Piping plans are a critical part of any seal installation. Piping plans cover everything from a dead-ended seal chamber to extensive external support systems. Previously these were referred to as API piping plans (such as API Plan 11). Since this document will be issued as an ISO document, they are now referred to simply as piping plans (e.g. Plan 11).
The Annex has a listing of all of the available piping plans. Most of the plans are carried over from the First Edition. There are however several new piping plans introduced in the Second Edition. One of these new plans was moved over from API 610 Eighth Edition. Two new plans are variations of dual pressurized liquid seal plans.
The remaining new plans are for supporting containment seals and dual gas seals. In addition ISO 21049 introduced an atmospheric collection and detection plan. This module will only discuss the piping plans which were new to the Second Edition and beyond.
Plan 14
This plan was moved not in the First Edition of API 682 but was included in API 610 Eighth Edition. This is now being moved to API 682.
Plan 14 is a combination of Plan 11 and Plan 13. This plan provides a seal flush from discharge (or a higher pressure intermediate stage) into the seal chamber. It also features a return line from the seal chamber back to the pump suction or low pressure area. This has been used most often on vertical pumps where the seal chamber is maintained at a pressure less than discharge.
Plan 53A
Plan 53A is really not a new piping plan. This is the plan historically called a Plan 53. While this plan has been used extensively, there are other variations of dual- pressurized seal piping plans that have developed over the years. These have used designations such as Plan 53 Modified. These
variations share many similarities but each has its own benefits and drawbacks. To help the industry specify the specific variation, the Second Edition has
developed the specific plan designations of Plan 53A, Plan 53B, and Plan 53C.
Plan 14
Plan 53A
supply of barrier fluid which is circulated through the support system. The reservoir also serves three other important functions. First the reservoir is designed to have a blanket of an inert gas at the top of reservoir. This gas provides pressurization for the support system. Secondly, the reservoir generally contains cooling coils which help control the temperature of the support system. Finally, the reservoir is equipped with instrumentation and a sight glass to monitor the level of barrier fluid and, consequently, the performance of the mechanical seals.
The advantage of the Plan 53 system is that it is a relatively simple system to operate and relatively inexpensive compared to other Plan 53 systems. It is also fairly well understood by most operators. The primary
disadvantage of this system is that the barrier fluid is in directly in contact with the pressurization gas. At higher pressures, this gas can be absorbed into the barrier fluid and cause operational problems with the outboard seal.
Plan 53B
The Plan 53B has the same basic purpose as the Plan 53A. It is used to provide a pressurized barrier fluid for dual liquid seals.
In this plan, the fluid is circulated from the seal through a seal cooler and back to the seal. There is no reservoir in this system. Instead, this system uses a bladder
accumulator. This accumulator serve two main functions.
The first function is to pressurize the seal system. The bladder is pre-charged to a specific pressure. As the system is filled with the barrier fluid, the gas in the bladder is compressed and the pressure increases. The second function of the accumulator is to provide make-up fluid to the system. As barrier fluid is lost across the seal, the bladder will feed make-up fluid into the system. As fluid is lost from the system, there is a decrease in pressure. The condition or performance of the seals is monitored by the pressure decay in this system. A loss of pressure also signals the need to refill the system with barrier fluid. Heat is removed from the barrier fluid by a separate water-cooled or air-cooled seal cooler.
One of the advantages of a Plan 53B is that the pressurization gas never comes into contact with the barrier fluid.
Therefore, this system can be used at very high pressures without absorption of gas into the barrier fluid. The bladder only needs to be pre-charged during the initial installation. This means the system can be used without a high pressurize nitrogen line. One of the disadvantages of this system is that it is a fluid loss results in a
pressure drop. To maintain a near constant pressure, the system must either be refilled frequently or the system must have a larger (and more expensive) accumulator. This system also tends to be more expensive than a Plan 53A.
Plan 53C
The Plan 53C is the last of the options for dual pressurized liquid seal. This plan uses a piston accumulator to pressurize the system. The piston accumulator is also known as a piston transmitter or piston pot. The are some important differences in this plan that need to be recognized.
Plan 53B
The piston accumulator is pressurized by a reference source in the pump. This is most often a vent line or some other connection into the seal chamber. This pressure acts on the bottom of the accumulator. Due to the differences in hydraulic areas in the piston, a higher pressure is created at the top of the accumulator.
There is a fixed ratio of pressures that range from about 1:1.15 up to 1:1.3. For a 1:1.2 ratio accumulator, this means that a 100 PSI pressure in the seal
chamber would create a 120 PSI at the top of the accumulator. This higher pressure source is used to pressurize the seal circulation system. Since this system relies on pump pressure to pressurize the system, it does not need pre-charging. Also, the accumulator tracks the pump pressure so the system will maintain the correct pressure differential even during pump upsets or pressure fluctuations. As fluid is lost from the system due to seal leakage, the piston
travels up in the accumulator to provide make-up barrier fluid. The
performance of the mechanical seals is monitored by watching the movement in the piston rod.
