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Introduction to Gate Valves and Gate Valve Types

Written by Said Hallouche in Engineering Materials,Mechanical,Pipeline,Piping Design Basics

A Gate valve is a linear-motion manual valve that has a vertical rectangular or circular disc that slides across an opening to stop the flow that acts as a “gate”. Generally used for isolation purposes fully open or closed, Gate valves are not suitable for throttling service because the high-velocity flow will cause a partially open disk to vibrate and chatter and will hasten the erosion of the disc and seating surfaces.

Functions of Gate Valve

The open/close flow is achieved by moving the gate of the gate valve into or out of the fluid-flow stream. The flow of the fluid through the valve can be in either direction. Gate Valve is commonly used in refineries and petrochemical plants where pressure is low, and less used in upstream facilities due to high operating pressure, long on/off times (requiring many turns of the handwheel to open it or to close it), and severe environmental conditions.

A full port gate valve provides a full line size (equal to pipe dimensions) thus resulting in a minimum-flow pressure drop, On the other hand, A Reduced port gate valve smaller than the line size (Flow area less than the pipe) causes a slightly high-pressure drop than a full port.

Gate Valve Parts

Refer to the below-attached figure (Fig. 1) which shows the main components of a gate valve.

Full-Port Gate Valve
Fig. 1: Full-Port Gate Valve

The items in Fig. 1 as per the corresponding numbers are given below:

  1. Body
  2. Bonnet
  3. Wedge
  4. Stem
  5. Gland
  6. Seat ring
  7. Yoke
  8. Packing
  9. Gland Flange
  10. Valve port
  11. Yoke Bush
  12. Lantern
  13. Back Seat Bushing
  14. Gland eyebolts & nuts
  15. Bonnet bolts & nuts
  16. Hand Wheel
  17. Hand Wheel nut
  18. Bonnet Gasket

There are three main parts in a Gate valve: body, bonnet, and trim.

  • The valve body is connected to piping or equipment by means of flanged, welded, or screwed connections.
  • The bonnet contains the moving parts which are connected to the body with bolts.
  • The valve internal parts (removable and replaceable) that come in direct contact with the fluid are termed Valve trim which consists of the stem, the gate, the disc or wedge, and the seat rings.

Types of Gate Valves/ Gate Valve Types

Gate valves are divided into a number of classes, depending on their disc and type of stems. Gate Valves are classified by:

I. Gate Valve types as per Type of Closing Element:

1. Parallel disk Gate Valve:

Parallel disk gate valves consist of two discs that are forced apart against parallel seats by a spring at the point of the closure. The most famous type is the knife gate valve which has a flat gate between two parallel seats (an upstream and a downstream seat) to achieve the required shut-off. The application of a parallel gate valve is limited to low pressures and low-pressure drops.

Parallel Disk Gate Valve
Fig. 2: Parallel Disk Gate Valve

2. Solid-Wedge Gate Valve:

The solid, or single wedge gate valve is the most widely used and the lowest cost used in the process industry for oil, gas, and air services. The purpose of the wedge shape is to introduce a high supplementary seating load. Solid-Wedge Gate Valve can be installed in any position, suitable for almost all fluids and practical for turbulent flow services.

In some situations, the valve cannot be reopened until the system temperature reheats the valve; this phenomenon is known as “Thermal blinding”. Wedge gate valves can be further described as inside screw or outside screw patterns. Solid wedge gate valves in the waterworks industry are popular as Sluice valves.

Solid Wedge Gate Valve
Fig. 3: Solid Wedge Gate Valve

3. Flexible Wedge Gate Valve

A flexible wedge gate valve employs a flexible wedge that is a one-piece disk with a cut around the perimeter (the cut varies in size, shape, and depth). Thermal expansion and contraction entail no problems in such kinds of gate valves as the disk is able to compensate for this and remains easy to open. Flexible wedge gate valves are widely used in steam systems to prevent thermal blinding.

Flexible Wedge Gate Valve
Fig. 4: Flexible Wedge Gate Valve

4. Split Wedge Gate Valve

Split wedges of this type of gate valve are made in two separate halves. This allows the wedge angle between their outer faces to fit the seat (self-adjusting and self-aligning to both seating surfaces).

Split Wedge Gate Valve
Fig. 5: Split Wedge Gate Valve

5. Double-disc Valves

In these types of valves, the gate is in the form of two discs that are forced apart against parallel seats by a spring. this provides tight sealing without relying on fluid pressure, making this type of valve particularly suitable for steam duties as well as handling gases and light oils.

6. Bellows Seal Gate Valves

Bellows seal gate valves are designed to minimize exposure to harmful substances through valve-stem leakage. The bellow is a metallic device capable of sealing between the valve stem and the bonnet to prevent the escape of the system fluid to the atmosphere. The bellows take the form of convolutions that can move linearly. During operation, the bellows eliminate the leak path to the atmosphere.

II. Gate Valve types as per Type of Stem:

1. Rising Stem Gate Valve with Outside Screw

This type of gate valve is also known as OS & Y type (Outside steam and York). The stem rises while opening and lower while closing the valve offering an indication of the gate valve position. The stem threads never contact the flow medium (not subject to corrosion/erosion).

Rising Stem gate valve
Fig. 6: Rising Stem gate valve

2. Non-Rising Stem Gate Valve

Also known as the Insider screw Valve, The stem of the non-rising stem gate valve is threaded into the gate. The hand wheel and stem move together and there is no rising or lowering of the stem. The stem is in contact with the flow medium.

