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What are Pickling and Passivation? Their Meaning, Procedure, Advantages, and Differences

Written by Anup Kumar Dey in Construction

Pickling and Passivation are chemical processes used in the metal industry to protect metals from corrosion. Both pickling and passivation are widely used for stainless steel products. Some acidic chemicals are used over the stainless steel to create a passive layer or to remove contaminants. In this article, we will explore more about the pickling and passivation process. Let’s start with the definition of both processes.

What is Pickling?

Pickling is basically a metal cleaning process. In the pickling process, thin layers of metal (in form of stains, inorganic contaminants, foreign matter, grease, oil, rust or scale, etc) are removed from the surface of stainless steel. For the pickling of stainless steel, usually, a mixture of nitric and hydrofluoric acid is used.

Pickling is a popular process for removing weld heat-tinted layers from stainless steel surfaces. However, the Pickling process causes etching of the surface and affects the surface finish making it dull.

What is Passivation?

Passivation is a chemical treatment process where the stainless steel is treated with an oxidizing acid. Passivation dissolves carbon steel, and sulfide inclusions and removes iron and other surface contaminants from the stainless steel surface. At the same time, the acid promotes a chromium-rich thin but dense passive film (oxide protective layer) formation. This passive film imparts corrosion resistance quality.

Passivation of stainless steel is performed using nitric acid. Similar to pickled steel, passivated steel does not affect the metal’s appearance.

Advantages of Pickling and Passivation Process

The processes of pickling and passivating steel offer various advantages to the metal products like:

  • Both pickling and passivation remove surface impurities and contamination generated during manufacturing and fabrication.
  • Increase the durability and longevity of the stainless steel products with reduced corrosion possibility.
  • Weld hint tint or weld discoloration is removed and the metal looks smooth without imperfections.
  • Chemical film barrier against rust.
  • Reduced need for maintenance.

Pickling and Passivation Procedure

Pickling Process:

A range of methods can be applied to the pickling process. The most popular methods are:

Tank Immersion Pickling– Can be done on-site or off-site. Provides a facility for treating all the fabrication surfaces at the same time. This achieves uniformity of surface finish and optimum corrosion resistance.

Circulation Pickling– This type of pickling method is recommended for piping systems carrying corrosive fluids. In this pickling process, the chemical solution is circulated through a system of pipework.

Spray Pickling– Spray pickling is done for on-site treatment. Proper acid disposal and safety procedures must be ensured during the spray pickling process.

Gel Pickling– This is a manual pickling operation in which gels are applied on metal surfaces by brushing. It pickling method is quite useful for the spot treatment of welds and other intricate areas that require manual detail.

Passivation Process:

The passivation of stainless steel is performed using weak acids like nitric acid or citric acid. The main aim of passivation treatment is the formation of a passive layer that does not easily interact with the environment. Before the acid passivation process, the surfaces must be cleaned to make them free from oxide scales, oils, grease, and other lubricant, heat tints must be removed. After that nitric acid chemical/paste is applied to the material surface.

Passivation is a post-fabrication process used for newly fabricated stainless steel parts. The effect of passivation was first discovered by chemist Christian Friedrich Schönbein in the mid-1800s. However, the process of passivation become widely useful in the 1900s.

The weak nitric or citric acid chemically dissolves the free iron present on the surface. The chromium remains intact which creates a chromium oxide layer upon exposure to oxygen over the next 24 to 48 hours. This passive layer provides a chemically non-reactive surface.

Please note that passivation is not an electrolytic process, this is not a process to remove scale, and It does not change the surface color or appearance. The steps followed for the passivation process are:

  • Alkaline cleaning of the metal surface.
  • Deionized (DI) Water rinse
  • Nitric or Citric acid immersion bath
  • DI Water rinse
  • Drying of the part
  • Testing the effectiveness of the process.

Codes and Standards for Pickling and Passivation

Widely used codes and standards that govern the pickling and passivation process are:

  • ASTM A380
  • ASTM A967
  • ISO 16048
  • AMS 2700
  • ASTM B600
  • AMS-STD-753
  • BS (British Standard) EN 2516

The treatment duration for pickling and passivation treatment normally varies from 5 minutes to 45 minutes. The oxide layer left by passivation is roughly .0000001 inch thick.

Pickling vs Passivation: Differences

Both pickling and passivation are chemical surface treatment processes and are widely used for stainless steel. However, there are some differences between the processes in terms of the intensity of the treatments. The major differences between the pickling and passivation processes are tabulated below:

PicklingPassivation
Acids used in the pickling process are more aggressivePassivation uses weak acids (either citric acid or nitric acid).
Pickling makes greater changes to the surfacePassivation only creates a thin surface layer and does not change material properties.
The pickling process removes metal impurities on a sub-level basis.Passivation normally does not remove metal impurities or contamination. It mainly makes the surface passive to corrosion.
Pickling vs Passivation

What is a Foot Valve? It’s Working, Types, and Applications: Foot Valve vs Check Valve

Written by Anup Kumar Dey in Mechanical,Piping Design Basics

A foot valve is a special type of non-return valve, with a strainer affixed to the open end. For suction lift applications, foot valves are widely used in the pump suction or at the bottom of pipelines. The use of foot valves, keeps the pump primed, the fluid flows in but does not flow back out, and hence they are ideal for wells, ponds, and pools. As the flow area of the foot valves is larger than the pipe size, there is very less head loss.

