As per Code ASME Section III, the Stress Intensification Factor or SIF is defined as the Fatigue Correlation Factors that compare the fatigue life of Piping Components (Tees, branch connections) to that of girth butt welds in straight pipe subjected to bending moments.
Note that, Stress Intensification factors are often confused with stress concentration factors, stress coefficients, or other stress indices used in various mechanical design and fracture mechanics problems. The stress intensification factor in piping stress analysis provides the fatigue correlation of piping elbow and branch connections for evaluating moment loading.
History of Stress Intensification Factor
Markl Fatigue Curve for Straight Pipe (Fig. 1):
Fig. 1: Markl Fatigue Curve for Butt Welded Steel pipe
Markl stress intensity factor: iS = 245,000N-0.2
i =( CN-0.2)/S
Where
i=Stress intensification factor
C=245,000 for carbon steel materials
N=Cycles to failure
S=Nominal stress amplitude
Markl Stress Intensity Factor is based on deflection control, fully reversed, cyclic bending fatigue tests.
Stress Intensification Factor Equation
As per Section III, for class 2 & 3 piping and B31.1
Effect of Pressure on Stress Intensification Factor:
Fig. 4: Calculation showing the effect of pressure on SIF
Finite Element Methods for Stress Intensification Factor Calculation
The various methods for calculating Stress Intensity Factor are
Analytical Methods defined by Piping Codes
FEM techniques
The user can see that the basic SIF procedure is:
Build the model.
Apply a moment through the nominal attached pipe.
Read the highest stress from the resulting plot.
Divide by M/Z to get the SIF.
The Fem Software widely used for calculating Sif are
FE-pipe
Ansys
Stress Intensification Factor Calculations
The basic definition of stress intensification factor (SIF) is:
SIF = (Actual Peak Stress in Part)/( Nominal Stress in Part)
The nominal stress in the part for a piping component subject to bending loads is M/Z where “M” is the moment that the pipe exerts on the component, and Z is the section modulus of the matching pipe welded to the part being analyzed.
Example Case:
For example, when Stress Intensity Factors are needed for a large D/T “Wye” Fitting, there are usually four SIFs involved.
one for the in-plane moment about the wye,
one for the out-plane moment
For both the main header and branch sections.
An example, demonstrating this calculation for a 32×0.375 wye fitting is shown in the example.
Markl’s definition of the SIF is the ratio of the actual stress in the part due to a moment “M”, divided by the nominal stress in a girth (circumferential) butt weld due to a similar moment “M”.
B31 Stress Intensity Factor (SIF) = Actual Stress in Part (due to M)/ Stress in Girth Butt Weld (due to M)
Fig. 5: FEM model for Y-type fitting.
Two load cases for the model are set up automatically by FE/Pipe.
They are
Operating, and
Occasional
Various displacements and stresses from each load case are shown in Fig 6 and Fig 7.
Corrosion is the natural enemy of steel pipes, threatening their structural integrity, lifespan, and overall performance. As the backbone of many industries, from oil and gas to water distribution, ensuring the longevity of steel pipes is paramount. Anti-corrosive coatings and linings are a formidable solution that safeguards steel pipes against the relentless forces of corrosion. In this article, we’ll dive into the world of anti-corrosive coatings and linings, exploring their importance, types, application methods, and benefits.
What is an Anti Corrosive Coating?
An anti-corrosive coating is a specialized type of protective material applied to the surface of a substrate, typically metal, to prevent or significantly reduce the occurrence of corrosion. Corrosion is a natural process in which metals degrade due to chemical reactions with their surrounding environment, such as exposure to moisture, chemicals, and atmospheric elements. Anti-corrosive coatings create a barrier between the metal surface and its environment, acting as a shield to inhibit or slow down the corrosion process. These coatings are designed to resist the effects of various corrosive agents, thereby extending the lifespan and maintaining the structural integrity of the coated material. The anti-corrosive coating is also known as the anti-rust coating.
What is an Anti Corrosive Lining?
An anti-corrosive lining refers to a protective layer or material applied to the interior surfaces of a substrate, often pipes or containers, to prevent or mitigate the effects of corrosion caused by contact with corrosive substances. Unlike anti-corrosive coatings that are applied to the exterior surfaces, anti-corrosive linings are specifically designed to withstand the challenges posed by the materials being transported or stored within the substrate. These linings create a barrier that shields the substrate from chemical reactions, abrasive agents, and other factors that could lead to corrosion, ensuring the integrity, safety, and longevity of the substrate and its contents. Anti-corrosive linings are widely used in industries where the transported materials are corrosive or abrasive, such as chemicals, petrochemicals, and mining.
