Most of the highly critical stress systems employ one or more Spring Hangers in Stress systems. This article explains the frequently asked spring hanger questions with answers:
What is the main difference between Constant and Variable Spring Hanger? When to use these hangers?
Ans: In Constant Spring hanger the load remains constant throughout its travel range. But In variable Spring hangers, the load varies with displacement. Spring hangers are used when thermal displacements are upwards and the piping system is lifted off from the support position.
A variable spring hanger is preferable as this is less costly. Constant springs are used:
a) When thermal displacement exceeds 50 mm
b) When variability exceeds 25%
c) Sometimes when piping is connected to strain-sensitive equipment like steam turbines, centrifugal compressors, etc and it becomes very difficult to qualify nozzle loads by variable spring hangers, constant spring hangers can be used.
What do you mean by variability? What is the industry-approved limit for variability?
Ans: Variability= (Hot Load-Cold load)/Hot load= Spring Constant*displacement/Hot load. The limit for variability for variable spring hangers is 25%.
What are the major parameters you must address while making a Spring Datasheet?
Ans: Major parameters are: Spring TAG, Cold load/Installed load, Vertical and horizontal movement, Piping design temperature, Piping Material, Insulation thickness, Hydrotest load, Line number, etc.
How to calculate the height of a Variable Spring hanger?
Ans: Select the height from the vendor catalog based on spring size and stiffness class. For the base-mounted variable spring hanger, the height is mentioned directly. It is the spring height. For top-mounted variable spring hangers ass spring height with turnbuckle length, clamp/lug length, and rod length.
Can you select a proper Spring hanger if you do not make it program defined in your software? What is the procedure?
Ans: In your system first decide the location where you want to install the spring. Then remove all nearby supports which are not taking the load in the thermal operating case. Now run the program and the sustained load on that support node is your hot load. The thermal movement in that location is your thermal movement for your spring. Now assume a variability for your spring. So calculate Spring constant=Hot load*variability/displacement. Now with spring constant and hot load enter any vendor catalog to select a spring inside the travel range.
Why horizontal displacement is specified in the datasheet? What will you do if the angle due to displacement is more than 4 degrees?
Ans: For bottom-mounted springs it is mentioned to avoid large spring bending by frictional force and displacement. So that additional measures can be taken to lower frictional force by providing PTFE/graphite slide plate. For top-mounted spring hangers horizontal displacement is mentioned to check angularity of 4 degrees to reduce transmission of horizontal force to piping systems as spring hangers are designed to take the vertical load only. If the angle becomes more than 4 degrees due to large horizontal movement then install the spring hanger in an offset position so that after moving the angle becomes less than 4 degrees.
Which spring will you select for your system: Spring with low stiffness or higher stiffness and why?
Ans: Springs with lower stiffness provide less load variation for the same travel. So this spring is a better choice than a spring hanger with higher stiffness.
Excavation is a fundamental part of many construction projects, from building foundations to laying infrastructure. However, while excavation is essential, it also comes with significant hazards that can lead to serious accidents if not properly managed. Excavation Hazards are the dangers associated with soil excavation at construction sites. During construction site excavation, both the workers inside trenches and on the surface are at high risk. So protective measures must be considered against the hazards in the excavation. In this article, we will explore different types of excavation hazards during site excavation and the protective measures that should be undertaken to reduce accidents.
Definitions related to Excavation Hazard
Excavation – a man-made cut, cavity, trench, or depression formed by earth removal.
Trench – a narrow excavation. The depth is greater than the width but not wider than 4.5 meters.
Shield – a structure able to withstand a cave-in and protect employees
Shoring – a structure that supports the sides of an excavation and protects against cave-ins
Sloping – a technique that employs a specific angle of incline on the sides of the excavation. The angle varies based on an assessment of impacting site factors.
The discussion of this topic covers four main points. At the conclusion of this article, you should be able to:
State the greatest risk present at an excavation.
Briefly describe the three main methods for protecting employees from cave-ins.
Name at least three factors that pose a hazard to employees working in excavations and at least one way to eliminate or reduce each of the hazards.
Describe the role of a competent person at an excavation site.
Types of Excavation Hazards
Excavation is the removal of soil or rock from a construction site that creates an open space for installing pipes, equipment, etc. using various construction tools, machinery, or explosives. So, excavation creates a hole or cavity that is hazardous. Various types of excavation hazards arise at the construction site. Cave-ins or collapses are the greatest risks. Other hazards include:
Asphyxiation due to lack of oxygen
Inhalation of toxic materials
Fire
Excavated Soil or Equipment falling on workers.