Working of a Foot Valve

Foot valves being unidirectional allow the flow only in one direction and the valve closes for reverse flow. The inlet strainer of the foot valve filters out the unnecessary solid particles from the fluid and thus prevents valve damage.

When pumps are used to move fluids from lower to higher elevations, a lot of energy will be required. At the same time when the pump is turned off, the liquid will flow back to the lower level. But the use of foot valves prevents this reverse flow. The foot valve maintains the liquid column even when the pump is not working.

Foot valves are basically a type of check valve that prevents the backflow of liquid. They are placed in the pick-up end of the pipe and are located at the very bottom. When the pump is started, a suction is created which opens the foot valve. Water or other liquid easily enters the pipe through the foot valve due to the pulling force of the pump. But when the pump is turned off, this pulling force is removed but still, the water level retains its level as the foot valve does not allow the water to flow back. thus the pump remains always primed.

Requirements for Foot Valves

Foot valves are used for various reasons like:

  • To keep the pump primed when pumping liquid from lower to higher levels.
  • To prevent damage to water pumps without foot valves there may be dry runs. Without a foot valve, the air will fill the pipe which will oppose the water flow and the pump will run dry.
  • To reduce energy wastage.

Functions of the Strainer for the Foot Valve

The strainer in a foot valve filters out the debris that may jam the foot valve and can cause damage to the pump. So, the strainers protect the valves and pumps and perform a very important function.

Features of a Foot Valve

Foot valves usually have self-tapping male and female threads that help in easy installation. They have internal balls for quick sealing and valve reaction. They are flexible enough to fit various types of water pump uses. Foot valves are cheaper compared to other valves.

Components of Foot Valves

Each foot valve consists of 4 basic components:

  • Screen: To remove sediments or debris.
  • Body: The complete mechanism is housed within the valve body.
  • Seat: The seat is an integral part of the body and uses o-rings to avoid leakage when the valve is closed. The valve lands on the seat when the pump is turned off.
  • Disc: This is the gateway of the foot valve. When the disc is raised, liquid can enter.

Materials for Foot Valves

Foot valves are usually constructed of heavy-duty cast iron, bronze, Stainless Steel, PVC, and Plastic. Foot valves are normally used for water services and these materials last longer when submerged in water.

Applications of Foot Valves

As foot valves prevent the suction column from draining when the pump is not in operation, they are widely used in all kinds of pneumatic systems. The major application of foot valves is found in pumps and because of that, they are sometimes called foot valves for pumps or well-pump foot valves. Typical applications of foot valves include:

  • Suction lines of the pipeline
  • Ponds, pools, and wells, where pumps are used to transfer water.
  • Sump pumps, and intake pumps, in rivers and lakes.
  • Pneumatic brake lines of commercial trucks.
  • Car wash systems.
  • Irrigation systems.
  • Rural fire protection systems.
  • HVAC systems.

Types of Foot Valves

Foot valves can be classified based on construction and flow systems. Based on the construction of foot valves, there are two types of foot valves, Membrane foot valve, and ball foot valve.

Membrane foot valve: In a membrane foot valve, a cylindrical rubber membrane is fitted inside a steel strainer. When the suction is formed in the strainer, the membrane is displaced and the liquid flows through the valve. The cylindrical membrane closes during a reverse flow and thus prevents the backflow.

Ball foot valve: In this type of foot valve, a cylindrical inclined chamber and seating have used that guide the ball valve. When inward flow occurs, the ball is displaced with its chamber, and fluid flows. On the other hand, when the flow rate decreases, it runs down the chamber onto its seat and the valve prevents reverse flow. Ball foot valves are mostly used for contaminated water.

According to the flow system, the foot valves are classified as Microflow system valves, high-flow system valves, and low-flow system valves.

  • The microflow system valves are mostly made of stainless steel and used in direct push technology micro-wells and multilevel good installation.
  • The high-flow system valves are used on 2-inch wells or larger and can stand high pumping rates and very deep wells.
  • The low-flow system valves are used in small diameter piezometers which lift up to 100 feet of water.

Based on the types of threads used, foot valves are of three types:

  • Female threaded foot valve.
  • Male threaded foot valve
  • Dual-threaded foot valve

Selection of Foot Valves

Foot valves are selected considering various parameters like:

  • The task that the foot valve will perform and fluid service.
  • Duty of valve; whether heavy-duty or light-duty.
  • Load the foot valve need to carry.
  • Durability.

