API Plans 65A and 65B watch for liquid leaking past a single seal: the leakage drains by gravity to a detection vessel, and a level transmitter alarms when the level climbs, on 65A because the leak outruns an orifice in the drain line and on 65B because a closed drain valve lets it accumulate. API Plan 75 watches the inner seal behind a dry-running containment seal: its leakage collects in a reservoir that gives a high-level alert, and an orifice on the vent to the flare or vapour recovery turns heavy leakage into a high-pressure alarm.

What to do depends on which signal fired. A Plan 65B high-level alarm and a Plan 75 high-level alert are calls to drain the vessel. A Plan 65B high-high alarm and a Plan 75 high-pressure alarm point to a failed seal. A Plan 65A alarm means either a failed seal or a plugged orifice, and a look at the pump separates the two.

API Plan 65A and 65B

Plan 65 is the API 682 piping plan for catching leakage from an Arrangement 1 single seal: leakage leaves the gland drain, runs by gravity to a detection vessel mounted below the pump, and a rising level in that vessel raises the alarm.

What Plan 65 Monitors

Plan 65 monitors liquid leakage from a single seal to atmosphere: process fluid that gets past the seal faces and is directed by the throttle bushing out of the gland’s drain port.

The fourth edition of API 682 split the third edition’s single Plan 65 into Plan 65A, which keeps its orifice, and Plan 65B. API 682 treats the two as technically equivalent: either one meets a requirement for Plan 65.

Plan 65A vs Plan 65B

Plan 65A drains continuously through an orifice in the drain line and alarms on leakage rate; Plan 65B replaces that orifice with a normally closed block valve and alarms on accumulated leakage. Everything else is the same in both, including the throttle bushing in the seal gland.

Choose 65A when you want a failure alarm with no routine operator task. Choose 65B when you want to trend a seal’s leakage and catch the slow deterioration that 65A cannot see, and the site can keep up a draining routine.

Plan 65 Hardware

A Plan 65 system is a detection vessel below the seal with a level transmitter, a sloped drain line from the gland, and the outlet arrangement that makes it 65A or 65B.

  • Detection vessel: API 682’s fourth edition requires a Plan 65 detection vessel of at least 3 L (0.75 gal), treated as part of the pressure boundary.
  • Level transmitter: on the vessel, with a local readout. Systems built to the third edition’s single Plan 65 use a level switch instead, which alarms at one level and gives no trend.
  • Orifice or block valve: in the vessel’s drain outlet, an orifice on 65A and a normally closed block valve on 65B.
  • Bypass: lets heavy leakage go around the orifice on 65A, and sets the overflow level on 65B, so leakage does not back up into the pump bracket.
  • Drain line: falls continuously from the gland to the vessel, heat-traced where the product can freeze or solidify, with no strainer screens, because a plugged screen stops leakage from ever reaching the vessel.

What Triggers a Plan 65 Alarm

A Plan 65A alarm is triggered by a high level in the detection vessel, which only happens when seal leakage arrives faster than the orifice can drain it. Low flows, including the normal weepage of a healthy seal, pass the orifice with no level rise at all.

There is no general leakage rate at which a Plan 65A alarms. A Pump Users Symposium paper by a member of the API 682 task force explains why: vessel design and alarm level, orifice size and installed elevation vary so much between sites that no generalised figure can be given. What your alarm represents can only be established on your own installation.

Plan 65B has two level alarms. The high-level alarm, set below the bypass level, is a maintenance alarm telling the operator to drain the vessel. An optional high-high alarm sits between the high level and the bypass, and reaching it before anyone has drained the vessel means the seal is leaking fast enough to indicate a failure. Between alarms, the rate of level rise, or how often the vessel needs draining, is the seal’s condition signal.

What to Do When a Plan 65 Alarm Sounds

On a Plan 65A alarm, go to the pump and treat the alarm as a seal failure until what you see there says otherwise; on Plan 65B, drain the vessel at the high-level alarm and treat a high-high alarm as a failed seal.

A 65A alarm means either the seal is leaking heavily or the orifice is plugged and normal leakage is backing up. If the seal is leaking, a large leak of a hazardous fluid means shutting down and blocking in the pump, while a small one may allow running on to a planned seal change with the level watched.

A sudden, large seal failure can fill and overflow the pump bracket before the transmitter alarms. Heavy leakage seen at the bracket is a reason to stop the pump whatever the vessel level reads.

