Analysis of the causes of leakage and bulge of ultra-high pressure hose

At present, whenever the main engine exhaust valve is replaced and repaired or the cylinder head bolts are removed and assembled on board, the ultra-high pressure hydraulic hose and hydraulic tensioner are used. Different models, its design disassembly oil pressure may be different. On the 7G80ME-C model, the specified oil pressure (parameter T76-02) during assembly is 2200bar. The oil pressure of the loosened Studs nut (parameter T76-01) during disassembly is 2200~2400bar.During the maintenance period, the high pressure hose suddenly burst when pressurized, which brought great safety risks to the disassembly work, and now share with you.One: the bulge phenomenon of ultra-high pressure hydraulic hoseOne time, when the cylinder head bolt was dismantled by pumping, the second tube wheel of the pneumatic booster pump was operating at a pressure of 2100bar, and suddenly shouted that the oil pressure could not fall, so as to check whether the hydraulic tensioner was leaking oil. The motor staff standing near the cylinder head immediately responded, let it relieve pressure, Shouting that the tubing joint was bulging, and scared everyone to retreat quickly. Fortunately, this time the pressure was relieved quickly and no tube burst.During the pressure boost period, when the hydraulic tubing bulging or the tensioner leaking, the following phenomena will occur:1: The oil pressure gauge pointer of the pneumatic booster pump will suddenly drop a little, although the pneumatic pump is pumping oil in the "boom boom" action, but the oil pressure gauge pointer will not see signs of recovery.2: There is a bulge phenomenon at the tubing joint or a bulge phenomenon in a section of the tubing, and the former is often encountered.3: or hydraulic tensioner oil leakage phenomenon, the actual work is also often encountered.In view of the above danger, in order to understand the seriousness and harm of its consequences, I specially searched the Internet for the pressure of the discharge chamber of the bullet, and compared the two, I know the power of the disassembly oil pressure value.Although this parameter (disassembly oil pressure value) is lower than the pressure in the shell of the domestic Type 95 5.8mm light machine gun at the time of firing a 2.5cm bullet with a muzzle energy of 284.3MPa [muzzle kinetic energy of 1952J, speed of 930m/s, tube length of 463mm], it also has enough lethality and penetration. If the Type 87 5.8 mm ordinary round is used, the machine gun can penetrate 10 mm thick A3 steel plate at a distance of 300 meters; At a distance of 600 meters, the warhead runs through a 14-centimeter thick pine board, which shows the large momentum and strong impact force of the instant it exits the chamber (Note: The above machine gun data comes from the network).Two: ultra-high pressure hose structure and technical parametersThe ultra-high pressure hose is composed of a tube core, a shell, a rubber layer, a steel wire layer, etc., and is equipped with joints or flange heads at both ends for conveying flexible components of various media. A German company produces ultra-high pressure hoses with working oil pressures up to 4000bar (400MPa). The hose structure is generally composed of an inner rubber layer, an inner rubber fabric protective layer, a wire winding layer, a middle rubber layer and an outer rubber layer.The inner adhesive layer contains the fluid medium, and the material is made of polyformaldehyde (POM) or polyamide (PA).The reinforcement layer is a skeleton, specially treated high-strength steel wire winding layer, which can ensure the pressure, the number of reinforcement layers is generally from 1 layer to a maximum of 6 layers, according to different pressure specifications, some reinforcement layers are woven with steel wire.The outer adhesive layer is used to protect the reinforcing layer and is composed of polyamide (PA) or polyurethane (PUR).Hose fluid resistance is small, small dissolve expansion, good chemical corrosion resistance, light weight, small outside diameter, single length up to 1200M.Hose joints are made of high-quality carbon steel or stainless steel, the use of international advanced clamping equipment and technology, with a high safety factor and application reliability.Material and application of ultra-high pressure wire wound hoseLining: nylonReinforcing layer: high tensile special steel wireOuter coating: polyurethaneTemperature range: -40°C to 120°CProduct features: resistance to all kinds of grease, acid and alkali, aging resistance, wear resistanceScope of application: hydraulic tool pipe, ultra-high pressure cleaning pipe, high pressure oil pump pipe and other equipment requiring ultra-high pressureThree: ultra-high pressure hydraulic hose use and safety precautions(1) : Ultra-high pressure hose use/storage/handling precautions1: Check the outer surface and joints of the hose before use. If the external adhesive layer is visually