Moving machinery near the edge of the excavation can cause a collapse.
Falling, Slips, Trips
The accidental severing of underground utility lines/power lines.
Material handling Hazards.
Excavation is one of the most hazardous construction activities. Most accidents occur in trenches 1.2 to 4.5 meters deep. There is usually no warning before a cave-in.
1. Cave-ins
Cave-ins are perhaps the most dangerous excavation hazard. They occur when the walls of a trench or excavation site collapse, burying workers under tons of soil.
1.1 Reasons of Cave-ins
The main causes of cave-ins include:
Unstable Soil: Soil types such as sandy or loose soils are more prone to collapse. Clay and silt can also become unstable when wet.
Improper Shoring: Shoring systems (support structures) that are incorrectly installed or inadequate can fail, leading to cave-ins.
Water Accumulation: Rain or groundwater infiltration can weaken soil stability, increasing the risk of cave-ins.
Vibration: Nearby construction activities or heavy traffic can cause soil to shift and destabilize excavation walls.
1.2 Precautions from Excavation Hazards, Cave-ins
Employees should be protected from cave-ins by using an adequately designed protective system. Protective systems must be able to resist all expected loads to the system.
1.3 Protective system from Cave-ins
A method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of adjacent structures. Protective systems include
support systems,
sloping and benching systems,
shield systems, and
other systems that provide the necessary protection.
Additionally, the following measures should be undertaken:
Soil Analysis: Conduct a thorough soil analysis to determine soil type and stability.
Shoring and Shielding: Use proper shoring (bracing) and shielding systems designed for the specific excavation depth and soil conditions.
Drainage Systems: Implement effective drainage solutions to manage water accumulation.
Regular Inspections: Conduct regular inspections of excavation sites to identify and address potential hazards.
1.4 Excavation Safety Plan Requirements
A well-designed protective system means
Correct design of sloping and benching systems.
Correct design of support systems, shield systems, and other protective systems.
Appropriate handling of materials and equipment.
Attention to correct installation and removal.
Several factors come into play when developing a total protective system. The design of the system itself, how materials and equipment are handled in and around the excavation, and the installation and removal of protective system components.
1.5 Design of Protective Systems against Excavation Hazards and Risks
The employer shall select and construct :
slopes and configurations of sloping and benching systems
support systems, shield systems, and other protective systems
Shield – can be permanent or portable. Also known as trench box or trench
Shoring – such as a metal hydraulic, mechanical, or timber shoring system that supports the sides
Sloping – from sides of an excavation that are inclined away from the excavation
1.6 Protect Employees Exposed to Potential Cave-ins
To protect personnel from cave-in excavation hazards (Fig. 1) the following preventive measures can be undertaken
Maintain at least a 2 m distance from the edge of the cut and use blocks to prevent over-run.
Slope or bench the sides of the excavation,
Make proper arrangements to barricade the area being excavated.
Support the sides of the excavation, or
Place a shield between the side of the excavation and the work area
Fig. 1: Excavation and Hazards
1.7 Controlling Factors for Excavation Protective System
Various factors need to be considered while designing a protective system against the hazards and risks of excavation. Those are
Soil classification
Depth of cut
The water content of the soil
Changes due to weather and climate
Other operations in the vicinity
The employer or his designee must select and construct designs of support systems, shield systems, and other protective systems.
Trenches more than 5 feet require shoring or must have a stabilized slope
Trenches less than 5 feet – a competent person must inspect to determine that a protection system is not necessary for soils where there is no indication of a potential cave-in
In hazardous soil conditions, trenches under 5 feet need protection
1.8 Shoring in Construction
Shoring in construction means erecting a temporary structure to support unsafe excavation walls or other unsafe structures till work is finished.
Provides a framework to work in
Uses Wales, cross braces, and uprights
Supports excavation walls
Must know the soil type
Must know the depth and width of the excavation
Must be familiar with the OSHA or other relevant standard Tables
Trench Shield: A trench shield must be built around the work area.
1.9 Hydraulic Trench Support
Using hydraulic jacks the operator can easily drop the system into the hole. Once in place, hydraulic pressure is increased to keep the forms in place. Trench pins are to be installed in case of hydraulic failure
1.10 Materials and Equipment
Materials and equipment used for protective systems shall be free from damage or defects that might impair their proper function.
Manufactured materials and equipment used for protective systems shall be used and maintained in a manner that is consistent with the recommendations of the manufacturer, and in a manner that will prevent employee exposure to hazards.
