A commissioned leakage limit gives operators a repeatable accept, investigate, or isolate decision for each hydrocarbon pump. Set that limit from the installed seal design, operating conditions, fluid hazards, containment arrangement, and mechanical-seal vendor guidance—not from a universal drip-rate rule.
Application and Acceptance Basis
Before anything else, confirm what is being observed and which seal arrangement is installed. A mechanical seal depends on a very thin fluid film between its faces for lubrication and heat removal. Fluid can cross this interface even when the seal is healthy, but it may evaporate, drain through a controlled path, or remain too small to appear as liquid at the atmospheric side. The statements “mechanical seals leak” and “mechanical seals do not leak” usually describe different boundaries: face-level leakage versus visible external release.
- Record the pump and seal identifiers from the equipment documentation. Obtain the seal arrangement, seal materials, seal chamber configuration, and auxiliary piping arrangement.
- Identify the process fluid and its relevant properties at the seal chamber: pressure, temperature, volatility, viscosity, lubricity, toxicity, and flammability.
- Define the observation boundary. State whether the limit applies at the seal faces, an atmospheric drain, a vent, a collection system, or the surrounding work area.
- Ask the mechanical-seal vendor for the expected leakage range and the leakage level that indicates damage for this specific application.
- Reconcile the vendor limit with the plant requirements arising from environmental controls and the applicable COMAH and DSEAR assessments. A mechanically tolerable release may still be operationally unacceptable.
Do not move on until the operating procedure identifies one observation point, one measurement method, and the authority that approved the acceptance limit.
Inspection and Measurement Preparation
Leakage changes with seal chamber pressure, seal-face velocity, fluid properties, and closing force. A reading has little diagnostic value unless those conditions are captured with it. Compare measurements only at equivalent operating states.
| Item | What to record | Why it matters |
|---|---|---|
| Pump state | Stopped, starting, steady operation, or shutting down | Separates transient wetting from steady leakage |
| Seal chamber condition | Measured pressure and temperature | Changes flashing, fluid-film behavior, and leakage |
| Operating point | Speed and process condition available to operators | Establishes repeatable face velocity and loading conditions |
| Auxiliary system | Valve lineup, vent condition, drain condition, and support-system status | Detects blocked or misrouted leakage paths |
| Observation point | Exact collection, drain, vent, or atmospheric location | Prevents measurements from different boundaries being compared |
Use a collection method compatible with the fluid and hazardous-area controls. Measure collected volume over recorded elapsed time and calculate leakage rate = collected volume / elapsed time. Do not count drops unless the procedure defines the drop-volume method; drop size varies with fluid properties and the discharge geometry.
Confirm that the selected point captures the intended release without including rainwater, washdown, flushing fluid, bearing lubricant, or leakage from nearby joints. Proceed only when the source and measurement boundary are unambiguous.
Leak-Path Identification
Before assigning a seal-face failure, locate the release path. Product near a seal can originate at the face interface, a gasket, a shaft sleeve connection, auxiliary tubing, a drain, or a vent. Venting can also prevent liquid accumulation and make an external surface appear dry while material still leaves the seal system.
- Inspect the seal gland, piping connections, drain, vent, and adjacent joints while the pump is in the defined operating state.
- Trace the liquid from its first visible point. Do not classify fluid found on a baseplate as seal-face leakage until the upstream path has been located.
- Confirm that vents and drains are open, routed correctly, and operating as the approved seal arrangement requires. Never treat venting as proof of zero release.
- Check for temperature-dependent flashing. A volatile hydrocarbon may cross the faces as liquid and become vapor before a visible drip forms.
- Verify that any collection or monitoring system is not blocked, full, bypassed, or returning fluid to another location.
The check passes when the observed material has been traced to a specific boundary and the vent and drain lineup matches the equipment documentation.
Stable Leakage Measurement
Take the acceptance reading only after the pump reaches the operating state defined in the procedure. Startup residue, condensation, and liquid retained from earlier operation can distort a short observation.
- Clean or clear the observation area using the site-approved method so old residue is not counted again.
- Start the measurement interval and record the pump state, seal chamber conditions, auxiliary-system lineup, and collection start value.
- Maintain the same operating state throughout the interval. If pressure, temperature, speed, or valve lineup changes materially, stop and repeat the measurement under stable conditions.
- Record the final collected volume and elapsed time, then calculate the rate using consistent units.
- Repeat the measurement to distinguish a stable rate from an intermittent release.
A correctly applied seal may show an almost insignificant rate—described for some applications as drops per day—but that observation is not a universal acceptance criterion. The installed seal vendor must translate the application conditions into a usable expected range. Do not move on until repeat readings agree closely enough for the plant’s measurement resolution and decision limits.
Acceptance and Corrective Decision
| Finding | Decision | Next action |
|---|---|---|
| Rate is stable and within the approved application limit | Accept for operation | Record the baseline and continue the defined inspection interval |
| Rate is below the mechanical limit but violates environmental, fire, exposure, or containment requirements | Do not accept | Apply the site response required by the COMAH and DSEAR assessments |
| Rate rises as chamber pressure, temperature, or speed changes | Investigate operating influence | Compare like-for-like conditions and review the duty with the seal vendor |
| Leakage comes from a vent, drain, connection, or gasket | Correct the identified path | Restore the documented lineup or repair the component under the maintenance procedure |
| Rate is unstable, increasing, or above the vendor damage threshold | Escalate or isolate | Follow the plant shutdown and maintenance criteria |
Do not tighten, adjust, or reconfigure seal components while operating unless the equipment procedure expressly permits it. Closing a vent simply to remove visible leakage can redirect pressure or conceal the release without correcting its cause. The decision check is complete when the measured rate maps to a documented action with no operator interpretation such as “minor drip” or “raging leak.”
End-to-End Verification
- Place the pump in the defined steady operating state and verify the documented auxiliary-system lineup.
- Inspect every identified leakage boundary, including vents, drains, connections, and the atmospheric side of the seal.
- Repeat the approved collection measurement and calculate the rate.
- Compare the result with the vendor’s application-specific expected range, damage threshold, and the plant’s tighter environmental or hazardous-release limit.
- Record the operating conditions, measured rate, observation point, disposition, and any maintenance performed.
- After any correction, repeat the entire measurement under equivalent conditions. Release the pump only when the source is identified, the rate meets every applicable limit, and the trend is stable.
Frequently Asked Questions
How do I set an acceptable mechanical seal leakage rate?
Obtain the expected range and damage threshold from the seal vendor for the installed arrangement, fluid, chamber pressure, temperature, speed, and closing force. Adopt the lowest limit required by that guidance and the plant’s COMAH, DSEAR, environmental, exposure, and containment controls.
How do I tell whether a mechanical seal is actually leaking?
Trace the release to its first visible point and inspect the gland, connections, vent, drain, and collection system. A dry atmospheric surface does not prove zero face leakage because a small release may evaporate or leave through a controlled path.
How do I verify a seal repair before returning the pump?
Run at the defined steady condition, confirm the auxiliary lineup, collect leakage at the same observation point, and calculate volume / elapsed time. Return the pump only after repeat measurements remain within both the vendor limit and the applicable site limit.