1. General requirements for flushing
1.1. Achieve and maintain satisfactory initial cleanliness levels
a. Chemical cleaning and treatment of internal surfaces of the system (components, steel pipes and hoses).
b. Perform hot oil flushing to achieve the target cleanliness of the system.
c. Check and evaluate whether the cleanliness meets the requirements.
d. Disassemble the flushing circuit according to the following steps to prevent pollutants from entering the cleaned system.
Seal all element joints and flanges.
e. Ensure that the cleanliness is controlled within the scope of daily maintenance.
1.2. Maintenance of cleanliness after flushing
a. Prevent new pollutants from entering the system.
b. Select the appropriate system filter. The new oil must be filtered before it can be added to the oil tank.
All new components and / or valve blocks connected to the system must meet the previous requirements. In component change
After replacement, disassembly or similar actions, new cleaning and hot oil flushing must be carried out.
1.3. Key points of flushing
a. Connect the flushing circuit in sequence.
b. Components that will be damaged by high flow rates, moisture, particles or chemical washes must be protected
Short circuit (not connected to the flushing circuit) and clean separately.
c. If the flow regulating element will increase the pressure drop of the system, it shall be short circuited from the flushing circuit and single connected
Cleaning alone.
d. Blocking, valve block, pump station, motor, oil tank and assembly shall be carried out according to specific procedures
rinse.
1.4. Cleanliness requirements for hydraulic components
Some components and assemblies will be connected to the cleaned main system, and the cleanliness of these components should be at least better than the cleanliness requirements of the system. The supplier of hydraulic components shall provide the cleanliness certificate of components. If the component cleanliness certificate cannot be obtained from the component supplier, the system installation unit must clean these components according to specific procedures. However, if the supplier's cleaning does not meet the requirements, the cleanliness certificate cannot be considered effective.
Note: if there are anti-corrosion additives inside the components that are incompatible with the hydraulic medium, 5% - 10% degreasing additives should be added to the flushing medium to flush these components. It must be selected not to damage the element
Degreasing additive for seals.
2. System flushing preparation
2.1. Pipeline mechanical cleaning
Sizing of steel pipes - cutting, bending, welding and removal of scale and corrosion - chemical cleaning
Washing and hot oil flushing. The welded pipes shall be mechanically cleaned internally with plastic pigs. 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 ensures that the pipe and pipe flange are smooth and removes welding slag and external particles.
All steel pipes and hoses must be carefully inspected and purged with highly filtered industrial compressed air. In this way, large particles generated during steel pipe cutting and hose joint installation can be removed.
2.2. Short circuit of important components
In order to effectively clean all components in the system and avoid damage to sensitive components, relevant components must be short circuited or removed from the flushing circuit. Each component or subsystem must be thoroughly cleaned to meet the cleanliness requirements.
When flushing the piping system, disconnect all components and systems that will limit flow and components that may be damaged during flushing.
3. Chemical cleaning and hot oil flushing
Each flushing circuit must be connected to obtain a specific flow rate and Reynolds number. At the same time, all elements, pipes and joints have sufficient fluid pressure and avoid particles remaining in prohibited areas and dead corners. The flow and pressure of flushing must also be taken into account.
3.1. chemical cleaning
According to dewa DPI system, chemical cleaning consists of some special chemicals, which
The chemicals will be put into the same acid-base washing tank in sequence. Dewa is Greek for "strong and born"
DPI means degreasing, pickling and inhibiting, which is developed by DPI chemical industry company of Norway. All chemicals
They are water-soluble, environmentally friendly and inorganic. The cleaning procedure consists of the following five stages.
a. Degreasing and alkaline washing
Fill the oil tank with clean water, heat it to 50c (up to 80C), and add chemical substance A to pH 14.
Circulate at the maximum flow rate for 30 minutes, and any grease and oil film should have been removed. PH value and temperature shall be controlled during operation.
b. Pickling
Add chemical B to reduce the pH value to 5.5, and then add 10% (volume ratio) of chemical C
Cycle at maximum flow for 60 minutes. Pay attention to controlling pH value and temperature.
c. Neutralization
Add chemical D and continue to circulate until the pH value is 7.5 and keep the temperature at the temperature of procedure a
And circulate at the maximum flow rate for 30 minutes. Pay attention to controlling pH value and temperature.
d. Chemical Anticorrosion
If the interval between chemical cleaning and hot oil flushing is less than 24 hours, no preservative shall be added. If the interval is more than 24 hours, 2% (volume ratio) of chemical substance e must be added, and the circulation shall be continued for 30 minutes without heating. These liquids must be diluted by adding 4-5% water before discharge, and the pH value shall be controlled.
e. Dryness
After neutralization, dry the pipe with dry hot air for 30 minutes. Use oil-free and anhydrous compressed air or clean nitrogen after effective filtration.
f. Flushing equipment
·Acid alkali washing pump station: oil tank, oil pump, filter and heating equipment. The best flushing flow is 3m / s. The filter shall be the same as that during hot oil cleaning.
·Equipment for supplying dry and clean hot air or nitrogen. The air must be absolutely oil-free.