foamed, brittle, hardened, cut, corroded (the wire mesh is exposed); The joint is broken and there is slip or corrosion on the hose, and its elastic seal fails; The hose flex is flattened or twisted; The above phenomenon should be replaced with a new hose. In particular, if the hose is stored for many years, if it is visually covered with cracks and rust, etc., pressure testing should be done before use. The test pressure is generally 2 times the working pressure, the pressure is maintained for 60 seconds, no leakage, no pressure drop. Its burst pressure is generally 4 times the working pressure value.2: Select the oil pressure distribution block according to the use requirements, connect the hose, ensure that the quick connector is installed in place (some quick connector with a lock ring buckle, the lock ring buckle after the connector is installed in place), straighten the hose and maintain a certain amount of slack, do not pull too tight, so as to avoid additional stress after pressure.3: Before pumping, check again whether the connection of the hose quick connector is proper and firm to prevent the quick connector from falling off during the pressure boost. At the initial stage of pumping, it is necessary to observe whether the quick joint joints and hydraulic cylinders leak oil. During the period from the pump to the high pressure, it is necessary to maintain a safe distance between the team personnel and the hydraulic hose and the tensioner, and the oil pump operator should keep an eye on the oil pressure gauge and declare the real-time oil pressure so that the team personnel can understand the oil pressure in the pipe. Other relevant designated personnel of the team shall be responsible for checking the working conditions of each hydraulic hose section, hose joint and hydraulic tensioner. If any abnormal phenomena such as oil leakage and bulging are found, they shall immediately inform the oil pump operator for rapid pressure relief. During the high pressure holding stage, the related personnel of the team should quickly loosen all Studs nuts, and the number or Angle of loosening should be roughly the same. During pressure relief, the oil pump operator should slowly open the pressure relief valve to relieve pressure. During pressure relief, the nut should be continuously rotated around and around to confirm that it is not stuck. Only after confirming complete pressure relief can you unplug the tubing quick connector.It can be seen that during the pressure period, the team members should concentrate on cooperating with each other, working together, and sharing risks to ensure safety.4: During the pressure period, slowly boost and relieve pressure to avoid pressure shock. And the working oil pressure must be equal to or less than the maximum pressure of the hydraulic system (the pulse pressure or peak pressure of the hydraulic system). When used on the ship, special personnel should be assigned to control the pneumatic booster pump, once not in use, the air tube should be removed immediately to avoid misoperation.5: Keep the working oil temperature in the specified range, generally between -40 ° C and +100 ° C, which is generally able to meet the requirements on board.6: During use, avoid rapid bending of high pressure hose. If the bending radius is less than the recommended value, the strength of the high-pressure hose will be seriously affected, including the hose joints must have a reasonable overbending area. Otherwise, the outer steel wire of the reinforcement layer will be stretched and the inner steel wire will be compressed, which will reduce the compressive strength of the entire ultra-high pressure hose, bring safety risks, and affect the service life of the hose.7: During the pressure period, the high pressure hose should be avoided due to stretching, compression, distortion, or friction at an acute Angle and damage, should not be used in a torsion state, can not disturb (shake) the hose quick connector.8: Regular inventory check, the ship should have appropriate specifications and quantities of qualified spare parts, in case of urgent needs. The length of the oil pipe required by the hydraulic tensioner on the ship is generally 1.5 meters, 3 meters, and 5 meters. If you need to apply for spare parts, be sure to apply according to the instructions on the manual, and note the relevant technical parameters of the hose if necessary, so as not to delay the use of wrong supplies.9: Regarding the storage and service life of the hose, the coil should be placed flat, but special attention should be paid to the bending of the section near the hose joint to be slowly folded. The joint should be coated with anti-rust oil and plastic protective cover to prevent dust from entering the pipe. Due to environmental factors such as temperature, humidity and light, its validity period is difficult to determine.10: During the handling of high-pressure hoses, it should not be dragged on sharp and rough surfaces, let alone excessive bending and flattening, and should always be handled with care.