If It’s Leaking, Think Before Tightening
EP Editorial Staff | February 8, 2016
Your natural inclination to stop a leak could lead to greater problems.
By Henri Azibert, Technical Director, Fluid Sealing Association
Whenever a piece of equipment is leaking, our natural inclination is to tighten whatever can be tightened. Applying more compression on the sealing element is typically assumed to be the solution. The expectation is that the tighter the fastener and the greater the clamping force, the higher the level of sealing performance. Unfortunately, this is not necessarily the case and, quite often, will make matters worse—much worse. Given the fact that safety should always be a primary concern, working on pressure-containing equipment requires careful thinking before any remediation is considered and implemented.
Flanges sealed with a gasket should have been tightened with a torque wrench according to the manufacturer’s specifications. The gasket compression loading must take into consideration, among other factors, the process pressure, process temperature, and the gasket material and style. This assumes using new bolts and an appropriate lubricant to achieve an accurate clamping stress from the torque level.
In case of a problem, tightening the bolts will often make conditions deteriorate. The gasket could be crushed and damaged. An elastomeric gasket could be extruded. The flange could become deformed. Further tightening will only exacerbate the leakage.
Personnel are expected to adjust compression packing on pumps to achieve desired leakage levels. While adjustments to reduce leakage are standard procedures, they should only be minor. If improvements aren’t quickly realized, you may have a significant problem on your hands. Extrusion, excessive sleeve wear, chemical attack, radial motion, and other factors can’t be remedied by increased compression. In those cases, increased tightening will aggravate the wear process.
Similar considerations apply to valve packing. Leakage levels are expected to be minimal. If those levels become excessive, only very small, incremental adjustments should be made—after first verifying that the originally specified torque levels are present on the gland packing bolts.
Mechanical seals typically aren’t subject to adjustments to reduce leakage. That said, there are some cases where tightening comes into play.
When the stationary seal ring is of a design that can be clamped, the clamping action can easily create distortion. A few millionths of an inch out of flatness will result in a leak. Any increased tightening of the gland bolts will worsen the condition.
Even when the seal ring isn’t clamped, it is often axially supported inside a gland plate. Deflection of the gland plate can be transmitted to the stationary seal face. In these cases, the only way to eliminate the leakage is to loosen the bolts.
The solution begins by confirming the specified torque requirements for the equipment—and verifying, with a torque wrench, whether those specifications had been met. If you don’t have time to research the situation, consider the possible implications of the leakage and what is most likely causing it. When it comes to leakage, your motto should be “Think twice, adjust once.” MT
Headquartered in Wayne, PA, the Fluid Sealing Association (FSA) is an international trade association of companies involved in the production and marketing of a wide range of fluid-sealing devices targeted mainly at industrial applications. Founded in 1933, the association continues to be recognized as, among other things, the primary source of technical information in the fluid-sealing area. For more information, visit fluidsealing.com. For more information on technical topics, email email@example.com.