Many of you are aware that the 2014 edition of ASME B 31.3 is scheduled to publish on 21st February 2015. Similar to every new edition this edition too contains several updates. Thanks to Mr. Don Frikken who has listed a few of the substantive changes in one of his blog posts. Here I am providing few major points. For details please read the complete article by clicking on the link provided at the bottom of this post.
In addition to the many clarifications, updated references to codes and standards, updates to basic allowable stresses, and added listed materials, there are several substantive changes to the 2014 Edition of ASME B31.3, Process Piping.
Some of these changes are listed below:
The definition of Category M Fluid Service is revised in the 2014 edition to provide better guidance on the selection of the Category M Fluid Service designation. As per the new edition of the code Category M Fluid Service is A fluid service in which all of the below-mentioned conditions apply:
The fluid is so highly toxic that a single exposure to a very small quantity of the fluid caused by leakage, can produce serious irreversible harm to persons on breathing or bodily contact, even when prompt restorative measures are taken; and
If after consideration of piping design, experience, service conditions, and location, the Owner determines that the requirements for Normal Fluid Service do not sufficiently provide the leak tightness required to protect personnel from exposure.
Flared laps are prohibited for use in Category M fluid service in the 2014 edition.
Because of the potential for misapplication of the alternative rules, and because many of the provisions of Appendix P had been incorporated into the base Code, Appendix P has been removed in the 2014 edition.
The 2014 edition explicitly requires that the maximum value of SL considering all conditions be used in calculating the allowable stress range.
The 2014 edition requires that thermo-wells need to comply with ASME PTC 19.3 TW.
The 2014 edition requires that when cold spring is used, the reactions be computed both with the assumption that only two-thirds of the design cold spring is present and with four-thirds of the design cold spring present.
The 2014 edition permits the hydro test pressure to be lowered to the design pressure while examining for leaks. The 2014 edition simplified the calculation of hydro test pressure.
The 2014 edition restricted the use of Fig. 323.2.2B to provide a further basis for the use of carbon steels without impact testing. The Code warns that the calculation of stresses due to cold springing or misalignment should be included as part of the stress ratio.
The 2014 edition added requirements for and illustrations of welds for integrally reinforced branch connections.
The 2014 edition revised the Preheat and Heat Treatment requirements somewhat. This revision, along with revisions to ASME B31.1, makes the preheat requirements in the two Codes the same.
The 2014 edition added specific examination personnel qualification requirements, which are those described in ASME B&PV Code, Section V.
The 2014 edition added specific acceptance criteria for magnetic particle and liquid penetrant examination.
The 2014 edition changed the leak test pressure from 1.5 times the design pressure corrected for temperature to 1.25 times the design pressure corrected for temperature.
In the world of piping engineering and fluid control systems, ball valves are a crucial component that plays a vital role in regulating the flow of liquids and gases. These valves are widely used in various industries, ranging from oil and gas to water treatment, due to their exceptional reliability, versatility, and ease of operation. This article provides everything you need to know from ball valve definition, types, parts, working, materials, end connections, specifications, advantages, and standards to testing and uses.
What is a Ball Valve?
A ball valve is a type of valve that uses a spherical perforated obstruction (a rotary ball) to stop and start the hydraulic flow. A ball valve is usually rotated 90° (quarter-turn valve) around its axis to open and close.It is one of the most widely used valve types. Ball Valves are suitable for both liquid and gas services. They are highly popular in the chemical, petrochemical, and oil and gas industry because of their long service life and reliable sealing throughout their service life. Ball valves can even be used for vacuum and cryogenic services. Developed around 1936, Ball valves are among the least expensive valves which are available in extremely wide size ranges.
Ball valves are sometimes used as control valves due to their cost-effectiveness but are not preferred as they don’t provide precise control and adjustments. The ball is positioned within a valve body, and a handle or actuator is used to rotate the ball either perpendicular or parallel to the flow direction, thus controlling the fluid flow. When the hole aligns with the flow direction, the valve is in the open position, allowing fluid to pass through. Conversely, rotating the ball to block the hole closes the valve, stopping the flow.
Applications of Ball Valves
Ball valves find application across a wide range of industries due to their versatility and ability to handle various types of fluids, from corrosive chemicals to high-pressure gases. Major applications of ball valves include
1. Use of Ball Valves in Refineries:
I have seen ball valves to be used as shut-off and isolation valves for tower bottom lines and thermal-cracking units; Gas/Oil separation lines, Gas distribution measuring, metering, and pressure regulation stations, Oil loading control stations, Pumping, and compressor stations, Emergency shut-down loops, Refining units, etc.
2. Use of Ball Valves in Chemical and Petrochemical Complexes:
Ball valves are used for low differential pressure control, emission control, and handling highly viscous fluids, and abrasive slurries in process and storage facilities. They are suitable for handling corrosive chemicals and hazardous materials, making them a preferred choice in chemical processing plants.
3. Power Industry Applications of Ball Valves:
For boiler feedwater control, such as burner trip valves, for control and shut-off for steam, etc.
4. Ball valves in Gas and Oil Production:
In subsea isolation and shut-down facilities, For oil-head isolation, pipeline surge control, processing separation, storage, transmission and distribution, secondary and enhanced oil recovery.
5. Use of ball valves in the Pulp and Paper Industry:
They are used as shut-off valves in pulp mill digesters, batch-digester blow service, liquor fill and circulation, lime mud flow control, dilution water control, etc.
6. Water Treatment:
Municipal water treatment plants utilize ball valves for controlling the flow of water in various processes, such as filtration, chlorination, and distribution.
7. HVAC Systems:
Heating, ventilation, and air conditioning systems use ball valves for regulating the flow of water and refrigerants in commercial and residential buildings.
8. Other uses of ball valves include
Food Industry
Marine and Solid transport
Water supply and transport
Manufacturing
Ball Valve Standards
Below-mentioned international Codes and Standards are used for Ball valve Design
Design Standard – API 6D / ISO 14313 / BS EN 17292/BS 5351/MSS SP 72
Testing Standard – API 6D / API 598 / BS 6755 Part I/MSS SP 61
Fire testing Standards – As per API 6FA, API 607, ISO 10497, or BS 6755 Part II.
Dimensional Standard – ASME B16.10 / API 6D
Parts of a Ball Valve
The housing, seats, ball, and lever for ball rotation are the major parts of a standard ball valve. Refer to Fig. 1 below which shows the internal parts of a ball valve.
Fig. 1: Ball Valve Parts
Ball valves are manufactured with the following crucial parts:
Valve Body:
The main part of a ball valve is the valve body which contains all of the internal components for on/off control.