Non-Rising Stem gate valve
Fig. 7: Non-Rising Stem gate valve

Working of Gate Valves

The working of a gate valve is quite simple. When the gate of the valve is lifted from the flow path, the valve opens and when the gate again returns to its position, the gate valve closes. This gate movement is achieved by manually turning the hand wheel. The hand wheel rotates the valve stem and the internal threaded mechanism provides a vertical movement of the gate. As the hand wheel is turned more than one full cycle to fully open or fully close the gate valve, they are also known as multi-turn valves. Electrically actuated gate valves are available but not cost-effective.

Actuation of Gate Valves

Manual actuation of gate valves is invariably by screw and handwheel. The screw mechanism may be exposed or protected and the screw rising or non-rising. A variety of materials for the working parts is offered by some manufacturers.

Power actuators are very often fitted when the gate valves are difficult to access and are operated frequently. automation and semi-automation control schemes make extensive use of actuators.

Advantages of Gate valve

Gate valves are adequate for high-pressure and temperature applications. The main advantages of gate valves are:

  • Provide very good shutoff characteristics.
  • Low Pressure-Drop; very low frictional loss.
  • the maintenance requirement is less.
  • can be used as a Bi-directional valve
  • low cost
  • available in various sizes.

Disadvantages of Gate valve

  • Cannot be used for throttling service.
  • Slow disc movement in operation, it takes time to fully open or fully close.
  • Lapping and grinding repairs are difficult to accomplish.
  • May create noise and vibration when partially open.
  • Prone to Seat and Disk wear.

Gate Valve Materials

Various types of materials are used for gate valve construction. Typical common materials used are cast carbon steel, cast iron, ductile iron, gunmetal, bronze, alloy steel, stainless steel, and forged steel. Brass and PVC gate valves are used for plumbing services. The material selection for gate valves primarily depends on fluid service and its design temperature. The following table provides a typical example of common materials used in Gate valve construction.

Gate valve materials
Fig. 8: Gate valve materials

Applicable codes and standards for gate valve design

The following codes and standards govern the design specification of gate valves:

  • Valve Design: API 600/ API 602/ BS5352/ API 603/ API6D/ IS780 /BS 1414 / BS 14846
  • Valve Pressure Testing: API 598
  • Valve Pressure Temperature Rating: API B16.34
  • Face-to-Face Dimensions: ANSI B16.10
  • Flange Drilling: ANSI B16.5 / ASME B 16.47/ BS 10 Table / DIN /IS /JIS Standards
  • Butt/ Socket Welded End: ANSI B16.25 and B16.11
  • Screwed End: ANSI B 1.20.1 (BSP/NPT)

Gate Valve Symbols

The gate valve symbols used in the different organization varies a little bit. Normally any one of the following three types of gate valve symbols given in Fig. 9 is used as a gate valve symbol.

Gate Valve Symbols
Fig. 9: Gate Valve Symbols

Gate valve vs Ball Valve

Both the gate valve and Ball valve are widely used for isolation services in the oil and gas industries. However, there are a few differences between the gate valve and the ball valve. Some of such differences are listed below in a tabular format for reference:

ParameterGate ValveBall valve
Working PrincipleGate valves control the valve using its gate. When lifted up, allows full flow, and when down, no flow.Ball valves feature a stem and a ball with an opening inside. When the opening is lined up with the pipe by turning the control lever fluid can pass, otherwise, the valve is off.
CostGate valves are Relatively cheaperBall valves are comparatively Costlier.
Turning of lever or hand-wheelGate valves feature a Multi-Turn mechanism.Ball valves are Quarter-turn valves.
WeightThe weight of the Gate valve is normally less than the ball valve for the same size and rating.Ball Valve weights are comparatively more than gate valves.
Shut off capabilities The shut-off capabilities of gate valves are not at par with ball valves.Comparatively better than gate valves; more reliable.
Surge ProbabilityAs the operation of a gate valve is slow, less probability of water hammer.Ball valves are more prone to water hammer or surge creation.
Vibration probabilityPartially open gate valves cause vibration or noiseThe possibility of noise production is less in ball valves.
Operating Space requirementThe operating space requirement for gate valves is usually less.More space is required to operate a ball valve.
Visual Clue for on/off positionNo clue from the outside, it’s simply guessing.Easy to understand if the ball valve is in the open or closed position.
Gate Valve vs Ball Valve in a Tabular Format
Typical gate valves
Fig. 10: Typical gate valves

Few more related articles for you.

Selection of Valves: A Few Guidelines
Details about Control Valves
Ball Valve Design Features: A Detailed Literature
A brief article on Valve Inspection & Testing
Control Valve Sizing Procedure: Valve Flow Terminologies, Control Valve Characteristics, Cavitation and Flashing

Caesar II Version 12 vs Caesar II Version 11

Written by Anup Kumar Dey in Caesar II,Piping Stress Analysis,Piping Stress Basics

Hopefully, by now all the Caesar II users are aware that the latest version of the piping stress analysis software Caesar II version 12.0 has already been released by Hexagon. Like every year they routinely update the code requirements and resolve user difficulties that appear in the earlier version of the software. In a similar way, they have come with new changes and updated capabilities in the latest edition called Caesar II version 12. 