When material or equipment that is used for protective systems is damaged, a competent person shall examine the material or equipment and evaluate its suitability for continued use. If the competent person cannot assure the material or equipment is able to support the intended loads or is otherwise suitable for safe use, then such material or equipment shall be removed from service and shall be evaluated and approved by a registered professional engineer before being returned to service.
1.11 Protection from Vehicles during excavation
Install barricades
Hand/mechanical signals
Stop logs
Grade soil away from the excavation
Fence or barricade trenches left overnight
1.12 Hazardous Conditions
The weight and vibrations of the crane make this a very hazardous condition.
They should not be working under this crane.
In addition to the unprotected trench, a cave-in hazard is increased by machinery which gets too close.
Even normal vehicular traffic, such as that along an adjacent interstate or road through an industrial part may impact an excavation. The vibrations from continuous or heavy traffic may undermine the soil and cause a cave-in.
1.13 Excavation Spoils
Excavation spoils are the soil, dirt, and rubble that are removed while excavating. The following considerations should be made for preventing hazards from excavation spoils.
Don’t place spoils within 2 feet of the edge of an excavation
Measure from the nearest part of the spoil to the excavation edge
Place spoils so rainwater runs away from the excavation
Place spoil well away from the excavation
2. Other Excavation Hazards
2.1 Falling Loads
Falling loads involve materials or equipment falling into an excavation site, which can pose severe risks to workers. Causes include:
Improper Material Storage: Materials stored too close to the edge of an excavation can fall in.
Equipment Movement: Construction equipment near the excavation site can accidentally drop loads.
Unsecured Loads: Loads that are not properly secured can shift and fall.
2.1.1 Preventative Measures from Falling Loads:
Secure Storage: Keep materials and equipment well away from the edge of excavations.
Use Barriers: Install barriers or guardrails to prevent accidental falls of materials.
Proper Training: Ensure that workers handling equipment are trained in secure load practices.
2.2 Falling into Excavations
Workers and pedestrians can accidentally fall into excavations if proper safeguards are not in place. This can result in severe injuries or fatalities.
2.2.1 Preventative Measures from Falling into Excavations:
Guardrails and Covers: Install guardrails and covers around excavation sites to prevent falls.
Warning Signs: Place clear warning signs around excavation areas.
Access Control: Restrict access to excavation sites to authorized personnel only.
2.3 Utility Strikes
Excavation work often intersects with existing utilities such as gas, water, or electrical lines. Striking these utilities can lead to dangerous situations such as explosions, floods, or electrocution.
2.3.1 Preventative Measures from Utility Strikes:
Utility Locating: Use utility locating services to map out existing underground utilities before digging.
Safe Digging Practices: Employ safe digging practices, such as hand digging near known utility lines.
Emergency Procedures: Develop and communicate emergency procedures for utility strikes.
2.4 Equipment Hazards
Excavation work involves various types of equipment, including backhoes, excavators, and bulldozers. Hazards associated with equipment include:
Equipment Overturns: Heavy machinery can overturn if used improperly or if the ground is unstable.
Moving Parts: Equipment with moving parts can cause injuries if proper safety precautions are not followed.
Blind Spots: Equipment operators may have limited visibility, increasing the risk of accidents.
2.4.1 Preventative Measures from Equipment Hazards:
Operator Training: Ensure that all equipment operators are properly trained and certified.
Maintenance: Regularly maintain and inspect equipment to ensure it is in good working condition.
Safety Measures: Use spotters to guide equipment operators and maintain clear communication on-site.
2.5 Exposure to Hazardous Atmospheres
Excavations, especially those of significant depth, can sometimes encounter hazardous atmospheres, including toxic gases, low oxygen levels, or high levels of particulates.
2.5.1 Preventative Measures from Exposure to Hazardous Atmosphere:
Air Monitoring: Use air monitoring equipment to check for hazardous atmospheric conditions.
Ventilation: Implement proper ventilation systems to ensure a safe working environment.
Protective Equipment: Provide workers with appropriate personal protective equipment (PPE) such as respirators.
Test excavations more than 1.2 meters before an employee enter the excavation for:
Oxygen deficiency
High combustible gas concentration
High levels of other hazardous substances
Employees shall not be permitted to work in hazardous and/or toxic atmospheres. Such atmospheres include those with:
less than 19.5% oxygen,
a combustible gas concentration greater than 20% of the lower flammable limit, and,
concentrations of a hazardous substance that exceed those specified in the Threshold Limit Values for airborne contaminants established by the ACGIH.
