Piping systems be protected against over-pressuring by Pressure-relieving devices like pressure safety valves, and pressure relief valves, … by realizing extra pressure (popping up) according to the system operating philosophy.
Regarding variation of service fluid pressure and velocity between the upstream and downstream of PSV, during popping up PSV exert considerable reaction force over the system. During stress analysis of PSV-involved systems, we have to consider this reaction force.
Also according to Appendix II B31.1, Pressure loads acting on the safety valve installation are important from two main considerations. The first consideration is that the pressure acting on the walls of the safety valve installation can cause membrane stresses which could result in the rupture of the pressure-retaining parts. The second consideration is that the pressure effects associated with discharge can cause high loads acting on the system which creates bending moments throughout the piping system.
ASME B31.3 and Caesar II approach for occasional load and pressure-relieving load
Some companies consider PSV/PRV reaction load like other occasional loads e.g. seismic loads/wind loads because it acts occasionally and according to clause 302.3.6 part (1) of ASME B31.3 (Refer to Fig. 1), use of 1.33 times the basic allowable stress provided in Table A-1/A-1M.
Fig. 1: Limits of Calculated Stresses due to Occasional Loads as per ASME B31.3
In the Caesar II equivalent static method, the PRV reaction force is entered in the input spreadsheet and proper load cases are prepared after adding those forces to simulate the behavior. But in the load cases, the OCC load Factor column is left blank and Caesar II by default use 1.33 as the occasional load factor similar to other occasional stress categories. Therefore, while calculating the allowable stress for PRV pop-up case, Caesar II software multiplies the allowable stress with 1.33 for the calculation of OCC allowable stress. Refer to Fig. 2 which shows a Caesar II snapshot for the same.
Fig. 2: Occasional allowable stress when OCC load factor is left blank
But note that factor 1.33 is for those occasional loads which occur into the piping design (operating) limitation but pressure reliving device duty is keeping away the system from over-pressurizing and does not operate since pressure is below design (set pressure) condition.
paragraph 302.2.4 part 2 Involves terms either or both of temperature and pressure variate from design condition. According to part (2) of 302.2.4 (B31.3), when the variation is self-limiting (e.g., due to a pressure-relieving event), and lasts no more than 50 h at any one time and not more than 500 h/y, it is permissible to exceed the pressure rating or the allowable stress for pressure design at the temperature of the increased condition by not more than 20%. Hence when Caesar II users leave the OCC load Factor blank for PSV/PRV load case, the relevant allowable load is calculated as about 11% more than the limiting of 302.2.4. Refer to Fig. 3 below.
Fig. 3: Allowances for Pressure and Temperature Variation per ASME B31.3
So, as per my understanding, it can be concluded that occasional loads like wind and earthquake, maybe as much as 1.33 times the basic allowable stress but pressure relieving loads like PSV/PRV discharge reaction loads should be limited to an OCC factor of 1.2. It is, therefore, mandatory for Caesar II users to fill the OCC load Factor for PSV reaction forces as 1.2. Refer to Fig. 4 below.
Fig. 4: Occasional allowable stress when OCC load factor is filled
I wish to know the inputs from other pipe stress engineers on the above subject on whether my understanding is right or I am missing somewhere. Kindly provide your input in the comments section.
Isolation Philosophy: Equipment, Instruments, and Utilities Isolation Methods
Isolation philosophy or positive isolation philosophy is a standard procedure that describes a method for isolating a section of a plant to permit safe operation & provide access for maintenance. The philosophy & criteria given in this article shall be incorporated into P&ID. It includes process equipment, piping, and utility equipment & piping as well as requirements of instrumentation isolation.
Positive Isolation Philosophy
The isolation philosophy has been classified into three different categories that include the isolation of
Equipment
Instruments
Utilities
Equipment Isolation Method
The following tabulated format (Table-1) outlines the circumstances when single and when double block and bleed valves are to be used for equipment isolation. This phenomenon and the resultant isolation valving must be consulted throughout this philosophy, as this isolation has to be incorporated in a whole range of contexts from battery limit to equipment isolation.
TIE-IN point to the existing and other process systems shall have ball valves. TIE-IN valves shall have spectacle blind, bypass ball valves (with spectacle blind). Also, spectacle Blinds shall be installed on all Battery Limit lines. At the blinding station, the block valve or valves shall be closed and the battery limit bleeder valve has been left open. Typical sketches for general hydrocarbon, high vapor pressure fluids, and two-way isolation are given in Fig. 1 below.
Fig. 1: Process and Utility Battery Limit
Equipment Isolation
Equipment can be isolated for several purposes like inspection, maintenance, etc. However, the main criterion for determining the level of isolation for equipment is whether personnel will enter into the equipment. Therefore the level of isolation for a large vessel will be greater than that for a small pump.
