A leaking gate valve has the ability to disrupt any system’s efficiency, performance, and environmental compliance. This article discusses leaking gate valves, causes of leakage, types of leakages, repair options, and how to replace them.
Gate valves are typically used to either enable fluid to flow freely through a conduit or to entirely stop the flow. They are used in a variety of cutoff applications due to their easy operation mechanism, including waterworks, power generation, and gas production. Over time, these valves accumulate damage in various parts and could leak even in the close position. In industry, valve leakages are common, even in valves classified as bubble-tight. Instead of a rigorous zero leakage requirement, each type of valve has a different tolerance threshold.
The consequences of a leaky gate valve are determined by the type of leakage, of which there are two. The first is fugitive emissions, which occur when process fluid seeps into the atmosphere. The other situation is when a leak persists within the piping system. Both types are dangerous, but fugitive emissions do additional environmental damage.
Causes of a Leaking Gate Valve
- Corrosion:Corrosion is one of the most common reasons for valve leakage. Corrosion causes the valve parts in contact with the process fluid to lose material over time. The rate at which this occurs should be predicted during the design stage, and the required material corrosion allowance should be factored into valve selection.
However, petroleum elements in facilities such as a crude oil production plant may vary when the oil well is depleted. As a result, corrosion rates may accelerate and induce valve failure considerably sooner than expected. In such cases, consistent monitoring of the process fluid aids in minimizing leakage difficulties.
- Wear of valve parts:Aside from corrosion, additional variables can cause valve part wear. In oil and gas facilities, for example, the presence of sand or other solid debris causes the loss of valve material along the flow channel. This becomes worse at high flow rates, particularly in gas production.
- Obstruction of valve stem:When debris collects on the valve seat or other regions inside the body, it obstructs the stem’s movement. As a result, the valve port is completely closed.
- Variation in process conditions:Changes in temperature and pressure along the process, while the valve is in service, may cause bolting torques to relax, particularly in the stem packing area, resulting in leakage through this location. If this is the case, live loading must be necessary in the packing area.
- Wrong valve size:Although this is uncommon in industrial applications, it is possible to use the wrong valve size on a project. The result would be the same if the proper size valve was used, but its design was inadequate. Either of these would result in leaks since the valve would not properly close.
Types of Leakages and Repair Options
Leakage from Stem Packing Area:
When opening and closing, both old and new valves might leak at the stem packing and handle area, this is due to silt buildup preventing the valve from fully closing or causing the stem to stick in the open position. Furthermore, corrosion or erosion might cause the stem to wear away over time.
Leakage from the valve stem packing may imply a poorly designed valve, the use of an inadequate stem material, or the wrong valve size. One solution is to retighten the bolts or replace the stem packing. To achieve this:
Valve in a Pressurized System:
- Fully open the valve until the stem is flush with the bonnet.
- Loosen and remove the packing flange bolting nuts to free the packing flange and gland, as well as the old stem packing.
- Replace the stem packing with a new one and reinstall the packing gland and flange.
- Tighten the packing flange bolting nuts to the torque levels specified by the manufacturer.
- Turn on the valve to observe if the leak persists. If this occurs, tighten the packing flange nuts 1/8 turn at a time until it does not.
Leakage from Seat or Seal
Because the valve seat is always in contact with the fluid, it makes it vulnerable to corrosion. Furthermore, there is frequently a buildup of solid deposits around the seal, which might cause it to shift. Either way, leakage from the gland nut and connecting parts to the main valve body occurs.
Another risk of damage to the sealing or seating surface is excessive heat inside the seal cavity or insufficient flushing fluid. A drain arrangement for seat washing could be a possibility.
Leaks When Closing or Shut-off
In most facilities, gate valves function as the primary supply valve. As a result, they are often open or in a particular position for long periods, leading to debris buildup in the seating area. This may cause damage to the valve, cause some parts to be stuck, and leakages even when the valve eventually closes.
When a valve leaks in the closed position, confirm that the wedge is entirely closed and in full touch with the seat rings, as the valve might not be closing entirely because of buildups between the seat rings. Pipeline flushing is required if this is the case. If the leakage continues, a valve part has been damaged and must be replaced.
Leakage between Actuator and Valve
A gate valve in an industrial pipeline involves an actuator, which can be electric, hydraulic, or pneumatic, depending on the power source available. The valve responds to the operator’s signal by adjusting the stem to close or open the valve. Although it is uncommon, there are times when the stem design is inadequate, with it being either too short or too lengthy. As a result, there is a space between the seat and the spool, and the lax closure causes internal leakage. This can be fixed in a number of ways:
- The actuator and stem must be updated to suit standards.
- Straightening or tightening the stem nut and keeping it clean on a regular basis.
- Maintaining sufficient lubrication of the stem.
How to Replace Leaking Gate Valves
When a gate valve leaks, the first step is usually to repair or replace the defective component. However, in industrial applications where system downtime could be costly, replacing the complete valve is frequently the best solution.
In addition, intervention is time-consuming and costly in some applications, such as undersea pipes. Thus, compared to comprehensive replacement, changing a single item and incurring a substantial labor cost is dangerous and unnecessary.
Here are some helpful hints for fixing a leaking gate valve:
- Flush the valve: Because most leaking gate valves do not shut off fully due to debris, they must be unclogged before being replaced. To accomplish this, turn on the supply at the highest flow rate feasible, then slowly open and close the valve. After the debris has been removed, the valve can be fully closed. If this does not dislodge the debris, turn off the supply at the source.
- Isolate and heat the valve: To totally isolate the valve from the fluid, turn off the power supply. Because gate valves are frequently left in place for lengthy periods of time, the parts harden and become difficult to remove. As a result, it is frequently essential to heat the valve, particularly around the joints and stem handle.
- Disassemble the valve: Loosen the valve from its connection to the pipe or wall. Next, use pliers to loosen the bonnet and other valve parts. The packing nut is what holds the valve components together and prevents fluid from seeping up the stem. As a result, it should be removed as necessary.
- Install the new valve: Before installing the new gate valve, be sure that the valve is adequately sized for the installation and compatible with the process media. Engineers may wish to consider installing a ball valve instead of a gate valve at times. The disadvantages of a ball valve are a high proclivity for a water hammer and a higher price tag.