Rotary Ball:
A ball with a center hole through which the media flows is the main characteristic of ball valves that differentiates these valves from other valve types. The hole of the ball through one axis connects the inlet to the outlet. The Stem controls the direction of the ball. The ball may be free-floating or trunnion-mounted. Trunnion-mounted ball valves reduce the operating torque to about 2/3rd that of the floating ball valves.
Stem:
The stem of a ball valve connects the ball to the external control mechanism.
Seats:
The seats of a ball valve are discs that lie in between the ball and the body. It provides the necessary seal between the two and also supports the ball.
Power Source:
A manual or actuated power source provides energy to the stem of the ball valve for rotating it. Manual actuation uses levers and handles, which the operator controls during requirements. Automatic actuators use electric, pneumatic, or hydraulic power sources.
Packing:
Packing is a seal around the stem to prevent the media escape.
Bonnet:
The bonnet is part of the ball valve body that contains the stem and packing.
The following video clearly shows the parts and working of ball valves using an animation.
Ball Valves: Parts and Working
Ball Valve Working Principle
A ball Valve is a rotary motion valve. When the stem (Item 04 in Fig. 1) transfers the motion to the connected ball (Item 03), the ball rotates. This ball of a ball valve is rested and supported by the ball valve seats (item 05). This rotation of the ball over valve seats allows the bore to open or close helping the fluid to flow or stop.
For manual ball valves with normal service, when the port opening of the ball is in line with the inlet and outlet ports, flow continues uninterrupted through the valve, undergoing a minimal pressure drop if a full-port ball is used. Obviously, the pressure drop increases with the use of a reduced-port ball. When the hand operator is placed parallel to the pipeline, the flow passages of the ball are in line with the flow passages of the body, allowing for full flow through the closure element. As the hand operator is turned to the closed position, the ball’s opening begins to move perpendicular to the flow stream with the edges of the port rotating through the seat. When the full quarter-turn is reached, the port is completely perpendicular to the flow stream, blocking the flow.
In throttling applications, where the ball is placed in a mid-turn position, the flow experiences a double pressure drop through the valve, similar to a plug valve. When a characterizable ball is used to provide a specific flow to position, as the ball is rotated from closed to open through the seat, a specific amount of port opening is exposed to the flow at a certain position, until 100 percent flow is reached at the full-open position.
As with all rotary-action valves, the ball valve strokes through a quarter-turn motion, with 0° as full-closed and 90° as full-open. The actuator can be built to provide this rotary motion, as is the case with a manual hand lever, or can transfer linear motion to rotary action using a linear actuator design with a transfer case.
When full-open, a full-port valve has minimal pressure loss and recovery as the flow moves through the valve. This is because the flow passageway is essentially the same diameter as the pipe inside diameter, and no restrictions, other than some geometrical variations at the orifices, are present to restrict the flow. The operation of throttling full-port valves should be understood as a two-stage pressure drop process. Because of the length of the bore through the ball, full-port valves have two orifices, one on the upstream side and the other on the downstream side. As the valve moves to a mid-stroke position, the flow moves through the first narrowed orifice, creating a pressure drop, and moves into the larger flow bore inside the ball where the pressure recovers to a certain extent. The flow then moves to the second orifice, where another pressure drop occurs, followed by another pressure recovery. This two-step process is beneficial in that lower process velocities are created by the dual pressure drops, which is important with slurry applications. The flow rate of a full-port valve is determined by the decreasing flow area of the ball’s hole as the valve moves through the quarter-turn motion, providing an inherent equal-percentage characteristic with a true circular opening. As the area of the flow passageway diminishes as the valve approaches closure, the sliding action of the ball against the seal creates a scissor-like shearing action. This action is ideal for slurries where long entrained fibers or particulates can be sheared off and separated at closing.
At the full-closed position, the entire face of the ball is fully exposed to the flow, as the flow hole is now perpendicular to the flow, preventing it from continuing past the ball.
With the characterized segmented ball design, only one pressure drop is taken through the valve—at the orifice where the seal and ball come in contact with each other. When the segmented ball is in the full-open position, the flow is restricted by the shape of the flow passageway. In essence, this creates a better throttling situation, since a pressure drop is taken through the reduction of flow area. As the segmented ball moves through the quarter-turn action, the shape of the V-notch or parabolic port changes with the stroke, providing the flow characteristic. Like the full-port design, the sliding seal of the characterizable ball provides a shearing action for separating slurries easily.
Ball Valve Types | Types of Ball Valves
Types of Ball valves are classified based on various parameters as listed below:
1. Ball Valve Types: Short Pattern vs. Long Pattern
Depending on the end-to-end dimension of the valves, two types of ball valves are available. They are
Short pattern ball valves, and
Long pattern ball valves
The end-to-end dimension and weight of short-pattern ball valves are less as compared to long-pattern ball valves. However, During piping design, a long pattern dimension is selected for ease of connection to pipe flanges. Also, short-pattern ball valves are not available after a specific size and flange rating. So, long pattern ball valves are the only option in such cases.
2. Types of Ball Valves: Soft Seated vs. Metal Seated
Depending on the seat materials of the valve, two types of ball valves are found; Soft Seated and Metal Seated Ball Valves.
Soft, non-metal seated ball valves satisfactorily cover most of the applications. Soft seated ball valves use a thermoplastic material such as PTFE, NBR, etc. However, abrasive media, high pressure, and temperature can severely stress the polymeric seals leading to damage. Because of this reason metal-seated ball valves were developed in the 1960s.
Metal seated ball valves use metal as seat material such as 316 SS, Monel, etc. Tight shut-off, no jamming, smooth control, good corrosion and wear resistance, wide temperature range, stability under pressure, etc. are the advantages that a metal-seated ball valve provides with its soft-seated counterparts.
The main differences between soft-seated and metal-seated ball valves are tabulated below:
Soft Seated Ball Valve
Metal Seated Ball Valve
Elastic non-metallic material like PTFE, Delrin, Nylon, PEEK, etc
Metal Alloys like Copper alloy, Nickel alloy, Chrome Stainless Steel, etc are used as seat material
Used for low or medium temperature and pressure service
Widely used for high-pressure and temperature services
Low cost
High Cost
High level of Sealing
Comparatively poor sealing
Used for clean services like air, water, etc
Used for severe service conditions like hot water, oil, gas, acid, and other chemicals.
Lower torque requirement for operation.
