Underground / Buried Piping System Design

Written by Ankur Srivastava in Piping Design Basics,Piping Stress Analysis,Process

Applications of Buried Piping

The piping that is in contact with soil or runs below grade level is called buried or underground piping. In the oil and gas industry, we find frequent use of buried piping mainly for cross-country pipelines where security and safety justify the pipelines to be underground. Here security means the difficulty of sabotage and intentional damage to an underground pipeline. Safety means the safety of the environment and the surrounding population centers due to accidental damage to the underground pipeline.

The firefighting system network piping mostly runs below ground with certain sections above-ground. Above-ground pipelines are also intermittently buried in roads and railway crossings. Other major applications include Cooling water lines inside process plants, Oily Water Sewer lines, Contaminated Rain Water Sewer from the process catchment area, Sanitary systems, Equipment drainage to slop tank, Closed Blow-Down system, Storm Water, Liquid Effluent to the Effluent Treatment Plant, etc.

However, note that Piping should not be buried or installed underground if it can be reasonably avoided.

A basic understanding of the concepts of buried piping installation along with routine process design calculations related to piping such as pressure drop, velocity and erosion/corrosion limits for various pipe metallurgies are always advantageous for engineers. This article will provide some important guidance on buried or underground pipe installation.

Underground Piping in Process Piping

In the process piping industry, underground piping falls into one of the following two categories:

Process lines &
Drain lines (Closed Process drains and Open Gravity Drains).

All underground pipes are buried with a minimum cover of 500 -1000 mm on top of the pipe known as the minimum depth of cover. The actual depth of cover may vary depending on pipe stress analysis requirements, rail/road calculation, etc. In practice, the more depth of cover the better it is, but the same will increase project installation cost. So, an optimized depth of cover is decided by buried piping stress analysis.

Underground Pipe Types

Based on the application and service fluid, different types of underground piping systems are found. Some of those underground pipe types are:

Underground Process pipes
Underground Process and gravity drain pipes
Contaminated and Uncontaminated stormwater.
Chemical sewers
Oily water service
Firewater systems
Solvent collection systems
Sanitary sewers
Combined sewers
Blowdown systems
Pump-out Systems
Potable water systems
Underground cooling water systems

Information required for designing an underground piping system

The major data or information required for designing underground piping systems are:

Plot plan
Topographic data
Piping specification
Soil investigation report/soil data
Underground specification
Types of the underground system
General arrangement drawings
Piping studies
Site data
Rainfall in the region
Firewater requirements
Frost depth
Local codes and regulations.
Invert elevations of lines at the process battery limit.
Electrical and instrument conduit routings if applicable
Client specifications
Paving details
Pipe Trench details
Foundation size and plans
Road limits, etc.

Underground Piping Materials

Different underground piping materials that are widely popular in the buried piping industry are:

Material	Uses in Underground Piping
Carbon Steel	closed-drain systems, cooling water, and firewater
Stainless steel	closed drains—chemical and corrosive service
Concrete pipe	surface drainage, and for 15″ and larger pipes
Glass Pipe	floor drains in process plants, mainly acid service
Fiberglass-reinforced plastic pipe	corrosive service, low-temperature and -pressure systems
PVC	corrosive service
Cast iron	stormwater and oily water drains (hub and spigot fittings)
Vitrified clay pipe	gravity drain systems
Ductile iron	Process water

Table 1: Underground Piping Materials

Codes and Standards for underground Pipeworks

There are a number of underground piping standards that provide guidelines for the design, fabrication, and installation of buried piping systems. Some of the most common underground piping standards are:

ASTM D2321
ASTM A74
ASTM A120
SAS 236
DIN 1230
SAS 14
ASTM D3034
ASTM D1785
ASTM C700
ASTM A746

Over the past few years, underground firewater piping has gained popularity because of the following:

When untreated water comes in contact with above-ground carbon steel or lined carbon steel pipes, it becomes a source of corrosion and undermines the integrity of the firewater system. For this reason, corrosion-resistant HDPE or GRE plastic piping systems are more frequently used in recent times.

Although plastic piping possesses higher corrosion resistance to untreated water, it has much lower mechanical strength compared to carbon steel pipes considering forces such as impact and vibration.

So, to maintain the mechanical integrity of the plastic pipe, It is a logical option to bury the firewater plastic pipe and running across the installation.