Even though there are many pipe stress analysis software like Autopipe, Caepipe, Rohr2, Start-Prof, etc, Caesar II is the most widely used software having a major market share in the piping stress analysis software domain. In the following table, I will present a comparison between Caesar II version 12 and Caesar II version 11.

MDMT Test requirements in Caesar II Version 12
Fig. 1: MDMT Test requirements in Caesar II Version 12
ParameterCaesar II 2019-Caesar II Version 11Caesar II Version 12
Piping Code Editions1. Caesar II 2019 complies with the process piping code ASME B 31.3 2016 edition
2. It complies with liquid pipeline code ASME B31.4 to the 2016 edition
3. ASME B31.8 piping code to the 2016 edition
4. Canadian Z662 piping code to the 2015 edition		1. Caesar II version 12 complies with the latest edition of Process Piping Code ASME B 31.3-2018
2. Complies ASME B31.4 pipeline code to the 2019 edition
3. ASME B31.8 piping code to the 2018 edition
4. Canadian Z662 piping code to the 2019 edition
Structural DatabaseThis version OF Caesar II complies with the older version of AISC; ASIC- 1989Structural databases have been updated to AISC 2017
License ManagerHASP Key. Transitioning to Intergraph Smart Licensing (ISL).Fully compatible with ISL, a cloud-based licensing system. This version no longer supports Smart Plant License Manager or HASP keys.
Year BrandingCaesar II version 11 is also known as Caesar II 2019Year branding has been removed from the CAESAR II version name. So there is no Caesar II 2020; It’s only Caesar II version 12.
In-Plane and Out-plane SIF–More detailed information on the use of in-plane and out-plane stress intensification factors (SIFs) is added with respect to FEA translation. Additional information on the local coordinate definitions is also included.
Material Database–The Russian material database is updated.
Interface with AFT ImpulseNo interface with AFT ImpulseDynamic surge analysis becomes easier as files can be directly imported from the AFT Impulse software.
MDMT ReportNot AvailableMinimum Metal Design Temperature (MDMT) data is added to the database (Refer to Fig. 1) to check the impact test requirements. The software checks the requirement.
Buckling Check as per ASME B 31.8Not Available in this versionBuckling check following ASME B 31.8 (Refer to Fig. 2) code has been added in Caesar II version 12. This provides strain values to calculate the buckling and lateral instability of piping elements.
Caesar II Help filesAll help files are available offline in the local drive.All help files are now online in the latest version of the software. It provides improved search, custom book creation, and quick updates.
Caesar II Version 12 vs Caesar II Version 11
B 31.8 buckling check in Latest edition of Caesar II
Fig. 2: B 31.8 buckling check-in Latest edition of Caesar II

The Caesar II owner Hexagon PPM has released one video explaining the enhanced capabilities for the latest edition, i.e Caesar II Version 12. The same has been embedded here for your reference.

Tutorial video explaining What’s new in Caesar II Version 12

Click here to learn more about piping stress analysis using Caesar II.

Learn the changes in the different versions of Caesar II software:

Caesar II Version 12 vs Caesar II Version 11
Major features of CAESAR II-2019, Version 11.00
Added Features of CAESAR II 2018, Version 10.00
What’s New in CAESAR II, 2016 (Version 8.0)
Practical changes in Caesar II version 7.0 (2014) with respect to its earlier version.

What is Piping Inspection?

Written by Shyam Mohan in Engineering Materials,Inspection and Testing,Mechanical,Piping Design Basics,Piping Interface

Piping systems are the backbone of many industrial processes, from oil and gas to water treatment and chemical manufacturing. Given their critical role, the integrity of these systems is paramount. Piping inspection is a systematic approach to ensuring that pipes and their associated systems are safe, reliable, and compliant with regulations.

What is Piping Inspection?

Piping Inspection is a comprehensive task that is performed following client/company-specific inspection documents. The main aim of the piping inspection is to ensure plant reliability, reducing probable errors, and thus safely operating the plant throughout its design life.

All plants are designed for a predetermined design life (normally 20 years for process piping). Periodic inspection help plants to operate with safety and efficiency.

Even after attending and completing various courses related to piping, most of the fresh graduates and professionals face difficulties in understanding the procedures when it comes to real-life jobs.

Considering the stigma, a simple way to understand the basic unique procedures that are to be followed during the fabrication and installation of carbon steel pipes is discussed in this article.

When it comes to piping it’s the Piping and Instrumentation Diagram or P & ID is the bible for an Engineer to execute his work.

Piping Inspection Procedure

For performing piping inspections, there should be a client-approved Inspection and Test Plan, or ITP, in place prior to the commencement of any job activities. This shall be prepared with reference to the piping design code and project specifications.

Piping design codes like ASME B31.3 PROCESS PIPING will be the design code for designing piping by the engineering team for the project.

Different types of design codes are available as per the project and product requirements. Understanding the codes and standards along with the particular project specification will provide basic ideas regarding the scope of work being executed.

 According to the requirements of the design code, the drawings will be developed and the same design code will be reflected in the drawings. All the construction procedures will be shortlisted with different intervention points as shown in the below Fig.1

List of Piping Inspection Points
Fig. 1: List of Piping Inspection Points

What is the Inspection and Test Plan or ITP?

