Unless otherwise agreed upon between the purchaser and the manufacturer, the jurisdiction of this specification terminates with the pressure vessel as defined in the Scope of Section VII
General
This specification outlines the essential requirements for the design, fabrication, and shop testing of oil-field type separators, including oil-gas-water separators, utilized in oil and gas production These separators are typically positioned along the producing flowline, between the wellhead and the pipeline, and can be designed in various configurations such as vertical, spherical, or horizontal (single or double barrel).
The jurisdiction of this specification concludes with the pressure vessel, as outlined in the Scope of Section VIII, Division 1 of the ASME Boiler, unless an alternative agreement is made between the purchaser and the manufacturer.
The ASME Code governs pressure vessels, which are typically categorized as natural resource vessels according to API 510, the Pressure Vessel Inspection Code Notably, centrifugal separators, filter separators, and de-sanding separators fall outside the scope of this specification.
Compliance
Manufacturers of equipment or materials claiming compliance with an API specification must ensure adherence to all provisions of that specification It is important to note that API does not guarantee or warrant that these products actually meet the relevant API standards or specifications.
The separation of gases and liquids is fundamentally based on their physical phase differences This section discusses the mechanical separation processes for these substances, highlighting that a separator vessel can be known by various names, including knockout, trap, scrubber, flash chamber, or expansion vessel, irrespective of its shape These terms are commonly accepted as foundational definitions in the field.
The destruction of a metal by chemical or electrochemical reaction with its environment (see Annex B).
A type of separator vessel used to separate free water from a flow stream of gas, oil, and water.
NOTE The gas and oil usually leave the vessel through the same outlet to be processed by other equipment The water is removed for disposal
The maximum pressure, permissible by the ASME Code, at the top of the separator in its normal operating position for a designated temperature
During normal operation, the pressure within the vessel should not exceed the Maximum Allowable Working Pressure (MAWP) and is typically maintained at a level below the pressure relief devices' settings to minimize frequent activations.
A specialized separator is engineered to manage flow streams with high gas-to-liquid ratios, making it ideal for use alongside dehydrators, extraction plants, instruments, or compressors to safeguard against entrained liquids.
A vessel utilized in the field is designed to extract wellstream liquids from gas components, functioning in either a two-phase system that eliminates all liquids from the gas or a three-phase system that additionally separates free water from the hydrocarbon liquid.
A type of separator vessel used to remove the combined liquids from a gas stream.
ASME Code
Separators furnished to this specification shall conform to the material requirements stipulated in the latest edition of the ASME Code.
Selection
When selecting materials for corrosive fluids, it is essential to consult relevant API or NACE publications that comply with standard 3.1 Factors such as weight loss, sulfide stress cracking, chloride stress cracking, and other corrosion types must be considered Users are responsible for assessing corrosion considerations for the vessel throughout its intended lifespan, as outlined in the applicable ASME Code For detailed corrosion guidelines, refer to Annex B.
Corrosion Consideration
Corrosion considerations for separators specified here apply solely to the pressure-containing components of the vessel, in accordance with the relevant sections of the ASME Code For the vessel internals, which are non-pressure parts, corrosion considerations will be determined through mutual agreement between the purchaser and the manufacturer, and are not included in this specification.
Type, Size, Pressure and Temperature Ratings
Separators provided under this specification can be vertical, horizontal, or spherical, with various sizes and Maximum Allowable Working Pressure (MAWP) ratings listed in Tables 1, 2, and 3 These tables reflect nominal industry standards, but actual available sizes and working pressures may differ from the specified ratings Additional sizes, pressure, and temperature ratings can be arranged through mutual agreement between the purchaser and the manufacturer.
Process Design and Sizing
Typical process design and sizing calculations are given in Annex C.
Design Checklist
A suggested checklist of separator design information is included in Annex E.
S PECIFICATION FOR O IL AND G AS S EPARATORS 3
Sample Calculation
Annex D gives an example calculation for separator sizing.
Fabrication
Separators must be fabricated, tested, and certified in compliance with the most recent ASME Code Furthermore, additional testing for internal or external leaks may be necessary based on an agreement between the purchaser and the manufacturer.
Table 1—Horizontal Separators Size and Working Pressure Ratings
Nominal Diameter in Maximum Allowable Working Pressure psig @ 130°F
NOTE 1 Shell length is generally expanded in 2 1 /2-ft increments measured from head seam to head seam and is typically 5 ft,
7 1 /2 ft, or 10 ft A minimum length-to-diameter ratio of 2.0 is normally used.
Vessel diameters typically increase in increments of 6 inches, measured as either outside diameter (OD) or inside diameter (ID) Generally, OD separators are available up to a diameter of 24 inches, while separators larger than this can be constructed as either OD or ID vessels.