Maintaining a Foot Valve

Even though a foot valve is a small element, it must be properly maintained. Some of the steps that can be followed to increase the life of foot valves are:

  • Regular cleaning of debris of the foot valve.
  • Regular checking of corrosion signs.
  • Ensuring that the tank or well bottom is clean

Difference between Foot Valve and Check Valve

Even though both the check valve and foot valve serves a similar function of a non-return valve i.e, preventing backflow, there are some distinct differences between the two valves. They are:

Foot ValveCheck Valve
The foot valve has a strainer affixed to the valveThe check valve does not have a strainer.
Foot valves are installed at the suction side of the pump.Check valves are installed at the discharge side of the pumps.
Foot valves have only one thread for installation.Check valves have threads on both ends.
Foot valves can be installed only at the end of the pipe.Check valves can be installed in the middle of pipes.
The use of foot valves is limited to pump lines only.Check valves have multiple uses.
Table 1: Foot Valve vs Check Valve

What is 3D Model Review? Significance of 30%, 60%, and 90% Model Review

Written by Anup Kumar Dey in Piping Design Basics

3D models are very popular in the engineering of process and power piping industries as they graphically represent the overall plant with all equipment, piping, structures, instruments, and electrical connections in a three-dimensional view. These 3D models are close to the real plant that will be built at the site after construction. Various 3-D piping design software packages like PDMS, SP3D, E3D, etc simulate the actual plant in the 3D model that gives a better representation of the plant as compared to the age-old 2D plant models. They are the electronic equivalents of real plants. In this article, we will explore the 3D model review procedures.

What is a 3D Model Review?

A 3D model review is a design procedure to present the electronic 3D model to the client to verify that the current stage of the design meets the minimum project requirements for operability, maintainability, constructability, safety, and functionality and that it reflects every discipline’s input to the design to date. All discipline engineers review the 3D model through a walkthrough of the plant. Any design changes required are discussed and listed as Model review comments which will be taken care of after the model review.

For small projects for which 3D software packages are not used a similar philosophy of review termed Desktop Review is followed.

Stages of 3D Model Review

3D Model review, in general, is performed in three stages; 30% model review, 60% model review, and 90% model review. The percentage term used along with model review denoted the percentage completion of the design stage. These model reviews are major checkpoints and milestones in the engineering design process. Deliverables required from each discipline to achieve each of these checkpoints are defined in the model review matrix.

Typically a model review will not proceed until such time that all of the deliverables required for the specific review have been incorporated. When deliverables are missing for a particular review, the model review may only proceed provided that the associated risks and mitigations have been identified and approved by the project manager.

30% Model Review

A 30% model review means the design is complete by roughly 30% and is the 1st milestone for model preparation. All design data is not yet firm at this stage. This phase aims to lay out the major design elements of the project. It establishes the cost and timeline of the project. 30% model review generates a basis for plant layout, accessibility, and safety measures recommendation. Only the large-diameter critical lines are routed and modeled. At the 30% model review stage, the contractor and client meet to set a basis for further development of the design.

The 30% model review phase is the foundation of the project. From this point onwards the design will be developed further continuously.

Objectives of 30% model review

The 30% 3D model review is performed to serve the following objectives:

  • To discuss and agree on overall plant layout qualifying hazard recommendations and other project requirements.
  • To fix the equipment location considering the available information.
  • To identify primary operational/assessable/maintenance points or platforms.
  • To identify improvements considering the safety and operation aspects.
  • To release foundation loads for structural design.
  • To finalize the equipment nozzle orientation and send the information to the vendor.
  • To finalize the main underground isometrics for fabrication.

Important points that are usually included and discussed during any model review are usually decided by the model review matrix. The model review matrix outlines the preparedness required by each discipline at each stage of the design review and the items to be reviewed at that stage. A sample model review matrix explaining the piping items is provided in Table 1 below.

Review Stage30% Model Review60% Model Review90% Model Review
Process StudiesComplete––
PFD and Mass BalanceIFEIFC–
P&IDIFAIFEIFC
HAZOP–Complete–
Line SizingCritical Lines completeAll lines complete–
Line ListIFAIFEIFC
Piping SpecificationsApproved––
ValvesPreliminary data for 6″ and AboveApproved data for 4″ and aboveAll valves approved
Specialty ItemsPreliminary data for 6″ and AboveApproved data for 4″ and aboveAll approved
EquipmentPreliminaryApprovedCertified
InstrumentsPreliminaryApprovedCertified
Plot PlanIFAIFEIFC
Equipment LayoutMajor Equipment modeledEquipment location finalized and modeledAll equipment approved
Pipe Stress Analysis6″ and Above critical linesAll critical linesAll stress reports approved
Piping Design6″ and Above critical linesAll critical linesAll lines modeled and approved
SupportsMajor SteelAll steel modeled–
TracingNot StartedPreliminary locationsFirm locations modeled
StructuresMain StructuresMinor StructuresFireproofing of all structures
 Escape routes, roads, paved areas, drainage30% model review comments60% model review comments.
Table 1: Sample Model Review Matrix

60% Model Review

60% Model Review is the second milestone of the model review process and serves the utmost importance of the project. All the doubts raised during the 30% model review are clarified during this phase. In this stage, the team focuses more on the analysis of constructability, budget consideration, modification, and potential issues or concerns. The model review team discusses the constructability of the drawings and any preferred equipment and material needed to build the project during this stage.

60% model review phase is also considered to be a good time for value engineering. Any changes or modifications after a 60% model review will significantly impact the schedule, cost, and overall design. In general, the 60 % model review is carried out and closed out prior to issuing the piping isometrics for construction.

Objectives of 60% model review

The main objectives of the 60% model review process are:

  • To check if the design is at par with the safety philosophies and requirements.
  • To determine the location of secondary fire/safety equipment
  • To find out if the main equipment locations are in order and updated.
  • To review the location of minor equipment.
  • To review the secondary operability/accessibility/maintainability as required.
  • To review and release buried isometrics for IFC.
  • To release the updated nozzle orientation information to the vendor.