Higher torque requirement
Table: Soft Seated Ball Valve vs Metal Seated Ball Valve
Soft Seat Ball Valve Design
Thermoplastic or Elastomeric seats are inserted in a metallic holder (seat ring) to provide soft seating action in a ball valve. The main features of a soft-seated ball valve are
Provide a good sealing ability.
Lower in cost than metal seated valves.
Limited temperature rating.
Should not be used in dirty services, particularly on floating ball valves.
Soft seat materials used are – PTFE, Nylon, Devlon, PEEK, etc.
It is generally accepted a leakage of ISO 5208 Rate A
Fig. 2 Soft Seat Design of Ball Valves
Metal Seat Ball Valve Design
The main features of metal-seated ball valves are
Direct metal-to-metal contact between seat ring & ball.
Ball Valves are used for abrasive service and for services where soft seated valves can not be used due to temperature limitations.
The ball & seat contact surfaces are hard-faced to improve resistance to wear & prevent scratching caused by the solid particles contained in the process media.
Metal sealing may be obtained by tungsten carbide coating (up to 200 deg. C), chromium carbide coating (above 200 deg. C), electroless nickel plating (ENP), or stellite hard facing.
Acceptable leakage of ISO 5208 Rate D.
Metal seats do not bed in as easily as soft seals under pressure. hence, ball and sealing rings to be precisely machined.
Metal-seated ball valves are posed to pitting, fretting, stress corrosion cracking, and intercrystalline corrosion damages.
3. Ball Valves Types: Reduced bore, Full bore, V-shaped, and Vented ball valves
Based on the inner diameter of the ball valve two types of ball valves are used in industries; Reduced Bore Ball Valve and Full Bore Ball valve.
Reduced Bore (Reduced Port) Ball Valve Design
Reduced port ball valves are quite common in the piping industry. However, reduced bore ball valves introduce frictional losses. The main design features of such ball valves are
The bore diameter is 1 size less than the pipe diameter for valve sizes up to 12” NB & 2 sizes less for 14” NB to 24” NB (and 3 sizes less for sizes above 24” NB).
These ball valves are comparatively smaller in size with less weight.
Fig. 3: Reduced Bore Ball Valve
Have lower operating torque, resulting in a lower cost actuated valve package.
Slightly higher pressure drop than full bore valve.
Prevents pigging
These valves are normally of a one-piece – end entry design for smaller sizes (up to 4”-150#) & two / three-piece – side entry design for bigger sizes.
These valves are also called regular port valves.
Full Bore (Full Port) Ball Valve Design
Full bore or Full port valves do not cause extra frictional losses, and the system is mechanically easier to clean as it allows pigging.
The bore inside diameter is the same as the pipe inside diameter.
Very little pressure drop.
Ball and housing are bigger.
Of higher weight than reduced bore valve, hence more costly.
Selected for specific process reasons, typically; minimum pressure drop, minimal erosion, pigging requirement, and gravity flow (to avoid liquid pocket)
V-shaped Ball Valves:
In V-shaped ball valves, The hole in the ball or the valve seat has a “V” shaped profile. This design offers more precise control of the flow rate.
Vented Ball Valves: In a vented ball valve design, a small hole is drilled into the upstream side to eliminate unwanted pressure within the valve.
4. Types of Ball Valves: One-piece, Two-piece, and Three-piece ball valves
Depending on the body construction of valves, there are three types of ball valve designs; One-piece, Two-piece, and three-piece ball valves
Single Piece Body Design Ball Valves
In the single-piece design ball valve, the body will be cast/forged as one piece. The insertion of the ball will be through the end of the body and is held in position by the body insert. This design offers the unique advantage of eliminating the possibility of external leakage to the atmosphere through bolted body joints. This design restricts the ball valve to be of reduced port floating design only (for sizes up to 4” NB).
Fig. 4: Single Piece Ball Valve Design
Two-piece / Three Piece Ball Valve Design
The two-piece design complements the single-piece design in sizes of 6” & above for reduced bore and for FB design valves. In a two-piece design, the body is constructed in two pieces and the ball is held in position by the body stud. There can be a full bore or reduced bore design possible in this construction.
In the case of a three-piece design, the body has two end pieces and one centerpiece. Three-piece design ball valves are most easily online maintainable. By removing the body bolts and keeping only one, the body can be swung away using the last bolt as the fulcrum, to carry out any installation or maintenance operation on the valve. This feature reduces maintenance downtime to a bare minimum.
Fig. 5: Multi-piece Design
For larger 2-piece or 3-piece ball valves, the dimensions between the body and flange should be checked so that sufficient clearance is available for bolting. During the vendor drawing review stage, the same should be checked and ensured.
Fig. 6: Ball Valve Design
5. Ball Valve Types: Side entry, Top entry, or welded body ball valves
From the perspective of Ball Valve Body Styles, they are divided into three types of ball valve designs. They are
Side entry or end entry ball valves
Top entry ball valves and
Welded body ball valves
Side entry or end entry ball valve design
In the case of a side entry ball valve, the ball is assembled from the side part. They normally have two pieces or three pieces of the body. Each part of the body is assembled by a bolt/stud similar to joining a two-piece of flanges. Side entry ball valves are usually made by forging the metal. Each piece of the body is forged separately and then assembled together to get the complete design. This construction is robust in design and minimizes the defects caused by casting valves. Side entry ball valves are also easy to assemble and the trim component is also easy to align. Another advantage of the side entry ball valve type is that they are easily available from almost all vendors rather than a casting product that still needs some additional testing.
Top Entry Ball Valve Design
The main design features of top-entry ball valve types are
Maintenance and repair of such ball valves are possible in-situ, by removing the top flange. This minimizes maintenance downtime.
Limited space is required around the valve for maintenance.
Available in welded as well as flanged end connections, but welded ends are preferred to reduce potential leak paths and minimize the ball valve weight.
Heaviest and most expensive construction.
Fig. 7: Top Entry Ball Valve Design
Welded Body Ball Valve Design
The main design features of this type of ball valve design are
Welded body ball valve construction eliminates body flanges, reduces potential leak paths, and increases resistance to pipeline stresses.
The minimum number of leak paths is hence beneficial in fugitive emission and vacuum applications.
Compact and lightweight design
The body draining & venting feature allows the ball valve maintenance technician to test each seat ring sealing ability with the ball in either the fully open or fully closed positions.
Sealant injection fittings access directly to each seat ring. This enables the technician to top up the quantity of lubricant inside the valve sealant injection system on a periodic basis.
Valve cleaner can also be injected into these fittings to flush out the old grease in the ball valve and to clean critical seal faces on the ball.