Advantages of Anti-Corrosive Coating and Lining
Anti Corrosive Coatings on Steel are widely used to protect the pipes from corrosion. The protective coating layer helps the steel material to prevent corrosion and increase the useful life of the material. Anti-corrosion coatings are one of the most effective and economical options for tackling corrosion. Corrosion-resistant anti-corrosive coatings serve the following purposes:
Protect metal surfaces from degradation due to oxidation, and moisture.
Prevents direct contact with environmental chemical hazards.
Acts as a barrier from corrosive materials.
Prolong the structural life along with increasing their efficiency.
Provides chemical protection, abrasion resistance, etc.
By preventing leaks and failures, anti-corrosive solutions contribute to environmental protection by minimizing the potential release of hazardous materials.
Coated pipes maintain optimal flow efficiency, ensuring the smooth transportation of liquids or gases without obstructions caused by corrosion buildup.
For industries like oil and gas, chemical, petrochemical, infrastructure, marine, power generation, etc., the use of anti-corrosive coatings and linings has become a necessity to safeguard the huge investments in terms of money, property, and safety of workers. The demand for high-performance anti-corrosion coatings is increasing day by day. Before jumping into the core of anti-corrosive coating and lining types, let’s learn a few words about Corrosion.
Corrosion in the Oil and Gas Industry
Corrosion in the Piping and Pipeline Industry is quite common.Corrosion is a loss of material due to “REACTION” with the environment.
The anti-corrosive coating itself must be environmentally friendly.
Types of Anti-Corrosive Coatings
A wide variety of anti-corrosive coatings are available in the market to suit the performance requirements of a specific application. Therefore, the selection of anti-corrosion coatings is not an easy process. Various parameters need to be ensured during anti-corrosive coating selection. Sometimes, the coating manufacturer needs to be consulted for some specific information.
Depending on the materials used, an anti-corrosive coating can be categorized into the following types
Natural Paints
Epoxy
Polyurethane
Synthetic Resins
Plastics
Phenolic
Composites
Alkyd
Again, depending on the anti-corrosive coating application they can be divided into two groups:
Anti-corrosive coatings for new pipes, and
Anti-corrosion coatings for maintenance and repair work.
Based on the application of the coating on the piping surface they can be classified as
Internal Pipe Coatings, and
External Pipe Coatings
The specific application dictates the type of anti-corrosion coating to be used.
Epoxy Coatings:
Epoxy coatings are renowned for their exceptional adhesion and resistance to various chemicals. They create a dense, protective layer on the pipe’s surface, shielding it from corrosion caused by exposure to chemicals, moisture, and abrasive substances.
Polyurethane Coatings:
Polyurethane coatings provide outstanding resistance to UV radiation, making them ideal for outdoor applications. They are often used in combination with epoxy coatings for enhanced protection against both chemical and environmental factors.
Zinc Coatings:
Zinc coatings, such as galvanization, involve applying a layer of zinc onto the steel surface. This sacrificial layer corrodes before the steel does, extending the life of the pipes. This method is commonly used for pipes exposed to high moisture levels.
Fusion-Bonded Epoxy (FBE) Coatings:
FBE coatings are known for their robustness and resistance to mechanical damage. They are applied as a powder and heated to form a strong bond with the steel surface. FBE coatings excel in pipelines that transport oil, gas, and water. The following video explains the process of coating a pipe using FBE coating and 3LP coating.
High temperature and corrosive service, where natural rubber fails.
Butyl Rubber
Used for High-Temperature Corrosive service e.g. Reaction vessels
For Hot and abrasive services
Applications
Chlor-Alkali Plant
Phosphoric Acid Plant
DI water plants
Fluoropolymer Coatings & Linings
Anti-corrosive fluoropolymer coatings offer a blend of high-performance resins and fluoropolymer lubricants. Consisting of a dry film lubricant, fluoropolymer coating generates a smooth, hard, and slick final coating to provide excellent corrosion and chemical resistance.
Advantages of Fluoropolymer Anti-corrosion Coatings & Linings
Anti-corrosion fluoropolymer coatings also provide the following advantages:
Weather-resistant and approved for food and drugs service
Because of so many benefits, the application of fluoropolymer coating is extensive. Typical examples of anti-corrosive fluoropolymer coating and lining are
PFA – PERFLUROALKOXY
FEP – FLUORINATED ETHYLENE PROPYLENE
ETFE – ETHYLENE TETRAFLUOROETHYLENE
ECTFE – ETHYLENE CHLOROTRIFLUORO ETHYLENE
PVDF – POLYVINYLIDENE FLUORIDE
PP – POLYPROPYLENE
Fig. 2: Properties of Fluoropolymers
Advantages of High-Build Coatings
Drastically reduces permeation through the coating and possible corrosion of the metal substrate.
