By Michael Huebner, Flowserve Corporation
Q&A: Plan 53 Start Up Considerations
Pump Engineer is proud to present Q & A | Plan 53 Start Up Considerations. This article will address the considerations that should be taken into account to ensure that a facilities start-up goes smoothly after the implementation of Plan 53. Readers are encouraged to ask questions for consideration in the future.
Q: A facility is preparing to start a new Plan 53 seal piping plan. What should be done ensure a proper start-up?
A: When commissioning a dual liquid seal piping plan, there are two main categories to consider: the unique characteristics of the Plan 53 system, and the ‘checklist’, or sequences of steps required for a successful start-up. It is not uncommon for an engineer or operator to simply walk up, give the system a cursory review, and start the system. In practice, it is always better to take a more systematic approach.
Differences in Piping Plan 53 Systems
In API 682, the term Piping Plan 53 does not refer to a single piping plan, but rather a family of plans which all serve the same basic function: to provide a pressurized barrier fluid to a dual liquid mechanical seal. Secondary functions include providing a supply, or ‘reservoir’, of barrier fluid to compensate for fluid losses during normal seal operation. This process provides a way to monitor seal performance (either directly or indirectly) through the consumption of barrier fluid. It also provides a method of controlling the barrier fluid temperature by transferring heat into either the environment or cooling water system.
The primary differences between the three Plan 53 options, Plans 53A, 53B, and 53C, is how the barrier fluid is pressurized. While all of these are effective at pressurizing the fluids, each has different operating characteristics which extends into the commissioning procedures.
Plan 53A – A Plan 53A is pressurized from an externally supplied pressurization gas (nitrogen). The pressure is set with a pressure regulator. In most sealing systems, this will be a non-relieving regulator to minimize the potential for process leakage reaching the atmosphere. The barrier fluid level will be maintained at a level near the middle of level indicator on the reservoir. Barrier fluid cooling is often provided by cooling coils internally to the reservoir.
Plan 53B – A Plan 53B is pressurized from a bladder accumulator connected to the barrier ¬ fluid circulation loop. The pressurization of the accumulator starts with pre-charging the accumulator based on the specific application requirements and ambient temperature. Barrier fluid is added to the system until the pressure reaches the refill pressure as indicated on the accumulator nameplate for the current ambient temperature (with a ¬floating alarm strategy). Barrier fluid cooling is provided by an air or water-cooled seal cooler.
Plan 53C – A piston accumulator is used to pressurize a Plan 53C. A reference line connects the bottom of the accumulator to a location in the pump (i.e., seal chamber) which provides the pressure source for the system. Note that prior to pressurizing the pump, the barrier ¬fluid pressure will be 0 PSIG since the seal chamber pressure is at 0 PSIG. The ‘level’ of barrier fluid will be indicated by the position of the piston extending from the top of the vessel. It is critical that the piston accumulator is not overfilled with barrier fluid especially at startup. Cooling is provided by either an air or water-cooled seal cooler.
There can be a significant difference in the specific steps required to start a seal system. This may be due to differences in the components used, the application conditions, regulations, or customer requirements. There are, however, some general steps which should be completed on any system. Many of these steps need to be completed long before the seal is installed and process fluid is added to the pump.
When a seal piping plan is selected, the end user must be aware of the requirements for the selected system. This includes not only the hardware and utility requirements, but also the responsibilities of the operators and maintenance personnel. They must be very familiar with the specific procedures for filling, pressurizing, monitoring, and refilling the system. The end user and seal/system OEM should define appropriate alarm points for the system based on the application and system instrumentation. This often includes: indicating maintenance requirements, monitoring seal leakage, or detecting component failures.
If a plant has the same system already in widespread use, training for these processes may only be a refresher; it can con rm that the new system is the same as existing systems. Training is extremely critical if a new piping plan is being introduced into a unit. If an operator has not previously used a Plan 53B or Plan 53C, there is a high probability that they will not start the system correctly based on their previous experience with a Plan 53A.
Before assembling and installing the piping plan, the end user should review the piping plan P&ID. This should include the specific pump number, seal, and piping plan components. If an end user is installing a single system, this may be straightforward. It can be become more challenging, however, if multiple systems are being installed into a new unit, or if an expansion is taking place. End users may pull system components such as reservoirs or seal coolers from their inventory, but it is critical that the correct components are used during the installation.
