: If there are anticorrosive additives incompatible with the hydraulic medium inside the components, 5% -10% degreasing additives should be added to the flushing medium to flush these components. A degreasing additive that will not damage the component seal must be selected.
2. System flush preparation
2.1. Pipeline mechanical cleaning
The length of the steel pipe-cutting, bending, welding and removing scale and corrosives-for chemical cleaning and hot oil washing. Plastic pipes should be used for internal mechanical cleaning after welding. Plastic pig is a plug with brush, scraper and roller on its outer surface. It moves in the pipeline under the action of oil pressure to achieve the cleaning effect. This will ensure that the pipeline and pipeline flanges are smooth and remove welding slag and foreign particles.
All steel pipes and hoses must be carefully inspected and purged with highly efficient filtered industrial compressed air. This removes the larger particles that are generated during steel pipe cutting and hose joint installation.
2.2. Short circuit of important components
In order to effectively clean all components in the system and avoid damage to sensitive components, related components must be shorted or removed from the flushing circuit. Each component or subsystem must be thoroughly cleaned to meet cleanliness requirements.
When flushing the piping system, disconnect all components and systems that restrict flow and components that may be damaged during flushing.
3. Chemical cleaning and hot oil rinsing
Each flushing circuit must be connected to obtain a specific flow rate and Reynolds number. At the same time, all components, pipes and joints have sufficient fluid pressure, and particles should not be left in prohibited areas and dead ends. The flow and pressure of flushing must also be taken into account.
3.1. Chemical cleaning
According to the DEWA DPI system, chemical cleaning consists of some special chemicals, and these
The chemicals will be put into the same acid-base washing tank in sequence. DEWA is the Greek word "Strong and Strong
"Life is strong", DPI stands for Degreasing, Pickling and Inhibiting, developed by Norwegian DPI Chemical Industries. All chemicals are water-soluble, environmentally friendly and inorganic. The cleaning procedure consists of the following 5 stages.
a. Degreasing and alkaline cleaning
The tank is filled with clean water, heated to 50C (up to 80C), and chemical A is added to reach PH 14.
Circulate at maximum flow for 30 minutes, any grease and oil film should have been removed. PH value and temperature should be controlled during operation.
b. Pickling
Add chemical B to reduce the pH to 5.5, then add 10% (volume ratio) of chemical C
Circulate at maximum flow for 60 minutes. Pay attention to control PH value and temperature.
c. Neutralization
Add chemical substance D, continue to cycle to PH value of 7.5, keep the temperature as the temperature of program a
And circulate at maximum flow for 30 minutes. Pay attention to control PH value and temperature.
d. Chemical preservation
If the interval between chemical cleaning and hot oil flushing is less than 24 hours, no preservatives need to be added. If the interval is greater than 24 hours, 2% (volume ratio) of chemical substance E must be added without heating, and the cycle is continued for 30 minutes. Before discharging these liquids, 4-5% water must be added for dilution, and the PH value should be controlled.
e. Dry
After neutralization, the pipes were dried with dry hot air for 30 minutes. Use oil-free, water-free compressed air or clean nitrogen after effective filtration.
f. Flushing equipment
· Acid and alkali washing pump station: oil tank, oil pump, filter and heating equipment. The flushing flow is preferably 3m / s. The filter should be selected the same as when cleaning with hot oil.
· Equipment that supplies dry, clean hot air or nitrogen. The air must be absolutely free of oil.
· Special flanges, valve blocks and joints should be cleaned in advance.
g. Control during cleaning
In order to identify whether the chemical cleaning is correct, the following test data must be recorded:
· PH value
· Temperature
· The amount of chemicals added in each step
· Flow
3.2. Hot oil flushing
Generally, the target cleanliness of system flushing should be better than the cleanliness of normal operation. If the cleanliness requirement of the system during normal operation is ISO15 / 13/11, then the system should reach at least ISO 14/12/10 when flushing. Washing must meet the cleanliness requirements of both solid particles and moisture
3.2.1. Flushing media
The flushing medium must have good compatibility with the medium when the system is working normally, and the viscosity at different temperatures should also be given. If the viscosity of the flushing oil at 40C is 10-15cSt, the standard flushing
The washing station can provide sufficient turbulent flow. In theory, as long as the temperature is not higher than 70C, the flushing oil can reach this viscosity.
In actual operation, the working medium is usually selected as the flushing medium.
3.2.2. Turbulence, flow velocity, temperature and pressure
· Turbulence and Reynolds number
When the Reynolds number is greater than or equal to 4000, the movement of the fluid will naturally be turbulent. The turbulent flow can effectively wash away the particles in the pipeline to avoid the suspension of pollutants in the oil during operation. The Reynolds number during flushing is required to be greater than or equal to 1.2 times the Reynolds number during normal operation, but it should be at least 4000.
