6 key points for quality verification of threaded lock ring heat exchangers
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When maintaining threaded lock ring heat exchangers, special attention must be paid to bolt removal, thread protection, handling of the sealing system, use of specialized tools, temperature difference control, torque management, measures to prevent sticking, and safety precautions. The specific considerations are as follows: 1. Bolt removal and thread protection – For high-temperature bolts, it is necessary to reduce their temperature to around 200°C before removal; diesel should be poured on them to prevent thermal adhesion, thereby avoiding damage to the threads caused by forced removal. As soon as each bolt is removed, apply a high-temperature anti-galling agent and screw it back into the threaded hole to prevent leaks of the medium from causing injury. Technique for removing bolts: If the bolt is stuck to the locking ring, an enlarging drill bit (with an outer diameter 3 mm smaller than the bolt’s diameter) can be used together with a triangular file to create a groove 0.5 mm deep, thereby allowing the bolt to be removed in sections. Violent striking is strictly prohibited to prevent bolt breakage or thread damage.
Technique for removing bolts: If the bolt is stuck to the locking ring, an enlarging drill bit (with an outer diameter 3 mm smaller than the bolt’s diameter) can be used together with a triangular file to create a groove 0.5 mm deep, thereby allowing the bolt to be removed in sections. Violent striking is strictly prohibited to prevent bolt breakage or thread damage. II. Handling of the sealing system – After disassembly, it is necessary to check the deformation and corrosion of the gaskets in the tube side and shell side (such as bimetallic wave-patterned composite gaskets and 022Cr12 stainless steel gaskets), and replace them if necessary. Before installing the gasket, the sealing surface must be cleaned to ensure there are no impurities or scratches. When adjusting and removing the split key rings of the sealing disc and the split-ring assembly, follow the counterclockwise marking sequence from the bottom: first remove the three pieces with slopes, then remove the remaining ones in sequence, and place them according to their numbers and the marking sequence to avoid incorrect installation. During reinstallation, the gap of the split key ring must be adjusted to ensure even sealing.
III. Special Tools and Operating Procedures: When removing pressure sleeves and pipe bundles, it is necessary to use a crane to lift the thread protection sleeve and secure it to the bolts on top of the pipe tray cover, thereby protecting the large threads of the locking ring from damage. When connecting the pressure sleeve to the tube bundle, ensure that the special tools are used to create a secure connection; use weights to achieve balance, and pull out slowly to prevent skewing and forceful core extraction. For torque control and balanced removal of the threaded lock ring, first use a small hook to lift the fixture in order to achieve balance; then gently lift the bolt with a large hook. Once it is loosened, use the large hook to hold the fixture steady while using the small hook to move the bolt, thereby avoiding thread deformation caused by uneven force application. When reinstalling, the outer ring bolts should be tightened diagonally to prevent the gasket plate from warping, and then tightened to the specified torque to ensure that the compression amount of the gasket meets the requirements.
IV. Temperature difference control and anti-seizure measures: The temperature difference removal method involves heating the tube box using a 10kW electric heating element, while simultaneously cooling the locking ring with dry ice to create a temperature difference of 80°C. This causes the thread clearance to increase by 1.4–1.5 mm, thereby reducing the resistance to disassembly. Suitable for situations where threads are seized or severely corroded. For lubrication and rust prevention, before disassembly, the bolts must be soaked in a mixture of kerosene, loosening rust remover, and lubricant for more than 12 hours to remove debris from the threads. Lubricant must be injected again before reinstallation to ensure smooth thread rotation.
V. Safety Protection and Emergency Measures: Maintenance personnel must wear heat-resistant gloves, goggles, and gas masks to prevent exposure to splashing hot fluids or toxic gases. Warning signs should be placed around the exhaust ports, drain ports, and oil filling holes to prevent people from approaching them. According to the emergency response plan, in the event of a broken bolt or seized threads, operations must be stopped immediately. A drill should be used to create a hole in the center of the bolt, after which a hammer can be used to break it into pieces so that it can be removed, thereby preventing further damage. Emergency equipment such as fire extinguishers and first-aid kits are available on site to ensure a rapid response.
VI. Quality inspection after maintenance – Pressure test on the shell side: The pressure value is calculated using a correction factor based on the temperature of the heat exchange tubes (e.g., 4.67 MPa); the verification formula is δT = 1.235δ, to ensure there are no leaks. Piping pressure testing: The pressure in the piping system must always be higher than that in the shell side, with the pressure difference being ≤ 3.0 MPa; special attention is paid to verifying the strength margin of the internal bolts at 4.67 MPa. The leak detection pipe fittings are tested for sealing integrity using the 10% ammonia leak detection method at a pressure of 1.0 MPa, to ensure there are no minor leaks. The welds must undergo 100% radiographic testing (JB4730 Level 2) and magnetic particle testing (Level 1) to ensure welding quality