Equipment Isolation for Personnel Protection:
The following criteria should be incorporated into the design of isolation for any equipment whose internal isolation is required.
All vessels, drums, and confined spaces shall be designed for positive isolation by blinding or by the removable spool.
All inlet and outlet connections except those used for atmospheric ventilation will be subjected to positive isolation
Vents shall be available on the equipment side of the isolation.
The furnace/Waste heat recovery unit shall be designed for positive isolation so that humans can enter (for inspection and maintenance purposes) inside the equipment safely during the gas turbine running.
Humans shall be able to enter inside the gas turbine exhaust duct (for inspection and maintenance purposes) safely during the Furnace/waste heat recovery unit running.
Equipment Isolation Configuration:
This section considers equipment that requires isolation for inspection and maintenance purposes but does not require internal access. The main examples of such equipment are
Pumps: The below figures show the schematic for isolation configuration.
Fig. 2: Schematic of isolation configuration
Notes:
Double valves may be required depending on temperature, pressure, services
Piping up to and including the suction isolation valve should be the same pipe rating as discharge where there are two pumps installed in parallel or where discharge can overpressure by backflow past the non-return valve.
Control Valve Isolation
Block and bypass valves shall be provided as standard for each control valve installation unless
Identical pieces of equipment or process systems are installed in parallel enabling online maintenance of any one control valve without affecting the required capacity.
Associated with intermittently operated or non-essential equipment.
In applications where for safety reasons manual operation by means of the bypass is not desirable.
For applications where it is impractical to operate the process on a manual bypass valve, no bypass will be provided. The control valve isolation philosophy shall follow the guidelines for single and double isolation as per Table 1. Single isolation is acceptable for control valves providing that the normal operating pressure is within the specified class rating. For example, if a control valve in sour service is linking 600# to a 150# system, only single valve isolation is required downstream even though the isolation valve will be a 600# valve.
Fig. 3: Control Valve Isolation Philosophy
Notes:
Double block & bleed valves as per Table 1
Control valve failure action to be shown e.g. fails open (FO). Besides, any requirements of tight shut-off and TSO class are to be shown.
It may not necessary to change the piping class across the control valve. If the downstream system has a higher rating the spec breaks need to be reviewed.
Deleted
Facility for flare vents may be required for large systems, etc.
Deleted
A gate valve shall be added in series along with the bypass globe valve on the product and sales gas lines.
An isolation valve at the outlet with a lock-open facility shall be provided for all safety relief valves that do not discharge directly into the atmosphere.
An isolation valve at the inlet with a lock open facility shall be provided for all safety relief valves except for pumps with an installed standby where the relief valve is between the discharge block valve and the pump.
The isolation valves shall be key-locked using a proprietary valve-locking mechanism.
A key-interlock system must be specified (for the inlet and outlet isolation valves for both the service and spare RVs). In the case of 3-way valves, the valves at the upstream and downstream should be arranged such that they can be (are mechanically linked) switch simultaneously.
RV for Thermal relief:
RV relieving to flare/vent or process, a single block valve with an LO facility, and bleeder shall be specified only on the inlet line. For each valve, separate tailpipes should be provided.
RV relieving to the atmosphere a single block valve with an LO facility and bleeder shall be specified only on the inlet line. For each valve, separate tailpipes should be provided
Bypass Line:
A bypass line across the relief valves with a single isolation valve shall be specified only where there is a requirement to vent the gas in the system to flare/vent and no other connection to flare is provided.
Bleeder Valve/Weep Holes:
Bleeder valve requirements shall be noted on the RV arrangement, together with any requirement to vent at a safe location. Weep holes are required for valves routed to the atmosphere (to prevent rainwater from accumulating), with shielding or diversion for personnel protection as necessary.
RV Arrangement:
For spare relief valves, the arrangement for the isolation philosophy and connections shall be shown in the P&IDs if requires and shall be shown as per the figure below. Isolation valves should be interlocked.
Bonnet Vents:
A vent connection may be there from the bonnet for balanced bellows valves. These should be routed to a safe location and should not be provided with isolation valves. Fig. 4 shows the isolation philosophy for closed relief systems & open relief systems.
Fig. 4: Isolation philosophy for closed relief system & open relief system
Notes:
From the vessel or from the piping on the vessel without intervening valves.