An ITP covers all the construction activities that are being carried out during and after the construction. Learning and understanding ITP along with the construction procedures and Method of statement for specific activities will give a wide range of understanding regarding the job being executed. The Inspection and Test Plan must meet the requirements of the design code (ASME B 31.3 for process piping).

Welding procedure specification or WPS shall be approved by the client prior to the commencement of any welding jobs. CSWIP and AWS-certified inspectors are preferred as inspectors or quality engineers for inspection-related jobs. Further to the approval of WPS welder qualification tests will be carried out based on the project requirements on the welding positions, process, and types. Only these welders who successfully pass the qualification test based on visual and Radiographic Testing reports can be used for all the project-related welding activities. Welder IDs signed by all parties shall be prepared and issued to the welder that shall be available with the welder during working hours.

Various certifications like API 570, API 650, Bgas, NACE, and Level 3 courses are available in the market to strengthen the requirements of a professional for a company.

Initially, after the approval of the above-said documents by the client, inspections shall be performed based on the ITP. No inspections or documents will be generated other than the ones mentioned in the ITP.

Inspection of Piping and Component Materials

Piping and Component Material inspection is the next step of inspection normally done by the quality personnel when a material related to the project is received at the site. The below points as a minimum are to be checked during the material inspection:

  1. Material purchased is from the client-approved manufacturer or vendor
  2. Material specification, grade, thickness, and size.
  3. Any mechanical damages.
  4. Heat numbers provided in the materials are matching with the Material Test Certificates provided prior to the inspection.
  5. Quantity of the material with reference to purchase order and delivery note.
  6. Reviewing of Material Test certificates with reference to project specification, design code, and drawings.
  7. Proper stacking of the materials.

Material inspection reports shall be generated with all the requested data like Material grade and type, quantity, Heat number, Material certificate number, and inspection status.

Once the materials are approved by the client it can be issued for construction.

Different Types of Piping Inspection

Fit-Up Inspection

Initially, the piping activities will commence with the fit-up inspection. This shall be carried out based on the approved isometric/weld map generated from the P&ID.

During the fit-up inspection, the joint number, date, spool number, drawing number, and sheet with revision shall be checked. The heat number of the material shall be noted for preparing the fit-up report. Taper gauge, Hi-lo gauge, cam gauge, and measuring tape will be used for checking the fit-up gap between the joints and for checking the dimension of spools. Further to the acceptance of fit-up the spool or joint can be released for welding.

Welding Inspection

Mostly GTAW and SMAW welding techniques are most commonly used for pipe welding. The welding inspections will be carried out in different stages by a certified welding inspector and the reports shall be generated with material grade and specification, heat number, drawing number with sheet number and revision, joint type, welding process, welder number, and dates.

Once the joints are completed will proceed with the RT i.e, radiography testing as per the percentage of NDE recommended in the design code and project specification.

Piping routing consists of elbows and fittings. Other than the weld joints flanged joints will be available based on the engineering requirements considering the stress analysis. Pipe supports and wear pads along with any other attachments shown in the drawings shall be checked twice.

Visual Inspection

Visual inspection is the most fundamental type of inspection. It involves examining the exterior of pipes for signs of wear, corrosion, leaks, and other visible defects. While it cannot detect subsurface issues, it is a valuable first step in identifying potential problems.

Destructive Testing

In certain scenarios, destructive testing may be necessary to evaluate the material properties of piping. This includes tensile testing, impact testing, and metallurgical analysis. While it provides detailed insights, it is not commonly used for routine inspections due to its invasive nature.

Piping Inspection Punch Lists

Once the welding activities and installation of piping spools or the system are completed a pre-hydro walkthrough will be conducted in order to find the balance/pending jobs. These are normally considered punches that are commonly grouped into two types, punch A & punch B. Punch A items consist of direct welding items, and punch B can be closed after the hydro tests. No direct welding shall be done in the piping system after the completion of hydro testing.

Hydro-test Package

After attending the punch A items, the spools can be released for hydro testing. A test package shall be prepared, not limited to the below-listed items.

Piping Hydro Test Package Items
Fig. 2: Piping Hydro Test Package Items

The test pressure and holding time will be confirmed subject to the project specification and design code.

Water will be filled into the pipe spools with a pump connected through a test manifold with pressure gauges, safety relief valves, and proper venting facilities. A water test certificate shall be attained prior to the filling of water along with the blind checklist, i.e. the list of blind flanges that are being used for hydro testing.

Understanding the above list will provide a basic idea regarding the hydro test.

Note that a hydro test is done in order to confirm the weld joints’ integrity and to ensure that the parent material is free of any leakage.

Bolt tightening with a torque wrench shall be done for the flanged joints. After draining the water, flushing the lines with water and air blowing shall be done in order to dry the lines.

Note that valves are not installed prior to the hydro test, inline valves are installed after the hydro test and cleaning process as the testing pressure and design code for valves are different.

The spools or piping system can now be released for blasting and painting as per the project requirements. A final walkthrough shall be conducted in order to confirm the installation of all the valves and instruments in the piping system are in place as per the P&ID.

Piping Inspection Flow Chart

The following figure shows a sample piping inspection flow chart.