2.6 Preventing Excavation Hazards from Water
Water is Hazardous. So,
Employees shall not work in excavations in which there is accumulated water, or in excavations in which water is accumulating unless adequate precautions have been taken to protect employees against the hazards posed by water accumulation. The precautions necessary to protect employees adequately vary with each situation but could include special support or shield systems to protect from cave-ins, water removal to control the level of accumulating water, or the use of a safety harness and lifeline.
If water is controlled or prevented from accumulating by the use of water removal equipment, the water removal equipment and operations shall be monitored by a competent person to ensure proper operation.
If excavation work interrupts the natural drainage of surface water (such as streams), diversion ditches, dikes, or other suitable means shall be used to prevent surface water from entering the excavation and to provide adequate drainage of the area adjacent to the excavation.
Water = Cave-in Hazard
2.7 Means of Egress
A stairway, ladder, or ramp must be present in excavations that are 1.2 meters or deeper
Structural ramps that are used solely by employees as a means of access or egress from excavations shall be designed by a competent person. Structural ramps used for access or egress of equipment shall be designed by a competent person qualified in structural design and shall be constructed in accordance with the design.
Ramps and runways constructed of two or more structural members shall have the structural members connected together to prevent displacement.
Structural members used for ramps and runways shall be of uniform thickness.
Cleats or other appropriate means used to connect runway structural members shall be attached to the bottom of the runway or shall be attached in a manner to prevent tripping.
Structural ramps used in lieu of steps shall be provided with cleats or other surface treatments o the top surface to prevent slipping.
2. 8 Protection from Falls, Falling Loads, and Mobile Equipment
Install barricades
Use hand / mechanical signals
Grade soil away from the excavation
Fence or barricade trenches left overnight
Use a flagger when signs, signals, and barricades are not enough protection
To protect employees from these hazards, take the following precautions:
Keep materials or equipment that might fall or roll into an excavation at least 2 feet from the edge of excavations, or have retaining devices, or both.
Provide warning systems such as mobile equipment, barricades, hand or mechanical signals, or stop logs, to alert operators of the edge of an excavation. If possible, keep the grade away from the excavation.
Provide scaling to remove loose rock or soil or install protective barricades and other equivalent protection to protect employees against falling rock, soil, or materials.
Prohibit employees from working on faces of sloped or benched excavations at levels above other employees unless employees at lower levels are adequately protected from the hazard of falling, rolling, or sliding material or equipment.
Prohibit employees under loads that are handled by lifting or digging equipment. To avoid being struck by any spillage or falling materials, require employees to stand away from vehicles being loaded or unloaded. If cab vehicles provide adequate protection from falling loads during loading and unloading operations, the operators may remain in them.
Competent Person against Excavation Hazards
Must have had specific training in and be knowledgeable about:
Soils classification
The use of protective systems
The requirements of the standard
Must be capable of identifying hazards, and authorized to immediately eliminate hazards
Inspections of Excavations
A competent person must make daily inspections (Fig. 2) of excavations, areas around them, and protective systems:
Before work starts and as needed,
After rainstorms, high winds, or other occurrences which may increase hazards, and
When you can reasonably anticipate an employee will be exposed to hazards.
Fig. 2: Inspection
If the competent person finds evidence of a possible cave-in, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions:
Exposed employees must be removed from the hazardous area
Employees may not return until the necessary precautions have been taken
Site Evaluation Planning
Before beginning excavation:
Evaluate soil conditions
Construct protective systems
Test for low oxygen, hazardous fumes, and toxic gases
Provide safe in and out access
Underground services
Determine the safety equipment needed
Summary
The greatest risk in an excavation is a cave-in.
Employees can be protected through sloping, shielding, and shoring the excavation.
A competent person is responsible for inspecting the excavation.
Other excavation hazards include water accumulation, oxygen deficiency, toxic fumes, falls, and mobile equipment.
Excavation work is an integral part of construction but comes with inherent hazards that require careful management. By understanding the common hazards, implementing effective safety measures, and adhering to regulatory standards, construction professionals can significantly reduce the risks associated with excavation. Continuous education, proper planning, and diligent supervision are key to maintaining a safe excavation environment. Prioritizing safety not only protects workers but also contributes to the overall success of construction projects.
What is the meaning of HOLD in Engineering Deliverables?
While dealing with day-to-day engineering activities It is required to issue many engineering drawings or documents by placing a “HOLD” in the drawing or document. During the initial phases of any project, all required data is not available. To progress any activity, Engineers and designers need to issue it as all process piping activities are interlinked with various departments, normally starting with the process engineering department.
If the process team does not issue the initial P&ID, other departments will not be able to proceed with their design work. So initial revision of documents is issued by placing “HOLD” for items that are not yet designed as final or vendor confirmation is not yet received. Also, Payments for any project is interlinked with document issue. So, with the initially issued documents, some percentage of project progress is achieved from the client, and accordingly, payment is received by the Engineering Consultant. So this hold term in project deliverables is very important. Should the work process stop when a “HOLD” is placed on some aspect of the work?
Various Reasons for HOLD
So, The average “HOLD” by itself does not mean a work stoppage. However, there are cases of unusual situations that might cause a complete halt to all the work. It would have to be a major issue of magnitude that would be a deal-breaker for the total project.
All other “HOLDS” tend to be:
A. HOLD for Undefined item
This might be any item like line size that is missed/not confirmed or an item like a Pump outline that has not yet been received and/or is yet due.
B. HOLD because of Unapproved Item
This might be the situation that an item has been completed and submitted to the Client (or Vendor) for approval but final confirmation of approval or comments is not yet received.
C. HOLD due to Unresolved Item
This might be an item of work in any engineering team that depends on input from another engineering group or entity. It could also be a case where something has been submitted to the Client for approval and not returned yet.
There might be a possibility that the Detailed Design Contractor of a project sees a “HOLD” as a way of increasing revenue if the project is being worked on a “Cost Plus” basis. With this, the contractor could fatten their Fee and Profits by extending the work process.
As a client representative, One might want to institute the Master “HOLD” Control list and a review process for all “HOLDS”.
In the project’s progress, A Hold Point is a very critical step that is required an inspection, approval, or permit prior to moving further steps according to the procedure or specification.
Good Engineering Practice
Good Engineering practice in design organizations is to maintain a master hold list and before issuing any deliverable as issued for construction, all HOLD items are cleared. But still, there may be some difficulties found during construction, mainly while working with existing plants due to clashing. In such aspects, the construction work is kept on “HOLD” for a certain period of time and after the resolution of the same by the concerned design team, the work is finished.
About the Author: Part of this article has been prepared by Dr. Javier Blasco Alberto, Associate Professor, School of Engineering and Architecture, University of Zaragoza. He also collaborates actively with InIPED.
Methods for WRC 107 (WRC 537) and WRC 297 Checking in Caesar II
WRC or Welding Research Council is a Scientific Research Corporation, involved in solving problems related to welding and pressure vessel technology. To date, they have published more than 500 bulletins that solve various problems of engineering.
Importance of WRC 107 (WRC 537) and WRC 297 in Piping Stress Analysis
Whenever Pressure Vessel nozzle loads exceed the allowable values provided by Vendors (Equipment manufacturer) or standard project-specific tables (guidelines), the piping stress professional can use WRC 107 (537)/297 (or any other FEA) to calculate the stresses at the Nozzle-Shell junction point and compare the calculated stresses with allowable values provided by Codes. If the stresses are found to be within the allowable limit then the load and moment values can be accepted without any hesitation.
However, there are some boundary conditions that must be satisfied before using WRC. This write-up will explain the required details for performing WRC 107 (WRC 537) and WRC 297 using Caesar II software and the step-by-step methods for performing WRC checks.
What are WRC 107 (WRC 537) and WRC 297?
Both WRC 107 (537) and WRC 297 bulletins deal with “local” stress states in the vicinity of an attachment to a vessel or pipe. As indicated by their bulletin titles, WRC-107 can be used for attachments to both spherical and cylindrical shells while WRC-297 only addresses cylinder-to-cylinder connections.
Both bulletins are used for nozzle connection. WRC-107 is based on an un-penetrated shell, while WRC-297 assumes a circular opening in a vessel. Furthermore, WRC-107 defines values for solid and hollow attachments of either round or rectangular shape for spherical shells but drops the solid/hollow distinction for attachments to cylindrical shells. WRC-297, on the other hand, is intended only for cylindrical nozzles attached to cylindrical shells.