It lowers the metal content of the fluid being handled due to the reduction of permeation, substrate corrosion, and back migration of corrosion products.
Extends the life of the coating when exposed to abrasive media
Thick coatings can be repaired by welding if mechanically damaged. Thin coatings (<20mil) must be stripped and recoated if repairs are not possible.
Thick coatings operate better under pressure-vacuum cycling than thin coatings.
The cost of a thick coating is not directly proportional to its thickness. Longer online performance is achieved at only a small additional cost with high-build coatings. Less maintenance is an important benefit.
No welds exist with a high-build coated vessel in comparison to one that is sheet-lined. Welds in sheet-lined vessels are a known point of failure.
Used in all chemical processes with hazardous, corrosive, abrasive and-or toxic media.
Well-established in the chemical, pharmaceutical, and petrochemical industry
Ideal in any plant because of their good chemical and physical resistance and long lifetime in service.
Absence of sensibility against:
-mechanical impact
-alternating pressure
-vibration
-temperature shock
-aging
Application of High-Build Coatings
Typical applications of anti-corrosion high-build coatings are
Difference Between Coating and Lining: Coatings Vs Linings
Coating and lining are two methods of protecting surfaces from corrosion, erosion, abrasion, and other forms of degradation. The main differences between these methods are:
Purpose: The purpose of the coating is to provide a protective layer on the surface of a substrate, such as metal, concrete, or wood, to prevent it from coming into contact with the environment or the substance being transported through a pipeline. The purpose of lining is to provide a barrier between the substance being transported and the surface of the substrate, to prevent it from reacting with the substrate and causing damage or contamination.
Material: Coatings are typically made of materials such as paint, epoxy, polyurethane, or thermoplastic, while linings are usually made of materials such as rubber, PVC, or fiberglass-reinforced plastic (FRP).
Application: Coatings are usually applied to the surface of a substrate using methods such as spraying, rolling, or brushing. Linings are applied to the interior surface of a substrate using methods such as pouring, spraying, or casting.
Thickness: Coatings are typically thinner than linings and are applied in a single layer, while linings are thicker and may be applied in multiple layers to achieve the desired thickness and strength.
Substrate: Coatings are used on a wide range of substrates, including metal, concrete, wood, and plastics, while linings are primarily used on substrates that are in contact with corrosive or abrasive substances, such as pipelines, tanks, and vessels.
In summary, the main differences between coating and lining are their purpose, material, application method, thickness, and substrate. Coatings provide a protective layer on the surface of a substrate to prevent it from coming into contact with the environment or the substance being transported, while linings provide a barrier between the substance and the surface of the substrate to prevent it from causing damage or contamination.
Other differences between pipe coating and pipelining are
In terms of Thickness:
Coatings – 10 to 1500 microns (0.01 to 1.5mm)
Linings – 3000 to 5000 microns (3 to 5 mm)
The coating can be done from outside and inside but the lining is done only inside the pipe.
Lining in a pipe means a pipe inside a pipe, but the pipe coating is not the same.
Coatings are better than linings for the following:
adhesive forces
vacuum application
heat transfer
thermal shock
Internal Pipe Coating vs External Pipe Coating
The main differences between internal pipe coating and external pipe coating are:
Location: Internal pipe coating is applied on the inside surface of the pipe, while external pipe coating is applied on the outside surface of the pipe.
Purpose: Internal pipe coating is primarily used to protect the inside of the pipe from corrosion, erosion, and abrasion, as well as to improve the flow of fluid or gas. External pipe coating is primarily used to protect the outside of the pipe from corrosion, UV radiation, and physical damage.
Material: The materials used for internal pipe coating are typically different from those used for external pipe coating. Internal pipe coatings are usually made of materials such as epoxy, polyurethane, or polyethylene, while external pipe coatings are typically made of materials such as polyethylene, polyurethane, or coal tar epoxy.
Application: Internal pipe coating is applied using specialized equipment that sprays or brushes the coating onto the interior surface of the pipe, while external pipe coating is typically applied using methods such as brushing, rolling, or spraying.
Thickness: The thickness of internal pipe coating is typically thinner than that of external pipe coating, as it only needs to provide a protective layer to the inside surface of the pipe. External pipe coating may be thicker to provide additional protection against external damage.
In summary, the main differences between internal pipe coating and external pipe coating are their location, purpose, materials, application methods, and thickness. Internal pipe coating is used to protect the inside of the pipe and improve fluid or gas flow, while external pipe coating is used to protect the outside of the pipe from corrosion, UV radiation, and physical damage. The materials used, application methods, and thickness may also differ between these two types of coatings.