For spared SVs, isolation valves shall be interlocked such that one SV is always available. Double block and bleed valves should be used for high-pressure applications, refer to Table-1. The material of the proprietary key-interlock system shall be stainless steel. All keys shall be tagged. For each & every proprietary key-interlock system, one key shall remain and keep in the control room; a key cabinet (metal) with an identification label for each key shall be provided. The keyhole shall have a waterproof cover. In addition, a set of master keys shall be provided. This set of keys shall be valid for all proprietary key-interlock systems in this project.
Deleted
Deleted
Special consideration is to be given to whether condensation could occur e.g. in steam service if valves leak badly, very hot water will come from the drain.
Instruments Isolation Method
Pressure Instruments:
Main Isolation valves shall be per Piping Specification. Screwed instrument connections may be used downstream of the main isolation valve only. Screwed connections shall not be used for instrument connections in hydrocarbon service. However, in applications where a flanged connection is not available, the following shall apply:
For sour services and non-sour services in piping class ANSI 600 and above, pressure instruments may be connected by threaded connections, if no alternative exists, but only after double block and bleed isolation valves.
In case of non-sour services of piping class ANSI 300 and below, pressure instruments may use threaded instrument connections after single block and bleed isolation valves.
Back welding of flanges onto instrumentation is not acceptable.
Isolation of Utilities
Flare/Vent Isolation
The below figure (Fig. 5) depicts the standard isolation philosophy for the system connected to a flare or vent. F stands for Flare or vent.
Fig. 5: Various Utilities Isolation Philosophy
Instrument & Plant Air Isolation:
The standard isolation philosophy for instrument & plant air systems is provided in Fig. 5.
Nitrogen Isolation:
The standard isolation philosophy for the nitrogen system is also depicted in Fig. 5. Please refer to the notes mentioned in that Figure.
Potable Water:
Potable water shall be supplied to process users via a break tank to avoid contamination
What is a Valve Trim? Types, Components, and Selection of Valve Trims, and Valve Trim Charts
Major valve parts include two types of functions, namely pressure-retaining, which includes a valve body, bonnet or cover, Cover bolting, Disc, and the other major non-pressure-retaining parts of a valve, like a valve seat(s), stem, yoke, packing, gland bolting, bushings, handwheels, valve actuators, etc.
Within all these removable and replaceable internal parts of the valve, some will be directly in contact with the fluid flowing through it. These internal parts of the valve are collectively called valve trim. Valve trims play a critical role in the functioning of fluid control systems across various industries, from oil and gas to water treatment and HVAC. In this article, we will explore what valve trims are, their types, applications, and the factors to consider when selecting them.
What Are Valve Trims?
The term “valve trim” refers to the internal components of a valve that control the flow of fluid through it. This includes elements such as the stem, disc (or plug), seat, and any additional components that contribute to the valve’s operation. While the valve body provides the outer structure and connects the valve to the piping system, the trim is responsible for regulating flow, preventing backflow, and sealing against leakage.
These operative parts control the flow of liquid and gas through a valve. They are the parts exposed mostly to the process elements, and so are very vulnerable to wear over time. The stem, ball, and seat are the three basic items of the high-pressure control valve trim. So as the valves change, trim components also may vary except the disc, valve seat, and stem. This will be common for all the valves. As the trim parts, the disc movements, and the flow control are possible.
Some of the other valve trim components, as the valve specific, include,
Back seat
Glands
Spacers
Guides
Bushings
Retaining pins
Internal springs
Valve Trims according to the Type of Valves
Refer to Table 1 which shows the valve trim elements for different types of valves.
The trim plays an important role in the characteristics of the valve. It determines the flow rate and the isolation of the valves. The shapes of the valve trim determine the flow characteristics of the valve. A valve trim’s characteristic is related to the percentage of flow and the valve stem travel between 0% and 100%.
Trim materials are sometimes the same material as the valve body or bonnet, and sometimes they differ. As per the different properties, required for the components to withstand particular forces and conditions. so that they are constructed of assorted materials. When suitable trim materials are selected, the flow-medium properties like chemical composition of the fluid, pressure, temperature, flow rate, velocity, and viscosity of the fluids are considered.
Valve trim components and valve characteristics
1. DISC
The disc is a part of the valve which allows, throttles, or stops flow depending on its position it is a pressure-retaining part of the valve. Types of discs present on the valve define the name of the valve. over plug or ball valve, the disc is called a plug or ball. A disc will be seated against the stationary valve seat or seats when the valve is in the closed position, during the closed position the disc performs a pressure-retaining function whereas, during the valve open position, the disc doesn’t perform the pressure-retaining function. It can be moved away from valve seats by the motion of the valve stem, except in the check and safety relief valves the disc is moved away from its seats by fluid flow and pressure. A valve disc is usually cast, forged, or fabricated.