Another option is to use exotic metallurgies (Stainless steel / Cupro-Nickel etc.) for firewater networks but that is not an economical choice. At the same time, common austenitic stainless steels are susceptible to chloride stress corrosion cracking in a water environment with high chloride content.

Problems Associated with Buried Piping

The main problems with underground piping are

Even after applying mitigating measures such as external coating and cathodic protection, Buried Steel pipes are subjected to external corrosion.
Draining, and cleaning buried pipes is difficult compared to an aboveground pipe.
Leak detection and repair of buried pipes is a difficult and expensive exercise. Modern underground pipeline leak detection systems are available in recent times but they are very expensive to install.
Buried pipes are subjected to mechanical damage when soil excavation work is being carried out in close vicinity.
Buried pipes carrying hot fluids and subject to thermal expansion can cause pipe deformation and/or partial/total removal of the external protective coating is applied.

Corrosion Protection of Buried Pipes

All buried steel piping with the possible exception of cast iron piping should be protected from soil corrosion with a suitable external coating.

Following is the list of the most commonly used acceptable coatings and wrappings with approximate pipe surface temperature limitations:

Fusion Bonded Epoxy (< 93°C)
Liquid epoxies (< 107°C)
Extruded Plastic (< 82°C)
Tape Wraps (< 60°C) (higher temperatures applicable in case of high-temperature thermosetting tape)
Coal Tar Enamels (< 60°C)

Tape wrap is often selected when small quantities of buried piping require protection because it is relatively inexpensive and easy to apply in the field. However, it has very low reliability with poor performance in water- and oil-saturated soils, and in cyclic temperature service. It requires proper pipe surface preparation and is easily applied improperly.

Protection for the coated pipe at weld joints and tie-ins is provided by field-applied fusion bonded epoxy, shrink sleeves of polyethylene, heat-cured liquid epoxy, or tape wrap.

Aside from the type of coating selected, proper application of the coating and maintenance of its integrity are required for the proper installation of a protected line. Because success or failure cannot be determined for an extended time after installation, usually years, attention should be paid to:

Proper surface preparation for the type of coating used
Coating Application as per the specified consistency and thickness
Proper Care during laying and handling to avoid coating damage
Proper cleaning, priming, and field coating of joints and pipe fittings
Thorough Inspection of the applied coating for any damage and proper repair
Finally, Backfilling and compacting to prevent contact with any material that could damage the coating

Cathodic Protection

Cathodic protection (CP) can be roughly defined as retarding or preventing the corrosion of a metal by imposing an electrical current flowing to the metal through an electrolyte. In the case of buried piping, the pipe is the metal and the soil is the electrolyte.

Cathodic protection is often used with coatings to protect piping. Regardless of the care used in coating and installing buried lines, there will often be small pinholes in the coating. A cathodic protection system can protect against corrosion at these points and significantly extend the life of the piping.

Cathodic protection is normally applied to buried piping as a system. At every place, where the cathodically protected pipe leaves the soil (or water), it must be electrically isolated from the aboveground continuation of the line if the continuation is not part of the CP system. This must be done with an insulating flange gasket kit that uses electrically insulating bolt sleeves, nut washers, and a sealing gasket in a conventional flange makeup.

The major users of cathodic protection are Cross country steel pipelines and steel submarine piping.

Online Buried Pipe Stress Analysis course using caesar II

If you need to learn the buried piping stress analysis basics then click here and join the course

Few more useful resources for you..

Buried GRP/FRP pipe Laying and Installation Procedure
Basics for Stress Analysis of Underground Piping using Caesar II
Underground Piping Stress Analysis Procedure using Caesar II
What if Piping Continuation is Unknown? Part 2. Underground Piping
Various Analysis methods for Underground Piping Using Caesar II
Cathodic Protection Basic Principles and Practices

Pressure vs Stress: Differences Between Pressure and Stress

Written by Anup Kumar Dey in Civil,Mechanical,Piping Interface,Piping Stress Analysis,Piping Stress Basics

In the piping industry, the term Pressure and Stress are always used and most of the time it creates huge confusion among users as the unit of both Pressure and Stress is the same (Pounds per square inch (P S I ) or Newtons per square meter or Pascal). However, Both Pressure and Stress are different. So, the differences between stress and pressure i.e, Stress vs Pressure must be known to clearly understand the terms.