Piping Inspection Flow Chart
Fig. 3: Piping Inspection Flow Chart

Codes and Standards for Piping Inspection

There are various international codes and standards that provide guidelines for piping inspection. Some of those codes are listed below for reference:

  • API 570, Piping Inspection Code
  • API RP 574, Inspection Practices for Piping System Components
  • API RP 577 Welding Inspection and Metallurgy
  • API RP 578, Material Verification for New and Existing Alloy Piping
  • API RP 583, Corrosion Under Insulation and Fireproofing
  • ASME PCC-2, Repair of Pressure Equipment and Piping
  • ASTM STP 880, Corrosion of Metals Under Thermal Insulation
  • API RP 571 Damage Mechanism Affecting Fixed Equipment in the Refining Industry

Developing an Inspection Program

Risk Assessment

A thorough risk assessment identifies potential hazards associated with piping systems. This process helps prioritize inspection efforts based on factors like system criticality, operating conditions, and historical data.

Inspection Schedule

Developing a comprehensive inspection schedule is crucial for maintaining piping integrity. Factors to consider include:

  • Age of the system
  • Operating conditions
  • Type of fluid transported
  • Previous inspection results

Documentation and Reporting

Maintaining detailed inspection records is essential for compliance and future reference. Inspection reports should include:

  • Inspection methods used
  • Findings and measurements
  • Recommendations for repairs or further action
  • Follow-up inspections and timelines

Common Piping Defects and Their Causes

Corrosion

Corrosion is one of the most significant threats to piping integrity. It can be caused by:

  • Chemical reactions: Interaction of the pipe material with transported fluids.
  • Environmental factors: Moisture, temperature fluctuations, and soil conditions can accelerate corrosion.

Cracking

Cracks can result from stress, fatigue, or improper installation. Common types include:

  • Stress corrosion cracking (SCC): Caused by the combined effects of tensile stress and a corrosive environment.
  • Fatigue cracking: Resulting from repeated loading and unloading cycles.

Leaks

Leaks can occur due to several factors, including:

  • Worn-out seals and gaskets
  • Erosion from fluid flow
  • Improperly installed fittings or connections

Mechanical Damage

Mechanical damage can arise from external forces, such as impacts from equipment or natural events (e.g., earthquakes). Regular inspections can help identify and mitigate these risks.

Hope, the above-mentioned details will provide some basic ideas to beginners regarding the sequence and structure of piping inspection. Overall, piping inspection is a critical component of maintaining the safety and reliability of piping systems across various industries. By understanding the importance of inspections, employing the right methods, and adhering to industry standards, organizations can mitigate risks and ensure the longevity of their piping systems.

Storage Tank Erection: Conventional vs Jacking Method

Written by Anup Kumar Dey in Construction,Mechanical,Piping Interface

Two types of storage tank erection methodology have become widely accepted and popular. The first one is the Conventional Method of Tank Erection & the other is the Tank Jacking method. Both of these tank erection methods are accepted by the API 650 and the constructor. The selection of the tank erection method basically depends on the site location or workshop where we are making these tanks.

There is a popular myth that API 650 guides us to adopt the tank erection methodology. But that is not true. API 650 only guides us in the design, fabrication, welding, hydro testing & inspection of storage tanks.

Conventional Method of Tank Erection

In conventional methods, cranes are used for tank erection as a sheet-by-sheet method. At first, the bottom and annular plates are erected. Then the lower course shell is erected and finally, the upper course shell is erected. Refer to Fig. 1 which shows an example of a double-deck floating roof Tank erection by the conventional method. Suppose there are a total of 9 shells in a Tank so the tank erection sequence shall be 1st shell coarse, 2nd shell coarse, 3rd, and then in last 9th shell coarse.  

Double deck floating roof tank erection by conventional method
Fig. 1: Double deck floating roof tank erection by a conventional method

In the case of a small diameter Tank, the tank is fabricated at the workshop and then brought to the site by a trailer for erection. But the handling should be proper to avoid buckling, bending, and any damage.

Tank erection by conventional method
Fig. 2: Tank erection by the conventional method.

In the case of Shop fabrication, the tank fabrication, erection, & assembly is done by EOT (electric overhead traveling) crane at the shop and then shifted to the site by a trailer.

Tank Fabrication at shop
Fig. 3: Tank Fabrication at shop
Mobilizing fabricated tank to the construction site
Fig. 4: Mobilizing fabricated tank to the construction site

Tank Erection by Jacking Method

A jacking method is an advanced form of tank erection. The jacking method uses the technology of the Swedish Company Bygging Uddemann AB. A number of hydraulic Jacks are placed inside the tank to be erected. Refer to Fig. 5. In recent times this method is widely used in all developed countries.

A system of hydraulic pressure hoses interconnects the hydraulic jacks which are energized by the action of a hydraulic pump.

Tank Erection by Jacking Method
Fig. 5: Tank Erection by Jacking Method

This method is just the opposite of the conventional method. The construction sequence is just the reverse of the conventional one. If there are a total of 9 shell courses, the erection in the jacking method will start from the 9th, then the 8th, 7th, and in the last 1st shell course will be erected.

The number of hydraulic jacks is decided based on the total weight of the roof & shell courses except for the bottom courses. Standard practice is to keep a 3000 mm distance between two jacks. However, the number of hydraulic jacks can be increased to meet additional wind load. Fig. 8 shows a typical jack used for tank erection.