2. SEAT
A valve seat is one of the non-pressure retaining parts of the valve. Valves will be having maybe one or more than one seat, as in the cases of globe or swing check valve, there will be one seat forming a seal with the disc to stop the flow. Whereas for the gate valve, there will be two seating surfaces that will come in contact with the seats. Likewise, ball and plug valves, depending on the number of ports will have several seats. Valve seats can be integral, renewable, or replaceable rings. Small valves are provided with screwed-in, swaged-in, or welded valve seats, and in big valves, they may have any of the seats used in small valves and they will have integrally cast or forged seats along the valve body.
The leakage rates within the valves are directly proportional to the effectiveness of the seal. Between the disc and its seat. The acceptable leakage rates are specified by the valve standards MSS SP61, API 598, and ASME B16.34.
3. BACK SEAT
The back seat is another non-pressure retaining part of the valve. The back seat is made up of a shoulder of the stem. When the stem is in a fully open position it forms a seal. Thus, preventing the leakage from the valve shell, to the packaging chamber and the environment.
4. STEM
The stem connects the actuator, valve handwheel, and the disc, plug, or ball. Required for the opening and closing of the valve motion. Thus, the motion of the stem opening and closing the valve took place. In a gate or globe valve, linear motion of the disc is needed to open or close the valve. Whereas in the plug, ball, and butterfly valve, the valve disc is rotated to open or close the valve. Stop check valves, and check valves do not have any stem.
5. BONET BOLT
Bolting includes bolts, nuts, and washers. They hold the bonnet and the body creating a tight pressurized seal between them. Bolting should be selected under the application code and standards as per the materials applied.
6. GLAND EYEBOLT
It connects the gland flange and the bonnet and tightens the bolts.
7. YOKE
Yoke is also called yoke arms. The actual mechanism of the valve is connected with a yoke to the valve body or bonnet. Over many valves, The yoke and the bonnet are designed as a one-piece construction. The top side of the yoke consists of the yoke nut and yoke bushing. To withstand forces, moments, and torque developed by the actuators, the Yoke is made hard enough.
8. YOKE BUSHINGS
It is the part where the internally threaded nut is held at the top of the yoke where the valve stems passes through. In some valves, like the gate and diaphragm. the nut is turned and the stem moves up and down which depends upon the direction of turning. Over some valves, the yoke nut is held fixed permanently and the stem is rotated through it. For the minimal effort of actuating, the yoke bushings are made up of softer material than the stem. anti-freeze yoke sleeve bearings are provided on the valves that require much effort to open or close. This will minimize the friction between the hardened stem and the yoke bushing.
9. GLAND FLANGE
Used to provide support for the gland bush to keep the gland packing under tension.
10. STEM PACKING
Depending upon the application stem packing performs applications like
Preventing leakage of flow medium to the environment.
Preventing outside air from entering the valve during vacuum applications.
It is contained in a stuffing box. Packing rings get compressed by tightening the packing nuts or packing gland bolts. Compression over here must be sufficient to make a good seal. Stem packing is made of graphite or PTFE as per the requirements.
Types of Control Valve Trims
The valve trim shape determines the flow of characteristics of the valve in the control valve. There are three primary types of control valve trims.
1. Snap Trim (also referred to as Quick-Opening trim)
it opens quickly and is used for isolation services. Which includes the primary operations like a liquid dump, pressure relief, and metering.
2. Nominal Trim(also called Linear trim)
It is used for throttling liquids, liquid level control, and in applications where a water hammer is an issue.
3. Equal Percentage Trim
They are used to control the pressure or flow of gases and vapors in throttling applications.
Trim selection against Corrosion & Erosion
Based on the service conditions like the temperature, pressure, type of fluids, chemical composition, flow velocity, pressure drop, maintenance need, etc. valve trims are selected. The sustainability of the material, to resist corrosion can be determined by corrosion resistance tables and selecting accordingly from them.
And erosion is caused due to high-velocity liquids with abrasive particles harder than trim material.
Metallic Valve Trim Material
AISI type 316 stainless steel has been the most common trim material. The metallic trim is good for all-around choice in general service for about -195 Deg C to +400 Deg C and moderately corrosive fluids. Alloys of steel, titanium, Cobalt-Chromium alloys and Nickel-Boron alloys are some of them used.
Non-metallic Trim Material
Operating temperature is the most important factor in selecting non-metallic trim material. Poly tetra fluoro ethylene (PTFE), Teflon, etc.
Valve Trim Chart
For standardizing trim materials API has assigned a unique number to each set of valve trim materials. Trim numbers or combination numbers consisting of materials like disks, stem, back seats, and sleeves are grouped and assigned to one number.
API 600 & 602 gives the list of Trim materials that can be used in the valve.