Pressure Vs Stress

Pressure is an intrinsic property and most of the time related to fluids. It depends on the momentum transfer between the atoms of a liquid or gas volume (molecules constrained inside the volume) on a micro-scale.

While Stress is a consequence of the tendency of a body undergoing arbitrary deformation to spring back to its own reference state; To simplify stress is generated whenever a force is applied to a body to deform it.

In this article, I will list down the major differences between Pressure and Stress in a Tabular format.

Difference Between Pressure and Stress

Sr. No	Pressure	Stress
1	Pressure can be defined as the intensity of external forces acting at a point. It is the amount of external force applied per unit area. The pressure is exerted on the body.	Stress can be defined as the intensity of internal resistance force that is developed at a point due to the application of force or pressure. It is the amount of internal force being exerted per unit area. Stress is produced inside the material body.
2	Pressure is a unique property of thermodynamics or physics.	Stress is a material property.
3	Pressure always acts normal to the surface on which it acts.	The stress can be in any direction and any angle depending on the application of force.
4	Pressure always tries to compress the surface on which it is applied.	Stress can be tensile or compressive depending on the load type.
5	Pressure can be exerted on both liquids and gases.	Stress can only be exerted on solid materials.
6	Pressure is physically measured (measurable quantity) using pressure gauges, barometers, manometers, and other pressure-measuring devices or instruments.	There is no device to measure stresses (not a measurable quantity). These are only calculated mathematically. Stress is calculated by measuring strain or elongation.
7	Pressure is a positive unit and can be represented as “p”= F/A (F positive as direct force)	Stress can be either a positive or a negative force, this can be represented as Stress “Ϭ”= – F/A. (-F as internal resisting force)
8	The pressure is independent of the area of the contact surface. It remains constant and does not vary with changes in surface area. For example, Assume a 500 Pa pressure is applied to a 100 m² area. Now even if you change the area to 10 m² the pressure will remain constant. However, the calculated force will vary depending on the area.	On the other hand, stress varies with changes in surface area. Here, Force remains constant but an increase in the area causes the stress to reduce and vice versa. The magnitude of Stress varies inversely with the surface area on which it applies.
9	The pressure is a scalar field variable and does not depend on the direction as it always acts normal to the surface. The magnitude of the pressure at a point in all directions remains the same.	Stress is a vector variable and depends on the direction of the applied force. The magnitude of stress at a point in a different direction is different.
10	Pressure is the cause of stress	Stress is the result of pressure.
11	Pressure is a thermodynamic property.	Stress is a material property.

Table showing the Differences Between Pressure and Stress

Few more handpicked articles for you.

Differences between Piping Engineering Terms
Piping Stress Analysis Basics
Mechanical Design Basics
Process Design Basics
Piping Layout and Design Basics

Storage Tank Piping Layout with Online Course

Written by Anup Kumar Dey in Piping Design Basics

Storage tanks are the containers/vessels which are used for storing the fluid. A group of tanks together is called ’Tank Farms’. The preferred design standard for Atmospheric storage tanks is API 650. The use of tanks is common in all kinds of plants. However, Petroleum and Water industries are the largest users of tanks.

Storage tanks are manufactured in different shapes, sizes, and capacities. Cylindrical tanks are the most common ones. Spherical tanks are used for storing LPG. Proper arrangement of tanks and pipes is required to optimize space and cost. Broadly, Storage tanks are used to

store feed products prior to processing.
hold partially processed products before further processing.
collect and hold finished products prior to delivery to market.

A) Process Plant

Refineries
Petrochemicals
Specialty chemicals

B) Terminals

Types of Tanks in Process plant

Based on the type of products to be stored, shapes, sizes, and potential to fire storage tanks can be grouped into various types like

Cone roof tanks: Low-pressure tanks for storing petroleum, water, food products, chemicals, and petrochemical products.
Floating roof tanks: The roof floats depending on the volume of stored products. Mostly used in oil refineries, such types of tanks reduce fire hazards.
Low-temperature storage tanks: Usually store cryogenic fluids line liquefied ammonia, propane, methane, etc.
Horizontal pressure tanks or Bullet tanks: Elliptical or hemispherical high-pressure tanks.
Hortonsphere pressure tanks: Store large quantities of fluids under pressure.
Underground Tanks for drain collection of the plant at atmospheric pressure.
FRP Tanks for corrosive fluids at atmospheric pressure.