On Plan 65B the alarms map to actions directly:

  • High-level alarm: open the block valve, drain the vessel, close the valve again and log the date.
  • Shortening drain intervals: the seal’s leakage is increasing, so plan the seal replacement.
  • High-high alarm before draining: treat it as a failed seal and respond as for a heavy leak on 65A.

API Plan 75

Plan 75 catches leakage from the inner seal of a dual seal with a dry-running containment seal: the containment seal holds that leakage, the leakage drains from the containment cavity to a collection reservoir, and the reservoir’s level and pressure tell you the inner seal’s condition. The point of the alarms is to shut the pump down and isolate it while the containment seal is still holding.

What Plan 75 Monitors

Plan 75 monitors leakage from the inner (process) seal of an Arrangement 2 seal whose outer seal is a dry-running containment seal.

It is for leakage that condenses or stays liquid at ambient conditions, or is a mix of liquid and vapour. Leakage that stays entirely vapour belongs to Plan 76, and a fluid whose leakage is part liquid and part vapour can carry Plans 75 and 76 together.

Plan 75 Hardware

A Plan 75 system is a collection reservoir below the seal, a level gauge and level transmitter on it, a pressure transmitter, and a restriction orifice in the vent line to the flare or vapour-recovery system. API 682’s fourth edition calls for transmitters.

  • Collection reservoir: on the pump baseplate below the shaft, fed by gravity from the containment seal drain. Liquid stays in it; vapour passes on to the vent.
  • Level gauge and level transmitter: the gauge shows the level locally against high and low marks, and the transmitter carries the high-level alarm point to the control room.
  • Pressure transmitter: reads the collector pressure for the high-pressure alarm.
  • Restriction orifice and block valve: in the vent to the flare or vapour recovery. The block valve upstream of the orifice isolates the collector for maintenance.
  • Drain valve: empties the reservoir into a safe container or the site’s leakage collection.

What Triggers a Plan 75 Alarm

Two readings trigger a Plan 75 alarm: a high liquid level in the reservoir and a high pressure in the collector.

The level alarm sits at the high mark on the level gauge and is a drain alert. A change in how fast the reservoir fills is usually the first sign the inner seal is deteriorating.

The pressure alarm works through the vent orifice: when inner-seal leakage arrives faster than the orifice passes it to the header, collector pressure rises and the transmitter alarms. The setpoint has to sit above the flare or vapour-recovery pressure, or the header alone will set it off, and below the pressure in the seal chamber, or a failed seal may never reach it.

Set the high-pressure alarm as a margin above the vapour-collection-system pressure, on rising pressure, using the value on the seal’s nameplate or data sheet.

What to Do When a Plan 75 Alarm Sounds

Drain the reservoir on a high-level alert; shut down and isolate the pump on a high-pressure alarm.

Drain the reservoir down to the low mark before the end of the next work shift, and before the level climbs above the top of the gauge. Log every drain: when the interval between drains shortens, the inner seal’s condition has changed, and the seal change should be planned.

A high-pressure alarm means heavy inner-seal leakage, unless the machine or the vapour-collection header is running at abnormal pressure. API 682 requires a containment seal to hold full seal-chamber conditions for eight hours after an inner-seal failure.

Telling a False Alarm From a Failed Seal

To tell a false alarm from a failed seal, rule out whatever other than the seal can raise the level or the pressure before the seal is pulled.

On Plan 65A the usual cause is a plugged orifice. A Plan 65A alarm with a level that rose slowly and a seal that looks normal at the gland and bracket points to the orifice. Clear the drain line and orifice: if the level falls and stays down, the seal was not the problem, and if it climbs again with the orifice clear, the seal is leaking.

On Plan 65B the alarm most often mistaken for a failure is the high-level alarm; the failure signal is the high-high alarm arriving before the vessel has been drained.

On a Plan 75 high-pressure alarm, compare the collector pressure with the vapour-collection header pressure. If the header has risen and the collector sits only its usual margin above it, the header caused the alarm; a collector well above the header with the reservoir filling fast points to the inner seal.

The same comparison catches a mis-set alarm. A setpoint entered as a fixed gauge pressure, instead of a margin above the header, loses that margin whenever the header runs above atmospheric pressure, and the alarm can sound with no extra leakage.