·Special flanges, valve blocks and joints shall 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
·罢别尘辫别谤补迟耻谤别
·Amount of chemicals added in each step
·贵濒辞飞
3.2. Hot oil flushing
Generally, the target cleanliness of system flushing should be better than that during normal operation. If the cleanliness requirement of the system during normal operation is ISO 15 / 13 / 11, the system shall at least reach ISO 14 / 12 / 10 during flushing. The flushing must meet the cleanliness requirements of solid particles and moisture at the same time
3.2.1. Flushing medium
The flushing medium must have good compatibility with the medium in normal operation of the system, and the viscosity at different temperatures shall be given. If the viscosity of flushing oil at 40C is 10-15cst, the standard flushing oil
The washing station can provide sufficient turbulent flow. Theoretically, 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, velocity, temperature and pressure
·Turbulence and Reynolds number
When the Reynolds number is greater than or equal to 4000, the motion of the fluid will naturally be turbulent. Turbulence can effectively wash away particles in the pipeline and avoid pollutants suspended 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 shall be at least 4000.
For example, the Reynolds number of a hydraulic system during normal operation is 3400, and the Reynolds number during flushing shall be at least 4080.
Reynolds number NR is used to determine whether the flow state of fluid in the pipeline is laminar or turbulent. The calculation formula is:
Nr = ρν D/ η
ρ = Fluid density
ν = Average velocity
D = pipe inner diameter
η = Dynamic viscosity
Dynamic viscosity η= ρμ ( μ Is the kinematic viscosity of the fluid), and the solid NR can also be calculated by the following formula:
Nr= ν D/ μ
For example, a hydraulic oil with a viscosity of 46cst flows at a flow rate of 4m / s in a pipe with an inner diameter of 800px, and its Reynolds number is:
Nr=(10000px/s)(800px)/(11.5px2/s)=2000
Empirical surface, laminar flow when NR < 2000; Turbulence when NR > 3000; NR is an unstable flow between 2000 and 3000, and changes between the two modes.
·痴别濒辞肠颈迟测
In any flushing circuit, the flow rate shall not be less than 2-3m / s, which can prevent particles from remaining in the pipeline
Department.
·罢别尘辫别谤补迟耻谤别
The temperature of the coldest part of the flushing circuit should be higher than 50c, which can be achieved by providing 60C flushing oil
·笔谤别蝉蝉耻谤别
Measured from the downstream oil return filter and sampling port of the flushing circuit, the pressure shall be greater than 3-5bar. In order 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 elements should be cleaned in different circuits.
·Oil tank: This is one of the most difficult components in the system to clean. The oil tank shall be cleaned manually first, and then add flushing oil. A flushing oil pump and filter form a circuit for flushing.
·Filter: it can be connected to the flushing circuit or a separate tank flushing circuit.
·Oil cylinder, animal energy device, motor and oil pump: clean separately.
3.2.4. Minimum flushing time
Once the flushing oil sample shows that the cleanliness has met the requirements, flush in the form of turbulence for an additional 30 minutes in order to increase the reliability of flushing.
3.2.5. Evaluation of flushing results
Each flushing circuit shall be unique and traceable. Establish the actual intention of each flushing circuit and corresponding pipelines, and mark the temperature measurement points, flow detection points and sampling points.
Record all parameters in the form of documents, such as start flushing time, temperature, flow, particle pollution degree, moisture and end time, etc.
If possible, ask a third party to evaluate the cleanliness of system flushing.
4. Flushing equipment
4.1. Filtration system
The filtration system shall have sufficient capacity and high performance to filter solid particles and moisture in a reasonable time and meet the cleanliness requirements.
The original filter in the system shall not be used as flushing filter.
The latest practice shows that it is equipped with a differential pressure transmitting device and a large enough pollution holding cavity, β ? > 100 filter is very effective. The sending device shall give an alarm before the filter is actually bypassed (the filter does not take the role of filtration).
There are many ways to remove water: filter element made of water absorbent material, combined filter, oil purifier (such as vacuum distillation), or simply change oil. Generally, water absorbent filters are effective.
Note: do not replace the filter for filtering solid particles with a water removal filter!
4.2. pumping station
The pump station shall be able to provide sufficient flow, flow rate, viscosity and pressure to clean the system.
4.3. Temperature regulation system
The temperature shall be frequently detected and adjusted to ensure that the flushing oil has appropriate viscosity, so as to form turbulence in the whole flushing circuit and meet the lubrication requirements of the flushing oil pump.
5. Detection of system cleanliness during flushing
5.1. Cleanliness of the system during normal operation (NAS or ISO 4406): according to the equipment manufacturer
Determine the requirements of. If there is no explicit requirement from the equipment manufacturer, it is recommended to be no less than ISO
4406 17 / 14 or NAS class 8.
5.2. Target cleanliness of system flushing: two orders of magnitude lower than that in normal operation. Such as normal work
If it is NAS grade 8 during operation, the target cleanliness of flushing shall be NAS grade 6.
5.3. Cleanliness detection: it can be carried out in the laboratory or portable cleanliness detector can be used
On site inspection. The following figure shows pall portable Contamination Tester, which can be tested on site by Mobil engineers.
Cleanliness test cycle: it shall be formulated according to the site conditions.
Sampling: it is best to take samples at the oil return header and oil return tank (sampling valve shall be installed on the oil return header).
Sampling container: clean sampling bottle.