Heavier sealants are also injected through the sealant injection fittings during an emergency when a critical seal is required.
Applications – Oil & gas pipelines, compressor stations, measuring skids, etc.
6. Ball Valve Types depending on the type of ball design: Floating Ball Valve vs Trunnion Mounted Ball Valves
Depending on the supporting and positioning of the ball, two types of ball valves are used; Floating Ball Valves and Trunnion Mounted Ball Valves
Floating or Seat Supported Ball Valve Design
In a floating ball valve, the ball is not fixed in place and is free to move slightly within the valve body. Sealing is achieved through the pressure of the fluid against the ball.
The major design features of a floating ball valve are
Ball valve design in which the ball is not rigidly held on its rotational axis & is free to float between the seat rings.
In the closed position, the ball is pushed against the seat by the pressure of the fluid from upstream and hence can pressure seal the downstream of the valve.
Ball seats on the downstream seat only.
Seat loading increases at a higher pressure and for larger sizes and becomes excessive, for the soft seated valve. Also, the higher the size the heavier the ball, and the less likely it is to be moved by pressure. Hence the need for a trunnion-mounted ball valve design comes into the picture.
Floating design ball valves have lower manufacturing costs.
Valves of small sizes and lower pressure ratings are seats supported (10” for 150#, 6” for 300# & 2” for 600# & above).
The seat-supported design generally needs higher operating torque.
Metal seated floating ball valves also incorporate spring-loaded seats.
Fig. 9: Floating Design of Ball Valve
Trunnion Mounted Ball Valve
Trunnion ball valves have a fixed ball with a shaft extending through it. This design provides more support to the ball, making it suitable for high-pressure and large-diameter applications. Trunnion ball valves are known for their increased durability and reliability in demanding conditions.
The major design characteristics of a trunnion-mounted ball valve are
The ball is fixed in position by the stem & the trunnion which are supported by bearings in the body.
The seat is spring-loaded onto the ball, giving reliable sealing at low pressures.
The key feature of this ball valve is that the ball does not shift as it does in a floating valve to press the ball into the downstream seat. Instead, the line pressure forces the upstream seat onto the ball to cause it to seal.
As the area on which the pressure acts is much lower, the amount of force exerted on the ball is much less, leading to lower friction values and smaller actuators or gearboxes.
Seat designs are either single or double-piston effects.
Valves of larger sizes and higher pressure ratings are trunnions mounted.
All standard trunnion-mounted ball valves shall be provided with self-relieving seats allowing automatic body cavity relief exceeding 1.33 times the valve pressure rating at 38°C (overpressure due to thermal expansion of trapped fluid).
Fig. 10: Trunnion Mounted Ball Valve
7. Types of Ball valves: Single vs. Double piston effect design
Based on the pressure relieving capability of the ball valve seats, two types of ball valves are designed; Single Piston Effect Design and Double Piston Effect Ball Valve Design
Single Piston Effect Seat Design
The important design features of single piston effect seat design are
Seats of the ball valves are pressed on the ball by means of spring load.
As the body cavity pressure increases than the spring load, the seats are pushed back and the pressure is released in the line. This is called a single-piston effect (the pressure in the body cavity is the only acting parameter)
Cavity relief to the downstream side, if both the ball valve seats are of single-piston effect design.
Each seat is self-relieving the body cavity overpressure to the line.
Fig. 11: Single Piston Effect Seat Design
Double Piston Effect Seat Design
The design characteristics of a double piston effect seat design ball valves are
In this seat design, the medium pressure, as well as body cavity pressure, creates a resultant thrust that pushes the seat rings against the ball. This is called a double piston effect (the pressure in the pipe & that in the body cavity, both are acting parameters)
Ball Valves with this design require a cavity pressure relief device to reduce the body cavity pressure.
DPE is synonymous with “bi-directional”, and SPE is synonymous with “uni-directional” as defined by API 6D/ISO 14313.
Fig. 12: Double Piston Effect Seat Design
The working of Single Pistion Effect and Double Piston Effect Design is clearly shown in the following video:
Single Piston & Double Piston Concepts
Body Cavity Relief (Pressure Equalisation)
Ball valves are double-seated valves that incorporate a cavity between the seats.
The body cavity will get pressurized only when the seats are damaged.
Cavity relief provision is required only for trunnion-mounted ball valves. Not required for floating ball valves as the seats are fixed & the ball is floating.
Where possible, cavity relief shall be to the upstream side of the valve.
Fig. 12: Body Cavity Relief
DPE – External pressure relief
When the body cavity pressure increases above the net spring load of the pressure relief valve, the cavity pressure is vented through the Pressure Relief Valve.
The Relief Valve outlet line can be vented to the atmosphere / connected to the vent system or back to the upstream piping.
Fig. 13: DPE – External pressure relief
Combination Seats
In some cases, a single-piston effect seat is used for the upstream side and a double-piston effect seat is used for the downstream side.
This enables the cavity overpressure to release to the valve upstream side and also doesn’t require an external relief valve.
These ball valves are unidirectional and the flow direction is clearly marked on the valve body.
Ball valve Seat Design for Export Line
This seat configuration gives a single barrier against normal flow conditions and a double barrier against reverse flow coming from the downstream pipeline.
For the ESD/PSD valve, a reverse configuration is required than that shown here. ESD valves require SPE for the upstream seat and DPE for the downstream seat.
Fig. 14: Seat Design for Export Line
Pressure Temperature Ratings of Ball Valves
The pressure-temperature ratings of ball valves are decided based on the valve body and sealing materials used for soft-seated ball valves. Sealing materials may be PTFE, 15 to 25% glass-filled PTFE, FPM, NRG, Celastic, POM, Lyton, and Steel. It is very difficult to pre-determine exact pressure-temperature ratings for all kinds of media under all imaginable loading conditions.
When the ball valve is in a fully closed or fully open position, each seat seals off the process medium independently at the same time between the up/downstream and body cavity; it allows bleeding of the cavity pressure through a drain or vent valve. This DBB feature permits in-line periodic inspection of the valves and the checking of sealing integrity when the valve is installed in the line. This feature is available with self relieving seat (SPE) configuration.
DBB Vs DIB
If a ball valve has both seats as unidirectional (SPE) seats, it is called a Double Block & Bleed (DBB).
If a ball valve has one or both bidirectional (DPE) seats, it is called a Double Isolation & Bleed (DIB).