Table 2—Vertical Separators Size and Working Pressure Ratings
Nominal Diameter in Maximum Allowable Working Pressure psig @ 130°F
Shell lengths are typically extended in increments of 2.5 feet, measured from head seam to head seam, with common lengths being 5 feet, 7.5 feet, or 10 feet A standard minimum length-to-diameter ratio of 2.0 is generally applied.
Vessel diameters typically increase in increments of 6 inches, measured as either outside diameter (OD) or inside diameter (ID) Generally, OD separators are available in sizes up to 24 inches in diameter, while separators larger than this can be constructed as either OD or ID vessels.
Painting
Prior to shipment, it is essential to clean separators of any rust, grease, scale, and weld spatter, followed by an external application of a high-quality commercial metal primer If agreed upon by both the purchaser and manufacturer, internal coatings and finish coatings may also be applied Additionally, special access might be necessary to effectively apply internal coatings to smaller diameter vessels.
Internal Coating
When internal coating is required by the purchaser, all non-removable internal attachments must be seal welded and prepared according to the purchaser's specifications If no specifications are provided, acceptable practices can be found in Annex B Once the coating process is complete, the vessel should be stenciled in a prominent location.
“Internal Coating—Do Not Weld.”
Preparation for Shipment
Before shipping, it is essential to eliminate all foreign substances, including hydro-test water, from both the interior and exterior of the vessel Additionally, all openings must be secured with appropriate shipping covers or plugs.
API Nameplate
Separators meeting this specification must have a corrosion-resistant nameplate securely attached to a welded bracket on the shell or stamped on a steel nameplate that is seal welded to the shell This nameplate should include the information specified in items 1 through 9, as illustrated in Figure 1.
Table 3—Spherical Separators Size and Working Pressure Ratings
Nominal Outside Diameter, in Maximum Allowable Working Pressure psig @ 130°F
S PECIFICATION FOR O IL AND G AS S EPARATORS 5
The maximum allowable working pressure, measured in pounds per square inch, must be established at the maximum design temperature in degrees Fahrenheit Additionally, if mandated by the ASME Code or specified by the purchaser, the minimum temperature should also be noted.
8) Additional information required by state or other political subdivision regulations.
9) Additional markings desired by the manufacturer or requested by the purchaser are not prohibited.
ASME Code Nameplate
Separators provided under this specification must feature a nameplate attached to the vessel, in accordance with the most recent ASME Code edition Instead of a distinct API nameplate, manufacturers may choose to include the information specified in section 6.1 directly beneath the ASME Code markings on the ASME nameplate.
Stamping
Stamping directly on the separator shell may be injurious and should be avoided See ASME Code for allowable stamping.
ASME Code Inspection
The authorized inspector, as mandated by the ASME Code, is responsible for conducting all necessary inspections to ensure that vessels eligible for the Code symbol comply with its requirements Upon confirming that the vessel meets all provisions of the Code, the inspector will sign the Certificate of Inspection on the manufacturer’s data report, affirming the vessel's completeness and compliance.
Inspection Notice
Purchasers must specify the required extent of additional inspections on the purchase order If the purchaser's inspector wishes to inspect the purchased separators or witness the process, this should be clearly indicated.
Manufactured in Accordance with API Specification 12J Manufacturer
Serial Number Year Built Weight Empty Shell Size Max Working Pressure lb
The manufacturer must provide reasonable notice regarding the timing of inspections for any specification tests or evaluations of nondestructive examinations, which are conducted based on the outer diameter (OD) and length measurements in feet, as well as the pressure in psi.
Inspection by Purchaser
The purchaser's inspector shall have unrestricted access to all areas of the manufacturer's facility relevant to the production of the ordered materials The manufacturer is required to provide reasonable facilities at no cost to ensure compliance with the specifications Inspections will take place at the manufacturing site before shipment, unless otherwise stated in the purchase order, and should be conducted in a manner that minimizes disruption to the manufacturer's operations.
Rejection
Materials exhibiting harmful defects during initial inspection or after acceptance at the manufacturer's facility, or those that prove defective when used correctly, may be rejected, and the manufacturer will be informed If destructive testing is conducted outside the manufacturing site, the purchaser is responsible for payment of materials that meet all specifications, but will not pay for any materials that do not comply.
Compliance
The manufacturer is obligated to adhere to all specifications outlined in this document The purchaser reserves the right to conduct investigations to ensure the manufacturer's compliance and may reject any materials that fail to meet these specifications.
This annex provides a general discussion of the functional requirements of oil and gas separators and their controls as used in this specification.
A separator's primary function is to eliminate free gas from oil and/or water under specific pressure and temperature conditions To ensure efficient and stable operation across various scenarios, a gas-liquid separator is typically designed with several key features.
This specification focuses on effectively eliminating the majority of liquid from the inlet stream Initially, it targets the removal of liquid slugs and large particles to reduce gas turbulence and prevent the re-entrapment of liquid This preparation is crucial for the subsequent separation step, which often requires the use of inlet baffling to absorb momentum and alter the flow direction.
The primary separation method discussed here is the gravity settling of liquid from a gas stream, which occurs after the gas velocity has been decreased The effectiveness of this process is influenced by the properties of the gas and liquid, the size of the particles, and the level of turbulence in the gas Some designs incorporate internal baffles to minimize turbulence and break down foam, while these baffles can also serve as collectors for droplets.
In this section, liquids are collected with minimal disturbance from the gas stream Adequate capacity is essential to accommodate surges and ensure sufficient retention time for effective gas separation from the solution and the removal of free water from oil in three-phase separators To prevent gas or oil entrapment in the bottom liquid, a vortex breaker may be installed above the liquid outlet nozzle(s).
The mist extractor in the coalescing section can feature various designs, including a series of vanes, woven wire mesh pads, or centrifugal devices Its primary function is to eliminate small liquid droplets, typically as small as 10 microns in diameter, from the gas stream before it exits the vessel This process ensures that liquid carryover remains below 0.1 gallons per MMSCF.
Gas back pressure valves, which can be weight loaded, spring loaded, or pilot operated, are used to control operating pressure In pipeline delivery, the minimum separator pressure is typically determined by the transmission or gathering system pressure Separators must have one or more liquid level controls, with two-phase separators commonly using a liquid level control to activate a liquid dump valve for maintaining the desired liquid level Three-phase separators generally employ two liquid level control systems Internal weirs and baffles complement these controls, while gauge glasses or sight glasses are installed to indicate liquid levels Additionally, separators are usually equipped with a pressure gauge and thermometer well.
All separators must be equipped with pressure protective devices in compliance with ASME Code requirements, regardless of their size or pressure To ensure adequate relieving capacity, multiple pressure relieving devices, such as a pressure relief valve and a rupture disk, may be utilized Typically, the relief valve is set at the Maximum Allowable Working Pressure (MAWP), while the rupture disk is chosen to activate above this set pressure Although the separator manufacturer is not obligated to provide these pressure relief devices, it is essential to ensure over-pressure protection is in place before the separator is put into service The responsibility for supplying these relief devices should be determined by the purchaser.
Discharge lines from pressure relief devices must be evaluated individually While a comprehensive discussion is not included in this standard, guidance on discharge line considerations can be found in Appendix M of the ASME Code, as well as in API 520 and API 521.
Purchasers can customize separators with various controls and accessories, including an inlet shut-in valve, pressure sensors or controls, level sensors or controls, and temperature sensors or controls.
Separators come in three distinct shapes: vertical, horizontal, and spherical The arrangement of the four main components varies across different vessels Typical configurations for these two-phase separators are illustrated in Figure A.1 and Figure A.2, showcasing the designs for vertical, horizontal, and spherical separators.
S PECIFICATION FOR O IL AND G AS S EPARATORS 9
Figure A.1—Two-phase Separator Configurations
Figure A.2—Two-phase Separator Configurations
Horizontal Two-phase Double Barrel
The following guidelines are recommended for determining corrosion considerations for an applicable vessel.
Well streams containing liquid water and gases such as oxygen (O₂), carbon dioxide (CO₂), and hydrogen sulfide (H₂S) are classified as corrosive and must be evaluated according to the specifications outlined in API 14E, ASME Code, and NACE MR 0175.
The following guidelines are not mandatory but may be used to judge the extent of the corrosive environment, with respect to carbon steels. a) Oxygen:
1) less than 0.005 ppm in natural brine—non-corrosive;
2) from 0.005 ppm to 0.025 ppm requires consideration;
3) greater than 0.025 ppm in natural brine—corrosive. b) Carbon dioxide:
1) less than 600 ppm in natural brine—non-corrosive;
2) from 600 ppm to 1200 ppm requires consideration;
3) greater than 1200 ppm in natural brine—corrosive. c) Hydrogen sulfide.
1) No lower limit of hydrogen sulfide has been identified as being non-corrosive With hydrogen sulfide presence, the environment should be considered corrosive.
The latest edition of NACE MR 0175 should be referenced for assessing the risk of sulfide stress cracking (SSC) in environments containing hydrogen sulfide It specifies that systems operating at total pressures below 65 psia or with hydrogen sulfide partial pressures below 0.05 psi are not covered by this standard.
Should alloy steel or stainless steel be used, other forms of corrosion should be considered such as, but not limited to, chloride stress cracking.
Some of the other factors that influence corrosion in a given vessel include: temperature, pressure, fluid velocities, metal stress and heat treatment, vessel surface condition, and time.
When the environment is assessed to be susceptible to Stress Corrosion Cracking (SCC) according to the criteria outlined in NACE MR 0175, it is essential to adhere to all relevant provisions of this NACE standard concerning the materials and construction of the vessel.
If the environment is deemed corrosive based on the criteria outlined in B.1.2, this specification can be satisfied by implementing one or more of the following practices An allowance for corrosion in the vessel components may be made in accordance with the ASME Code, Appendix E, Suggested Practices.