(2) : Personal protection and safety precautions when using ultra-high pressure hoses1: Wear appropriate PPE, always wear safety goggles and protective gloves when using hydraulic stretchers.2: At the pre-work meeting, publicize the risk points of using hydraulic tools and emphasize the risk. Reasonable allocation of team personnel, designated special persons are responsible for the operation of pneumatic booster pump and hydraulic tensioner. During the pressure period, designate a special person to check the working conditions of the hydraulic hose and joints, as well as the hydraulic tensioner.3: Pay attention to the position, always keep away from the upper area of the tensioner during the pressure process, it is possible to break the bolt and cause sudden spring injury.4: Before using hydraulic tools, the operator must carefully read the relevant instructions (including pneumatic booster pumps and hydraulic tensioners). And carefully operate the relevant valves in order to avoid damaging the pressure gauge.5: Keep the work site clean and orderly.Four: Analysis of the causes of leakage and bulge of ultra-high pressure hose1: Product quality problems:① : Materials selected for high-pressure hose production are not qualified.② : poor production process: uneven wall thickness of flexible pipe; The wire braid is too tight, too loose or the number of wire layers is too few; The amount of deformation (elongation, shortening or bending deformation) of the hose after pressure is large; Poor outer rubber air tightness leads to corrosion of steel wire; The sealing property of the inner layer is poor, which makes the high pressure oil easily enter the wire layer. The adhesive force between the rubber layer and the steel wire layer is too small. The above conditions will reduce the pressure of the hose, and eventually burst in the weak point of the pipe wall.③ : The joint clamping process of the high-pressure hose is poor, resulting in oil leakage and bulge at the connection of the hose and the joint. Or the high pressure oil directly leaks into the steel wire layer from the joint pressure holding point, and then squirts out to the end of the outer rubber layer along the crack between the steel wire, or constantly along the steel wire layer to a place for pressure storage expansion, causing the outer rubber to bulge or even break.④ : The material selection of the joint is not qualified, and the deformation occurs during the clamping process, which affects the clamping quality and sealing, and makes the hose leak or bulge in use.2: Improper use problem:① : The working pressure is higher than the rated value or is extremely unstable, the operation of the oil pump or valve is too fast, resulting in violent and frequent pressure pulses, resulting in high pressure hose bulge tearing oil leakage.② : During the operation, the high-pressure hose is abnormally twisted, rapidly bent, smashed by heavy objects, and hurt by sharp instruments.③ : improper selection, the rated pressure of the high pressure hose does not match the actual oil pressure value specified in the manual. Generally, the high-pressure hose should be selected according to 1.5 times the actual working pressure of the hydraulic tensioner. For industrial production, it is recommended to use high-pressure metal hoses that are resistant to pressure and temperature.④ : Improper storage, resulting in high pressure hose erosion, mechanical damage and premature aging deterioration.⑤ : The working oil temperature exceeds the rated value.⑥ : The service life of the high-pressure hose is too long, aging deterioration, and the damage of the inner rubber layer causes media leakage.Five: The severity of the injury caused by the rupture of the high pressure hose bulge:In fact, there are many cases of injury caused by high pressure tubing (including hydraulic oil, diesel oil, and high pressure gas) ruptured on the Internet, which is an injection injury. Some were shot in the wrist by high pressure oil, damaging soft tissue. Once the soft tissue or skeletal muscle is damaged, there will be a microcirculation disturbance, sterile inflammation, resulting in local swelling and pain. This requires immediate treatment by a doctor in a regular hospital. Depending on the condition of the injury, the doctor will generally debridement, disinfection, drainage, dressing, and in serious cases, surgery is required.Safety warning:1: High pressure oil may cause serious personal injury, hydraulic oil shot from the eye of the needle is even difficult to see with the naked eye, but it can shoot through the skin into the human body.2: Do not use any part of the body to contact the hose under ultra-high pressure.3: If you are injured by a high-pressure liquid (gas) jet, be sure to treat it as a medical accident and seek medical treatment immediately!4: The hose assembly pressure test should be away from the danger zone, and wear the correct personal protection.