In the DBB valve, the downstream seat pushes away from the valve once the body cavity pressure is higher than the downstream pressure, allowing fluid to flow downstream past the closed valve. In the DIB valve the downstream seat seals and prevents the upstream pressure from reaching the downstream piping.
Fig. 15: Double Block & Bleed (DBB) feature
A clear animation of the DBB vs DIB philosophy is presented in the following animation:
DBB vs DIB concept Explanation
Blow-Out Proof Stem Design Feature of Ball Valve
When the ball valve is in the open/closed position, the pressure is always acting upon the bottom of the stem, trying to push the stem up.
The stem is sealed by o-rings and graphite packing rings.
The stem is held in position by the stem housing, which is bolted to the body.
The graphite packing rings are compressed and held in position by the gland flange, which is bolted to the stem housing.
Therefore, when the gland flange is removed to replace the graphite packing rings, the stem is still held securely, by the stem housing.
That means the blow-out-proof stem feature ensures that the top graphite packing rings can be replaced while the valve is under pressure, without the stem being pushed out (blown out).
Fig. 16: Blow-Out Proof Stem Design
Anti-Static Design Feature of Ball Valves
The build-up of static electricity can occur as a result of the constant rubbing of the ball against the PTFE seats. This can be a potential fire hazard, especially while handling flammable fluids.
In the anti-static feature, spring-loaded balls are provided between the ball & stem and stem & body which provides electrical continuity.
1) Internal Leakage Prevention (from the pipeline to the body cavity)
When non-metal resilient seats are destroyed in a fire, the upstream medium pressure pushes the ball into the downstream metal seat lip to cut off the line fluid and prevent internal leakage due to secondary metal-to-metal seals.
Another fire-safe packing is provided at the seat ring for internal leakage prevention to the body cavity.
Graphite is normally used as a fire-safe packing material because the melting point of graphite is 1000 degrees C.
Fig. 18: Fire Safe Design
2) External leakage prevention (from body/stem joints to atmosphere)
All the possible external leakage points between the stem & gland flange, gland flange & body, and body & adapter are sealed with a primary O-ring and then a secondary graphite gasket. When the fire burns out the primary O-ring seal, the secondary graphite gasket seal can prevent the process medium from external leakage.
Fire-safe seals are generally not designed for fugitive emission performance (fugitive emission – emissions of gases or vapors from pressurized equipment due to leaks).
The fire testing of valves is carried out as per API 6FA, API 607, ISO 10497, or BS 6755 Part II.
Fig. 19: External Leakage Prevention
Fire Safe vs. Fire Tested Design
Fire-safe design is a design that by the nature of its features and materials is capable of passing a fire test.
It is capable of passing a fire test with specified limits on leakage to the atmosphere and downstream after being closed subsequent to fire exposure.
A fire-tested design is a design subjected successfully to fire testing as per the applicable testing standard.
That means the fire-safe valves are not necessarily fire-tested by the manufacturer.
Ball Valve Fire Testing Criteria
One test valve may be used to qualify valves larger than the test valve, not exceeding twice the size of the test valve.
A 16” size valve will qualify all larger sizes.
One test valve may be used to qualify valves with higher pressure ratings but no greater than twice the pressure rating of the test valve.
The above criteria are acceptable for valves of the same basic design as the test valve & the same non-metallic materials.
Ball valve Sealant Injection System
Ball Valves are to be equipped with sealant & lubricant injection connections located at the stem and seat area if specified by the purchaser.
The valve design & material selection should negate the need for such a connection.
If specified, this injection connection is integrated with a check valve to provide backup sealing, Also a check valve is equipped at the front of seat sealant injection to avoid blowing out in case of the wrong operation.
When the soft sealing materials (seat inserts and o-rings) are damaged and leakage happens by fire or other accident, the sealant can be injected through the injection fittings.
Fig. 20: Sealant Injection System
The sealant injection system through the seat up to the ball contact circle may provide temporary sealing until it is possible to restore the primary seal.
No seat sealant injection shall be provided for ESD valves.
Extended Bonnet Ball Valve
The integrity of stem seals at very low temperatures (-30 degrees C & below) is the major hurdle that must be overcome. Specially designed extended bonnets installed to valves offer a safe & efficient method to accomplish stem seal integrity.
The bonnet extension provides a gas column that allows the gas to vaporize from contact with the warm ambient temperature outside the service line. This vapor column insulates the stem seal and maintains the seal integrity. Bonnet extension also helps with thermal insulation installation.
Fig. 21: Extended Bonnet
Weld Overlay
Sealing areas & other wetted parts of the ball valve can be cladded in case of corrosive service. More frequently used materials for the overlay process are stainless steel, DSS & high nickel alloys. This technology is cost-effective for ball valves in highly corrosive or erosive services. Considerable cost saving without sacrifice to service life or performance. It can be done cost-effectively for sizes 8” and larger. Welding is performed in accordance with ASME BPV section 9.
Fig. 22: Weld Overlay
Ball Valve Seat Insert Materials
Thermoplastic seat/seal inserts
Fig. 23: Thermoplastic seat/seal inserts
Devlon V: Temp. Range -100 deg. C to 150 deg. C
Elastomeric seat/seal inserts
Fig. 24: Elastomeric seat/seal inserts
Zero leakage is easier obtained by softer seals (elastomeric), while the resistance to scratches and other factors (temperature, pressure, erosion) is obtained by harder seals (thermoplastic).
PTFE is generally not recommended for high pressure (cl. 900 & higher) while it is suitable for a wide range of temperatures and resistant to many fluids.
Nylon 12G is more suitable than PTFE for higher pressure but has a limited range in temperature.
Nylon 6 should not be used as it absorbs humidity.
Devlon V is similar to Nylon 12G but with a wider range of temperature applications (lower & higher)
PEEK is recommended for high temperatures (up to 260 deg.C) but it is very hard compared to other nonmetallic materials.
Kel-F is especially recommended for cryogenic service.
O-Rings (Elastomeric)
O-rings are used for below applications:
Stem seals
Seals between seat and body/closure
Seals between body and bonnet/closure
Materials are generally as follows:
Viton (fluor elastomer)
NBR (nitrile butadiene rubber)
HNBR
O-rings are not allowed in the seat ring-body joint as well as for the body-bonnet joint. The ball valve seat ring shall have a primary lip seal with a fire-safe graphite ring.
On the stem side, if the seal material specified in the requisition as thermoplastic, it shall be of lip seal type with Inconel 718 spring. If the seal material is specified as elastomeric, it shall be of AED type.
Fig. 25: O-rings
Lip Seal
For applications where elastomeric O-rings are not reliable, lip seals are used (for body & stem sealing).