Tank Jacking Procedure

The following steps are followed while erecting tanks by jacking procedure:

  • Tank pad to be checked and tolerances to be verified.
  • Since jacks are to be mounted on the annular plates, these need to be placed.
  • Annular plate joints are to be aligned and welded.
  • Next, erect the floor plates and align the joints to complete the welding of the bottom seams.
  • After that, Erect the top 2 courses. Align properly and weld. All the works on these two courses including the erection of the curb angle, wind girder for Floating Roof Tanks (or) roof structure, and roof for Cone Roof Tanks, hand railing, etc to be completed.
  • Next, Place the hydraulic jacks along the circumference of a circle drawn about 100 mm from the shell plate circle. The maximum arc distance between the two Jacks shall not exceed 3000 mm.
  • Jacks are available in 8 T / 12T capacities. So arrange hydraulic jacks of predetermined quantities before starting the erection. Anchor the jack supporting columns to the base plate.
  • When, the sub-assembly consisting of the top 2 courses, roof structure/roof (or wind girder) railing, etc. is lifted, erect the shell plates of the third course from the top, after lifting the entire subassembly to the required height.
  • Align the vertical joints and weld. Next, the sub-assembly is lowered to complete the alignment and welding of the girth seam.
  • The hydraulic jacks can be released and lowered after the alignment of the girth seam,
  • In a similar way, erect the other shell courses till all courses are erected.
  • Finally, Align the shell to the bottom joint and check for the verticality of the completed tank. Weld the shell to the bottom joint.
  • Now, all other balance works like fixing and welding of shell manholes, nozzles, etc. can be completed.

Various terms are used while erecting tanks as mentioned below:

Stay Pipe and Power pack machine
Fig. 6: Stay Pipe and Powerpack machine
  • Power Pack Machine (Fig. 6): This Machine is used to lift the Jack. This machine Pumps the oil to Jack through the hose pipes to lift the jack.
  • Stay Pipes (Fig. 6): Also known as supporting pipes; These pipes provide support to jack and trestle pipes. Basically, these pipes are supporting the vertical trestles to maintain verticality.
  • Trestle Pipes (Fig. 7): These are the vertical members in the Jacking system that carries loads of Jacks. While installing this assembly we need to take extra care of these vertical members so that the verticality of the Tank is maintained. Jacks Move over the Trestles by teeth. These get support from base plates in the Tank bottom.
Example of Trestles
Fig. 7: Example of Trestles

Difference between the Conventional and Jacking Methods

The main differences between the conventional tank erection and jacking tank erection methods are provided in a tabular format below:

Typical Jack for Jacking Method
Fig. 8: Typical Jack for Jacking Method
Conventional Tank Erection MethodTank Erection by Jacking Method
Suitable for all types of tanks with any diameter and heightLarge diameter tanks with higher plate thickness requiring double-sided welding are not possible to erect by this method. Not fully feasible for double-wall tanks.
Very good dimensional control is possible: Shell and bottom shapes obtained can be close to the designed dimensions.Dimensional control is comparatively less.
Erection time is comparatively moreErection time is less.
Safety issues as working at heightSafe erection as working at ground level. So lower risks.
Resource requirement is more, hence more costlyEconomical erection.
Possibility of wind damage while erection.Protective tank roofs and wind girders eliminate the possibility of wind damage.
Inspection Access is difficultEasily accessible
Lower productivityBetter productivity
High-capacity cranes are requiredThe involvement of high-capacity cranes is comparatively less.
Difficult operation with less efficiencySmooth operation with high efficiency
Conventional Method vs Jacking Method

To summarize, the tank erection methodology by jacking method has many advantages over the conventional ones which include easy to operate, safe and reliable, accurate control of the weld gap and the height of the lifting rod, good quality of the project, and providing an outstanding economic benefit.

References and Further Studies:

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What is Fireproofing? Types, Materials, Methods

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

Fireproofing provides materials and structures resistance to fire so that during an accidental case of fire the critical structures keep operating until the fire is brought under control. Fireproofing means applying certain products over the materials or structures which minimize the escalation of fire and thus plant operators get sufficient to act against the fire.

In refineries, petrochemical plants, power plants, process terminals and many other places where the chances of fire are high, various codes and standards (like NFPA) suggest the licensor use fireproofing. For that purpose, Equipment and structures are fireproofed up to a certain height or whole equipment as dictated by guidelines. Refer to Fig. 1, which shows the whole equipment is fireproofed.

Example of Fireproofing of whole equipment
Fig. 1: Example of Fireproofing of the whole equipment

Reason for Fireproofing – Why do we do fireproofing?

There are various reasons to do fireproofing equipment and structures. Some of those are listed below:

  • To full filling, the industrial requirement of completing NFPA (National fire protection academy) & OSHA requirement
  • To increase the resistance of fire
  • To keep equipment and critical control systems operating during the Fire.

It is believed that at around 1000°F (538°C), the structural steel loses roughly 50% of its design strength. So by using fireproofing the time to reach that temperature is prolonged. Just to note that a normal fire normally burns in the 1800°F to 2000°F range.

Refer to Fig. 2 which shows the fireproofing in equipment after a certain height.

Fireproofing after a certain height
Fig. 2: Fireproofing after a certain height

Similarly, in Fig. 3, The fireproofing has been done only in columns and the down portion of spheres as per guidelines.