Seal systems can be provided in many different forms. In some cases, the end user will only purchase individual components and will pipe the systems in place themselves. In other cases, the seal OEM may provide a pre-engineered packaged system where all the components are pre-mounted and piped together on a common stand. Regardless of how the system is received, there is always the chance that the components, or system, may have become damaged or contaminated prior to installation. This is especially a concern if the components have been stored outside for any length of time. The end user and seal/system OEM should therefore inspect the equipment, correct any damage, and flush the system as appropriate.
The sealing system has very specific requirements for the mounting of the system components and interconnecting piping. Components, such as reservoirs or seal coolers, have specific mounting height requirements. Piping and tubing must be installed to promote venting and thermosyphoning in the system. The entire system must be designed so there is a low flow restriction in the barrier fluid circulation loop. This includes using large diameter tubing, smooth bends, short piping runs, and a minimum number of fittings.
The sealing system also includes the mechanical seal aspects of the installation. The end user and seal/
OEM must ensure that the seal is installed correctly. On a double-ended pump, there may be specific seal features designed for clockwise or counter clockwise rotation. The piping to the seal must be connected to the correct ports on the seal gland and the setting plates must be removed or positioned to allow for seal sleeve rotation.
Ensure that the instrumentation is connected into the plant DCS system. The operator should ensure that correct alarm points are established along with the appropriate alarm responses. Many end users will also use some of the monitored parameters for permissive in the pump commissioning; e.g., only allow pump startup if the barrier fluid system is pressurized.
Different Plan 53 systems and seal coolers will have different utility requirements. A Plan 53A will require nitrogen from a supply header. Water-cooled seal coolers must be connected to the plant’s cooling water system, and forced convection air coolers must be connected to the appropriate power supply.
Adding barrier fluid
As stated above, each of the Plan 53 options will have different strategies for adding barrier fluid. A Plan 53A will be filled to a specific fluid level. A Plan 53B will be filled to a specific barrier fluid pressure. A Plan 53C will be filled to a specific piston position. In all cases, the end user should not overfill any of the systems thinking that more barrier fluid will improve system performance.
Pressurizing the barrier fluid system (Plan 53A only)
The Plan 53A will be pressurized by the operator opening the nitrogen supply valve and setting the correct barrier fluid pressure. This step is not required for the other plans since the Plan 53B will be pressurized during the addition of barrier fluid and the Plan 53C will become pressurized when the pump is pressurized.
Commissioning a Plan 32 (if applicable)
A Plan 32 is a piping plan designed to prevent the mechanical seal from being exposed to the process fluid. For this reason, a Plan 32 must be commissioned prior to adding process fluid into the pump.
Filling the pump
Different pump designs and different application conditions will require different pump start-up procedures. The operator is responsible for ensuring the correct procedure is used. For example, a high temperature pump may have time requirements to allow the pump to slowly reach thermal equilibrium.
Commissioning inner seal piping plan (if applicable)
Once the pump is filled with¬ fluid, the inner seal piping plan must be ready for operation. In some cases, this is done automatically (e.g., Plan 11 or Plan 13). In other cases, the operator may need to vent the piping plan and/or establish cooling water flow to the plan (e.g., Plan 21 or Plan 23).
This is first point in the commissioning process where all of the systems are pressurized and utilities are operational. The operator and seal/system OEM should inspect the system checking for leaks, correct levels and pressures, and properly functioning utilities.
Starting the pump
The pump should be started according to the operator’s normal practice. This should have been discussed with the seal/system engineers to ensure it is compatible with the seal requirements. During start-up, the end user should look for leaks, listen for unexpected sounds, and confirm proper instrumentation reading.
After the pump and sealing system has reached equilibrium, the operator and seal/system engineers should record initial reading as a baseline for system performance. This monitoring will continue, both through the plant DCS system and, periodically, in-person by the operator.
Inspecting the commissioning of a seal piping plan is far more that showing up at the actual starting of the pump. The end user and seal/system supplier must work closely together through the lifecycle of the application to have the best chance for long-term system reliability.
About the Author
Michael Huebner is a Principal Engineer at Flowserve Corporation in Pasadena, Texas. He has over 30 years of experience in the design, testing and application of mechanical seals both in the USA and Europe. He has authored numerous articles and lectured extensively around the world. He has a BS in Engineering Technology from Texas A&M University.