The term Camouflage is widely used in the defense industry. Camouflage means using any combination of color, materials, or illumination for concealment. In recent times, the same painting technique is used by various countries to conceal the oil storage tank locations.
Camouflage for tanks is the painting technique or procedure that is used for confusing others to save the Oil Storage Tanks from air attacks during any war situation. The whole process is subjected to the art of color as well as the application of paint. Refer to Fig. 1 which shows an example of camouflaged oil storage tanks.
Fig. 1: Camouflaged oil storage tanks
Reason for Camouflaging
Tank Camouflaging is done to save Tanks from attacks. Environmental friendly color is added to tanks such that it matches with the nearby environment, thereby making them difficult to locate. Same as lizards changing their color to make us confused about their exact location. Army Tankers and their dresses are also camouflaged environmentally.
Camouflaging Colors
Normally used colors are terracotta, sea green, and yellowish color. There is no straight answer to this question it’s purely subject to client specification and the particular environment where Tanks are located on.
Codes and Standards for Camouflaging Tanks
The governing codes and standards used for tank camouflaging vary from country to country. A few of the codes and standards used are listed below for reference:
BS-4232
IS-5
IS-101
IS-161
IS-2074
Tank Camouflaging Methods
Camouflaging on tank surfaces can be done by following methods:
Manual Method using a brush
Using a roller or any traditional method
Air spray.
Disruptive painting for tank camouflaging shall be done in three colors in the ratio of 5:3:2 (all Matt finish)
Dark green or sea green-5
Light green -3
Dark medium brown-2
Once the camouflaging is done, the tank is inspected and tested as per
Surface preparation test
DPT measurement
Crosscut test
Peel off test or
Holiday test
Cost Impact of Camouflaging
It increases your labor cost and decreases risk. As cost is directly proportional to risk obviously budget & safety both shall be increased.
A few of the organizations that perform the tank camouflaging in India are:
Tanks or Storage Tanks that are designed following the rules and guidelines of API 650 codes are API 650 Tanks. API 650 is the governing code for Welded tanks for Oil storage normally operating in the atmospheric pressure range. The code API 650 provides guidelines for the design, fabrication, material, erection, and inspection of welded vertical and cylindrical storage tanks. Such Tanks must be above ground with a closed or open top.
Fig. 1: API 650 Tank
What is API 620 Tank?
API 620 covers the design and construction of field-assembled large storage tanks operating in the low-pressure zone. Normally, API 620 tanks have more design pressure as compared to API 650 tanks.
Fig. 2: Typical API 620 Tank
In this article, we will study the major differences between these two types of tanks i.e. API 650 vs. API 620
Similarities between API 650 and API 620 Tanks
Both tanks are used for storage purposes.
Both API 620 & API 650 Tanks can be constructed from carbon steel, austenitic stainless steel, and nickel alloys (low temperature only).
For both tanks, a Non-Destructive inspection is required but a third-party inspection is not required.
Differences between API 650 and API 620 Tanks: API 650 vs. API 620
The major differences between API 650 and API 620 tanks are produced below in a tabular format.
Parameter
API 650 Tanks
API 620 Tanks
Description
API 650 provides guidelines for Welded Steel Tanks for Oil Storage
API 620 provides guidelines Design and Construction of Large, Low-Pressure Storage Tanks
Configuration
The configuration of API 650 tanks is Ground-Supported Bottom, Open or Closed Roof
API 620 tanks can be of any configuration that has a single centered, vertical axis of revolution
Configuration
For API 650 tanks, the entire tank bottom has to be uniformly supported.
API 620 tanks must have a single vertical axis of revolution.
Shop/Field Erected
Tanks designed by API 650 can be Shop Fabricated (Appendix J) or Field Erected.
API 620 tanks are Field Erected
Tank Sizes
Any
Tank size larger than 300 ft.
Temperature Range
The usual temperature range for API-650 tanks is -40 Deg. F to 500 Deg. F
The usual temperature range for API 620 tanks is -325 Deg. F to 250 Deg. F
Maximum Pressure
The maximum pressure for API 650 tanks is 2.5 psig (pounds per square inch gauge) or 17.2 Kpa
The maximum pressure for API 620 tanks is 15 psig
Materials
Common materials for API 650 tanks are Carbon Steel, Austenitic Stainless Steel, Duplex Stainless Steel, Aluminum
API 620 tanks are usually made of Carbon Steel, Austenitic Stainless Steel, and Nickel Alloys (Low Temp only)
Uses/Industries
API 650 tanks are used for Oil, Gas, Chemical, Water, and Biofuel storage. A maximum of the most common welded steel tanks used in industry are designed following API 650. Tanks are typically found in Refinery tank farms, Terminals, Pipelines, and other process facilities use these tanks.