Fireproofing Codes and Standards

Below mentioned Codes and standards provide guidelines for fireproofing applications:

  1. BS 476: Part 20-24, Test Methods, and Criteria for the Fire Resistance of Elements of Building Construction.
  2. API 2218: Fireproofing Practices in Petroleum & Petrochemical Processing Plants
  3. API 2510: Design and Construction of LPG Installation (Section 10.7)
  4. NFPA 30: Flammable and Combustible Liquids code
  5. NFPA 58: Liquefied Petroleum Gas code
  6. Loss Prevention in the Process Industries by F P Lees, 2nd edition
  7. International Building Code
  8. ASTM E119, Fire Tests of Building Construction and Materials
Fireproofing up to a certain height
Fig. 3: Fireproofing up to a certain height

Fireproofing Materials

The design codes and standards do not provide any direct indication of the material to be used for fireproofing. The material must be durable and corrosion-resistant. Based on construction practice, the following materials are used as fireproofing materials:

  • Gypsum plasters
  • Pyrocrete 241
  • Mesh
  • Cementitious plasters
  • Carbomastic 801(a+b)
  • Carboguard 890 (a+b)
  • Carboguard 1340 (a+b)
  • Carboline 139 (ral 7042)
  • Fibrous plasters containing either mineral wool or ceramic fibers
  • Thinner # 2
  • Thinner # 76
  • Thinner #25
  • Thinner # 33
  • Concrete
  • Intumescent coatings
  • Asbestos

Fireproofing application method

The following steps are performed for applying fireproofing in mechanical equipment:

  • Do the equipment surface preparation
  • Apply the primer up to 65 -75 microns.
  • Fix nut by tack weld to keep tie mesh.
  • Apply Pyrocrete 241
  • Apply 2 coats of epoxy paint and check the DFT of the paint as well as the thickness of the fireproof.
  • If it is accepted by the engineer in charge or SOP then Vessel can be released for further work.

Types of Fireproofing / Fireproofing types

In many industrial facilities, to secure any insurance fireproofing is a pre-requisite. On a broad scale, Fireproofing is divided into two groups:

  • Active Fireproofing and
  • Passive Fireproofing

In the case of active fireproofing, human intervention is required for some kind of action to activate the fireproofing system. Whereas, passive fireproofing is planned and designed considering safety plans beforehand. The most common type of passive fireproofing is

  • cementitious fireproofing,
  • intumescent fireproofing and
  • firestop fireproofing.

Cementitious Fireproofing:

These are gypsum-based, plaster-like coatings that look like white stucco when dried. These coatings are sprayed on the structural surfaces requiring fireproofing. Cementite fireproofing is used to keep structural girders and beams below 540 C, where the steel will bend.

Intumescent Fireproofing:

When heated, intumescent paints expand and form a heat-resistant barrier. They usually contain sodium silicates. Under high heat conditions, the intumescent paint coating thickens, entraining air and forming a layer of greater insulation. Intumescent fireproofing paints are used on metallic pipes, tanks, and valves.

Firestop Fireproofing:

In Firestop fireproofing, all openings and joints are sealed with fire-resistance-rated walls and floors. Fire dampers are used to fill the ductwork holes, Hole cuts for pipes, and electrical wiring trays.

Comparison of Cementitious and Intumescent Fireproofing

Intumescent fireproofing is easier to apply than cementitious fireproofing. As they are applied similarly to traditional coating, moisture can not settle inside. As Cementitious fireproofing is done using inexpensive materials, they are applied for fireproofing facilities under some circumstances. However, from a technical standpoint, intumescent fireproofing is more advanced and offers the flexibility of added fire protection.

Required resources for fireproofing

While fireproofing mechanical equipment following resources are required:

  • Air compressor- 2 nos
  • Hopper- 2 nos
  • Spray machine-4 nos
  • Compressor for fireproofing- 4 nos
  • Mixer machine-3 nos

Even after a simple fireproofing application, it may not work properly due to the following reasons

  1. Failure of the compressor –Always use TPI inspected Machine for applying Pyrocrete & Paint Properly.
  2. Over/less application- over-applying Pyrocrete or Painting would cause mud cracking & less application may cause peel-off or orange peel.
  3. Lack of expertise- Lack of SME (Subject matter expert) may cause repair or failure.
  4. Lack of Curing- To achieve the milestone or Target sometimes people overtake curing time which may cause repair or Fail.

Storage Tank Failure: Examples, Causes, and Prevention

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

The storage tank is a very important static equipment for the oil and gas industry to store fluids. Even though various codes and standards stipulate its design to avoid failure of storage tanks, still there are many incidents of storage tank failures. So, storage tank failure is not at all a new phenomenon. In this article, we will explore the causes of such tank failures and steps for prevention.

Types of Storage Tanks (API 650)

Storage Tanks can be classified on many bases based on service, based on construction, based on Pressure & Temp & based on the roof (Atmospheric Pressure). Here, We will list the storage tank types based on the roof construction.