Lip seals are self-energized seal systems, made of a Teflon cover and a spring (Inconel 718 material).
Fig. 26: Lip Seals
The spring provides the initial load (due to the low elasticity of Teflon), while the fluid pressure provides the load to force the lips on the sealing surfaces.
Lip seal housing on CS valves shall be SS316 weld overlayed (3mm thick)
Ball Valve End Connections
The type of ball valve ends are as follows:
Flanged ends with raised face or ring joint face
Threaded ends
Socket weld ends
Butt-weld ends – Soft, as well as metal seated butt-welding end valves, shall be provided with butt-weld pup pieces.
This avoids damage to the ball valve seat as well as soft seal materials due to welding heat.
The pup piece length shall be
200mm for sizes up to 2” NB,
400mm for up to 12” NB size &
800mm above 12” NB sizes
Ball Valve Operator
Ball Valves can be operated by a lever, wrench, or hand wheel or they can be pneumatic, hydraulic, or motor-operated. A ball valve is rotated in a clockwise direction to close & anti-clockwise direction to open. The maximum lever length shall not exceed 450 mm & maximum handwheel diameter shall not exceed the valve face-to-face dimension of 800mm whichever is smaller. A gear operator is required to be provided for valves as per the below criteria:
6” & larger for class 150 ball valves
4” & larger for class 300 & 600 and
3” & larger for class 900 onwards
Fig. 27: Valve Operator
Ball Valves as ESD Valve
Ball valves as ESD valve application shall be of trunnion mounted type with metal seat design. The minimum size shall be 2” NB. Upstream seats of such ball valves shall be with a single-piston effect and downstream seats with a double-piston effect.
The SPE & DPE shall be marked permanently on the respective seat side and the flow arrow shall be embedded on the ball valve body. However, the valve shall be suitable for bi-directional isolation. The seat ring shall have 2 primary leap seals with a fire-safe graphite ring. The stem shall have a minimum of 2 primary lip seals or U or V-shaped packing with fire-safe secondary seals.
Grease injection fitting shall be provided between primary & secondary seals on the stem side with 2 in-built check valves. No seat sealant injection shall be provided for ESD valves.
Ball Valve Lifting & Supporting Provision
Ball Valves of sizes 8” NB and above or 250 Kg & heavier shall be equipped with lifting lugs. Tapped holes & eye bolts are not acceptable. Ball valves weighing more than 750 kg shall have support lugs and these should be designed to take care of the vertical & lateral loads of valves. The support height shall be as minimum as possible.
Other Requirements of Ball Valves
Drain and vent connections of Ball Valves
Drain and Vent connections shall be drilled & threaded for ball valves up to 900# pressure class & for sizes less than 6” –FB & 8”-RB. The connections shall be fitted with a threaded plug. The plug shall be suitably locked by a locking ring to prevent loosening.
The drain & vent connections for ball valves above 900# pressure class & 6” –FB / 8” -RB & above sizes shall be fully welded flanged type, fitted with a blind flange. If drain/vent/sealant injection is asked, ensure the orientation of the connections is accessible at the site. During the ball valve vendor drawing review, the same should be checked.
Ball Valve Specification
While purchasing a ball valve, the following information should be provided to the vendor/manufacturer:
Ball Valve Size and Pressure Class Rating
Type of the Ball: Floating or Trunnion mounted design
The pattern of the ball valve: standard or short
Bore type: full or reduced bore
Ball Valve End Connection type.
The requirement of drain connection.
The requirement of the Sealant Injection system.
The need for a Locking device
The requirement of Valve support – if any
Anti-Static device
Operator Details: Lever/Gear/ Actuator (Electric, Pneumatic, or Hydraulic Operated)
The material Valve Body, Seat Rings, Trunnion, Trim, Seals, Gaskets, Bolts, Nuts, and Packing material
Seating Type: Soft or Metal Seated
Valve orientation
Specific Certification requirements
The requirement for a Fire-safe test
Applicable Painting details
The requirement of an Integral bypass connection
The requirement of Lugs or Lifting arrangements.
Advantages of Ball Valves
The important Advantages of a Ball valve are listed below
Quarter turn straight thru valve / fast opening & closing
Tight Shut off as well as very easy to use
Application as isolation valve (on and off condition)
Suitable for Emergency shutdown conditions
Multi-design flexibility
Compact, economical designs
Suitable for high-pressure service conditions.
Long service life.
Suitable for a range of industrial applications.
Low maintenance
Because of all these benefits, ball valves find wide application in the following industries.
Oil & Gas, Chemical, Petrochemical, Refinery
Food & Beverage Equipment
Vehicle Wash Systems
Automotive
Home Appliances
Power Processing
Manufacturing Facilities
Pharmaceutical
Irrigation & Water Treatment Equipment
Chemical Admixtures & Treatment
Disadvantages of Ball Valves
However, there are a few disadvantages of ball valves like
Not suitable for throttling
Fluid trapped in the body cavity
Limited working temperature range
Ball Valve vs. Gate Valve
The major differences between a Ball Valve and a Gate valve are tabulated below:
Ball Valve
Gate Valve
Ball Valve uses a ball for opening or closing
Gate valve uses a gate or wedge for opening or closing
The ball Valve is a quarter-turn rotary motion valve
A gate valve uses a gate or wedge for opening or closing
The sealing capacity of Ball Valves is comparatively higher
Comparatively less sealing.
Durability more
Less durability
Quick operation, prone to surge
Operation is slow hence, less probability of surge creation.
More number of valve configurations
Less number of valve configurations
More expensive
Comparatively low cost
Less Corrosion
Higher Corrosion
Low-Pressure Drop
High-Pressure Drop
Table 1: Ball Valve vs. Gate Valve Table
In the realm of fluid control, ball valves stand as a testament to the ingenuity of engineering. Their versatile design, reliable operation, and ability to withstand challenging conditions make them an indispensable component across industries. Whether in oil and gas pipelines, chemical plants, or everyday household systems, the unassuming ball valve plays a crucial role in ensuring the smooth and efficient flow of fluids that power our modern world.
Frequently Asked Questions
What is a ball valve, and how does it work?
A ball valve is a type of valve used to control the flow of fluids. It operates by rotating a spherical ball inside the valve body. When the hole in the ball aligns with the flow direction, the valve is open, allowing fluid to pass through. Rotating the ball to block the hole closes the valve, stopping the flow.
What are the main types of ball valves?
There are two primary types of ball valves:
Floating Ball Valves: The ball in these valves is not fixed in place and relies on fluid pressure to create a seal.
Trunnion Ball Valves: These valves have a fixed ball with a shaft extending through it, providing additional support and reliability, especially in high-pressure applications.
Where are ball valves commonly used?
Ball valves are widely used across various industries, including:
Oil and Gas
Water Treatment
Chemical Processing
HVAC Systems
Manufacturing
Agriculture
Residential Plumbing
What are the advantages of using ball valves?
Some key advantages of ball valves include:
Quick and reliable operation
Minimal pressure drop
Versatility in handling different fluids, temperatures, and pressures
Low maintenance requirements
Tight sealing to prevent leaks
Can ball valves be used for both on/off and throttling applications?
Yes, ball valves are suitable for both on/off and throttling (partial flow control) applications. However, for precise control in throttling situations, it’s important to choose the right type of ball valve and size it appropriately.
Are ball valves suitable for high-pressure applications?
Trunnion ball valves, with their fixed ball and additional support, are well-suited for high-pressure applications. Floating ball valves are generally used in lower-pressure situations.
Are ball valves suitable for controlling slurries and solid-laden fluids?
While ball valves can handle some solid-laden fluids, they are not the best choice for controlling highly abrasive or viscous slurries. In such cases, specialized valves like knife gate valves or pinch valves may be more appropriate.
Can ball valves be automated for remote control and monitoring?
Yes, ball valves can be equipped with actuators (electric, pneumatic, or hydraulic) for remote control and automation. This is especially useful in industrial processes where precise control and monitoring are essential.
How do I select the right ball valve for my application?
To select the right ball valve, consider factors like the type of fluid, operating temperature and pressure, pipe size, the specific application, end connections, material requirements, flow control requirements, actuation types, etc
Common questions asked in Piping stress interviews related to Jacketed piping are listed below:
1. Why is Jacketed Piping used?
Ans: It is commonly used to convey very viscous process fluids in an inner pipe, heated by steam/hot water/hot oil or other heating media between the jacket and core pipe. Vacuum jacketing is also used as an insulator for cryogenic fluids and can be analyzed using the same calculation method for heated jacketed piping.
2. If water (density=1000Kg/m3) is flowing through the jacket then what is the value of density you will enter into the Caesar spreadsheet?
Ans: We have to calculate the equivalent density for the same. The following formula can be used
Actual jacket fluid equivalent density = [(rj2 – Rc2)/ rj2 ] x dj
Where,
rj = Inner radius of core Rc = Outer radius of pipe
dj = Density of heating medium
3. What are the major stress checks that you will perform while analyzing the Jacketed Piping system?
Ans:
Sustained And Expansion Stress Check: Limits of calculated stresses due to sustained loads (primary stresses) and displacement strain due to expansion (secondary stresses) should be evaluated separately for core and jacket pipe (as per clause 302.3.5 of ASME B31.3).
Checking of the buckling load. (Manual Calculation): This check will not be performed by Caesar-II as it is not in the code. However, it will provide force calculated at the junction point (P) between the core and the jacket. It should be less than Pcr which is given by the formula
Pcr = (4π2 *Ec*Ic)/L2, For Core and
Pcr = (4π2 *Ej*Ij)/L2 , For Jacket
Where,
P = Force calculated by a computer program at the junction point
Pcr = Critical force
Ec, Ej = Modulus of Elasticity of core/ jacket material
Ic = Moment of Inertia of Core
Ij = Moment of Inertia of Jacket
L = length of pipe between the junction of the core/ jacket.
If P ≤ Pcr then no buckling failure ·
Weld strength check between the jacket and core pipe: P calculated at the junction point between core & jacket pipe compared with allowable load at the weld point.
P allowed = area of weld * 80% of hot allowable stress of the material
Area of weld = π D * root of the weld
D = Diameter of the core pipe
The root of weld = 0.707 * weld size
If P calculated ≤P allowed, then the system is safe ·
Checking of deflection of jacket: In this case, it is assumed that no spider/spacer is used between the core and jacket. The deflection for the jacket with available length has to be computed and should be ensured that it does not create an obstruction to the flow of hot medium in the jacket. Normally maximum allowed deflection of the jacket is T/2, where T is the thickness of the jacket.
Checking for External Pressure (By material Group): Sometimes the jacket may be subjected to partial vacuum conditions due to failure of the steam supply and subsequent condensation of steam inside the jacket. In such cases, the jacket should be checked for vacuum conditions. As another example, in a system, the core is at a pressure of 30 PSIG and the jacket is at a pressure of 180 psig, then the core is subjected to an external pressure of 150 PSIG. For this, the core must be investigated for collapse or local buckling from the external pressure load (Refer para 304.1.3 of ASME B31.3 and UG-28 through UG-30 of ASME BPVC Section-VIII Division-I) ·
Checking for Axial Stress: As per ASME B31.3, the calculated displacement stress range (Expansion case stress) is SE = (Sb2 + 4St2)1/2. The code does not take into account the axial forces and consequent axial stress in calculating expansion stresses. This is because for the normal pipe axial forces are normally due to longitudinal stresses which are already taken care of in thickness calculation and sustained stress calculations, but in the case of jacketed piping, axial stresses at the core-jacket junction point are just not due to longitudinal stresses, but mainly due to differential thermal expansion of core and jacket pipes. Thus calculated stress should be corrected by adding axial stresses for local analysis of that particular junction point. Thus,
Actual Stress SEa = SE + Axial Force/ Area Axial force can be obtained from CAESAR output or can be calculated by the equation,
Faxial = (E x ΔL x Area) / L
Or else, CAESAR also calculates the value of axial stresses which it calculates for operating cases. Activate the option “Add F/A in stress” in the configuration file. Axial stress due to thermal differential is added to the calculated expansion stress and then it should be compared with the allowable loads as per ASME B31.3.
4. What allowable value is considered for welding check at core jacket interconnection?
Ans: Two methods are prevalent. You have to consider any one of the following (discuss with the stress lead) a) Consider the 0.6 times electrode tensile strength (As per AISC code) b) Consider SE=1.25Sc+0.25Sh of the electrode as allowable (as per secondary stress generated theory)
Top 180+ Piping (Stress) Interview Questions with Answers
The following list will provide a few interview questions asked in the different interviews for a Piping Engineering (Stress) position. Answers to most of the questions are added here for reference. I hope you will be able to find remaining answers from ASME B 31.3 and any piping engineering textbooks or from the piping handbook. In case you could not find out a specific answer reply in the comments section.
Kind request to Readers to list other questions that you might have faced/ received in some interviews in the comments section to help fellow colleagues.