90% model Review

This is the final model review and the design is almost final with all data and information. 90% model review finalizes the total design of the model. All the comments from the 60% model review stage are resolved and incorporated into the 90% model review. All drawings and specifications are ready with the design team for issue as final. 90% model review is the last stage for the client to suggest any minor changes. The construction schedule, phasing plan, logistics plan, etc are finalized at this stage.

During the 90% model review stage, the model must be substantially complete, including instrumentation and all Manufacturer/Supplier information, to allow final comments to be made.

Objectives of 90% model review

The main objectives of the 90% model are:

  • To ensure that the final design is acceptable to the client and agree to IFC issues of all drawings and specifications.
  • To ensure that operational and maintenance access has been provided to all required items.
  • To ensure the construction feasibility of all plant components.
  • To ensure all safety philosophies and recommendations are implemented prior to the publication of drawings.
  • To ensure the model reflects all project requirements.

3D Model Review Responsibility

3D Model Review is the joint responsibility of the piping lead, the designer/drafter, the project engineer, and other related disciplines. The piping engineer and the project engineer are the primary organizers of the model review. In most cases, the piping leads show the plant by walk-through of the complete plant. All comments are recorded in a proper project format for resolution and incorporation. Any necessary changes and comments are agreed upon and immediately recorded and marked with reference numbers and model pictures to allow follow-up and avoid misunderstanding.

The main responsibilities of the primary organizers are as follows:

Responsibilities of the project engineer:

Project engineers

  • Decides the required attendees, and schedules and manages the formal model reviews.
  • Ensures that the design progress meets the requirements for the review as defined in the model review matrix.
  • Prepares and issues an agenda for the review.
  • Coordinates the discussions and documents resolutions and action items.
  • Ensures proper filing of all documentation.
  • Distributes the model review comments to the attendees.

Responsibilities of the piping lead:

The piping lead engineer

  • Coordinates with CAD support for the assembly of the 3-D models required for the review.
  • Operates or designates a team member to operate the computer “walk-through” during the review.
  • Ensures that an interference check has been completed prior to the review.
  • Ensure that a “snapshot in time” of the 3-D model files used for the review is archived for future reference and record-keeping after each review.
  • Captures all comments/action items in the software package.
  • Maintains a hard copy binder and logs and distributes the action items to the designers.

The important activities and responsibilities can be listed as follows:

  • Schedule for model review: Project Manager
  • Model review document preparation: Project Engineer
  • Distribution of review document and agenda to the client: Project engineer
  • Organize model review venue: Project engineer
  • Review tools and create a model file: Design Administrator
  • Report status of 3D CAD model: Lead piping engineers
  • Report of hold item list: Lead piping engineers
  • Coordination during model review meeting: Project engineer
  • Preparation and Summarize of the action list: Project engineer
  • Review, reconciliation, and distribution of action list report: Project manager
  • Follow up and Updation on Action list: Project engineer/Lead piping engineer
  • Review model and Status files: Design Administrator

Supporting Documents and Drawings for Model Review

Various documents may be required during the actual model review process. Hence the following documents with their latest approved revision should be made available during the model review session. These drawings are usually marked as “Model Review master“. These important documents and drawings are:

  • Piping and Instrumentation Drawing (P&ID)
  • Equipment layout
  • Escape route Layout
  • Equipment list
  • Line list
  • Previous model review action list as applicable.
  • Equipment dimensional details
  • Instrument Index
  • Firefighting equipment layout
  • Safety equipment layout
  • PFS
  • Plot Plan
  • Equipment GA Drawings
  • Civil Structural Drawings
  • Stress Calculations
  • Piping Studies
  • Engineering and procurement Work packages
  • Existing Drawings
  • HSE Reviews

Participants of Model Review

For each model review session, the contractor notifies the client and all other disciplines about the venue and time of each model review session. Usually, the following professionals participate in the model review session:

  • Client Representatives
  • Process: Full-time involvement
  • Maintenance: Full time
  • Construction: Full time
  • Operations: Full time
  • Project Engineers: Full time
  • Other Discipline: Full-time/As per requirement
  • Contractor Representatives
  • Project Manager/ Engineers: Full time
  • Model Drafting Team: Full time
  • Lead Piping Engineer: Full time
  • Process engineer: Full-time for process-related clarification
  • Mechanical Engineer: As per the requirement
  • Instrument/Electrical engineer: As per requirement
  • Structural Engineer: As per the requirement
  • Safety Engineer: Full time
  • HVAC: As per requirement
  • Civil Engineer: On-call

3D Model Review Checklist

Checklists of 3D model reviews are prepared to ensure that important checkpoints are discussed and not missed during the session. The 3D model review checklist varies with the stages of the model review. Some typical points that are included in the 3D model review checklists are listed below:

30% Model Review Checklist

The 30% model review checklist usually considers the following checkpoints:

  • Location of all equipment and their orientation
  • Major critical piping routes
  • Separation distance within plots
  • Constructability
  • Drainage philosophy
  • Access to major valves
  • As-built coordinates of tie-ins with existing pipe or equipment.
  • Major wall and floor penetrations.
  • Equipment status

60% Model Review Checklist

The 60% model review checklist emphasizes the following major points:

  • Comments from 30% model review
  • HAZOP comments
  • Equipment latest information
  • Access to equipment, instrument, and valves.
  • PSV locations.
  • Battery limit layout
  • Special pipe supports.
  • Fireproofing.
  • Pipe support location and type confirmation.