Click here to know more about atmospheric storage tanks

The design of the tank farm and tank farm piping layout should take into consideration the following guidelines

Local rules and regulations.
Client specifications.
Maintenance and operation requirements.
OISD 118, 117, 117
NFPA 30
API 2030, etc.

Tank Farm Layout Consideration

The main considerations for tank farm layout are

The storage tanks shall be located at a lower elevation, wherever possible.
The storage tanks should be located downwind of process units.
All process units and diked (diked) enclosures of storage tanks shall be planned in separate blocks with roads all around for access and safety.
Provide a minimum of two-way access to enter the storage tank area. Preferably roads shall be provided all around the dike. Also, vehicular access is to be provided inside the dike for maintenance purposes.
Due to the risk of failure of storage tanks, an Earthen / RCC Wall(Dike) must be provided around the tank in order to hold the liquid.
A staircase shall be provided to enter in storage tank area from the outside dike.
The tank farm should be secured by fencing & access gates shall be provided.

Relative location for Area Layout

**Fig. 2: Relative Location of Storage Tank Farm**

Tank Farm Layout (Dike Enclosures)

Tanks shall be arranged in a maximum of two rows. Tanks having 47,700 cu.m capacity and above shall be laid in a single row.
The minimum distance between the tank shell and the inside toe of the dike wall shall not be less than half the height of the tank.
The Dike enclosure for the petroleum class shall be able to contain the complete contents of the largest tank in the dike.
Height of Dike(H): 1m<H<2m (Click here to learn about the tank dike wall height calculation)

Width of Dike(W): Minimum 0.6m (Earthen dike); No specific (RCC dike)

The separation distance between the nearest tanks located in separate dikes shall not be less than the diameter of the larger of the two tanks or 30 meters, whichever is more.

In a diked enclosure where more than one tank is located, the intermediate dike is provided. The height of the intermediate dike wall should be 450 mm if concrete and 600 mm if earthen.

Types of Dike

Tank Foundation Height

For fixing the tank foundation height, discuss with the Process and Mechanical team, the Net Positive Suction head requirement (NPSH) of the pump, especially for crude oil service.

Sleeve Details in a Dike or Bund Wall

For locating tanks with respect to other tanks & equipment or vice versa, Refer to the minimum separation distance as mentioned in the company standard.

Tank Nozzle Orientation

Nozzle orientation shall be standardized for ease of operation & following points are to be noted:

The nozzle on the roof is to be oriented such that under no circumstances operator step on the roof.
Group the nozzles in one plane, so that operator movement on the roof is minimum.
Instrument nozzles on the roof & shell shall be planned such that they are in the silent zone & do not experience fluid turbulence.
The dip hatch nozzle is to be oriented such that there is no product spillage on the staircase & operating area.
For Spiral stairways orientation, show the start point & endpoint of the platform. Also, provide a mid-landing platform base on tank height.
Nozzles & platforms on the tank roof shall be marked separately in the nozzle orientation drawing. For more details about the tank-nozzle orientation, Click here

Tank Piping Layout

The optimum tank piping arrangement in a tank farm is the most direct route between two points allowing for normal line expansion and stresses. Usually, the following guidelines are followed while designing tank piping layout:

Piping located in a diked enclosure should not pass through any other diked enclosure directly.
The number of piping in the tank dike shall be kept minimum and routed directly outside the dike to Sleeper/Pipe rack.
Pumps and associated piping shall be located outside the dike wall.
A pipe may only be routed through bund walls if it cannot be passed over the Dike walls (eg. Suction line). Pipe passing through the dike shall be sleeved and sealed.
Access platforms shall be provided for valve operation & for the instrument.
The pump shall be provided in a curbed area with proper provision for draining.
No piping shall be routed in the dropout(Maintenance)area.
The tank outlet line to the Pump suction nozzle is a gravity flow line. Pump suction piping from the tank shall be as short as possible.
A pipe connected to tanks shall be sufficiently flexible.
Analyze the pipelines connected to the tank as per stress criteria given on a stress analysis basis.
Blanket gas(Fuel gas) & Vent gas line (Big bore size) can be routed & supported over the tank roof. Support location & load of such lines shall be marked in the tank vendor drawing. So the vendor will take care load for the design of the raft and will provide support cleat at the required location. Again need to discuss with the vendor for the high load if any.