Conclusion
The battle against corrosion in steel pipes is ongoing, but with anti-corrosive coatings and linings, industries can gain the upper hand. By implementing the right solution for the specific environment and application, steel pipes can be shielded from the damaging effects of corrosion, leading to prolonged service life, enhanced efficiency, and cost savings. As technology continues to advance, the development of even more effective and sustainable anti-corrosive solutions holds the promise of a corrosion-resistant future for steel pipelines across various industries.
In the process or the power piping industry, many a time several non-standard valves are used for some specific requirements. A few examples of those are Angular Valves, Three-Way valves, Four-way valves, valves with heavy Actuators, etc. This need to be modeled properly to get the actual effect is stress analysis. this article will briefly discuss the modeling of such valves.
Angular Valve With Equal Legs
If the angular valve has equal legs, then it can be modeled using an ordinary valve element. Just put it into a node between two pipes. Pipes can have a different diameter. One half of valve length will be placed through the first pipe direction and one half through another.
Modeling Angular Valve with Equal Legs
Angular Valve With Unequal Legs
If the valve has unequal leg lengths, then it can be modeled using rigid elements. The total weight of rigid elements should be equal to the valve weight. To model temperature expansion the temperature and material should be specified in a rigid element. Also, flanges can be added into end nodes of the valve to check leakage.
Modeling Angular Valve With Unequal Legs
Three-Way Valve
The three-way valve can be modeled just using 3 rigid elements. The total weight of rigid elements should be equal to the valve weight.
Modeling Three Way Valve in Start-Prof
Four-Way Valve
In START-PROF four-way valve can be modeled using 4 rigid elements. The total weight of rigid elements should be equal to the valve weight.
Modeling 4-way Valve in Start-Prof
Valve with Heavy Wheel, Actuator or Actuator Modeling
In START-PROF the heavy wheel or actuator can be modeled as node weight load at the actuator center of gravity. This mass should be connected to the valve using rigid elements with zero weight to consider eccentricity. Proper modeling of actuator eccentricity is especially important for seismic analysis of piping systems because the eccentric mass will produce a great additional torsion and bending moments on the piping system.
In the context of pipe stress analysis in engineering, a “pipe model” refers to the representation of a piping system used for analysis purposes. Pipe stress analysis is crucial in designing and evaluating piping systems to ensure their safety and reliability under various operating conditions.
The pipe model includes the geometric and material properties of the piping components, such as pipes, fittings, valves, and supports. The goal of pipe stress analysis is to assess the effects of external loads, thermal expansion, and other forces on the piping system to ensure that it can withstand these conditions without failure.
Key aspects of a pipe model in pipe stress analysis include:
Geometry: The layout and dimensions of the piping components, including pipe lengths, diameters, bends, branches, and connections.
Material Properties: The material specifications of the pipes and fittings, including information about the modulus of elasticity, thermal expansion coefficients, and other relevant material properties.
Loads and Forces: External loads, such as pressure, temperature changes, weight, and seismic forces, are considered in the analysis. These loads can lead to stresses and deformations in the piping system.
Boundary Conditions: The support and restraint conditions at pipe supports, hangers, and other connection points are modeled to simulate the actual conditions in the field.
Operating Conditions: The range of temperatures, pressures, and other operating conditions that the piping system may experience during its lifecycle.
Pipe stress analysis is typically performed using specialized software that utilizes finite element analysis (FEA) techniques to simulate the behavior of the piping system under various conditions. The analysis helps identify potential issues such as excessive stresses, displacements, and loads that could lead to failure or damage.
It’s important to note that accurate modeling of the piping system is crucial for obtaining reliable results. Engineers use their expertise along with industry standards and guidelines to create realistic pipe models for stress analysis.
The following training video shows how to create a piping model in Piping Stress Analysis Software PASS/START-PROF
Creating Pipe Model in PASS/START-PROF
Technical Bid Evaluation Criteria and Vendor Offer Review
Technical Bid Evaluation or TBE is the organized evaluation and examination process of the vendor’s technical bid documents or proposals from the technical requirement point of view. For all items, a Material Requisition (MR) document is prepared and sent to several vendors stating the requirements for any item on a specific project. Based on availability and experience different Vendors provide their bids or offers. All these offers need to be reviewed before selecting the final vendor. So, Technical Bid Evaluation(TBE) or Vendor Offer Review is an important step before final procurement. This article will provide a sample guide on the general activities to be carried out during Vendor offer review, TBE (Technical Bid Evaluation) & Vendor drawing Review:
The Technical Bid Evaluation basically assesses the technical capability along with the quality, compliance with codes, standards & specifications, experience, operating cost, and performance penalties to meet the project-specific requirement as well as execution capability.
Guide for Vendor Offer Review
The following points are to be checked during the Vendor Offer Review of any item.
Offer to be reviewed with respect to Material Requisition.
The vendor should be listed in the list of Approved Vendors by the Client.
The manufacturer location shall be as per the Approved Vendor List.
Scope & Interface clarity is to be checked.
Vendor to stamp and comply with MR (Material Requisition), Specification & Table of compliance
Technical queries preparation.
Check whether the vendor is taking any Deviation with respect to MR.
Ensure that the Vendor shall comply with all in-house Specifications, Guidelines, Procedures, Work Instructions, and International Code & Standard requirements.
Design Change to be covered as part of TQ (Technical Queries).
Response to Vendor TQ clarification.
Vendor Clarification Meeting, if required.
Close all Technical Queries (TQs) & clarifications.
Guide for Technical Bid Evaluation
While performing technical bid evaluation (TBE), the following points are to be considered.
Compile all vendor offers into one document (excel sheet or some other document).
List down all the requirements of MR& Specifications.
Attach all the Technical Queries, Justification letters, Deviation & Clarification lists.
All vendor deviations are to be approved by the Client.
Delivery time to be mentioned.
Technical Acceptance or Rejection against each vendor is to be mentioned.
Issue TBE for Client Comments & Approval
TBE (Approved for Purchase) is to be issued to procurement for Commercial Acceptance.
After finalization of the Vendor, Purchase Specifications are to be issued to a particular vendor
Guide for Vendor Drawing Review
The following points are to be kept in mind while Reviewing the vendor drawings
Vendor drawing to be reviewed with respect to Purchase Specifications.
Any design change at this stage will be an additional activity for the Vendor which may incur an additional cost.
Drawings are to be reviewed based on technical requirements and to be commented on accordingly.
Normally each organization has its own checklists for vendor drawing review and those are to be followed with close attention to avoid any major mistakes.
Various Types of Equipment for Review
Types of Equipment, Packages & Piping Components that are normally reviewed
Static Equipment for Technical Bid Evaluation
Important static equipment for technical bid evaluation is
Important package items used in the oil & gas industry for the technical bid evaluation process are
Compressor package
Flare package
WTP package
Separator package
Chemical Injection Skids
FMS
Mechanical (Static & Rotating) discipline will be the Lead for Vendor offer review, Technical Bid Evaluation & Vendor drawing review for Static / Rotating equipment & Packages.
Piping will provide inputs to mechanical.
Technical Bid Evaluation for Piping Components
The main piping items used for technical bid evaluation are
Piping will be the Lead for Vendor offer review, Technical Bid Evaluation & Vendor drawing review for Manual valves, Relief valves, and Piping Specialty Items.
Technical Bid Evaluation for Valves
The following steps are followed for the TBE of valves.
Vendor to comply with MR, mandatory requirements.
TQ preparation
Review of TQ response from Vendor.
TQ-2, if any.
Review of vendor deviation, if any.
The vendor should comply & stamp on the table of Compliance.
Pressure Testing requirements to be checked.
Painting requirements are to be marked with respect to line design parameters.
For the Full Bore valve requirement, the Valve ID is to be checked.
Fire Safe Design requirements are to be checked for soft seated valves.
Sample format for Technical Bid Evaluation, Vendor offer Review
Piping Inputs to Vendor Packages for Technical Bid Evaluation
While performing the technical bid evaluation the following inputs are provided from the piping.
Vendor to perform the engineering of interconnecting piping between all internal skids of Package.
The vendor shall perform the stress analysis/ calculation, and other required engineering for interconnecting piping between all skids of the Package (for example GRC Package-LR Compressor, Air Cooler, Sealing, Drums, etc)
The vendor shall provide maximum allowable forces and moments at the interface flanges.
Vendor to provide Piping layout drawings, and Isometrics drawings for all Interconnecting piping between all skids of Package.
The vendor shall comply with the Client/ In-house Piping Specification & Shell Standard Piping Class
Vendor to provide Proper access / Platforms / Ladder for Maintenance and Operation of the GRC Package.
Vendor to comply with all client requirements.
Vendor to comply with the client Specifications, Guidelines, Procedures, Internal Codes & Standards, and requirements as stated in MR.
Location & Available Area for the Packages
Piping Inputs to Static Equipment for Technical Bid Evaluation
Piping loads at supports taken from Equipment Shell / Roof.
Platform Access requirements for top Nozzles
Piping Inputs to Rotating Equipment
Technical Bid Evaluation for Centrifugal Pumps
The following guideline should be satisfied during technical bid evaluation for centrifugal pump selection:
The offered model should be proven and should have been operating satisfactorily for a minimum of 1 year in at least one installation.
The pump should not be selected in case the difference between NPSHA is less than 0.5 meters. NPSH testing must be asked whether the liquid is at/or near its boiling point, the liquid is gas saturated, or wherever NPSHA is less than 3 m.
Pump performance must be corrected for viscous fluids; the performance correction factor given by the vendor should be checked with respect to hydraulic institute standards. An equivalent parameter for water must be mentioned on the datasheet.
In case a low-speed pump is required, a higher-speed pump should not be accepted unless substantiated with plausible technical reasons and operating experience for a similar application.
The pumps required for parallel should have a minimum of 10-20% higher shut-off head than the operating head.
Pump with flat and drooping characteristics towards shut-off should not be selected for parallel operation.
In the case of a single pump operation, the pump minimum flow shall be greater than the flow corresponding to the differential head coinciding with the shut-off head in the drooping characteristics.
In the case of any indigenous pump vendors offering the pump with an inducer, his experience, and technical backup should be checked.
Double volute pumps will be preferred for high-capacity pumps (more than 250 m3/hr) and specifically for applications where continuous part-load operation is envisaged.
Impeller type should conform to that specified in the datasheet, generally open impellers will be preferred for liquid with suspended solids.
Non-standard flanges i,e 1-1/4’’, 2-1/2’’,5’’,7’’, and 9’’ should be provided with companion flanges by the vendor with nuts, bolts, and gaskets.
In the case of large water pumps, suction-specific speed should be calculated at the BEP of the maximum diameter of the impeller. Generally, this should be below 12,000 (US units). Pumps with suction-specific speeds above 12,000 with inducers are only acceptable.
Sundyne pumps with higher specific speeds are acceptable. The vendor should be asked for a reference list for higher specific suction speed pumps. In case the vendor has provided pumps with satisfactory results even with suction specific speed >12000, pumps should be accepted with at least 20% minimum continuous flow of BEP flow.
Flushing piping generally is in SS and in the vendor’s scope of supply. Flushing piping of size less than ½’’ shall not be accepted. Piping with a screwed and threaded connection is not accepted. All the flushing plan piping shall be welded and flanged and terminated with ANSI flanges.
Spring, hardware, and secondary elastomeric of the mechanical seal should be compatible with liquid handled.
In the case of Plan 32 dilution of pumped liquid with flushing, the liquid will take place. The rate of dilution should be obtained from the vendor and should be exceeding the limit specified flow if any.
Cooling/heating fluid quantities must be obtained from vendors. In the case of jacketed pumps where casing, bearings housing, and/or stuffing boxes are required to be jacketed, it should be checked whether the vendor has supplied a pump of similar capacity in jacked construction.
Jacket design/test pressure should be specified in the inquiry.
Material of Construction:
In the case of pumps with special metallurgy, it must be confirmed by the vendor if he has supplied an equivalent model in similar metallurgy.
Any deviation in the material of construction should be brought to notice for acceptance or rejection.
Hardness difference of 50 BHN should be maintained between wear rings. In the case of Austenitic steels, hard-faced wear rings should be asked for.
Heavy-duty base plates wherever absolutely necessary should be taken for pumps conforming to API 610 requirements.
Wherever pumps are expected to start on open discharge valve, motor KW selection shall be as per end of curve KW required. Also, GD2 value starting torque and speed-torque characteristics of the pumps should be asked for all motors rating of pumps starting to open discharge.
Inspection and testing, documentation requirements should be checked according to project specification.
The technical recommendations should be clear and without any open points. Reasons for acceptability/non-acceptability should be clearly indicated.
In the case of vertical pumps, the vertical pumps the installation length of pumps to be asked.
Design and engineering for Interconnecting piping between Fluid Coupling, Flushing Plan, Seal Plan, and Cooler.
Piping Interface flange connections shall be as per ASME B16.5. Confirm nozzle allowable loads shall be 2 times the loads as indicated in Table 5 “External nozzle forces and moments” of API 610.
Technical Bid Evaluation for Metering Pump
These pumps are generally used as dosing pumps. The following major points should be checked while evaluating the offer and making a technical recommendation:
The offer should be not be accepted if the model offered is not developed by the vendor and it is not in operation in at least one installation.
The pumps type i.e. plunger or diaphragm (single, double, sandwich) should be checked as per technical specification. For diaphragm pumps, the vendor should include a diaphragm failure detection device in his scope for double diaphragm pumps.
For very low flow applications (<10 lph), electronic type diaphragm pumps are acceptable. In such cases, motor to be included in vendor scope.
The turndown ratio should be checked. Generally, below 10% rundown, the dosing accuracy of pumps will not be as per API specified limits.
Plunger/piston details such as plunger diameter, stroke length, and strokes per minute should be checked. It should be ensured that the rated capacity furnished by the vendor is correct and matches the quoted volumetric efficiency.
For packed plunger pumps, it is recommended to have strokes per minute less than 100, from a wear and tear point of view. Also, the plunger shall be hardened and the average linear speed at the maximum capacity shall not exceed 1.4 m/s.
Variable-capacity adjustment method shall be checked as per technical specification. If a remote operation is required, the details of the servomotor pneumatic positioned and the operating scheme shall be furnished by the vendor. Instruments groups should be consulted for these schemes.
Specific requirements such as cooling, heating shall be checked as per specification.
NPSHA is to be specified in the pump inquiry specification without considering the acceleration head (based on suction line size and length). NPSHR quoted by a vendor should include acceleration head and same is to be checked from relevant data available in the offer.
Gear and gearbox details should be checked. The gearbox service factor must be at least 1.5 for continuous operation. The manufacturer should be furnished the maximum power rating for the gear. Gears shall be reputed make. The gear ratio should be checked with respect to motor speed.
In the case of a diaphragm pump, the compatibility of diaphragm material shall be checked for suitability of process fluid.
Sandwich-type diaphragm-type pumps, if specified are to be checked for vendor’s reference.
Process side safety valve shall be externally mounted and shall have flanged connections (applies mainly for plunger type).
Externally mounted safety valves should be supplied from approved vendors only.
Technical Bid Evaluation for Centrifugal Compressor
Check deviations furnished by vendors (from specified standards) if the deviations are acceptable or not.
Performance curve should be available and should include the following information:
Capacity at surge limit
Capacity at the choke point
Power versus capacity pressure versus curves.
Check that offered model is a developed model and has been working for a minimum of two years.
Check that the compressor manufacturer has guaranteed pressure at the battery limit specified in the specifications
Generally, the surge limit should be below 75% of the specified rated capacity, and the choke point must not be near the operating point. Also, check the surge limit at the minimum supply frequency of the electric motor.
Check the tip speed and Mach number for all the stages. It is preferred to have lower Mach nos. as it gives better efficiency.
Ensure that critical speeds furnished by vendors are a minimum of 30% away from the operating speed. In the case of turbine drive, any critical speed should not be close to the speed trip value of the turbine.
Bearings should be tilting pads. Hydrodynamic thrust bearings should be suitable for thrust in both directions.
Gear’s and couplings should be spacer type. Couplings and gears should be suitable for higher speed (due to an increase in frequency in case of electrical motor drive and up to trip speed for turbine drive) as required in the specification (Minimum service factor 1.4 for motors drive and 1.6 for turbine drives).
The oil system should conform to API 614 requirements, if not specified. It is generally preferred to have the same capacity as Main oil/Aux.oil/Emergency oil pumps. Oil piping downstream of filters should be SS. Oil pumps should preferably be positive displacement screw pumps.
The cooler should be a removable bundle; water through tube design, conforming to ASME Sec VIII, TEMA ‘C’, and with auto drain traps (for air coolers). Coolers tubes should be a minimum of 19″ OD, 18BWG; waterside fouling factor should be as per design basis with water velocity which should be 1.5-1.8 m/s
Heat loads and surface area available for Heat Exchangers should be obtained from vendors. The coolers should be provided with 10% excess area. The quantity of cooling water required should be checked from heat loads given by vendors.
All major rotating parts should be dynamically balanced. Balancing speed and procedure should be obtained from vendors for records and review.
Guaranteed vibrations should be within limits as per API standards.
The entire single-stage compressor should be preferably provided with inlet guide vanes. IGV is effective only at part load operations. The effect of IGV on multistage compressors is very small, hence, to compare power consumption at part loads, capacity vs. power curves should be obtained for compressors with and without guide vanes. The selection of guide vanes for multistage compressors should be based on techno-commercial considerations.
For all process compressors where leakage of a medium cannot be allowed to lead into the atmosphere, positive sealing should be provided by the vendor.
Controls and protection provided by the vendors must be as per requirements specified in datasheets.
During deciding on motor rating following points should be considered,
Highest supply frequency to the electric motor. Ask the vendor to furnish the performance curve at the highest supply frequency.
Power consumption at the lowest inlet temperature.
Power consumption at worst gas compression (in case of varying composition of gas constituents).
Technical Bid Evaluation for Flare System
A flare system package normally comprises of flare stack with flare tip and molecular seal, water seal drum, and knock-out drum. The following point needs to be checked for preparing a technical recommendation.
Plants may have a normal (corresponding to continuous venting) and a peak load (corresponding to emergency venting) for flares. These may be with wide variations as regards to the capacity. In such cases possibility of using different flare tips for these two loads should be considered also.
