Problems and Measures in High Sulfur Natural Gas Field Valves (Part One)
Dec 06, 2023
In the realm of natural gas extraction, high-sulfur natural gas fields present unique challenges. The presence of sulfur compounds in these fields necessitates the use of specialized valves to ensure safe and efficient operations. High-sulfur natural gas field valves serve a vital role in ensuring safe and efficient operations in challenging environments. Their ability to resist corrosion, handle extreme conditions, provide effective sealing mechanisms, and undergo regular maintenance makes them indispensable components in the extraction process.
High-sulfur gas field valves have harsh working conditions, high acidity, and many impurities. Since they were put into production, they have not been properly and periodically maintained. There is no standardized historical operation data for the status and function of the entire valves, and it is impossible to carry out targeted purchasing and maintenance plans for complete valves and spare parts.
1. The problem with the gearbox
On-site reports of gearbox valves in high-sulfur gas fields often indicate that they cannot be opened or closed. More than half of these problems are caused by gearboxes. Since the gearbox body is generally made from carbon steel, it is easily corroded and rusted. Rainwater seeps into the connection between the valve indicator and the valve bonnet, accelerating the rust inside the wheel box. In addition, many valves have not operated for a long time, and rust has formed between the turbine and worm of the gearbox, and between the valve stem and the central shaft of the gearbox, causing them to become stuck and unable to operate.
1.1 Water accumulation in gearbox
The main sealing points of the valve gearbox driving mechanism include the joint surface between the valve position indicator piece and the gear shaft end, the joint surface between the gearbox cover and the gear shaft; the screw hole at the upper end of the gearbox cover and the joint surface between the gearbox cover and the gearbox, the joint between the bottom of the gearbox and the valve connecting plate. The specific structure is shown in Figure 1. Rainwater enters ball valves in high-sulfur gas fields mainly through the joint surface between the valve position indicator plate and the gear shaft end and the joint surface between the gearbox cover and the gear shaft. Rainwater is not easy to evaporate after entering. A large amount of water enters, causing the grease to emulsify and deteriorate, and it is not timely replaced, which can not provide lubrication and rust prevention.
Figure 1 Main sealing points of gearboxes
Solutions
Add grease. Clean the grease that has entered the rainwater and emulsified and deteriorated, including the valve bonnet, worm gear, valve stem, valve body and gearbox connecting plate, and fill the valve body, valve stem, gearbox connecting plate, and the inside of the gearbox with grease. Rainwater does not penetrate, which can not only achieve lubrication but also prevent rainwater from entering. Some gearboxes adopt a solution that is filled with grease. After being disassembled for an overhaul this year, it was found that rainwater did not enter the inside of the gearbox, and only the grease on the surface was slightly emulsified. This shows that this solution is suitable for the maintenance of gearboxes in high-sulfur gas fields.
After removing the deteriorated grease, adding new grease can prevent water accumulation. Use metal sealant. The rubber pad between the gearbox cover and the gearbox body is aged and damaged, resulting in sealing not being achieved. For ease of disassembly and repair and sealing, the metal sealant is chosen for sealing. Replace the sealing O-ring. Water accumulation inside the gearbox mainly occurs through the joint surface between the valve position indicator plate and the gear shaft end and the joint surface between the gearbox cover and the gear shaft. The former is a static seal, and the latter is a dynamic seal. In the maintenance process, it was found that the two had become hard and brittle, and did not have enough elasticity to achieve sealing. It is recommended that O-rings be purchased for replacement during overhaul next year.
1.2 Water accumulation in the gearbox
Most valves are operated infrequently and only opened and closed once every half a year or a year. For example, unused water-jacketed furnace ball valves at well stations, test separator valves, and valve chamber bypass pipeline valves are all rusted and stuck, and the valves cannot be operated. After disassembly, it was found that the gearbox valve cover, gearbox central shaft, and the joint between the gearbox central shaft and the valve stem were rusted and stuck. At the same time, there was also rust at the bottom of the turbine, the gearbox, and the turbine worm, causing excessive torque and preventing the valve from opening and closing. When valves in high-sulfur gas fields become stuck during maintenance, in addition to internal corrosion of the gearbox, the other cause is damage to the gearbox body structure, such as bearing fractures, and positioning pin grinding.