ASTM A410 (13Cr), ASTM A316, Alloy 20 (19Cr-29Ni), and Monel (Cu-Ni Alloy) are commonly used trim grades.
Refer to the figure below to find a typical Valve trim chart as provided by API 600 and API 602. The chart is defined by Trim numbers.
Fig. 1: Valve Trim Chart
Valve trims are integral to the functionality and efficiency of fluid control systems. By understanding the components, types, and considerations involved in selecting valve trims, engineers and operators can make informed decisions that enhance system performance and reliability. Whether in oil and gas, water treatment, or HVAC applications, the right valve trim can lead to significant operational improvements and cost savings.
For more than 50 years, Hydrogen piping and pipeline systems have been in use. There are several hundred miles of hydrogen pipelines that are laid to transport hydrogen to serve as fuel. Even though Hydrogen is so highly flammable, there are no reports of injuries because of hydrogen pipelines. In this article, we will explore more about hydrogen piping and pipeline systems.
Hydrogen is a non-toxic, odorless gas that is highly flammable and around 14 times lighter than air. They leak very easily and so special care must be exercised for the design of mechanical joints. As the flame of hydrogen is invisible in the daylight, it is very hard to detect and extinguish hydrogen fires.
Codes and Standards for Hydrogen Piping and Pipeline System
The governing code and standard for hydrogen piping and pipelines are ASME B31.12. ASME B31.12 code provides information about hydrogen pipes and pipelines in four parts. The 1st part is General requirements known as Part GR. The 2nd part of the ASME B31.12 code provides information about Industrial hydrogen piping systems. This section elaborates on the design code requirements, design conditions, pressure design criteria, and equations for piping components, Flexibility, and support requirements, Service requirements for piping components and joints, fabrication, erection, inspection, testing, and assembly requirements. 3rd part provides guidelines for hydrogen pipelines. This section details pipeline system components, fabrication details, design, installation, and testing requirements. The final part of ASME B31.12 is the Appendices part which covers 9 mandatory and 7 non-mandatory appendices. All required figures and tables are also provided in this section. So, all the design, inspection, testing, fabrication, and construction requirements are properly provided for both hydrogen piping as well as hydrogen pipeline systems.
The hydrogen pipes and pipelines code was first introduced in the year 2008 and the latest edition is the 2019 edition. Prior to the release of the ASME B31.12 code, ASME B31.3 was used for Hydrogen Piping and ASME B31.8 for Hydrogen pipeline transportation systems.
Differences between ASME B31.3 and ASME B31.12
The majority of the sections of ASME B31.12 are identical to the sections of ASME B31.3. However, there are some significant differences. Some of the differences between ASME B31.12 and ASME B31.3 are listed below:
Code Application:
The major difference between ASME B31.3 and ASME B31.12 is in their application. ASME B31.3 is applicable for a range of process fluids whereas ASME B31.12 only provides guidance regarding only hydrogen piping and pipeline systems.
Pressure Design Thickness Calculation:
The equation for pressure design thickness is approximately similar in both codes. However, the weld joint strength reduction factor, W of ASME B31.3 is replaced by a performance factor Mf in ASME B31.12. This Mf addresses the loss of material ductility in hydrogen services. So, the calculated thickness for Hydrogen piping for a specified design temperature and pressure will be more than the process piping requirements.
Allowable Displacement Stress Range:
The allowable displacement stress range calculation in B31.12 also addresses hydrogen embrittlement of carbon and low alloy steels by increasing the actual full displacement cycles by a factor of 10 when designed below 150ºC (300ºF).
Branch Connection Requirements:
ASME B31.12 requires a full weld joint penetration for stub-on and stub-in branches. The code also prohibits the use of piping joints associated with materials not permitted by B31.12 including caulked, soldered, bell and gland, and plastic joints although it does permit threaded and tubing joints.
Materials:
There are some differences in material manufacturing requirements. For example, in ASME B31.12, DSS is an unlisted material. Also, the code guides to avoid the use of nickel-based alloys.
The NDE requirement in the ASME B31.12 code is more as compared to ASME B31.3 which increases the cost. Also, the ASME B31.12 NDE requirements are much more stringent.
Welding Requirements:
In B31.12, an 80ºC (175ºF) preheat is mandatory for carbon steel of any thickness.
So, all these above requirements mainly increase the cost of Hydrogen piping systems by a large amount as compared to normal process piping.
Common Materials for Hydrogen Piping and Pipelines
Common materials used for Hydrogen piping systems are:
High-purity stainless steel with a Hardness of less than 80 HRB
Composite pipes like PFA, PTFE, FRP, FEP, MFA, etc
300 series austenitic stainless steels that meet the temperature limits of ASME B31.12 are used for liquid and gaseous hydrogen product piping, tubing, valves, and fittings.