Piping Stress Interview Questions with Answers
1) How to make a critical line list or flexibility log? How will you decide the critical line list with help of ASME B31.3?
5) Draw a typical Sketch & supporting arrangement for tank farm piping? How tank Piping analysis is different from normal pressure vessel connected piping system analysis?
13) What is slug flow? What parameters are required to calculate the Slug force? How do you perform Slug flow analysis using Caesar II? Do you design for vibration arresting along with slug?
19) What do you mean by the term “liberal stress”?
20) What is the hot-cold philosophy (operating standby philosophy) for a pump? Have you heard the term Pump alignment? How do you ensure proper alignment of pumps with piping during analysis? What considerations do you make?
32) How does the layout of a pump piping change with changes in temperature?
33) Why the allowable for primary stress is different from that of secondary stress?
34) Is the stress due to the seismic anchor movement occasional stress? Explain with proper reason.
35) What is meant by the sentence ”primary stress is not self-relieving but secondary stress is”? Explain in detail the meaning of the term “ self relieving”.
36) Will SIF increase or decrease with an increase in pressure, other parameters be kept constant? Justify your answer.
37) What is the role of the ‘Y’ factor in the pressure thickness equation of B31.3 and B31.1?
63. What will be the consequences of steam piping having a low pocket but not having a steam trap?
64. When and why the reducer of a pump suction piping is installed in bottom flat condition?
65. If you found a specification break (at flange) between carbon steel and stainless steel in a typical P&ID. What are the additional arrangements that a piping engineer should make for this?
66. Assume a straight pipe of length L anchored at both ends. When a temperature change occurs the anchor force at one anchor becomes F1. Now the length of the same pipe increases to L2 and with a similar temperature change anchor force becomes F2. What is the relation between F1 and F2?
67. What is the Piping Speciality item? How many types of piping specialty items are used in piping engineering? Can we include them in the standard piping specification, and explain with reason?
70. In a normal tie-in where do you insert the spectacle blind? a) before the block valve and towards the new plant or b) after the block valve and towards the existing plant. Explain why.
71. What is the difference between a pipe elbow and a bend?
72. Among the following which material has the highest coefficient of thermal expansion? A) Carbon steel b) Cast Iron c) Duplex steel d)Stainless steel e) Galvanized Carbon steel
73. What are the major parameters to be reported in the support tag for a Shoe/Saddle type support?
74. What are the Metallic expansion joints? When they are used and when they could be avoided?
93. Which parameters do you seek from the civil department for performing underground piping analysis in Caesar II? Describe briefly the method of performing underground piping analysis using Caesar II. What are the outputs to check and what to interpret from Caesar results?
95. What do you mean by the term flexibility? How to ensure that the flexibility of a piping system is appropriate? What are the means for increasing flexibility? What will happen if more flexibility is provided to a piping system?
96. As per code ASME B 31.3, how many types of fluid services are available?
109. Why sustained stress is considered as primary stress?
110. What are the major differences between SIF and SCF (Stress Concentration Factor)?
111. Let’s assume from a 24-inch pipe header two tappings, one 2 inches, and another one 4 inches, are taken. At the interconnection point in which case the SIF will be higher?
112. What is the industry-accepted procedure for transferring anchor load for intermediate anchors (anchor in between two loops) where normally Caesar shows very less value?
113. How to analyze stress packages when a D/T ratio for the pipe exceeds 100?
114. Arrange the following piping elements with respect to flexibility and SIF (either increasing or decreasing order). Assume pipe size and thickness are constant.: 1.5D bend, 1D bend, Straight Pipe, 4D bend, 10D bend.
117. Can we call piping shoe a pipe component as per the code? Explain with reason. What is your opinion about the RF pad in this respect?
118. What does the piping code say about the operation and maintenance of the piping system?
119. You want to make some changes in the existing plant and want to add a new line by hot tapping. From which point the ASME B 31.3 code will be applicable?
120. What are the terms Code Case and Code Interpretation signifies?
121. How to model an Air fin Fan Cooler in Caesar II? Why do you consider equipment weight in AFC modeling while for other heat exchangers, we do not consider it? What code needs to be followed for nozzle load checking and what the code says about nozzle load checking? Why do we need thrust blocks for the air-fin fan cooler?
122. Can you write the NEMA equipment nozzle equation sets? What are the major differences between API 617 and NEMA SM 23 from the stress point of view? Draw a typical steam turbine piping layout.
123. Which standard is used for designing a plate-fin heat exchanger? Which table is normally followed for nozzle load checking?
124. How do you consider tank settlement while piping stress analysis? Is it primary or secondary stress? Do you add tank settlement with sustained load cases? If yes why? What code says about tank settlement? What is tank bulging and why does it happen?
127. What standard say about rotary equipment alignment checks? What are the criteria mentioned in that standard? While the alignment checking, spring will be in locked or as-designed condition?
128. Calculate the number of loops for a 400-meter-long carbon steel pipe having a temperature of 400-degree centigrade running over a pipe rack.
129. How do you calculate PSV reaction forces in the absence of reaction force in vendor data? What is the major difference between the pressure safety valve and the pressure relief valve?
133. What does Appendix F of API 610 ensure? What are the equations? What does the standard say for vertical inline pumps?
134. What do you mean by weld joint strength reduction factor and quality factor? What is the importance of these factors?
135. While providing preliminary rack loading what assumptions do you consider?
136. What was the most critical system you analyzed in the last company? Draw the layout? What changes did you recommend? What is the temperature and pressure of that line?
137. What are the minimum load cases required to consider while performing a stress analysis of a vertical reboiler-connected piping system?
138. Have you performed a stress analysis of reciprocating compressor-connected lines? What are the considerations? What is the minimum frequency you achieved before sending for a pulsation study? How do you consider up to what length of piping is to be sent for the pulsation study?
139. What actually do you check during flange leakage checking by NC 3658 method?
172. A chemical plant has been operating fine for the last 10 years. Now a part of the pipe in between two two flanges will be replaced during the next shutdown. The length of the pipe to be replaced is 50 m. Which piping code should be followed for the entire piping system design?
173. Let’s assume a material (DSS) is having a Sy value of 550 MPa. What will be its Sc value?
174. As per stress analysis considerations, What’s new in ASME B31.3-2022?
175. What are the criteria for applying the NC 3658.3 method? Can we apply this method for flange leakage checking of 30″, 150 rating flanges?
176. What is low-yield strength bolting?
177. What is the major difference between series A and Series B flanges in ASME B16.47?