Supporting Tank Piping

In general, the following rules can be considered for supporting pipes connected to storage tanks:

The tank Inlet & Outlet line can be supported either from the tank shell or the Tank foundation. If the support is taken from the tank foundation, this information shall be sent to the Civil department during the initial stage of the project & to the Tank vendor for providing vessel cleat.
Spring support or a Teflon pad may be introduced as the first support from the tank as per stress analysis based on tank settlement.
Keep the first support from the tank as far as possible. Group the lines for combined support.

Tank Farm & Piping

**Fig. 6: Typical Tank piping arrangement inside dike wall**

Fire Fighting for Tanks

The following firefighting requirements should be considered for tank and tank piping arrangements:

A fire in one part/section of the plant can endanger another section of the plant.
If a fire breaks out, it must be controlled/extinguished as quickly as possible to minimize the loss of life and property and to prevent the further spread of fire.
Foam systems & water spray systems are often provided as part of the fire protection system.
Permanent fire hydrants and monitors alternatively are used.
Locate hydrant & monitor along the road for easy access and for operation.

Online Course on Tank Farm Piping Layout and Stress Analysis

If you are hungry to learn more about the tank farm piping layout and stress analysis procedure using Caesar II then the following online course will be ideal for you. The online Tank Piping course is designed by a highly experienced PMP-certified piping engineer who has worked with some of the renowned MNCs of the Oil and Gas design industries. So, what are you waiting for!! Simply click here to check the topics covered and then join the course at the cheapest price.

Few more Useful Resources for You.

Considerations for Storage Tanks Nozzles Orientation.
A Brief Presentation on Storage Tanks
Various Types of Atmospheric Storage Tanks
Tank Settlement for Piping Stress Analysis
An article on Tank Bulging effect or bulging effect of tank shells
An article on Tank Pad Foundation
Storage Tank design using software TANK and re-rating with API 620 & API 579
EMERGENCY VENTS FOR STORAGE TANK: A PRESENTATION
Modeling Piping Connection to Storage Tank
The Basic design of High-Pressure Storage Tanks to store liquefied petroleum gas (LPG)

Comparison of Pipe and Tube | Pipe Vs Tube

Written by Anup Kumar Dey in Engineering Materials,Mechanical,Piping Design Basics,Piping Interface

What is a Pipe?

Pipes are used for transporting fluids and gases in Chemical, Petrochemical, Power Plants, Refineries, Storage units, Compressed air systems, Plumbing systems, etc. They are circular in cross-section and specified by Nominal Pipe Size.

What is a Tube?

Tubes are used for mechanical applications (Heat Exchanger, Fired heater, Boiler, etc.), for instrumentation systems (used for measuring instruments); for structural applications, etc and could be rigid or flexible. They are specified by their outer diameter and tube wall thickness, in inches or in millimeters.

Differences between Pipe and Tube

From a layman’s viewpoint, Both Pipe and Tube seem to be the same as they have many similarities like both are hollow, usually made from metals, can transfer fluids, etc. Many a time, these terms are used interchangeably. But in actual practice Tubes and Pipes are not the same as both possess different features. Through this article, we will try to investigate all such characteristics based on a few parameters like Size, Shape, Diameter, Thickness, Use, Availability, End Connection, Design Standard, etc.

Sr No	Parameter	Pipe Characteristics	Tube Characteristics
1	Shape	Pipes are always cylindrical or round in shape	Tubes are usually cylindrical in shape. However, tubes of different other shapes like square, rectangular, etc. are available.
2	Size	A pipe is Specified by Nominal Pipe Size (NPS) or Nominal Bore (NB).	The size of the Tubes is specified in millimeters or in inches by outside diameter.
3	Diameter	The outside diameter of pipe up to size 12” is numerically larger than the corresponding pipe size	The outside diameter of tubes is numerically equal to the corresponding size.
4	Thickness	Pipe Wall thickness is expressed in schedule numbers that can be converted into mm or inches.	Tube Wall thickness is expressed in millimeters, inches, or BWG (Birmingham wire gauge.)
5	Thickness Increment	Pipe thickness depends on the schedule, so there is no fixed increment	The thickness of tubes increases in standard increments such as 1 mm or 2 mm