Carbon steel can be used for gaseous hydrogen product piping.
The suitability of using carbon or low-alloy steel must be evaluated using the “Nelson charts” in American Petroleum Institute (API) RP 941 for high-temperature applications,
Seamless pipes and tubes are preferred for hydrogen piping systems.
Typical Guidelines for Hydrogen Piping System
In general, Single wall piping is used for gaseous hydrogen service Vacuum-insulated piping is used for liquid hydrogen service. The following considerations are usually followed during Hydrogen pipe system design:
System isolation during maintenance
Depressurization for maintenance
Purging of the system with an inert gas before maintenance.
Piping and other piping components are decided based on the temperature and pressure of the hydrogen service. the potential for leaks, mechanical strength, material, and fire safety acceptability will dictate the selection of piping joints. All electrical equipment and electrical grounding apparatus shall comply with NFPA 70
Before being placed in hydrogen service, the hydrogen piping systems should be cleaned thoroughly. The cleaning procedure selected shall be suitable for the type of contaminant and shall provide the level of cleanliness required by the application. Hydrogen pipe installation must be done in accordance with ASME B31.12 and local, state, and national codes.
The design must minimize the potential for leaks and allow for easy detection. The following guidelines can be followed:
Use welded joints where possible to minimize leakage.
For leak checking, access to joints and fittings must be provided.
Chances of contact with cold surfaces, head impact, tripping hazards, etc. shall be minimized.
Properly labeled shutoff valves must be provided at safe locations.
The piping system must be labeled to indicate content and flow direction.
Hydrogen Pipelines
To transport the hydrogen from the production point to the delivery point, Hydrogen pipeline transport is used. High Strength Line pipes and FRP pipes are usually preferred for transporting hydrogen through pipelines.
What is an FPSO? Its Components, Working, and Advantages
The full form of FPSO is Floating Production Storage and Offloading. These are floating vessels over the sea used for the production, storage, and off-loading of crude oil. FPSOs are very important as it facilitates the processing and storage of oil and gas. Extensively used by the offshore industry, FPSOs are one of the primary methods of oil and processing as well as storage. In general, they are leased by oil and gas companies.
The vessels contain various processing equipment that helps in the separation, storage, and offloading of crude oil and gas that is extracted from sub-sea oil wells or platforms. After processing the oil and gas, FPSOs store it safely it is offloaded onto a tanker or transported through a pipeline. In the year 1977, Oil and Gas major, Shell built the world’s first FPSO.
Advantages of FPSO
In recent times, the FPSOs have become more vital for the oil and gas industry due to the fact that onshore oil discoveries have started to decline. There are 270+ FPSOs that are successfully operating around the globe. The main reason behind their utmost popularity is that they are flexible, efficient, safe, and way cheaper as compared to traditional offshore oil and gas platforms. Other benefits of FPSOs are:
FPSO provides wide flexibility in operation. Any pipeline can be connected to an FPSO. They can be moved to other locations easily. Permanent structures and pipelines are not required. All these reduce the total cost of FPSO systems as compared to the conventional methods.
A substantial amount of processed oil and gas can be stored in an FPSO.
FPSO systems provide better safety as compared to conventional processes.
The time requirements for FPSO solutions are significantly smaller.
Highly effective in deep water and remote locations, where seabed pipelines are not economic.
FPSOs are extensively suitable for smaller oil field as the need to lay long-distance expensive pipelines are eliminated.
FPSOs provide cost-effective maintenance.
Components of an FPSO
Let’s explore the main components of an FPSO. The major parts of an FPSO are:
Hull
The hull of an FPSO is the topside of the ship above sea level. They are usually newly built or made by converting from existing tankers with the specification needed to match the project-specific conditions. which differ depending upon the regions as well as the standards defined.
Mooring System
They are the equipment that holds the FPSO in place against forces, waves, winds, and currents. Mooring systems play an important role in supporting the safe operation of FPSOs. They are made up of mooring lines, anchors, and connectors.
Topside
It’s the oil and gas processing unit at the top. Which are designed and constructed under fixed offshore platforms and refinery standard specifications as per API & ASME. It should also consider the loading due to wave action. As sit has a serious effect on the fatigue life of the equipment.
Fig. 1: FPSO Components
Risers
This permits the FPSO to move both vertically and laterally. This connection to the subsea wells is made through flexible steel reinforced risers. They are designed to absorb any motion which affects the position of the vessel by waves. Swivel stacks are used to transmit well streams from the turret to the topside while the ship rotates. It also conveys gas for injection back into the reservoir to provide pressure support.