Tanks like LNG tanks or Cryogenic tanks which require high internal pressure are designed as per API 620.
Bolted joints are one of the most common elements in piping design. Whenever flanged joints are used, bolted connections play an important role in keeping flanges together and avoiding flange leakage problems. So Bolting is an important component of piping systems.
In general, Boltings seem petty things for a whole lot of piping system design. Therefore, they tend to be “forgotten” when it comes to detailing their features, especially the length.
It is true that with nowadays technology of 3D modeling, it will be automatically calculated. However, this is only applicable when it is a normal joint consisting of Flange-Gasket-Flange. In some other cases, Piping Engineers need to put more attention to details and define the length manually.
It would be one of the “failures” if these lengths cannot be rectified upfront and only discovered when installation comes in hand. Imagine if you are doing a big-scale project, it will definitely delay the progress. And unfortunately, just because of these “petty” things.
Let’s see what are the bolting design features that Piping Engineers required to define and check in order to have technically complied boltings.
Bolting Features to be Checked in Bolted Connection
While deciding on a bolted joint or bolted connection the following bolting design features must be thoroughly checked to ensure a leak-free long-lasting piping system.
Like any other piping items, the bolt material will be based on the service that they will be used for. This will be defined when Piping Engineers are preparing their Piping Material Specifications. No ratings are required for boltings as they are not pressure-containing parts.
Other than the OWNER’s specification and requirement, another reference that can be taken into account is API 6A. Below attached is an example and guideline on boltings material to be used based on its service;
Fig. 1: Bolting Material guidance as per API 6A
ASME B16.5 also showed materials for boltings as below;
Fig. 2: ASME B 16.5 Bolting Material Guidance
Size and Quantity of Bolts
The size of the boltings will relate to the size of the flange, and quantity will relate to the flange rating. Flange with sizes from 1/2″ up to 24″ will refer to ASME B16.5 and ASME B16.47 for larger sizes. From the table, the size, quantity, and standard length (normal joint of Flange-Gasket-Flange) will be provided.
The length would largely depend on the Flange class rating as the thickness of the flange differs when the rating increase. Examples of Class 150 and Class 300 are shown in Fig. 3 and Fig. 4 below;
Fig. 3: Bolt Lengths for ASME Class 150 flanges
Fig. 4: Bolt Lengths for ASME Class 300 flanges
This length has been calculated with all considerations as in Nonmandatory Appendix C. We will cover this calculation again.
Washer Requirement for Bolted Connections
A common practice the boltings do not require a washer. Thus, when will washers be required? Washers in bolted joints are used:
When used with an insulation gasket kit. This is to provide an engagement grip to the non-metal washers.
When the non-metal flange is used to avoid flange damage due to the force exerted.
Special case if the bolt holes are bigger and may cause loose boltings.
Type of Washers
ASME B18.21.1 provides the following types of washers:
Plain (Flat) Washers
Helical Spring Washers
Tooth Lock (Internal, External) Washers
Fig. 5: Washer types per ASME B18.21.1
Bolting considerations for Inline Items
Normal flange joints will consist of Flange-Gasket-Flange, and usually by 3D modeling setup; this has been auto-calculated to define the length of the bolt. However, whenever inline items involved Vendor data incorporation, it is wise to check manually and implement it inside the 3D setup. Actual thickness to be incorporated to avoid the insufficient length of the bolt.
Examples of inline items that require Final Vendor Data to be incorporated;
Valves (manual & control valves) – sometimes its end-to-end dimension as per Manufacturer’s Standard.
Gaskets – especially insulation gaskets, the thickness may exceed the standard 3 mm that the usual 3D system would assign for spiral wound gasket (after compressed). Extra care for a joint that consists of multiple gaskets joint.
Instrument Items – other than Control Valves, all instrument items that are connected to piping shall be checked. Sometimes it came with non-standard flange thickness or upper-Class rating that requires an extra length of bolts.