  • Double-Deck Floating Roof Tanks (DDFR): Double-deck floating roof Tank has two layers of the deck that floats over the product inside the Tank. This type of Tank construction consumes too much material as the deck is double. But it is used only for highly volatile products.
  • Single Deck Floating Roof (SDFR): Single deck floating roof Tanks are similar to DDFR; the only difference is the deck that floats is single. It uses bouncy for this type of Tank to maintain floatation.
  • Cone Roof (CR): Cone roof Tanks have a Cone roof. The roof slope is subject to the designer but 1:100 is common practice.
  • Internal Floating Roof (IFR): Internal floating roof Tanks are basically a collaboration of deck and roof. So, these types of tanks will have a Deck as well as a roof. The type of deck can be any type it may be single deck or Double deck Pan type.
  • Dome Roof (DR):– Dome roof Tanks are almost the same as the Cone roof; the only difference is they would not carry any deck and the shape of the roof will be Dome type.
  • Click here to know more about various types of atmospheric storage tanks

Detailed indication and nomenclature of roof-type storage tanks could be seen in Fig 1. Normally storage tanks fail in any one of the locations mentioned in Fig. 1.

nomenclature of roof type storage tanks
Fig. 1: nomenclature of roof-type storage tanks

Common Causes of Storage Tank Failures

Various studies conclude that majority of the storage tank failures are due to any one or combination of the following causes:

  • Corrosion: Most Common cause of storage tank failures
  • Improper Construction
  • Poor Maintenance
  • Incompatibility of fluid with the tank wall
  • Dispensing problems
  • Lack of Physical Safety i.e, Internal/External forces or events (Flood, fire, impact, etc.)
  • Excessive Pressure due to overfilling of Storage Tanks
  • Age/UV-related issues with non-metallic tanks
  • Failure of Pressure Vacuum Relief Valve (PVRV)
  • Seismic design failure
  • Scada failure
  • overturning because of Wind girder
  • Sabotage
  • Operational Errors on human interference
  • Violent weather changes

Types of Storage Tank failures

Storage tank failure modes can again be divided into various types such as

  • failures based on Pumping,
  • based on Material,
  • based on service,
  • Mechanical, civil, or electric failure, etc.

You will get many references for storage tank failures over the net caused by corrosion, improper construction, poor maintenance, etc. We will explain a few storage tank failure examples based on Mechanical Failure.

Storage Tank failure due to Overfilling

In the Guru Gobind Singh Refinery, India (2012), the refinery was handed over for commissioning after the completion of all necessary details. Because of the inadequate time frames and some construction requirements, water was filled into a big tank so that water could be used for hydro testing of other Tanks.  It was evening time and the operational people had to go for a shift change. But without informing the other relevant people on the next shift, the responsible person took the bus. So naturally, the valve is not closed. The Tank is filled totally and started overflowing but the overflow rate was not able to control the Pump flow rate. Within a short time span the tank failed, the rafter damaged the roof, the Deck stuck on the top & Weld of the plates of the lower thickness of the upper side gets sheared.

Tank failure example
Fig. 2: Tank failure example

Storage Tank Failure due to failure of the PVRV breaker

In the Sulfur Recovery Unit of the same refinery, one tankage failure incident occurred during commissioning. This failure occurred because of PVRV failure. The operator opens the valve to pump out but because of the PVRV failure, the Tank gets collapsed. Within seconds the tank explodes like a bomb. The products were water and so spreading around didn’t affect them much.

Root cause analysis shows that the PVRV installation had not been cross-checked. Because as per API 650, it’s not necessary to install a pressurized part during Hydro Testing because it’s just like the Water fill test in ATM pressure Tanks.

The following Fig. 3 explains the stage-wise incident of the storage tank failure.

Stage wise explanation of storage tank failure due to PVRV failure
Fig. 3: Stage-wise explanation of storage tank failure due to PVRV failure

Reason for Failures-

The most common reason for storage tank failure is the lack of knowledge, training, and inspection. In both of the above-mentioned failures, it was found that in both cases operator was not well-trained. The first failure is solely the mistake of the operator. In the second one, it was a PVRV failure but if we check the PVRV before every operation it can save the equipment and human lives. The second failure was in small diameter tanks (9 m diameter) as we can see in Fig 3. it was 9 m dia tanks. We could easily imagine the fatality if the tank diameter was larger.

The root cause analysis is performed to find out the root reason for what happened. After that, the finding is documented in the Lessons learned register for future reference to eliminate the reason for failure in future projects. In this article, we can understand the root was a lack of training & PVRV (supporting) equipment failure.

To make the lesson learned register, help from SME (subject matter expert) can be taken. They will guide and help to document the basic reasons for failure.

Prevention of Storage Tank failures

Failure of Storage Tank systems can be reduced by the following methods.

  • All necessary mounting shall be TPI (Third Party Inspection) inspected. Even after FAT (Factory acceptance test) they should be checked at the construction site by the Engineer in charge or in the presence of the Engineer in charge.
  • PVRV (Pressure vacuum relief valve) is something that is commonly used. It should be frequently checked during the operation.
  • All Tankages shall be protected by the emergency vent system.
  • All Tankages shall be inspected periodically.
  • The design of the Firewall and bund wall should be considered for contingency reserves.
  • External roof supports/self-supporting roofs
  • The design of tank thickness has to be proper
  • Proper Metallurgy of the used compatible material to reduce corrosion

Code and Standards for Tank inspection to reduce storage tank failures

The following codes and standards provide guidelines for inspection to reduce the failure probability

  • API 575 – Inspection of Atmospheric and Low-Pressure Tanks
  • API 653 – Tank inspection, repair, alterations, and reconstruction
  • API 570 – Piping Inspection Code
  • UL 142 – SteelAboveground Tanks for Flammable and Combustible Liquids
  • STI SP001 – Standard for Inspection of Above-ground Storage Tanks

Reference and Further Study: