Pressure Vessels and Drums - Types & Design Guidelines - PDFYAR

This article is about Technical Design Guidelines, Working Principle and Types of Pressure Vessels and Drums in Plants and Refineries and useful for engineers, designers, engineering managers and supervisors. All here discussed practical knowledge of industrial field.

What is Pressure Vessels?

Pressure vessels are containers designed to hold gases or liquids at a pressure higher than atmospheric pressure. They are used in a wide range of industries and applications, including oil and gas, chemical processing, power generation, and manufacturing.

The primary function of a pressure vessel is to safely contain and store substances under pressure. They are constructed with materials that can withstand the internal pressure and are designed with specific dimensions, thickness, and reinforcement to ensure structural integrity.

Pressure vessels come in various shapes and sizes, including cylindrical, spherical, and rectangular. They are equipped with safety features such as pressure relief valves and inspection ports to monitor and regulate the pressure inside the vessel.

Common examples of pressure vessels include storage tanks, boilers, heat exchangers, reactors, and compressed gas cylinders. These vessels undergo rigorous design, fabrication, and testing processes to meet industry standards and ensure safety.

Proper maintenance and inspection of pressure vessels are essential to prevent failures or leaks, which can have serious consequences. Regular inspections, periodic testing, and adherence to regulatory standards help ensure the safe operation of pressure vessels and protect both human life and the environment.

How Does a Pressure Vessel Work?

A pressure vessel works by safely containing fluids or gases at a pressure different from the surrounding environment. It is designed with materials and structural features to withstand the internal pressure and prevent leaks or failures.

Safety mechanisms like pressure relief devices are included to protect against overpressure situations. Regular inspection and maintenance are necessary to ensure its continued safe operation.

Types of Vessel in Oil and Gas

In the oil and gas industry, various types of pressure vessels are used for different purposes. Some common types of vessels found in oil and gas operations include:

Storage Tanks: These are large containers used to store crude oil, refined petroleum products, natural gas liquids, and other hydrocarbons. They come in different shapes and sizes, such as horizontal cylindrical tanks, vertical cylindrical tanks, and spherical tanks.
Separators: Separators are vessels used to separate oil, gas, and water in the production process. They allow the different components to be separated based on their density and can be either horizontal or vertical in design.
Heat Exchangers: Heat exchangers are used to transfer heat between fluids in oil and gas processing operations. They help to cool or heat fluids by allowing heat exchange between the process fluid and another fluid or medium. Shell and tube heat exchangers are commonly used in the industry.
Reactors: Reactors are vessels used for chemical reactions in the refining and petrochemical industries. They provide a controlled environment for chemical reactions to occur, such as the conversion of hydrocarbons or the synthesis of various products.
Condensers: Condensers are vessels used to condense vapor or gas into liquid form. They are commonly used in natural gas processing to condense and collect valuable hydrocarbon liquids from the gas stream.
Pressure Vessels: Pressure vessels in the oil and gas industry are used for various purposes, such as storing and transporting compressed gases, containing fluids under high pressure, and maintaining the pressure of process streams. They can be found in compressor stations, refineries, and other facilities.

These are just a few examples of the types of vessels used in the oil and gas industry. Each vessel has its specific design and function, playing a crucial role in the processing, storage, and transportation of oil and gas products.

Pressure Vessels and Drums Design guidelines

A. Technical Design Guidelines for Engineers

1. Sizing Criteria

The following design considerations will be used in sizing vessels and tower sumps.

a. Minimum level for the low low low (LLL) in vertical vessel will be 300mm above the tangent line, and in horizontal vessel will be 150 mm above the bottom line.

b. Generally normal liquid level in the horizontal vessels should be half full.

c. Low liquid level in the tower bottom should be 300 mm above the tangent line.

2. Means shall be available for purging process equipment with Inert gas (N2).

3. Vessels shall be provided with a steam out connection with a block valve and blind. The steam-
out connection shall be below the normal liquid level to allow for wet streaming.

4. Mist eliminator shall be used for vapor minimizing entrainment, typically in Reciprocating
Compressor suction knock out drum (KOD).

5. Mist eliminator shall be used for Vapor/Liquid separators, to reduce the drum size unless
pressure drop or other limitations exist.

6. Design Factor – the maximum allowable velocity shall not exceed 0.7-0.8 times the terminal velocity, for systems, which have foaming tendency (such as Glycol & Amine Solutions).

7. For draw-off boots, the boot diameter shall be sized such that the heavy liquid draw-off velocity
does not exceed about 80% of the rising velocity of the light liquid.

8. Vessel internals may consist of Overflow Dams (Weirs) when Hydrocarbons may have to be
skimmed from an aqueous solution such as oil in wastewater skimmers or hydrocarbon liquid in
amine flash drums.

9. Surge Time – Additional surge time shall be provided above High – high level alarm for drums
upstream of compressors. Additional surge time shall be provided below Low – low level alarm
when the drum is operating at high pressure & supplies liquid to low-pressure fractionation
equipment.

10. All nozzles shall be flanged, including instrumentation and thermowell connections.

11. The nozzles for instruments on the vessel shall be on the same side as the feed nozzle to avoid
impingement of the feed on the instrument itself and cause false indication.

12. Bridle connections are 2 inches flanged.

13. Nozzle sizes 2-1/2, 3-1/2, 5 and 7 inch shall not be used.

14. Turndown requirements shall be specified on the tray data sheet.

15. To minimize the build-up of static charges, all liquid inlet nozzles should be located below the low liquid level or shall be provided with a dip pipe for top entry. Refer to NFPA-77.