Pipe vs Tube

Sr No	Parameter	Pipe Characteristics	Tube Characteristics
6	Application	Pipes are extensively used in all Process, Power & Utility lines to carry fluids.	Tubes are used in tracing lines, tubes for heat exchangers & fired heaters & instrument connections. They are more prevalent in the medical area, construction, structural, or load bearing.
7	Availability	Pipes are available as the small bore and the big bore	Normally small-bore tube is used in process piping. For structural use, tubes are available in custom sizes.
8	Structural Rigidity	Pipes are always rigid and resistant to bending	Tubes are available as rigid as well as flexible depending on the application. Rigid tubes are normally used in structural applications whereas copper and brass tubes can be flexible.
9	Joining and Stability	Joining pipes is more labor intensive as it requires flanges, welding, threading, etc.	Tubes can be joined quickly and easily with flaring, brazing, or couplings, but for this reason, they don’t offer the same stability
10	Tolerance	Pipe tolerances are not too restrictive.	Tolerances are very strict with tubes compared to pipes and tubes are often more expensive to produce than pipes

**Pipes used in operating process plant**

Sr No	Parameter	Pipe Characteristics	Tube Characteristics
11	Manufacturing	Pipe manufacturing is easier as compared to tubes	Tubes need more cumbersome tests, inspection, and quality control than pipes.
12	Cost	Cheaper	Costlier
13	Packing & Delivery	Delivered in the bundle as a bulk item. Delivery time is short.	Tubes are usually wrapped with a wooden box or thin film and delivered with much care. Delivery time is longer.
14	Production Quantity	Pipes are produced in mass quantity and for long-distance applications.	Tubes are produced in small quantities depending on requirements.

Sr No	Parameters	Pipe Characteristics	Tube Characteristics
15	End Connection	The end connection of pipes is normally plain or beveled for welding purposes	Tubes are available with coupling ends, irregular ends, special screw thread, etc.
16	Surface Finish	The inner and Outer surface of the pipe is rough in comparison to the tube	Tubes are manufactured on both the inner and outer surfaces as smooth
17	Common material	Common pipe material is Carbon Steel	The common tube material is Alloy Steel
18	Design Codes & Standards	The Thickness of the pipe is decided as per governing codes like ASME B31.3/ B31.1/ B31.4/ B31.8 or IBR Codes	The thickness of tubes is dependent on the use thickness is decided.

I am sure there will be many more differences, so I request the readers to list out those in the comments section.

Few more useful resources for you.

Difference between Tee and Barred Tee
Comparison between Piping and Pipeline Engineering
Difference between Stub-in and Stub-on Piping Connection
Difference between Centrifugal and Reciprocating Compressor
Differences between Hot-dipped galvanization and Electro-galvanization
CAESAR II vs START-PROF Piping Stress Analysis Software Comparison
API vs ANSI Pump

Considerations for Storage Tanks Nozzles Orientation

Written by Anup Kumar Dey in Piping Design Basics,Piping Interface

The function of a Storage Tank

A storage tank is one of the most important static equipment used frequently in tank farm areas to store liquids for further processing or use. They serve two important functions:

Serves as a container to store fluids and
Provide a pressure head for further distribution of the stored product.

For processing plants (refineries, chemical and petrochemical complexes, etc ), Storage tanks find their uses in several phases like

to store the feed (For example Crude Oil) before processing
to hold partially processed products and
to collect finished products.

In every plant, a number of storage tanks are used. Hence, a good arrangement of these storage tanks not only saves land space but also reduces the cost of a plant.

What is Nozzle Orientation?

Each tank has several nozzles to allow the Fluid in or out. All these nozzles must be arranged in a cost-effective efficient way such that they work smoothly without overloading the nozzle connections during operation. Proper nozzle orientation of storage tanks helps in reducing the maximum of operational problems. Good nozzle orientation is thus one of the most important activities in the piping layout and design stage.

Considerations for Storage Tank Nozzle Orientation

The number of tank nozzles is dependent on the operation and fluid handled. The orientation of each nozzle and providing platforms shall be considered together.

Normal practice is to collect body (shell) nozzles on one side of the tank and roof tanks in the same direction along with of roof platform (Fig 1). By this design, these nozzles and the valves, connected to each nozzle are easily accessible. Lesser platforms are required in such cases. Hence, the design is economic.