90% Model Review Checklist

90% model review checklist is an exhaustive document that covers all items. The important checkpoints of the 90% model review checklist are:

  • Special item details
  • 60% model review comment status
  • HSE comment status.
  • Model updation as per the latest available data.

Types and Working of Pressure Regulators

Written by Anup Kumar Dey in Instrumentation

Pressure regulators play a critical role in ensuring the safe and efficient operation of equipment and processes in the oil and gas industry. From drilling to refining, maintaining optimal pressure levels is essential for the smooth functioning of systems that involve the handling of volatile substances.

What Are Pressure Regulators?

A pressure regulator is a device designed to maintain a desired output pressure by controlling the flow of gas or liquid from a high-pressure source to a lower-pressure environment. It automatically adjusts the pressure to the required level, ensuring consistent performance of the downstream equipment.

In the oil and gas industry, pressure regulators are used extensively to manage the pressure in pipelines, storage tanks, and processing equipment to ensure safety, reduce risks, and improve efficiency.

Pressure regulators are devices used for controlling fluid pressures within a range. The main function of a pressure regulator is to reduce a high input pressure to control lower output pressure. Pressure regulators can even find applications in situations where constant output pressure is required to be maintained.

The Role of Pressure Regulators in Oil and Gas Operations

Oil and gas extraction, processing, and transportation involve highly pressurized fluids and gases, making pressure regulation essential at various stages. Below are some key areas where pressure regulators are indispensable:

  1. Drilling Operations: During the drilling phase, pressure regulators are used to control the flow of drilling mud and prevent blowouts. This ensures that the well remains under control even in high-pressure reservoirs.
  2. Gas Distribution: In natural gas distribution systems, pressure regulators manage the flow of gas from high-pressure pipelines to lower-pressure delivery systems that supply consumers.
  3. Processing and Refining: Refineries use pressure regulators to maintain the optimal pressure within reactors, distillation columns, and other equipment. Proper pressure regulation ensures that chemical reactions occur efficiently and that safety is maintained in case of overpressure.
  4. Pipeline Transportation: Long-distance transportation of oil and gas requires precise pressure control to minimize energy loss and ensure the integrity of pipelines. Regulators help manage pressure drops across pipelines and maintain steady flow rates.
  5. Storage: Pressure regulators control the pressure inside storage tanks, especially when storing liquefied natural gas (LNG) or other compressed gases. This prevents hazardous conditions, such as over-pressurization, which could lead to explosions.

Other applications of pressure regulators are:

  • gas grills,
  • heating furnaces,
  • dental equipment,
  • pneumatic automation systems,
  • automotive engines,
  • aerospace applications,
  • hydrogen fuel cells,
  • reclaim driving helmets
  • pressure cookers and pressure vessels,
  • welding and cutting,
  • gas-powered vehicles,
  • mining and natural gas industries,
  • hyperbaric chambers,
  • inflating tires, etc

Functions of a Pressure Regulator

As already stated the main purpose of installing a pressure regulator is to reduce the pressure. However, they can effectively be used to perform the following functions:

  • Regulating the back-pressure
  • As pressure switching valves in pneumatic logic systems.
  • As vacuum regulators, to maintain a constant vacuum.

Components of a Pressure Regulator

All pressure regulators are characterized by the reduction of the inlet pressure to lower output pressure. There are three main components that help a pressure regulator perform its intended function are:

Refer to Fig. 1 below which shows the schematic diagram of a typical pressure regulator.

Schematic of a Typical Pressure Regulator
Fig. 1: Schematic of a Typical Pressure Regulator

The pressure-reducing valve is also known as the restricting element. It provides a variable restriction to the flow. Examples include a globe valve, butterfly valve, poppet valve, etc.

The loading element is a part that can apply the needed force to the pressure-reducing valve. A weight, a spring, the diaphragm actuator in combination with a spring, or a piston actuator can act as the loading element.

The measuring element or sensing element determines when the inlet flow is equal to the outlet flow. Often, the diaphragm itself works as a measuring element; it can serve as a combined element.

Types of Pressure Regulators

Depending on the number of stages employed to get the final reduced pressure, there are three types of pressure regulators.

  • Single-Stage Pressure Regulator: For relatively small pressure reduction in the range of 100 to 150 psi. Used for machine tools, test stands, linear actuators, automated machinery, leak test equipment, etc.
  • Dual Stage Pressure Regulator (Suitable for large variations in the inlet pressure), and
  • Three-Stage Pressure Regulator: They provide a stable outlet pressure and are able to handle larger pressure reduction. Typical examples are UAVs, medical devices, analytical instruments, hydrogen fuel cells, etc.

Again, based on the working methods they can be broadly categorized into the following two classes.

Self-operated Pressure Regulator: Simplest design. They have greater accuracy at lower pressures and lower accuracy at higher pressures. They do not require external sensing lines for effective operation.