FPSO Turret
The turret is integrated into the FPSOs hull. The turret thus helps the hull to weathervane around the mooring system and the mooring line. For harsh weather conditions, a turret mooring system is critical. Using the turret the FPSO can rotate freely while moored to various locations on the seafloor.
Detachable FPSO turret
Sometimes detachable turret systems are used. This is useful to disconnect from the vessel while being attached to the mooring system on the seabed. During hazardous situations like storms, the vessel can quickly react by detaching the turret system, and once the threat alleviates, they can reattach and start operation. So, a detachable turret system essentially increases the flexibility of the system.
There are some other components that are part of the FPSO system as listed below:
Hydrocarbons (mixtures of oil, water, and gas) produced in the subsea wells are carried onboard through subsea pipelines, flexible risers, etc. These hydrocarbons in the process get separated into oil, water, and gas at the topside production facility (which consists of water separation, gas treatment, oil processing, water injection, and gas compression.
From the turret, the hydrocarbons move on to the inlet production and test manifold. Which is consisting of modules like crude separation module, gas separation module, and water separation module.
Each separation module is having different equipment as per the process conditions. The oil separation consists of,
Crude separation module: This consists of a sand filter, slug catcher, and production separator.
Crude stabilization module: having electrostatic coalescer- desalting/dehydrate, LP separator, and LLP separator.
Crude oil storage and offloading system: module consisting of an oil cooler and storage tank for storing and offloading of the oil.
Gas separation includes,
Gas low-pressure compressed module
Gas medium pressure compressed module
Gas high-pressure compressed module
All three modules have a cooler, scrubber, and compressor in common.
The water treatment module has,
Sand filter
Hydro cyclone
Degasser
Cooler
Separated crude oil after processing gets stored in storage the tanks will get loaded onto shuttle tankers moored at the stern. The gases from the hydrocarbons can be used as fuel for vessels, gas turbine power plants, or else transferred through pipelines onshore.
What is an FSU?
A Floating storage unit (FSU) is a type of simplified FPSO without the scope of oil and gas processing on the board. FSU units are used to store and offload the processed oil and gas to the refineries. The processed oil and gases will be stored in large silos placed over the top of the vessel.
Difference between FSO and FPSO
The main difference between FSO and FPSO is that FPSO is concerned with production as well as storage whereas the main function of FSO is mainly storage.
Disadvantages of FPSO
Though there are many benefits of an FPSo system, it has some limitations like:
High initial cost.
It may take up to two years to convert a tanker into FPSO.
FAQs related to FPSO
What is the biggest FPSO in the world?
Based on capacity, Total’s Egina FPSO is the biggest FPSO in the world. It has a capacity of 2.3 million barrels of oil. This FPSO is situated in the Egina field in Nigeria.
Is FPSO a ship?
FPSOs are floating vessels. they are made by converting a former supertanker into a new purpose-built vessel. They are ship-shaped but with other processing parts. The tanker will be idle over the place till the production facility produces enough oil. The vessels can also be moved from one place to another after the field has been depleted.
Does FPSO drill?
Apart from commonly used FPSO, additionally built FDPSO (Floating drilling production storage and offloading vessel) incorporates deepwater drilling equipment which will help to develop the field and can be removed and reused after the production wells are drilled.
How are FPSOs moored?
The FPSO is usually anchored to the seabed, Anchor spreads usually consist of wires and chains which get tensioned by winches within the turrets. Mooring lines consist of 6 to 10 chains or wires. They get moored by a mooring system within a wide range of water depths, From deep as 20m to 2000m. They contain a spread of 8 to 14 anchors to ensure that the FPSO remains on location. Conventional anchors, suction anchors, or piles are used to make the connection with the seabed.
The mooring lines get connected to the hull by the turret system using giant rotating bearings.
Different mooring systems available are
Internal turret: often used inside the hull. Used up for severe marine conditions and where cyclones are severe.
Disconnectable turret: it can detach from mooring systems and be evacuated to a safe distance. Whenever there are severe weather conditions.
External bow-mounted turret: used up for severe monsoon regions
Tower yoke: used in shallow waters.
Catenary anchor leg mooring is installed in areas where sea conditions are moderate.
What is a turret in FPSO?
Turrets inside the FPSO are integrated into the hull at the center of the ship. it contains a bearing system consisting of giant rotating bearings which connect the mooring to the turret. These reduce external forces like waves, winds, and currents on the FPSO by freely rotating around the turret and performing stable oil and gas production. It also allows the vessel to rotate around the fixed part of the turret. Moorings are attached along with the fluid transfer system that connects pipelines to the FPSO for processing.