Bolt Length Calculation and Considerations
Appendix C of ASME B16.5 provides an example of how the bolt length has to be calculated and what considerations need to be taken;
Fig. 6: Bolt Length Calculation for Bolted Joints
For the size of bolts more than 1″, the bolt tensioning requirements shall also be considered. For this, add another 1D or 1 thickness of nut for the total length.
The following Bolt tensioning video tutorial explains clearly the requirement of the above-mentioned 1D or 1 thickness of the nut.
Video Tutorial: Bolt Tensioning Requirements
Bolt Coatings on Bolted Connections
Coatings on bolts can be said quite common nowadays. Even some OWNER would specify ALL bolts shall be coated. As stated before, even though bolts are seemed petty, non-pressure-containing parts; bolts will be sitting in the weather dry and wet maintaining the force of tightening for the pressure-containing parts. To ensure the strength are efficient, corrosion is one of the major things to be avoided.
The most popular coating that is used is Fluorocarbon Coating (Xylan, PTFE, Teflon).
But, there were other types of coatings such as;
Galvanized (Hot Dip, Mechanical)
Electroplating (Cadmium, Zinc)
It is important to ensure the requirement of the project on the bolt coating. Some projects may be delayed just because this one little thing (but important) has been missed out of consideration.
Piping Expansion Joints or Expansion Bellows are highly engineered mechanical devices containing one or more metal/rubber bellows. Expansion Joints are used to absorb dimensional changes caused by thermal expansion or contraction of a pipeline, duct, or vessel while containing the system pressure. The flexible element of the expansion joint that expands or contracts to absorb thermal movement is called Bellows. It consists of one or more convolutions. Expansion joints are successfully used in Refineries, Chemical and Petrochemical Plants, Cryogenic plants, Nuclear power plants, Automotive, Aerospace, and heating & cooling systems.
Fig. 0: Piping Expansion Joints
Why Install Piping Expansion Joints?
Piping Expansion Joints serve various purposes when installed in a piping system. Those are:
To absorb movement (Thermal expansion as well as compression)
Special Attachments like Pantographic linkages, etc
Refer to Fig. 1 which shows the main elements of a piping expansion joint.
Fig. 1: Components of an Expansion Joint
Bellows:
Bellows are the most important element of a piping expansion joint. This is the basic unit of every expansion joint. They are of two types:
Formed Bellows
Formed from a thin-walled tube
Contains only longitudinal welds
Single & Multiply
Fabricated Bellows
Series of thin gauge discs welded together
Uses heavier gauge materials than those formed bellows
Regardless of the manufacturing method used, all bellows consist of the same basic components as shown in Fig. 2. Bellows can be single-ply or multi-ply designed.
Fig. 2: Basic Components of Bellow
Additional components are added to bellow to create expansion joints of increasing complexity and capability which are suitable for a wide range of applications.
Tie Rod of Expansion Joint:
As the name indicates, Tie rods are basically bars or rods, attached to the expansion joint assembly. Tie rods are designed to absorb pressure loads and other extraneous forces like dead weight. Sometimes, Tie rods (Fig. 3) are used as Limit rods to protect the bellows from movements in excess of design that occasionally occur due to plant malfunction or the failure of an anchor.
Fig. 3: Tie rod and Limit rod of a piping expansion joint
Expansion Joint End Connections:
Three types of end connections (Fig. 4) are available in a piping expansion joint to attach it to a piping system. They are
Flanged End including Special flanges, slip-on, or angle flanges.
Vanstone Ends are a type of modified flanged ends that adds flexibility and resolves bolt-hole misalignment.
Welded ends: Any pipe or duct can be directly welded to such bellows.
Fig. 4: Expansion Joint End Connections
Protective Covers and Liners for an Expansion Joint:
The expansion joint components are put inside a metallic cover to protect them from external sources as shown in Fig. 1.
A liner is provided to minimize the effect of flowing media on the bellow inner surface. Refer to Fig. 5.
Fig. 5: Protective Cover and Liner
Purge connections are provided along with internal liners to reduce the bellow’s skin temperature while using in high-temperature applications such as catalytic cracker bellows. Normal air or steam can be used as a purge medium. Purging helps in flushing out the particulate matter between the bellows and the liner. Harmful solids built up in the convolutions can also be stopped by purging.