For example, the Reynolds number of a hydraulic system during normal operation is 3400, and the Reynolds number during flushing should be at least 4080.
The Reynolds number Nr is used to determine whether the state of fluid flow in the pipe is laminar or turbulent. The calculation formula is:
Nr = ρνD / η
ρ = fluid density
ν = average flow rate
D = pipe inner diameter
η = dynamic viscosity
And the dynamic viscosity η = ρμ (μ is the fluid kinematic viscosity), the solid Nr can also be calculated by the following formula:
Nr = νD / μ
For example: a hydraulic oil with a viscosity of 46cSt flows in a pipe with an inner diameter of 800px at a flow rate of 4m / s, and its Reynolds number is:
Nr = (10000px / s) (800px) / (11.5px2 / s) = 2000
According to the empirical surface, Nr <2000 is laminar flow; Nr> 3000 is turbulent flow; Nr is an unstable flow between 2000-3000, which changes between two ways.
· Flow rate
The flow velocity should not be less than 2-3m / s in any flushing circuit, which can prevent particles from remaining in the pipeline
unit.
· Temperature
The temperature of the coldest part of the flushing circuit should be higher than 50C, which can be achieved by providing 60C of flushing oil
· Pressure
Measured from the oil return filter and sampling port downstream of the flushing circuit, the pressure should be greater than 3-5 bar. To ensure that all areas are effectively cleaned, the hydraulic components should be fully open.
3.2.3. Cleaning of oil tank, filter, oil cylinder, accumulator, oil pump and motor These components should be cleaned in different circuits.
· Oil tank: This is one of the most difficult components to clean in the system. The oil tank should be cleaned manually before adding the flushing oil, and a flushing oil pump and filter are used to form a circuit for flushing.
· Filter: Can be connected to the flushing circuit or a separate tank flushing circuit.
· Oil cylinder, animal function, motor and oil pump: clean separately.
3.2.4. Minimum rinse time
Once the rinsing oil sample shows that the cleanliness has reached the requirements, rinsing for 30 minutes in the form of turbulent flow in order to increase the reliability of rinsing.
3.2.5. Evaluation of flushing results
Each flush circuit should be unique and traceable. Establish the actual intention of the flushing circuit and the corresponding pipeline, mark the temperature measurement point, flow detection point and sampling point.
Record all parameters in the form of files, such as the start flushing time, temperature, flow rate, particle contamination level, moisture and end time, etc.
If possible, find a third party to assess the cleanliness of the system rinse.
4. Flushing equipment
4.1. Filtration system
The filtration system should have sufficient capacity and high performance so that it can filter out solid particles and moisture in a reasonable time and meet the cleanliness requirements.
Do not use the original filter in the system as a flushing filter.
The latest practice shows that a filter with a pressure difference signaling device and a sufficiently large dirt-holding volume, β 3> 100 is very effective. The signaling device should give an alarm before the filter is actually bypassed (the filter does not take filtering action).
There are many ways to remove water: use water-absorbing filter elements, combined filters, oil purifiers (such as vacuum distillation), or simply change the oil. Generally, water-absorbing filters are effective.
Note: Do not replace the filter that filters solid particles with a water removal filter!
4.2. Pumping station
The pumping station should be able to provide sufficient flow, flow rate, viscosity and pressure to clean the system.
4.3. Temperature regulation system
The temperature should be constantly tested and adjusted to ensure that the flushing oil has a suitable viscosity, so that turbulence is formed in the entire flushing circuit while meeting the lubrication requirements of the flushing oil pump.
5. During the flushing process, the detection of system cleanliness
5.1. Cleanliness of the system during normal operation (NAS or ISO 4406): according to the equipment manufacturer
The requirements are ok. If the equipment manufacturer does not have clear requirements, it is recommended to be no less than ISO
4406 17/14 or NAS 8 level.
5.2. Target cleanliness of system flushing: Two orders of magnitude lower than normal operation. As normal
When the operation is NAS 8 level, the target cleanliness of flushing should be NAS 6 level.
5.3. Cleanliness test: it can be carried out in the laboratory, or a portable cleanliness tester
On-site testing. The picture below shows the PALL portable pollution tester, which can be inspected by Mobil engineers on site.
Cleanliness testing cycle: specific formulation according to the site conditions.
Sampling: It is best to sample at the return tank of the oil return main pipe (a sampling valve needs to be installed on the oil return main pipe).
Sampling container: clean sampling bottle.