Pilot Operated Pressure Regulators: They are complex in design but can handle larger pressure fluctuations. Pilot-operated pressure regulators provide precise control of pressure.

Based on the application of pressure regulators they are sometimes termed as:

  • Water pressure regulator
  • Gas pressure regulator
  • Fuel pressure regulator

Working of Pressure Regulators

A pressure regulator matches the gas flow through the regulator to the gas demand placed upon it. At the same time, they maintain a sufficiently constant output pressure. When the load flow decreases, the regulator flow also decreases. Again, when the load flow increases, then the regulator flow also increases and thus keeps the controlled pressure from decreasing due to a shortage of gas in the pressure system. The pressure regulators are so designed that the controlled pressure does not vary greatly from the set point for a wide range of flow rates. At the same time, the flow through the regulator is stable and the regulated pressure is not subject to excessive oscillation.

Pressure Regulator Materials

The material of pressure regulators varies depending on the operating environment and compatibility of the fluid handled. Common materials that are used in typical pressure regulators are:

  • Brass
  • Aluminum
  • Stainless Steel
  • Plastic

Stainless Steel and sometimes carbon steel are used for spring materials. Seal material is usually Fluorocarbon, EPDM, Perfluoroelastomer, or Silicone.

Selection of Pressure Regulators

Even though pressure regulators are found in various sizes and constructions, Some parameters must be considered for proper selection. Common parameters that influence the selection process of pressure regulators are:

  • Operating temperature and pressure range (Both inlet and outlet temperature and pressure)
  • Fluid service medium and properties (Gas or liquid, Corrosive or Non-corrosive, Hazardous or Non-toxic, Explosive nature, etc)
  • Capacity or flow required (Maximum, minimum, and flow variation)
  • Material requirements
  • Accuracy required
  • Connection Size
  • Dimension, weight, and size

Installing Pressure Regulators

Installation of pressure regulators must be performed considering manufacturer guidelines. In general, the following steps are followed for pressure regulator installation:

  • Step 1: Connect the pressure source to the inlet port and the reduced pressure line to the outlet port. These ports are usually marked, else contact the manufacturer.
  • Step 2: Turn on the supply pressure gradually to avoid any shock.
  • Step 3: Set the regulator at the desired outlet pressure. Slight adjustments can be done to get the desired pressure.

Pressure regulators are fundamental to the safe and efficient operation of oil and gas systems. From wellheads to refineries, these devices help control the flow of gases and liquids, protect equipment, and ensure worker safety. By selecting the right type of pressure regulator and maintaining it properly, oil and gas companies can optimize their processes, reduce risks, and comply with environmental and safety regulations.

What is a Shut-Off Valve? It’s Working, Function, Types, and Selection

Written by Anup Kumar Dey in Piping Design Basics

A shut-off valve is a valve that safely manages the flow of hazardous fluids (liquids, gases, slurries, and fluidized solids). Shut-off valves are also known as on-off valves, cut-off valves, lockout valves, stop valves, etc. They safely stop or continue the fluid flow. When not in use they isolate the sub-system.

Shut-off valves belong to a large family of valves. Various types of valves like ball valves, globe valves, gate valves, pressure valves, temperature control valves, solenoid valves, instrument valves, etc may work as a shutoff valves. Shut-off valves are widely used where system safety is of importance as they represent a positive action safety device. Some examples of shut-off valve applications are:

  • Air preparation unit.
  • Industrial Automation Process.
  • Fuel units
  • Pneumatic industry.
  • Water Industry

Working of Shut off Valves

Each shut-off valve consists of two fundamental components.

  • The valve body through which the fuel, liquid, slurry, or gaseous fluids pass and
  • The control device, which is equipped with a sensitive element.

The control element ensures the required closing and opening of the valve. When everything works correctly, the fluid passes through the valve smoothly. However, when any anomaly (for example excessive fluid expansion, breakage of capillary, etc) arises the control device closes the flow passage inside the valve.

Selection of a Shut-off Valve

Based on the application there are various types of shut-off valves. So, the selection of the appropriate shut-off valve is not easy. Various parameters need to be considered while selecting the shut-off valve for a specific service and operation. The important factors to consider are:

  • Type of application
  • Size and weight
  • Temperature and Pressure
  • Range
  • Working Environment
  • Port size, position, and type

Types of Shut-off Valves

Shutoff valves are categorized based on various parameters like working, configuration, application, etc.
Depending on the turning of the handle there are two types of shut-off valves;

  • Multi-turn shut-off valve and
  • Quarter-turn shut-off valve

Depending on configuration shut-off valve types are:

  • Straight shutoff valve
  • Angle shut-off valve

Again, depending on the applications they are popularly categorized as

  • Water shut-off valve
  • Gas shut-off valve
  • Fuel shut-off valve, etc

Various materials are used to manufacture shut-off valves based on fluid service compatibility. Common shut-off valve materials are Brass, Carbon Steel, Stainless Steel, Alloy Steel, etc. For low-pressure temperature applications in the water industry plastic or polypropylene, valves are used.

Functions of a Shut-off Valve

All shut-off valves are designed to provide fully on or fully off functionality. So they function similarly to an electric switch, either stopping the flow completely or allowing it fully.