Boundary conditions for using WRC 107/ WRC 537
To determine whether the WRC 107/ WRC 537 bulletin can be used for local stress checking, the following geometry guidelines must be met:
d/D<0.33
Dm/T=(D-T)/T>50 (Here, T=Vessel Thickness, Dm=mean diameter of vessel)
Boundary conditions for using WRC 297
To determine whether the WRC 297 bulletin can be used for local stress checking, the following geometry guidelines must be met:
d/D<=0.5
d/t>=20 and d/t<=100 (Here t=nozzle thickness)
D/T>=20 and D/T<=2500
d/T>=5
The nozzle must be isolated (it may not be close to a discontinuity) – not within 2√(DT) on the vessel and not within 2√(dt) on the nozzle
Difference between WRC 107 (WRC 537) and WRC 297
The major differences other than the boundary conditions mentioned above are listed below:
1. WRC 107 calculates only the vessel stresses while WRC 297 calculates Vessel stresses along with nozzle stresses.
2. WRC 297 is applicable only for normally (perpendicular) intersecting two cylindrical shells whereas WRC 107 is applicable for cylindrical as well as spherical shells of any intersection.
3. The attachments for WRC 297 checking must be hollow but WRC 107 analyzes cylindrical or rectangular attachments that can be rigid or hollow.
4. WRC 297 is not applicable for nozzles protruding inside the vessel (Fig 1), Tangential Nozzle (Fig 2), and Nozzle at an angle (Fig 3).
5. Typically, WRC-107 is used for local stress calculations and WRC-297 is used for flexibility calculations.
Fig. 1: Nozzles and Vessels for WRC
Limitations of WRC 107 (WRC 537) & WRC 297
Other than the boundary conditions mentioned above there are some more limitations as mentioned below:
Neither bulletin considers shell reinforcement nor do they address stress due to pressure.
CAESAR II, PVElite, & CodeCalc will not extrapolate data from the charts when the geometric limitations mentioned above are exceeded. Extrapolated data may not be appropriate.
WRC-107/ WRC-297 Calculation Methodology in Caesar II
Inputs required for performing WRC checking
The following documents must be ready with you before you start to perform WRC 107/297 checking:
Equipment Details/ General Arrangement Drawing
Nozzle details
Line list
WRC Calculation Steps in Caesar II
Step 1: Perform Static analysis of the stress system and find out the nozzle loads required for checking local stresses.
Step 2: Enter the WRC module from Caesar II. Provide a file name for your job. Refer to Fig. 2
Fig. 2: Opening WRC Module in Caesar II
Step 3: The following screen will appear. Enter the Nozzle data as shown in Fig. 3 below.
Fig. 3: WRC Input Screen in Caesar II
Step 4: Now enter the vessel details i.e, diameter, wall thickness, corrosion allowance, and material (Fig. 4)
Fig. 4: Input Vessel Details in Caesar II
Step 5: Input vessel and Nozzle direction cosines, Internal design pressure, and load and moments values from Caesar static analysis output (Sustained, Expansion, and occasional as applicable).
Fig. 5: Entering Force Details
Step 6: On options, it is suggested not to change any parameter. Now click on analysis to read the results. The output will inform you whether WRC checking is passing or failing. Use results as per your requirements.
Fig. 6: Sample WRC Output Screen
For entering loads and moments as per local convention following description and figure (Fig. 7) can be used for converting global forces into local forces.
Fig. 7: Force and Moment Direction Consideration
As shown in Fig. 7, Stretch your right hand with the Middle finger along the Vessel Centerline. Index Finger should parallel to the nozzle centerline and should point in a direction from the nozzle towards entering the vessel. And the Thumb should be perpendicular to both. Then
The direction of the Index Finger represents +P.
The direction of the Middle Finger represents +VL
The direction of the Thumb represents +VC
ML will be positive if by applying the right-hand thumb rule to ML, the direction of thumb is the same as that of VC.
MC will be positive if by applying the right-hand thumb rule to MC, the direction of thumb is opposite to the direction of VL.
MT will be positive if by applying the right-hand thumb rule to MT, the direction of the thumb is opposite to the direction of P. Get the loads and moments from CAESAR output. Compare the direction of Forces and Moments in CAESAR output with conventional Force and Moment directions and enter the values of P, VL, VC, MT, MC, and ML accordingly.
Used for Vertical storage tanks, Circular in shape having a larger diameter
Used where there are no anchorage requirements for the tank (as specified by the tank vendor)
Components of Tank Pad foundation:
Tank Pad body
Tank Pad Shoulder
Finishes
Tank foundation functions and requirements :
The functions of a tank foundation are:
To spread and transfer the load from the tank and its contents via the tank foundation body and shoulder to the subgrade so that the settlement remains within the allowable limits.