Pipes are defined as circular tubular products used for conveying fluids (liquids, gases, and fluidized solids). Pipes are designed for a particular design pressure corresponding to the design temperature. Various parameters related to pipes are Pipe Size, Pipe Schedule or thickness, Pipe Material, Pressure withstanding capability, Temperature withstanding capability, etc. Different types of pipes are used in the industrial sector for different purposes.
Common industries that find extensive use of pipes are oil and gas, process industries, chemical and petrochemical complexes, food and beverage industries, power sectors, steel industries, HVAC industries, plumbing industries, pipeline industries, refineries, etc. Today, the use of pipes is so wide that modern industrial plants can not be thought of without pipes. Types of pipes are decided based on various factors. In this article, we will explore different types of pipes that are widely used in industries.
Pipe Types based on Material
Pipes are normally classified based on the material which is used to produce the pipe during manufacturing. In general, there are two types of pipes:
Metallic Pipes and
Non-metallic Pipes
Metallic Pipes
The pipes made of metal are known as metallic pipes. They can be grouped into two categories:
These types of pipes are stronger and heavier. These pipes have iron as their main constituent element. Common examples of pipes made from ferrous materials are
This category of pipes is suitable for higher temperature and pressure applications. Most of the pipes used in oil and gas, refineries, chemical, petrochemical, power plants, etc. are made of ferrous materials. Click here to learn more about Steel Pipes.
Type of Pipes made from Non-ferrous materials:
In this group of pipes, iron is not the main constituent element. They are usually made of copper, aluminum, brass, etc. Common pipes made from non-ferrous materials are
Non-metallic pipes are widely used for services where the temperature is not significant. Non-critical services like water industries and drainage systems make use of most of the non-metallic pipes. Common non-metallic and widely used pipes are:
The main advantages of reinforced plastic and composite pipes are that they are highly corrosion-resistant and durable. While metallic pipes are usually designed for up to 25 years of service. Composite and Reinforced plastic pipes can easily serve up to 50 years. However, their main limitation is the temperature. Non-metallic pipes are not suitable for high-temperature applications.
Cement pipes, manufactured from reinforced concrete are usually used for stormwater, gravity service, irrigation industries, and culverts.
Types of Pipes depending on the industry they are used
Depending on the type of industry there are three types of pipes.
Pipes for Chemical and Power Piping Industries.
Pipes for the Plumbing industry.
Pipes for the Pipeline industry.
Types of Pipes for Chemical and Power Piping Industries
These types of pipes are suitable for high-temperature and pressure applications. Mainly pipes made from ferrous materials are used in chemical, power, petrochemical, steel, oil, and gas industries. They are usually designed following codes like ASME B31.3, ASME B31.1, and various other international codes. They are usually selected based on their ability to sustain pressure, temperature, corrosion resistance, etc.
Types of Pipes for the Plumbing Industry
Common plumbing pipes are PVC pipes, PEX pipes, Copper pipes, ABS pipes, CPVC Pipes, HDPE Pipes, Cast Iron and galvanized steel pipes, etc. They are mainly used for water distribution purposes.
Pipes for the Pipeline Industry
Pipes used in pipeline industries are usually known as line pipes and are designed by API 5L standards. Pipes for pipeline industries are designed following ASME B31.4 and ASME B31.8 codes. There are various grades of API 5L pipes that are used to convey oil, gas, or water through pipelines. Other types of pipeline materials are SS, DSS, SDSS, GRE, FRP, etc.
Types of Pipes based on the fluid they transport
Depending on the type of fluid they transport, pipes are categorized as follows:
Pipes can also be classified based on the method of manufacture. These are again sub-categorized depending on the material of the pipe. For example, Metallic pipes can be categorized as
In general, pipes with a diameter of less than 16 inches are seamless, and larger-diameter pipes are welded. Seamless pipes are preferred due to the absence of the weld seam which is considered a weak point. However, they are costlier than welded pipes. Also, For large-diameter pipes, producing seamless pipes becomes difficult.
Carbon steel pipes (A53, A333, A106, and API 5L) have the largest market share due to the fact that they are cheaper and suitable for a wide range of applications ranging from -29 Deg C to 427 Deg C.
Finally pipes can also be classified based on connection types as follows:
Types of Pipes based on Connection Type
Threaded: Pipes with external or internal threads for screw connections.
Flanged: Pipes with flanges for bolted connections.
Welded: Pipes that are joined by welding.
Push-fit or Compression: Pipes that use fittings to join without welding or threading.
Conclusion
So, the subject types of pipes are very broad and there are various parameters that contribute to the classification of pipes. However, the most widely accepted pipe classification is based on the material used to manufacture the pipe.