Shut off Valve Symbols

All valves are indicated in P&ID and isometric with specific symbols. Shut-off valves also have their symbols. The symbols of shut-off valves are decided based on the specific valve type used as a shut-off valve. So, the shut-off valve symbols differ from ball valve to angle valve or globe valve.

Fig. 1 below shows some typical images of shut-off valves.

Typical Shut off valves
Fig. 1: Typical Shut off valves

What is Pressure Drop? Piping Pressure Drop Equations and Calculation

Written by Partha Pratim Panja in Piping Design Basics,Process

Pressure drop is a widely used term that is frequently used in design engineering, process industries, etc. So it is very important to have a thorough knowledge of pressure drop. Pressure drop is the difference in pressure between two points provided that there is a fluid flow between those points. So pressure drop occurs when a fluid (gas/liquid) material enters one point of the piping system and exits through the other points. In that case, process piping systems should have losses of pressure, and this phenomenon is known as pressure drop.

Pressure drop occurs due to friction caused by fluids rubbing against the pipe surface and the internal walls of a pipeline. 

For a system, pressure drop can be calculated with engineering equations that require the type of fluid, flow rate, fluid properties, plot plan, and piping material specifications (including thickness, schedule number, and pipe diameter).

Why does Pressure Drop important?

If the pressure drop in a system is high then the process fluid temperature rises, and energy consumption will be high. Overall system pressure also increases for the high-pressure drop. The high-pressure drop also increases wear on components and causes potentially dangerous & over-pressure scenarios. Lastly, a large pressure drop may render some piping component systems disable due to insufficient operating pressure.

Process engineers should have a clear understanding of the pressure drop of the whole network associated with a fluid to be handled so that they can determine the size, capacity of the pump and motors, and piping diameter required to carry the specific fluid through the piping system.

The larger the pressure drops in the pipeline, the larger the energy required to retain the required process flow, requiring a higher horsepower motor. On the other hand, for low, pressure drop in a pipeline, less energy is required, providing the potential to use a smaller hp motor. Pressure drop also governs the overall pressure of the system or head requirements. 

What is a Pressure Head?

In short, the pressure head is defined as the height (m/ft) to which a selected pump can bring a column of water that is usually expressed in meters. 

It is the magnitude of the force the pump exerts on the fluid that is being pumped. From the Pump vendor, data pressure heads may be available or they can be calculated from the formula. 

What factors affect the Pressure Drop?

The following factors affect the pressure drop in a fluid-carrying network,

Fluid Component

Various fluid parameters like Density, Heat capacity, Temperature, and Viscosity affect the pressure drop of the fluid.

Some products change their viscosity drastically while being pumped through a pipeline due to shear. These kinds of products will become due to frictional effects caused by the passing through the pumps and the internal surfaces of the pipes. This type of fluid is called the thixotropic fluid which is a time-dependent fluid. Thixotropic fluids are usually viscous fluids in stagnant conditions. But it gets thinner or low viscous during movement while shaking or mixing & it returns to its normal state while the means of mixing is removed.

On the other hand, some others are called Newtonian fluids under certain processing conditions. Newtonian fluids are not thixotropic fluid, and it is not subjected to vary their viscosities upon exposure to shear force. Fluids that show Newtonian characteristics may add to higher pressure drop while being pumped through a piping system because their viscosity will not vary as it passes through the system.

Mechanical Component

The mechanical elements in a piping system that imparts pressure drops are valves, strainers, flow meters, couplings, fittings, bends, and tubing. Excluding pumps, all of these other elements commonly available in a process piping system contribute to an overall pressure drop of the system as they remove pressure energy from the process fluid, rather than adding to it. 

This dynamic pressure drop depends on the cross-sectional area of the piping system as well as an internal surface roughness (roughness factor), the equivalent length of the pipeline.

Changes in Elevation

Changes in elevation in the Piping system significantly affect the pressure drop. The additional pressure drop will occur if the starting elevation of a pipe is lower than its end elevation. This elevation difference is measured in the fluid industry in terms of the fluid head.

For a general piping system, the overall pressure drop is usually calculated using equations similar to the following:

P(end)= P(start) – friction loss- fittings loss -component loss + elevation (start-end) + pump head

Pressure Drop Equations/ Pressure Drop Calculation

Due to different elevations, turbulence caused by changes in flow direction and frictional losses while flowing through piping and losses due to fittings pressure drop or head loss is caused. The widely used methods used to calculate the head loss in glass pipe are Manning, Darcy-Weisbach, and Hazen-Williams, equations. The applicability of each method governs by the flow pattern (gravity flow or pumped flow).

Hazen-Williams Equation

The Hazen-Williams equation is normally used for water pipes while the flow is fully turbulent flow. It has achieved a wide range of acceptance in the water and wastewater industries as it is very simple to use. The equation is as follows,

V=0.85 C R0.63 J0.54

where

  • v = velocity, m/s
  • C = Hazen-Williams Coefficient
  • R = Hydraulic mean radius, m
  • J = Hydraulic gradient, m/m
  • Hazen-William coefficient, C for ADPF fiberglass pipe is taken as 150.

Manning Equation

For gravity difference flow, the Manning equation typically is used to solve gravity flow problems where the flow partially fills the pipe under the influence of changes in elevation.
The equation is as follows,

V= (1/n) R0.667J0.5

where

  • v = velocity, m/s
  • n = Manning’s Coefficient
  • R = Hydraulic mean radius, m
  • J = Hydraulic gradient, m/m
  • Manning’s Coefficient, n for ADPF fiberglass pipe is taken as 0.01.