To provide a smooth surface with sufficient bearing capacity and stability for tank construction and operation
To channel rainwater away from the tank shell and tank bottom quickly
The requirements for the shoulder of the tank foundations are:
To provide sufficient lateral support to the tank foundation during construction, operation, and maintenance activities
To resist edge settlement beneath the tank shell
To resist erosion by wind and/or water
Design Parameters:
The tank foundation shall be designed to ensure that it is capable of:
absorbing subsoil deformations to ensure deformations in the tank base remain within limits
the possible unequal foundation pressures
Under certain circumstances, soil improvement under the tank foundation shall be considered in order to:
provide a foundation with sufficient strength
reduce large settlements
The minimum elevation of the tank foundation at the base of the tank shall be 0.60 m above the adjacent terrain.
Fig. 1: Example of Typical Tank Foundation
Drain pipes shall be placed around the circumference of the foundation in order to detect leakages (if any) and to prevent the build-up of pore pressure due to liquid accumulating in the tank pad.
Geo-textile membrane shall be installed under the surface finishing to the shoulder if there is a possibility of washout of fine materials
Stability analysis of the shoulder and tank foundation shall take into account the following aspects :
wind loads
earthquake loads
initial height above adjacent ground level
highest possible groundwater level
the angle of slope of the shoulder
geotechnical properties of the tank foundation materials and subsoil
load provided by the tank and its contents during hydrostatic testing, operation, and maintenance
Tank Foundation Shoulders:
The shoulder width shall be selected such that the stability of the foundation, shoulder, and subsoil is ensured. The minimum width of the tank foundation shoulder (S) depends on several aspects:
height of the tank (H)
the density of the product
the slope of the tank foundation edge
height of the tank foundation (T)
The shoulder shall have a gradient of 1:10. The slope to the shoulder shall not exceed a gradient of 1:1.5.
Materials:
Tank pad foundations are constructed with durable, granular materials, such as crushed rock, coarse sand, etc.
The tank foundation body shall be constructed from clean granular materials which meet the following requirements:
not crushable
low compressibility
high friction properties
low silt content
free draining
insensitive to weathering, chemical changes
easy to compact
not sensitive to liquefaction (especially when constructed in earthquake zones).
Well-compacted sand, especially coarse sand, meets the above requirements providing the chemical and mechanical stability of the minerals is guaranteed.
In order to prevent the capillary rise of the groundwater the upper 200 mm of the tank foundation shall comprise coarse sand.
Tank foundation finishes:
The purpose of the surface finishing layer under the tank is:
To act as a barrier to corrosion promoted by water or water vapor, together with chemicals that may be present in the tank foundation or subsoil
To promote a uniform distribution of stress from the tank bottom to the tank foundation
To allow thermal expansion of the tank bottom
The function of the surface finishes of the tank foundation shoulder is to protect the foundation from damage caused by weathering, erosion, and construction, operation, and maintenance activities.
The surface finish layer under the tank shall be a mixture of sand and bitumen.
The final levels of the placed and compacted surface finish under the tank edge between any two points 10 m apart around the periphery of the tank shall not be greater than +/- 6 mm.
The tank foundation shoulder may, like bund walls, be covered by a mixture of sand, bitumen, and cement or lime (i.e. a wet sand mix).
The surface finish to the shoulder shall have a gradient slope of 1 vertical in 10 horizontal from the underside of the annular plate of the tank, to avoid ingress of water under the tank.
During the construction of the tank foundation, necessary tests are performed on each 0.3m thick layer placed and compacted.
Piping Specifications | Piping Material Specification (PMS) | Piping Class
Piping Specification (pipe spec, in abbreviated form ) is the most important piping document for a project that is prepared during the design phase of any project. They provide all the basic guidelines that need to be followed while proceeding with the design of the project.
The Function of a Piping Specification
Piping Specifications are engineering documents, generated by design consultancies to cover additional requirements applicable to a specific product or application. Piping Specs provides specific/additional requirements for the materials, components, or services that are beyond the code and standard requirements and based on engineering experience and best practices of the design companies.
Types of Piping Specifications
In Piping Design Companies/Consultancies, more than twenty-five (25+) Specifications (most of the time they are referred to as pipe spec, in abbreviated form) are used that cover piping-related issues. There will be a “piping specification” for:
This partial list provides some of the specific piping specifications that are found on most projects in design companies.
How to Make a Pipe Material Specifications?
All Piping Material Class Specifications must have a front cover with a written section containing the following:
Document Title
Document Number along with Revision history
Name of Responsible person, checker, and approver along with creation date
Contents in Tabular or properly arranged format
Functional or Purpose Statement
General Notes
A list mentioning all the applicable Codes that apply to the materials added in the specification
A list specifying the Line Classes with data like Material, Commodity, Flange Rating, etc.