However, there are some exceptions like the tank manhole. It is better to locate the manhole in a different direction to other nozzles, the reason being easier entrance and exit.

A proper understanding of the fluid flow concept and nozzle performance helps the piping design engineer with better nozzle orientation design.

**Fig. 1: Sample of Nozzle Orientation**

Manhole of the Tank

Manholes are provided for frequent maintenance purposes. So it must have good access. It has to be provided based on the requirements set forth in the contract specifications. Locate manholes close to the dike accessway, far from the pipe way, and also accessible from the ground then operators can enter and exists easily.

Sealed and Vented manholes are to be provided at strategic points of the tank system when separate major groups of storage tanks, process blocks, and loading facilities are involved.

Two types of tank-shell maintenance access openings are used: the standard and the round opening. The large tanks or those that use internal heaters normally use the larger, oval-shaped, flat-bottom opening.

The access opening area must be kept free of any obstructions like large pipe supports, piping, and light poles.

Orienting the Input/output nozzles

The main process nozzles of a tank are input/output nozzles. The main point, where there is no other process requirement, is the minimization of pipe length (and so pressure drop). For example, sometimes it is required to locate these nozzles on different sides of the tank to mix fluid inside of the tank. Nozzle elevation also affects orientation; locating the elevated input nozzle and output nozzle in the same orientation vapor, which is soluted during the falling of liquid, will make gas traps in piping or cavitations in pumps. In Fig 1, A1 stands for the inlet and B1 for the outlet nozzle.

In Fig 1, A3 is the recycling or circulation nozzle used for circulating fluid via the outlet nozzle and pump then entering the tank through this nozzle, when the risk of freezing, choking or sedimentation of tank fluid exists. Consideration for the orientation of this nozzle is the same as the inlet nozzle.

Consideration for Tank Draw-off Nozzle

For Storage tanks in hydrocarbon services, to permit periodic draw off of water which normally collects in the product, an API low-type shell nozzle, and a drain valve are normally provided at the bottom of the tank. The water draw-off valve is normally positioned over an open concrete box with an outlet discharging into the gravity oily water collection system. For this nozzle, consideration of OSW lines is mandatory, to use less sump and pits in this system. In a group of tanks that are in one row, this nozzle can be located on the same side. In Fig 1, D1 is a draw-off nozzle.

Sampling Nozzles

A manual gauging-sampling well may be used where the stored product, is specified as a static accumulator. Gauge well shall be burr-free. If a manhole or a separate roof connection is used for gauging-sampling purposes it shall be located near roof support. All sampling valves shall be accessible and since valves are to be installed as close as possible to nozzles, so all nozzles shall be accessible. Normally, samples can be taken two liters per at 3 points at upper, middle, and lower levels daily. So, sample points are normally located at the grade, top platform, or along with the stair landings. In Fig 1, S1 and S2 are sampling nozzles to be accessible.

Level Nozzles

Minimum, one internal float level gauging instrument per tank, readable from grade consider. Other level gauges shall be readable and all their connection shall be maintainable, so nozzles are to be located along stairs.

storage tank — **Fig. 2: Typical Storage Tank**

Temperature Indication Connections

Connections for temperature indication shall be furnished for a flanged or threaded thermowell installation accessible for removal of the well and required space shall be considered in front of it. (Nozzle T1 in Fig 1)

Breathing and Safety Valves nozzles

Each tank has a minimum of one safety valve and one breathing valve, which is very important for tank safety during its life, installed on top of the roof shall be accessible from a platform. Also valves of an inert gas line which is connected to the tank for pressure balance when considered. In Fig 1, SV1 and BV1 are located close to the platforms.

Tank Mixers and heaters

When on a tank, a mixer or a tube bundle heater is installed via a nozzle, orientation of it shall provide adequate area for removal and easy movement to the outside of the dike.

Fire Fighting Nozzles

Do not forget that fire water is never injected directly inside the tank, so the only nozzles are related to the foam system if existing. The most important point that shall be considered during the design of nozzle orientation for these systems is the number of nozzles and also the fact that nozzles shall be in a symmetrical arrangement to provide uniform coverage of foams.