Solutions
For the situation where the valve is rusted and cannot be opened, remove the gearbox and soak it in WD-40 diesel to remove rust. Polish the contact surface. Remove the modification and apply enough grease; open and close the valve 1 to 3 times to ensure that the valve can be opened and closed normally. Disassemble and inspect the valve during the annual overhaul, and open and close the valve 1 to 3 times to ensure that the valve is not corroded or stuck. For jamming caused by damage to internal parts of the gearbox, after on-site processing and grinding, the working conditions must be recorded at any time. If there is any abnormal noise or it gets stuck again, it needs to be dealt with promptly and new spare parts purchased for replacement. Gearboxes are consumables, and a batch of gearboxes can be purchased as spares. The on-site valve models are not many, and the gearbox specifications are not many. Purchase spare parts for the entire gearbox to reduce production losses caused by the valve being unable to operate due to the gearbox being stuck and unable to open and close.
1.3 Limit error
In the internal leakage detection process of high-sulfur gas field valves, it was found that the opening and closing of the gearbox were abnormal, and the valve could not seal at the normal sealing surface position, resulting in internal leakage of the valve. After moving back 1/4 turn to 1 turn of the open position, the valve seals correctly and there is no internal leakage. Keep the valve in the normal sealing position; adjust the gearbox limit bolt and re-lock it, and the valve will be in the normal position. After the valve is operated for a long time, the worm gear in the gearbox will wear out. Excessive operating torque will deform and loosen the keyway. At the same time, the mechanical limit of the valve itself will also be damaged due to excessive torque. On-site operators believe that the internal leakage of the valve is caused by not closing the valve to the position, so they will use the booster rod to perform high-torque switching operations, which cannot solve the problem of internal leakage of the valve. Instead, it will cause problems with the connection and limit of the gearbox and valve. Therefore, it is recommended that if it is difficult or impossible to open the valve on site, you should contact the valve maintenance team for diagnosis and repair, and then operate after determining the problem.
1.4 Loose actuators
The size of key ball valves in high-sulfur gas fields exceeds 6 inches, and the valve gearboxes are mostly two-stage transmission mechanisms. The handwheel shaft, worm shaft worm shaft and external fixing bolts of the gearbox have become loose due to the lack of maintenance for a long time. The entire gearbox is loose. At the same time, the rolling bearings at both ends of the worm are cracked and damaged, causing the handle to become loose and misaligned, and the opening and closing of gearboxes to become stuck.
Solutions
After finding looseness on site, tighten it in time and perform a movable test to ensure that it does not affect the normal opening and closing of the valve. At the same time, a series of problems such as missing or deformed handwheel positioning pins, damaged or missing handwheels, missing fixing bolts and missing cover bolts should be discovered and solved promptly on site. At the same time, in view of the low maintenance value of manual gearboxes and a few gearbox models on site, it is recommended to purchase 1 to 3 entire gearboxes and spares of the same model to deal with emergencies that cannot be repaired on site.
High-sulfur gas field valves have harsh working conditions, high acidity, and many impurities. Since they were put into production, they have not been properly and periodically maintained. There is no standardized historical operation data for the status and function of the entire valves, and it is impossible to carry out targeted purchasing and maintenance plans for complete valves and spare parts.
1. The problem with the gearbox
On-site reports of gearbox valves in high-sulfur gas fields often indicate that they cannot be opened or closed. More than half of these problems are caused by gearboxes. Since the gearbox body is generally made from carbon steel, it is easily corroded and rusted. Rainwater seeps into the connection between the valve indicator and the valve bonnet, accelerating the rust inside the wheel box. In addition, many valves have not operated for a long time, and rust has formed between the turbine and worm of the gearbox, and between the valve stem and the central shaft of the gearbox, causing them to become stuck and unable to operate.
1.1 Water accumulation in gearbox
The main sealing points of the valve gearbox driving mechanism include the joint surface between the valve position indicator piece and the gear shaft end, the joint surface between the gearbox cover and the gear shaft; the screw hole at the upper end of the gearbox cover and the joint surface between the gearbox cover and the gearbox, the joint between the bottom of the gearbox and the valve connecting plate. The specific structure is shown in Figure 1. Rainwater enters ball valves in high-sulfur gas fields mainly through the joint surface between the valve position indicator plate and the gear shaft end and the joint surface between the gearbox cover and the gear shaft. Rainwater is not easy to evaporate after entering. A large amount of water enters, causing the grease to emulsify and deteriorate, and it is not timely replaced, which can not provide lubrication and rust prevention.
Figure 1 Main sealing points of gearboxes
Solutions
Add grease. Clean the grease that has entered the rainwater and emulsified and deteriorated, including the valve bonnet, worm gear, valve stem, valve body and gearbox connecting plate, and fill the valve body, valve stem, gearbox connecting plate, and the inside of the gearbox with grease. Rainwater does not penetrate, which can not only achieve lubrication but also prevent rainwater from entering. Some gearboxes adopt a solution that is filled with grease. After being disassembled for an overhaul this year, it was found that rainwater did not enter the inside of the gearbox, and only the grease on the surface was slightly emulsified. This shows that this solution is suitable for the maintenance of gearboxes in high-sulfur gas fields.