Darcy-Weisbach Equation

This equation states that pressure drop is directly proportional to the square of the velocity and the length of the pipe. This equation is applicable for all fluids for both laminar as well as turbulent flow. The disadvantage of this equation is that the Darcy-Weisbach friction factor is a variable that can be found in the standard chart available. The equation is as follows,

J= (fLV2)/2gD

where

  • J = Head loss, m
  • g = Gravity constant, 9.81 m/s²
  • v = Velocity, m/s
  • D = Inside diameter, m
  • f = Friction factor
  • L = Length of the pipe, m

Types of Fluid Flow

The well-known Reynolds number equation is used to characterize the fluid flow.

Re = v.D / ν

where ν= Kinematic viscosity, m²/s

The table given below determines the type of flow of fluid from the Reynolds number.

Type of FlowReynolds Number
Laminar FlowRe≤2200
Transition Flow Zone2200≤Re≤4000
Turbulent FlowRe≥4000
Types of Fluids as per Reynold’s Number

If the flow is Laminar, f = 64 / Re
If the flow is Turbulent, the friction factor can be determined from the Moody diagram found in most fluid mechanics texts or calculated from the Colebrook equation.

1/√f=-2Log(ε/3.71D+2.51/(Re√f))

where

  • ε = Roughness.
  • Re = Reynolds number

The Colebrook correlation friction factor for fiberglass pipe is determined as 0.04 mm which includes the head losses over joints.

Pressure drops in Pipe Fittings

Head Loss or pressure drop in Pipe fitting is usually defined as the equivalent length of pipe that is added to the straight run of pipe. This approach is mostly associated with the Hazen-Williams or Manning’s equations. This method does not consider the effect due to turbulence and subsequent losses caused by different velocities.

Equivalent Length (in m)

Pipe Fittings1502002503003504004505006007008009001000
90ᵒElbow8.56.47.99.410.712.214.017.023.028.032.437.142.3
45ᵒElbow3.53.44.25.05.76.58.210.913.616.220.123.525.6
Tee11.014.417.821.124.027.532.838.349.561.572.984.696.8
Equivalent Length for Pipe Fittings in m

For a more accurate calculation, head loss in fittings can be determined using loss coefficients (K-factor) for each type of bend & fittings. In this method, K-factor is multiplied by the velocity head of the fluid flowing through the bends and fittings.

The relevant equation is H=K x (V2/2g).

where,

  • H = Head loss, m
  • V = Velocity of flow, m/s

K-Factors for Pipe Fittings

Type of Pipe fittingsK-Factor
90ᵒElbow, standard0.5
90ᵒElbow, single miter1.4
90ᵒElbow, double miter0.8
90ᵒElbow, triple miter0.8
45ᵒElbow, standard0.3
45ᵒElbow, single miter0.5
Tee, flow to branch1.4
Tee, flow from branch1.7
Reducer, single reduction0.7
K-factors for various Pipe Fittings

Water Hammer

It is caused due to pressure surge or internal shock, resulting from a sudden change of velocity within the system. As a result, these shock waves can reach a sufficient level to rupture or collapse a piping system irrespective of the material of construction. The surge pressure is the faster moving wave that increases as well as decreases the pressure in the piping system that depends on the source of the direction of the shock wave travels. Fast valve closure can result in the building-up of shock waves as the kinetic energy of the faster-moving fluid is converted to the potential energy that must be accommodated. These pressure waves traverse throughout the whole piping system and may cause mechanical damage far away from the source of the shock wave.

The effect of the water hammer depends on,

  • Physical properties of the fluid
  • Volumetric flow rate
  • Elastic modulus of the pipe material
  • The equivalent length of the pipeline
  • Rate of change of momentum

The lower value of elastic modulus fiberglass generates a dampening effect as the pressure wave moves along the piping system. As the elastic modulus of piping material is very high so the pressure waves generated in the pipeline are very high in magnitude. Additionally, due to the fast closure and opening of the valve, sudden air release, and start-up or shut down of the pump can cause water hammer.

Talbot formula gives:

P= (a.w.V)/(144.g)=(a/g).(SG/2.3).V

where,

  • a=Wave velocity (ft/s)
  • P = Surge Pressure (psi)
  • v = fluid velocity (ft/s)
  • w = Density of fluid (lb/ft³)
  • SG = Specific gravity of the fluid
  • K = Bulk modulus of fluid (psi)
  • E = Hoop modulus of elasticity (psi)
  • d = Inside diameter of the pipe (inch)
  • t = Pipe wall thickness (inch)
  • g = Acceleration due to gravity (ft/s²)

How to prevent water hammer?

Standard design practices can avoid water hammers in most systems.

  • Rapid opening and closing of valves are to be avoided.
  • Avoid starting pumps into empty discharge lines unless mechanically actuated valves gradually open.
  • NRV or check valves on pumps should be closed as fast as possible to reduce the velocity of fluid flowing back.
  • Proper anchoring of the piping system can stop this problem.
  • Accumulators, and feedback control loops around pumps can be implemented to prevent occurring of water hammers.