Implementation of the above points in the design, will reduce the number of structural attachments to the tank and also the capital costs of the plant as well as operational problems and increase personnel safety.

Few more useful resources for you..

Articles related to Tanks
Articles Related to Pumps
Articles Related to Exchangers
Piping Design and Layout basics
Piping Stress Analysis Basics
Piping Materials Basics
Articles related to Process, Civil, Mechanical and instrumentation Design

About the Author: The author of this article is Mr. Amir Razmi, an International, a dynamic and multi-functional chemical engineer with 14 years’ experience in engineering and EPC of oil and energy projects from pre-contract activities to execution, and closeout. The author has added the above article as a part of his book “Storage Tank Farms Layout and Piping” which you can purchase by clicking here.

Pump Suction Intake Design with Sample Calculation

Written by Anup Kumar Dey in Mechanical,Piping Design Basics,Piping Interface

We all see pumps day in and day out. We see them in our houses, roadsides, industries etc. They are extensively used in adverse applications to transport fluids from one place to another.

What is a pump?

A pump is a mechanical device that moves fluids, solid wastes, chemicals, and slurries by mechanical action. The pump has two important components i.e. Flow & Head.

Flow: It determines the amount of fluid pumped.
Head: It tells the extent or distance to which fluid is to be exported.

There are two types of Pumps based on their operating principle.

Dynamic pumps: They are further classified as Centrifugal Pumps, Vertical centrifugal, Submersible pumps, etc.
Displacement pumps: They are further classified as Gear pumps, Piston pumps, Lobe pumps, etc.

As the pump works 24*7 in adverse environmental conditions, it has to be designed properly. Starting from NPSH(A) calculation to pipeline sizing calculation everything should be perfect. In this article, we will learn about “Pump Suction Intake Design Calculation.” The pump suction is designed as per the HIS (Hydrological Institute Standard). So, let’s see what the different terms are associated with pump suction design & how they are calculated.

Terms Associated with Pump Suction Intake Design

Bell Mouth

It is a piping structure that guides the intake of fluid to the pump. Bell Mouth width is given by D. Width of the bell mouth is calculated as 1.5 to 2 O.D. of the suction pipe.

End Wall Clearance (B)

It is the Clearance between the centreline of the pump suction intake bell and the end wall of the tank. It is calculated as 0.75D.

Centreline Spacing (a)

Centreline spacing between two adjacent pump bell mouths in the same tank will be calculated as 2.5D. This 2.5D is the minimum value.

Bell Mouth Floor Clearance (C)

It is the minimum gap that should be maintained between the bell mouth bottom and the top of the tank floor. It is calculated as 0.3D to 0.5D.

Minimum Submergence (S)

It is the minimum submergence of the pump bell inlet in water. This is calculated as D (1.0 + 2.3F_D). Where F_D stands for Froude’s number.

Minimum tank width (A)

This is the minimum distance between the pump bell centreline and the next pump wall. It is given by 5D.

Minimum Liquid Depth (H)

It is the minimum liquid depth required in the tank. This is given by the submission of Minimum submergence(S) + Bell Mouth Floor clearance(C). The lowest water level intake is calculated by minimum liquid depth.

The angle of floor slope (α)

This is the slope of the floor required in the tank. Generally, the floor is sloped so that an adequate amount of water is always available near the pump suction.

Fig. 2: Typical Pump Suction Cross section

Impacts of Improper Design

Cavitation
Pump Dry Run
Improper process parameters
Improper calculation of NPSH(Available)
Increase in OPEX.
Vibration in pump body & suction piping
Pump Head Loss

The pump suction should be designed considering the above-mentioned parameters. If the suction of the pump is not designed properly there may be problems like cavitation, pump dry run, the problem of priming, etc. So, if you don’t want that these problems to be part of your real life & you want your OPEX to be the least these design considerations should be followed carefully while a pump system is being designed.

Typical Calculation of Pump Suction Intake Design

Consider a pump of flow Q = 1640m3/hr.

Pump suction bell design (D) = 1.5* O.D. of pipe

To Calculate the Diameter of the Pipe: Q = A.V.

Where

A = Cross-section area of Pipe or (A=π/4 * D²)
V= Velocity in pump suction side (velocity in the suction pipe is generally considered in the range from 06 to 1.5m/s.

Minimum submergence (S): S = D (1+2.3Fd)