After removing the deteriorated grease, adding new grease can prevent water accumulation. Use metal sealant. The rubber pad between the gearbox cover and the gearbox body is aged and damaged, resulting in sealing not being achieved. For ease of disassembly and repair and sealing, the metal sealant is chosen for sealing. Replace the sealing O-ring. Water accumulation inside the gearbox mainly occurs through the joint surface between the valve position indicator plate and the gear shaft end and the joint surface between the gearbox cover and the gear shaft. The former is a static seal, and the latter is a dynamic seal. In the maintenance process, it was found that the two had become hard and brittle, and did not have enough elasticity to achieve sealing. It is recommended that O-rings be purchased for replacement during overhaul next year.
1.2 Water accumulation in the gearbox
Most valves are operated infrequently and only opened and closed once every half a year or a year. For example, unused water-jacketed furnace ball valves at well stations, test separator valves, and valve chamber bypass pipeline valves are all rusted and stuck, and the valves cannot be operated. After disassembly, it was found that the gearbox valve cover, gearbox central shaft, and the joint between the gearbox central shaft and the valve stem were rusted and stuck. At the same time, there was also rust at the bottom of the turbine, the gearbox, and the turbine worm, causing excessive torque and preventing the valve from opening and closing. When valves in high-sulfur gas fields become stuck during maintenance, in addition to internal corrosion of the gearbox, the other cause is damage to the gearbox body structure, such as bearing fractures, and positioning pin grinding.
Solutions
For the situation where the valve is rusted and cannot be opened, remove the gearbox and soak it in WD-40 diesel to remove rust. Polish the contact surface. Remove the modification and apply enough grease; open and close the valve 1 to 3 times to ensure that the valve can be opened and closed normally. Disassemble and inspect the valve during the annual overhaul, and open and close the valve 1 to 3 times to ensure that the valve is not corroded or stuck. For jamming caused by damage to internal parts of the gearbox, after on-site processing and grinding, the working conditions must be recorded at any time. If there is any abnormal noise or it gets stuck again, it needs to be dealt with promptly and new spare parts purchased for replacement. Gearboxes are consumables, and a batch of gearboxes can be purchased as spares. The on-site valve models are not many, and the gearbox specifications are not many. Purchase spare parts for the entire gearbox to reduce production losses caused by the valve being unable to operate due to the gearbox being stuck and unable to open and close.
1.3 Limit error
In the internal leakage detection process of high-sulfur gas field valves, it was found that the opening and closing of the gearbox were abnormal, and the valve could not seal at the normal sealing surface position, resulting in internal leakage of the valve. After moving back 1/4 turn to 1 turn of the open position, the valve seals correctly and there is no internal leakage. Keep the valve in the normal sealing position; adjust the gearbox limit bolt and re-lock it, and the valve will be in the normal position. After the valve is operated for a long time, the worm gear in the gearbox will wear out. Excessive operating torque will deform and loosen the keyway. At the same time, the mechanical limit of the valve itself will also be damaged due to excessive torque. On-site operators believe that the internal leakage of the valve is caused by not closing the valve to the position, so they will use the booster rod to perform high-torque switching operations, which cannot solve the problem of internal leakage of the valve. Instead, it will cause problems with the connection and limit of the gearbox and valve. Therefore, it is recommended that if it is difficult or impossible to open the valve on site, you should contact the valve maintenance team for diagnosis and repair, and then operate after determining the problem.
1.4 Loose actuators
The size of key ball valves in high-sulfur gas fields exceeds 6 inches, and the valve gearboxes are mostly two-stage transmission mechanisms. The handwheel shaft, worm shaft worm shaft and external fixing bolts of the gearbox have become loose due to the lack of maintenance for a long time. The entire gearbox is loose. At the same time, the rolling bearings at both ends of the worm are cracked and damaged, causing the handle to become loose and misaligned, and the opening and closing of gearboxes to become stuck.
Solutions
After finding looseness on site, tighten it in time and perform a movable test to ensure that it does not affect the normal opening and closing of the valve. At the same time, a series of problems such as missing or deformed handwheel positioning pins, damaged or missing handwheels, missing fixing bolts and missing cover bolts should be discovered and solved promptly on site. At the same time, in view of the low maintenance value of manual gearboxes and a few gearbox models on site, it is recommended to purchase 1 to 3 entire gearboxes and spares of the same model to deal with emergencies that cannot be repaired on site.
