A piping plan gives everyone a common language, but the plan number by itself doesn’t guarantee the installation will work. Each plan has a job to do and limits on where it can do it. The work is making sure the system as built does that job in your process and at your site.
01 Choosing a plan out of habit
Two similar pumps can be handling fluids with very different vapor pressure, solids content, viscosity or temperature. Those differences decide whether the seal needs cooling, an external flush, product circulation or pressure control to help keep contamination out, and one plan won’t always cover what is needed.
02 Ignoring layout
Tubing length, elevation, restrictions, cooler location, venting and drainage all affect circulation and how easy the system is to maintain. A good schematic can be undone by an installation that traps gas, adds resistance, or makes the system hard to fill and inspect.
A system can match the spec and still run poorly.
03 Getting the pressure relationship wrong
This matters most on dual seals. Alarm settings and refill practices need to match whichever arrangement you have.
UNPRESSURIZED
Buffer < Process
The buffer fluid runs below process pressure, and you monitor and manage leakage differently. A liquid level rise in the reservoir indicates a primary seal issue.
PRESSURIZED
Barrier > Process
The barrier fluid pressure must stay above maximum seal chamber pressure. Barrier fluid consumption will be measured by either liquid level (53a, 53c) or pressure (53b)
04 Treating instruments as an afterthought
Pressure, temperature, level, flow and leakage indication give early warning and help you tell normal consumption from a developing problem. They need to measure something useful, and someone has to be able to reach them when it’s time to check.
Start with the function
When I review a system, I start with three questions:
- What does the seal need from it?
- What could cause that to be lost?
- How would we know early?
Once those are answered, the plan number is just the label on the answer.
FIELD CHECKLIST
Before you sign off a seal support system
- Plan chosen for this fluid’s vapor pressure, solids, viscosity and temperature
- Tubing runs, elevation and cooler location support circulation
- System vents, drains and fills without trapping gas
- Barrier or buffer pressure confirmed across the full operating range
- Alarm settings and refill practice match the pressure philosophy
- Instruments read something useful and are reachable
Use with your plan’s functional requirements.
KEY TAKEAWAYS
- Choose the plan for the job it has to do and the fluid you actually have.
- Check layout, circulation resistance, venting, filling and maintainability.
- Settle the pressure philosophy and instrumentation before commissioning.