All individual Line Class sheets
All common drains, vents, and other miscellaneous details with the proper connection.
Header and Branch Connection Tables
All of this will then be issued as a single document with the title “Piping Material Specification” or PMS.
Basic Data Required for Piping Material Specification
Data Requirements for Pipe Material Specification
The piping material engineer will need the following information:
List of all commodities like feed, all products, all waste streams, all utilities, and all additives that are part of the project.
Complete chemistry of each commodity which includes Toxic classifications and reactions to changes in temperature.
Maximum sustained operating pressure and temperature of every commodity. Also, Any short-term or upset condition that may cause an increase or decrease in pressure or temperature.
Corrosion rate for different pipe materials when in touch with the above commodities.
Expected maximum and minimum pipe size (Nominal Bore) for the project.
The next importance is in knowing the Client’s preferences and or restrictions for materials, valves, flanges, or any other items.
Next, required to know the expected “Design Life” of the plant to determine the corrosion allowance for selecting the final pipe schedule.
Now to prepare the finished “ Piping Line Class” or “piping material specification”, The Engineer may create a word or excel document with the following headers:
Block indicating piping class details and revision status
A piping class is defined as an assembly of piping components that are suitable for a defined service and design limits within a piping system. The piping class or Pipe Class is an important document that specifies all the required components under a specific design limit. Typical components that are covered in a piping class are the type of pipe, material, schedule, corrosion allowance, flange ratings, branch types, valve types, valve trim material, gasket, and all the other components’ specific requirements.
Pipe class development mainly considers the Design and Operating Pressure, temperature, and corrosive environment. Different piping material specifications are segregated into separate “Piping Classes”. Pipe class is included in the line number to help engineers easily identify the MOC of each piping item.
What are the advantages of a Piping Class?
The generation of piping class provides multifold benefits to plant design engineers. Some of the advantages of designing and purchasing piping following piping classes are listed below:
A large reduction in piping system engineering and procurement effort due to internal design standardization.
Group-wide standardization of piping material and piping systems design;
Variety control which leads to reduced costs for stocking materials;
Integrity and Quality control in relation to applied standards;
Increased leverage for centralized purchasing;
Reduction of the risk associated with wrong material selection.
Differences between Piping Specification and Piping Class
Here’s a tabulation of the major differences between a piping class and a piping specification:
Aspect
Piping Class
Piping Specification
Definition
A piping class is a collection of related piping components, defined for a particular application or service.
A piping specification is a document that provides detailed information about the requirements and standards for piping materials and components.
Purpose
A piping class is used to group and categorize piping components for ease of design, procurement, and installation.
A piping specification is used to define the technical and material requirements for the components used in piping systems.
Scope
A piping class typically includes a set of materials, components, and accessories organized for a specific type of service or environment.
A piping spec. focuses on the technical details, including material grades, dimensions, and pressure ratings for piping components.
Components Included
Includes pipes, fittings, flanges, valves, and supports, often categorized by service or fluid type.
Includes detailed descriptions of pipe materials, wall thicknesses, pressure ratings, and other technical specifications.
Detail Level
Generally broader, categorizing components and materials based on service requirements.
More detailed, providing specific standards and requirements for each component.
Usage
Used by designers and engineers to select and use components based on the type of system or service.
Used by engineers and procurement teams to ensure all components meet the required standards and specifications.
Documentation
May include tables, diagrams, and descriptions to categorize components.
Usually a formal document or set of documents detailing technical standards, material requirements, and testing procedures.
Customization
Can be customized based on project needs or industry standards, reflecting the specific requirements of a project.
Highly specific, based on industry codes, standards, and project requirements, with less variation.
Examples
A class for high-temperature steam service, including appropriate materials and components for that service.
A specification detailing the requirements for carbon steel pipes, including allowable pressure ratings and material grades.
Table 1: Piping Class vs Piping Specification
Both piping classes and piping specifications are critical for designing and maintaining effective and reliable piping systems, but they serve different purposes and provide different types of information.
Who is responsible for generating Piping Material Specification?
Piping material engineers prepare the piping material specification and piping classes by discussing with process engineers. Most of the data required for producing a pipe material class is received from the process team.
About the Author: This article has been prepared by Dr. Javier Blasco Alberto, Associate Professor, School of Engineering and Architecture, University of Zaragoza. He also collaborates actively with InIPED.