For all of the advantages, this system does have one significant drawback - the accumulator is exposed to actual pump fluid. This means that the accumulator must be constructed of materials compatible with the process fluid.
Since the piston must be free to move in the accumulator, process fluids that have contamination or will solidify under ambient conditions may not function properly with the plan. This plan also tends to be more expensive than either the Plan 53A or Plan 53B
Plan 65
Plan 65 is designed to collect atmospheric side leakage from the drain to a liquid collection system. In this piping, there is a small collection vessel, an orifice, and a high level switch. If the seal experiences high leakage to the atmospheric side, liquid will be directed towards the drain port. As leakage flows towards the liquid collection system, the flow will be throttled by the orifice in the drain line. If the leakage is high enough, fluid level will back up into the collection vessel and trip the high level switch. If the level continues to rise, it will by-pass the orifice and go straight into the liquid collection system.
Plan 65s are most commonly used with non-hazardous fluids in remote locations such as pipelines and tank farms where there is infrequent maintenance surveillance.
This Plan is only for collection of atmospheric side leakage. Leakage must be non-vaporizing and have the ability to flow under atmospheric conditions. For
collection of leakage from containment seal cavities, please see Plans 72, 75, and 76.
Plan 65s will be most effective when used with a close clearance throttle bushing.
This plan has been used for many years but has never had an official designation. Plan 65 first appears in ISO 21049 followed by API 682 Third Edition.
Plan 53C
Plan 65
The 70 series piping plans are dedicated to gas seals and containment seals. The first of these plans is Plan 71. Plan 71 is a dead-ended containment seal with all the connection ports plugged. This plan may be used in a dead-end configuration but is more often specified when the purchaser will provided connections in the future.
This plan is analogous to Plan 61 where the atmospheric connection are plugged for purchaser’s use.
Plan 72
Plan 72 provides buffer gas to the containment seal cavity of a 2CW-CS or 2NC-CS configuration seal. The buffer gas is normally used to sweep leakage from the containment seal cavity to a liquid or vapor recovery system. The pressure in the containment seal cavity is maintained below seal chamber pressure and should not exceed 10 PSI. This plan is generally used in conjunction with a Plan 75 or Plan 76.
The standard also details requirements for the control panel.
Plan 74
Plan 74 provides barrier gas to a dual pressurized gas seal. The barrier gas is maintained at a pressure at least 1.75 bar (25 PSI) greater the seal chamber pressure.
Historically this plan has seen operational problems in pumps where the process fluid will crystallize on exposure to air (e.g. caustics). Also in pumps with solid contaminants, the seal should utilize a device designed to exclude the solids from the seal faces.
There will be some barrier gas leakage into the pump even during standby condition. In some cases it may be necessary to vent the pump casing prior to starting the pump or design the system to be self-venting.
The standard also details requirements for the control panel.
Plan 71
Plan 72
Plan 74
Plan 75
Plan 75 is used on 2CW-CS and 2NC-CS configurations where the process fluid does not completely vaporize under containment seal conditions. If the leakage is allowed to
accumulate in the containment seal cavity, it will result in an increased leakage to atmosphere or failure of the containment seal.
Plan 75 processes liquid or mixed phase leakage from the containment seal cavity. Leakage is drained from the bottom of the cavity and gravity flows to the condensate collection reservoir. The reservoir provides a location for the separation of gas and liquid phase leakage. It is connected to a vapor and/or liquid recovery systems or flare.
The reservoir is instrumented with both a visual
level indicator and pressure gauge. By blocking in the reservoir, the
accumulation of pressure and liquid level can indicate the condition of the inner seal. The standard gives requirements for the design of the condensate collection reservoir.
Plan 75 may be used alone or in conjunction with a Plan 72 to provide a sweep of buffer gas through the containment seal cavity.
Plan 76
Plan 76 is used on 2CW-CS or 2NC-CS configurations where the process fluid will completely vaporize under containment seal cavity conditions. Vapor phase leakage will be piped directly to a vapor recovery system of flare.
An orifice and pressure gauge is installed to detect a high flow of product which would indicate failure of the inner seal.
The standard gives details of construction of the piping and tubing required on this plan. There is a small drop leg in the piping to help prevent leakage from the flare from draining back to the seal.
Plan 76 may be used alone or in conjunction with a Plan 72 to provide a sweep of buffer gas through the containment seal cavity.
Plan 75
Plan 76