16. The selection of Material for Construction of a process drum / vessel shall also consider the need for specific cleaning methods and conditions that can significantly impact the steel selected or fabrication requirements.

17. For vessels in continuous operation, a low alloy or carbon steel process drum may be designed with a corrosion allowance of 3 mm. Allowances ranging from 1.5 to 3 mm. may be used depending on the jacket fluid and conditions for jacketed process drums.

B. Liquid Surge Requirements Guidelines

Surge requirements will be established for each unit to assure process stability. The following table provide Company’s typical requirement.

Table 9 – Vessel Liquid Surge Requirement

C. Nozzles

1. Generally all nozzles will be flanged including instrumentation. However welded nozzles may be specified for high pressure, cyclical and/or hazardous services. These will be evaluated on a case by case basis considering LICENSOR’s advice and process critically.

2. Minimum flange nozzle size will be 2 inch (vent, drain and cold blow down 1-1/2 inch). Flanges for instrumentation attached to lined tanks and vessels may be dictated by lining requirement.

3. Steam out and purge connection nozzles will be 2 inch minimum.

4. Vent, drain (cold blowdown as required) nozzles are based on the vessel volume as indicated in
the following table. Drain nozzle size is 2 inch minimum and direct connected. The drain should be sized in accordance with following schedule. Utility connections can be used for various functions including nitrogen purge, steam out, water fill, depending on requirements. The connection sizing is based on steam out. For larger vessels requiring water fill, the utility connection size to be used as shown in brackets.

Table 10 – Vessel Functional Connection Size Schedule

Minimum 10-inch exhauster nozzles will be provided at the top and bottom for all vessels greater than 1000 mm ID or 2000 mm tan to tan (T/T), if a suitably located man way is not available.

5. Drains shall be provided on the low points of all process lines. Vents shall also be provided on high points, if deemed necessary.

6. All drains and vents shall be either capped, plugged, blinded, or have two closed block valves in series.

7. All drains pipelines to trench shall be preferably below ground level to avoid tripping hazards.

8. All drain piping shall be taken up to the nearest trench with minimum short radius bends and suitable break off flange for maintenance incase of blockage.

9. Valving of operating vent, drain shall be as follows:

a. Vents and drains with ANSI Class-600 rating or less shall have single block valves.

b. Vents and drains in ANSI Class-900 rating and over shall have double block valves.
c. Drains for piping or equipment in flammable fluid service shall be provided with a shut-off
valve upstream of a throttling valve regardless of rating.

10. Equipment in flammable vapour service shall be provided with two vents one of which will connect to the flare system for safely depressuring the equipment. The second vent will discharge to the atmosphere and will be blind or plugged on the downstream side of the vent valve. The equipment vent may be located in connecting piping provided there is no valve or blind located between the vent and equipment. Minimum size of the vessel vent is 2 inches.

11. When the bottom outlet line extends into the vessel, the drain will be directly on the vessel.
Minimum size of drain at vessel is 2 inches.

D. Internals

1. Vapour/ Liquid Separator

Vessels with mechanical separators such as wire mesh shall not be used in plugging or fouling
service or on the suction side of reciprocating compressors.

2. Water Collection Sumps (Boot)

A sump will be provided in accumulators, where water is to be drained during normal operations. In
general, this sump will have a volume equivalent to 7 minutes water flow minimum, with 5 minutes
residence time below the hydrocarbon/water interface. Water sump, if required, will be located
between inlets and pump suction.

3. Manways

Manways will be provided for maintenance of all vessels and tank. For vessels and columns of 1000 mm and greater diameter; the minimum size of the manway will be 24” or larger as appropriate for
the equipment, unless changed by Company. In general the manways will be located near the base of the vessel, at the top and the midway points for trayed columns and between packed beds in
packed columns.

Location and spacing shall be in accordance with SABIC Engineering Standard, Q01-S01, and
Pressure Vessels – General.

Platforms for man-way access will be provided for manways located 4-m and higher. For manways
less than 4 – m from grade, platforms shall be provided if maintenance access is required at the
intervals 6 months or less. Columns/Vessels of less than 1000 mm will be of flanged construction.

4. Vortex Breaker

Vortex breakers are required on vessel nozzles where liquid lines are routed to a pump.

E. Isolation and Valving

Fire safe valves will be used in systems for storage of flammable fluids or fluids stored above
their flash point.

2. Fire safe valves with fire safe seats will be used as primary block valves for hydrocarbon and toxic storage vessels containing flammable fluids or fluids above their flash point. The actuation system of the fire safe valves will also be fire safe. Refer to the SSD-27 for storage tank valves and their remote isolation.

3. Fire safe valves will be provided in piping at vessel and storage tank nozzles as follows:

a. In piping at all nozzles below the liquid level of flammable liquid storage tanks.

b. In liquid draw-off lines at the nozzles of process vessels containing 5.7 m3 or more of a flammable liquid at the maximum normal liquid level when the line does not contain a block valve located within 9 m in a horizontal direction from the vessels.

4. Block valves shall be provided in liquid draw-off lines at the nozzles of process vessels containing 5.7 m3 or more of a flammable liquid at the maximum normal liquid level when the line does not contain a block valve located within 9 m in a horizontal direction from the vessel.

Pressure Vessels and Drums – Types & Design Guidelines

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