Pantographic Linkages:
Pantographic Linkage is a scissors-like device that is a special form of control rod attached to the expansion joint assembly. They are used to positively distribute the thermal movement equally between two bellows of the universal joint throughout its full range of movement. However, note that they are not designed to restrain pressure thrust.
Fig. 6: Pantographic Linkages
Types of Expansion Joints
Broadly Piping Expansion Joints can be grouped into two categories:
Unrestrained Expansion Joint and
Restrained Expansion Joints
Unrestrained Type Expansion Bellows:
Unrestrained Expansion joints are assemblies not capable of restraining the pressure thrust of the system. So, The pressure thrust must be contained using main anchors or equipment. They are of the following types:
1. Single Expansion Joint Assemblies are the simplest type of expansion joint consisting of a single bellows element welded to end fittings, either flange or pipe ends.
2. Universal Expansion Joint Assemblies consist of two bellows connected by a center spool piece with flange or pipe ends. The main advantage of a universal expansion joint over a single expansion joint is that the universal arrangement provides greater absorption of axial, lateral, and angular movements than a Single Expansion Bellows Assembly.
3. Externally Pressurized Pressure Balanced Assemblies are used when a large amount of axial movement is required to absorb and pressure thrust must be absorbed by the expansion joint. The opposing force balancing theory is quite similar to the In-Line Pressure Balanced Expansion joint Assembly. However, in the current case, the opposing forces are generated from pressure acting on the outside of the bellows.
Fig. 7: Unrestrained type expansion joint
Restrained Type Piping Expansion Joints:
In Restrained type piping expansion joints, the expansion joint hardware is capable of restraining the pressure thrust of the system by their design. Intermediate anchors are installed to withstand the spring force generated due to the deflection of the expansion joint. The main anchors are not required. They are again of various types as mentioned below:
1. Tied Single Expansion Bellows Assemblies add tied rods to a Single Bellows Assembly to increase design flexibility in a piping system. The tie rods are attached to the pipe or flange with lugs. These tie rods carry the pressure thrust generated in the system, eliminating the need for main anchors.
Fig. 8: Externally Pressurized and Tied Bellows
2. Tied Universal Expansion joint Assemblies are mostly similar in construction to a Universal Assembly. The only difference is that tie rods absorb pressure thrust and limit movements to lateral offset and angulation only.
3. Hinged Expansion Bellows Assemblies limit movement to angulation in one plane. Hinged Assemblies (Fig. 9) are normally used in sets of two or three to absorb large amounts of expansion in high-pressure piping systems.
4. Gimbal Expansion Bellows Assemblies are designed to absorb system pressure thrust while allowing angulation in any plane. Gimbal Assemblies (Fig. 9), when used in pairs or with a Single Hinged unit, have the advantage of absorbing movements in multi-planer piping systems.
Fig. 9: Hinged and Gimbal expansion joints
5. Pressure Balanced Elbow Assemblies are used in applications where space limitations are a concern. A system of tie rods or linkages is used in such a fashion that the pressure thrust acting on the line bellows is equalized by the balancing bellows. The only forces transmitted to equipment are low spring forces created by the axial, lateral, or angular movements. An elbow must be present in the piping network to install this style of expansion joint.
Fig. 10: Pressure Balanced Elbow Assembly
6. In-Line Pressure Balanced Bellows Assemblies are used if a piping elbow is not present in a piping network to use the pressure-balanced elbow assemblies and pressure thrust has to be absorbed by the expansion joint. The inline bellows are tied in the expansion joint through a series of tie rods which equalizes the pressure thrust force. The opposing pressure forces cancel each other leaving only the low spring forces generated from the bellows deflection.
Fig. 11: Inline Pressure Balanced Expansion Joint
Expansion Joint Materials
The selection of bellows material is another important factor to be considered in the design of a piping expansion joint. Some of the factors which influence the proper expansion bellow the material selection process are:
Corrosion Properties: Process media, surrounding environment, and internal cleaning agents.
Mechanical Properties: High-temperature service, cryogenic service, and operating stresses.
Manufacturing Properties: Forming and cold working capabilities and cost & material availability.
Expansion Joints are available in metallic and non-metallic materials. The most common expansion joint materials, widely used in the piping industry are:
Steam traps are very essential in power piping as these devices remove unnecessary condensate from the steam lines. A steam trap serves two basic purposes:
Separate the condensate from the steam as quickly as it is generated and
Stop the stream discharge.
Every steam systems normally employ many steam traps at strategic locations to avoid the condensate to mix with the steam and create a two-phase flow. The steam condensate two-phase flow can damage the piping, supports, or even the connected equipment if not removed. Thus steam traps play a major role in plant safety.
In this article, we will discuss the best practices for steam trap installation.
Steam trap Installation Best Practices
Studies have shown that incorrect steam trap installation creates a high percentage of steam trap failures. Certain faulty installation negatively impacts the steam trap performance. As per process heat transfer considerations, A properly installed steam trap needs
a 24-in. minimum from the steam supply line to the steam-trap inlet and
an 18-in. maximum from the vertical leg to the steam trap as shown in Fig. 1 below.
Fig. 1: Minimum distances of steam trap assembly
Experiences showed that a properly installed steam trap should efficiently work for six years without any maintenance.
A few of the Steam trap installation best practices are outlined below:
Ensure Gravity Flow:
The most important rule to remember for steam-trap installation is one of Mother Nature’s Laws — Gravity (Fig. 1). Installation should ensure the condensate flow from the process to the steam trap by the gravity forces. Pressure and velocity can not be relied on to remove the condensate from the process.
Ensure Steam Leakage Rate of Steam Traps:
For the Steam Traps that are being purchased, determine the steam leak rate following the leak rate standards mentioned below:
a. PTC-39
b. ISO 7841
A quantifiable amount of steam always leaks through the steam traps. Hence, The selected steam traps must ensure that steam traps with the least amount of steam loss are specified. Such Steam Traps will prevent unnecessary energy loss.
Threaded Connections:
Steam traps with 1 in. or smaller connections should use tubing with tube connectors. Such an arrangement will avoid leak points (for example, threaded connections). Traditionally, threaded connections are obvious sources of leaks in the system due to expansion, contraction, and corrosion that occurs in a steam system. Refer to Fig. 2.
Fig. 2: Installation of Steam-trap using tubing and tubing connectors
Material Pressure rating:
Tube connections for steam trap installations are available from numerous steam-component manufacturers. Before placing an order ensure that the pressure ratings of the component material are acceptable.
The piping connection from Process to Steam Trap:
The Piping from the steam trap to the process connection shall be equal to or larger than the process outlet connection. Hence, it is suggested not to reduce the piping/tubing diameter before the steam trap or reduce the connection size of the steam trap. For example, a steam unit heater with a 1-in. condensate outlet would require 1-in. or larger piping/tubing from the unit heater to the same connection size on the steam trap.
Piping Connection Downstream of Steam Trap:
The pipe/tube diameter downstream of the discharge connection of the steam trap should be expanded. For example, 1-in. (connection) steam-trap discharge tubing/piping should be increased to 1.25 in. or 1.5 in.
Universal Mounts:
Universal mounts shall be used for connecting the steam trap devices with a connection size of 1 in. or smaller to the tubing or piping. With the universal mount, the steam trap is connected to the application with two bolts. This reduces the time required for the installation of the steam trap.
Use of Strainer:
Including a strainer as part of the steam trap installation is always suggested. The strainer can be accomplished by the following:
a. External strainer ahead of the steam trap
b. Steam trap with integral strainer
c. Universal mount with an integral strainer
Premature Steam trap failures due to corrosion will be eliminated by the strainer.
When installing an external or internal strainer, always install a blow-off valve on the strainer. This allows the strainer to be blown down during operation and, more importantly, permits the steam trap cavity to be safely depressurized during service.
Some other important Steam trap Installation Best Practices are:
The steam trap should be installed in an accessible location.
A visual indication (can be a sight glass or test valve) of the steam trap performance shall be installed on all process applications.
Always locate the steam trap below the lowest condensate discharge point of the equipment.
Ahead of the steam trap, A rise in pipe elevation is not at all desirable.
In most applications, check valves are installed after the steam traps.
Installation standards for all applications shall be maintained for future reference.
As per layman’s language, Piping Stress analysis is the analysis of stresses in the piping system. Now the question arises what are these stresses? Piping Stress is generated whenever a load acts on a piping system and tries to deform it. Due to the inertia effect, the piping system will resist that force with an internal resistance force creating stress. So, first, we need to know the loads that create these stresses. There are various kinds of loads that generate stresses in a piping system as listed below:
As we know the loads that create stresses in a piping system, let’s proceed to explore the types of stresses in a Piping System.
Types of Piping Stresses
The following kinds of piping stresses are generated in a piping system.
Normal Stresses
Normal stresses act in a direction normal to the face of the material crystal structure. Normal stresses may be tensile or compressive and can be applied in more than one direction depending on the application and type of loads. Three types of normal stresses exist in a piping system. They are:
Longitudinal or Axial Stress
Hoop or circumferential Stress and
Radial Stress.
Axial Stress or Longitudinal Stress in a Piping System:
Fig. 1: A typical piping system
Axial Stresses or Pipe Longitudinal Stresses are the normal stresses that act parallel to the longitudinal axis of the pipe centreline axis. In a piping system, Longitudinal stress can be generated for three reasons:
An Axial force of some kind
Internal Design Pressure
Bending Moment
Refer to Fig. 2 and let’s assume that force Fax is acting in the pipe Axially. So this force will generate axial pipe stress or longitudinal stress in the pipe metal, SL
Hence, The Longitudinal Stress, SL=Fax/Am.
Fig. 2: Longitudinal piping stress due to axial load
Here, Am is the pipe metal cross-sectional area that can be calculated as follows
Now this Axial Load, Fax can be created due to internal pressure, P which acts on internal pipe area Ai. So in that situation, the longitudinal force will be given by:
As dm is always greater than di, P di2/4dmt <Pdi2/4dit = Pdi/4t
Conservatively, the longitudinal pressure stress is approximated as
SL=Pdo/4t
Again, the axial load, Fax can be generated by bending which is given by the following equation:
Now adding all the above component stresses we get,
SL=Fax/Am+Pdo/4t + Mb/Z
Hoop Stress or Circumferential Stress in a Piping System:
The Normal Stress that acts perpendicular to the axial direction or circumferential direction is known as Hoop Stress. Hoop stress is caused by Internal pressure.
Fig. 3: Piping Hoop Stress
The Hoop stress is conservatively calculated as
SH=Pdo/2t
As can be seen from the simplified equations of pressure stresses, Hoop stress is twice the longitudinal stresses and hence is of utmost importance.
Radial Stress is the normal Stress that acts parallel to the pipe radius and is caused by internal pressure. It varies between the internal design pressure at the inside pipe surface and atmospheric pressure at the outside pipe surface as shown in Fig. 4 below.
Fig. 4: Radial Stress in a Piping System
Now if we compare, radial stress with respect to longitudinal pressure stress or hoop stress we can find that radial stress is many times lesser than those two stresses. This is the reason radial stress for piping systems is ignored most of the time.
Shear Stress in a Piping System:
Shear stresses act in a direction parallel to the face of the plane of the material crystal structure. This stress provides a slipping tendency to one plane against the other. Shear forces can be caused by
the shear forces acting on the pipe cross-section or
the twisting or torsional moments.
Since the shear stresses caused by shear forces in a piping system are very small, this is neglected. However, Shear Stresses caused by torsion are of considerable amount.
Fig. 5: Piping Shear Stress due to torsion
Shear Stresses caused by torsion are calculated by the following equation:
Thermal or Expansion Stresses in a Piping System:
Thermal or expansion stress in a piping system is generated when the free thermal movement of the pipe is restricted. The pipe is installed at ambient or atmospheric temperature and during operation, it carries fluids of different temperatures. So with a change in temperature, the pipe length is changed. As this free thermal movement is restricted by the supports or end equipment connections expansion stress is created.
Fig. 6: Thermal Stresses in a Piping System
In the above figure due to the change in temperature ΔT, the pipe length changes ΔL= α.ΔT. L.
Thermal Strain= ΔL/L= α.ΔT
So Thermal Stress= Thermal Strain X E= E.α.ΔT
Piping Stress Types as Per Piping Code
As per the piping code, piping stresses are categorized into three groups.
Sustained Stress
Expansion Stress and
Occasional Stress
Sustained stress is the stress present throughout the plant operating life. Weight and Pressure are called Sustained stresses.
Expansion stress is a displacement-driven secondary stress generated due to temperature changes from installed to operating conditions.
Occasional stresses are stresses those are present in a piping system for a very short period of time. Stresses due to Seismic events, Surges, Wind, Vibration, etc. are called occasional stresses.
