01 Existing problems

The main oil supply pipeline of the hydraulic system of the grate cooler of a company is a 50mm seamless steel pipe. Most of the hydraulic conveying pipelines are laid in the grate cooler air chamber. The conveying pipe in the grate cooler air chamber is connected with the hydraulic cylinder through tee, reducer or hose. Pipe interface mainly adopts welding mode.

Since it was put into operation at the end of November 2010, the main oil supply pipeline and the three-way welding of the grate cooler leaked oil for a total of 11 times. 10 times of oil leakage at the tee, reducing diameter and joint welding; Cracks in the main oil supply pipeline resulted in two times of oil leakage, each time wasting a large amount of hydraulic oil.

Due to the company’s hydraulic system USES the pipe in the wind, every time looking for oil spill will be checked, eliminate wind chamber, and inspections and the handling of oil spill is to reduce load operation, handle funnelled must also stop the wind chamber for the wind, the other three columns in the absence of air supply run result in driving and the sealing part wear speed up, grate bed material leakage, high oil pressure system and high temperature period phenomenon of shortening the service life of parts.

If there are oil leakage points in the air room, it is not suitable to check, which is easy to cause the waste of lubricating oil. In addition, the treatment of oil leakage points in the air room will easily cause oil pollution because of the poor environmental conditions, and then cause the damage of hydraulic system components. On the one hand, the oil leakage in the air chamber will cause the blockage of the grate and affect the rapid cooling of the clinker. On the other hand, if the wind indoor leakage is easy to cause fire accidents (a company had a fire accident).

02 Cause analysis and improvement

2.1 Raw material analysis

The hydraulic tubing of the company is now using 50mm×5.5mm hot rolled seamless steel pipe. The working pressure of the system at ordinary times is 15 ~ 18MPa, and occasionally reaches 21MPa(less than 25MPa). And according to JB 827-66, JB/Z 95-67 analysis and calculation, with the diameter of 50mm×5.5mm and 42mm×5mm steel pipe strength and flow to meet the requirements. Since the strength of the base metal used for steel pipe welding is generally higher than that of the original material, the welding strength can be checked by tensile stress strength when the steel pipe is used for conveying fluid. If the strength of the material meets the requirements, the general welding strength also meets the requirements. Cylinder welded connection calculation, steel pipe welding strength can be borrowed, for steel pipe welding, D= D ₁.

At present, the solder wire specifications: 2.5 mm * 1000 mm, and brand: THT50-6, models: ER50-6, mechanics performance parameters: tensile strength sigma Ь = 500 mpa. Safety factor n=3 ~ 4, take n=4. ф 42 mm steel tube can withstand tension (P = 5085 kg) on the absolute value is lower than 50 mm ф tensile strength of the steel tube can withstand (P = 6185 kg), however, is that the actual pull force on the ratio of (safety factor), ф 42 mm steel pipe for the P/P ₁ = 3.01, ф 50 mm steel pipe for the P/P ₁ = 2.34, that is to say, ф 42 mm steel pipe have higher safety coefficient (of course, the overall safety factor should also contain n = 4, ahead of the actual safety factor should be respectively n ₄ ₂ = 12.01 and n ₅ zero = 9.36).

In addition, 42mm steel pipe and the following are cold rolled pipe, and 50mm steel pipe is hot rolled pipe, its chemical properties and rolling defects are worse than cold rolled. According to the field use and analysis and calculation, we decided to change the 50mm×5.5mm hot rolled seamless steel pipe to 42mm×5mm cold rolled seamless steel pipe.

2.2 Field pipeline analysis and measures

Most of the field pipeline oil leakage occurred in the tee and elbow, for straight pipe welding generally did not appear oil leakage. According to the analysis, at the tee and elbow, the pressure changes from laminar flow to turbulent flow due to the change of pipeline direction and diameter. In order to reduce the occurrence of this problem, the tee and elbow are lengthened appropriately, and the steel pipe at the outlet of the proportional valve block is changed into a temperature and pressure resistant hose to reduce its impact and reversing vibration.

03 Transformation Process

3.1 Preparation before transformation

(1) Get familiar with the function of hydraulic and control process according to the system drawing and piping drawing, verify the position, and check whether the tools and materials are appropriate.

(2) Pickling, neutralization, passivation, sealing, etc.

3.2 Transformation requirements

(1) Oil pipeline groove, all the use of argon arc welding, a welding joint is divided into three welding, reduce the stress concentration after welding, welding seam to protrude more than the pipeline, joints and other welding parts of the height. After the welding is finished, it should be cleaned with dry compressed air and cooled naturally.

(2) 8 hoses are added at the outlet of the pumping station to reduce shock and vibration.

(3) The site as far as possible to go straight pipe (as far as possible with standard length, easy to use), less elbow, elbow, multi-purpose support, pipe clip; Pipeline does not use stamping elbow, the use of pipeline bending (hydraulic bending machine cold bending). The bending Angle meets the specification.

(4) The pipe tee no longer uses the stamping elbow, but uses the machine-made reducing tee, in order to increase the pressure resistance of the tee.

(5) In the grate cooler air chamber, the U-bend at the end of the hydraulic pipeline is directly bent by seamless steel pipe.

(6) At the lowest point of the entire hydraulic pipeline, a pressure relief valve is installed on each tubing for inspection and maintenance.

(7) Refine the pipeline after flushing and pressing meet the requirements, carefully check whether the joints and seals are damaged, and solve the problems in time if found. Apply anti-rust paint to the pipeline after all the above problems.

04 Transformation Effect

In a few years after the renovation, there was only one oil seepage phenomenon in the main tee. Since our tubing is of standard length, it is just enough to replace a standard tubing directly outside the ventilation room without welding during operation. The revamping reduced maintenance work, reduced fuel loss, avoided accidents (fires) and reduced production.

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