Calculations should be obtained from the vendor for the height of the stack. Along with heat radiation, the ground-level concentration of toxic gaseous effluents needs to be considered for this calculation. These calculations should be checked against both Vol. I Ch 13/API RP-521.
Between the flare tips and the molecular seal, there are 2-3 temperature zones. The design temperatures of the material and therefore the material changes accordingly. The length of zones should be obtained from the vendor.
It should be checked no refractory material is used for the flare tip.
If the vendor is supplying material for the flare tip that is different from the one specified, the design temperature for the material should be obtained from the vendor and compared with the required value.
Molecular seal or velocity seal designs should be checked carefully.
It is recommended to include the supporting structure in the vendor scope.
The ignition panel should be forced draft type (using plant air) with electric spark ignition. The natural draft should not be accepted. The air/Fuel ratio for a pilot burner for alternate fuels should be asked from the vendor.
Smokeless capacity is normally specified for the greater of the following loads:
Normal load
10% of maximum load.
However, check project-specific also.
Water seal height should be checked for minimum back pressure in the flare header to avoid the seal from breaking (API RP-521).
If the knock-out drum is in the vendor’s scope, sizing details of the knock-out drum should be obtained from the vendor. The basis of sizing should be normally be specified in the inquiry. 5-10% consideration in the flare header can be assumed as a basis.
Providing adequate clearances and access to process equipment, valves, and instruments are of utmost importance for the proper maintenance, operation, and safety of any plant. This present article can be used as a guideline for the preparation of plot plans and equipment layouts for various process plants, offsite, and utilities. This article covers general requirements for on-shore plant layout of process units, equipment, and general facilities, utility plant, and offsite areas. It gives basic considerations for plant clearances and access, equipment elevation, paving, grading, sewers, and other related items.
Plant Clearances and access for the operation and maintenance of proprietary equipment shall be in accordance with the manufacturer’s or equipment vendor’s drawings/operating guidelines or manual.
Considerations during Plant Layout Design
While designing the plant layout, the following guidelines need to be considered.
Process units and other facilities shall be integrated within a common plant area only where independent operation and shutdown for planned maintenance of different facilities are not required.
Where the process units and other facilities need to be separated from each other from an operations and maintenance point of view, they shall be located at sufficient distances apart from each other with separating spaces or roads. These shall be interconnected by pipe racks/pipe sleepers. It shall be noted that most of the time, these separating distances are governed by statutory / insurance rules.
Layout and design shall be based on, and provide access for, maximum use of specific mobile equipment for normal planned maintenance work.
Access ways for mobile handling equipment shall be normally 6m wide with 6m overhead clearance. Overhead clearances shall be finalized only after ascertaining the type of mobile equipment proposed to be used in the plant.
Where inaccessible to mobile maintenance equipment, facilities such as davits and trolley beams shall be provided. Proper passages shall be planned for the movement of equipment to the workshop for carrying out repairs and for the provision of maintenance space.
The plant layouts shall take into account the requirement of turning radii of mobile equipment and tanker lorries etc. Road-turning radii shall be suitable for the movement of proposed mobile equipment and tanker, lorries on the plant roads.
It is essential that the layouts meet statutory and insurance requirements as well as other requirements noted therein.
Typical Plant Layout Design
Plant Clearance and Access Consideration for proper Accessibility
Proper Access shall be provided to equipment, valves, and instruments requiring operational control or normal maintenance during plant operation, by operating passages or elevated walkways, platforms, and permanent ladders.
Main operating or service levels are defined, as those areas during plant operation requiring plant personnel to be normally or intermittently present for substantial periods of time.
Stairways shall be provided as a primary means of access to main operating or service levels in structures, buildings, or furnaces. Cage ladders are not acceptable as the primary means of access.
Storage tanks shall also be provided with stairways where tank heights are more than approximately 6 m. It is preferred to provide independent staircases for lined storage tanks.
Auxiliary service platforms are defined as those areas which, during plant operation do not require the presence of plant personnel except for short periods of time.
Primary access to platforms attached to vessels, auxiliary service platforms in structures, furnaces, and storage tanks for platforms up to approximately 6 m (20 ft) high, shall be by vertical cage ladders.
Auxiliary exists from platforms shall be by means of ladders. Such exists shall be required when platforms are longer than 7.5 m and shall be located so that no point on an operating platform is horizontally more than 22.5 m from a primary or auxiliary exit. The dead-end length of a platform shall not be greater than 7.5 m.
The vertical rise of any stairway shall not exceed 4.5 m in a single flight at a maximum angle of 40° and shall provide a minimum clear headroom of 2.1 m.
The vertical rise of ladders shall not exceed 5 m for a single run. Ladders that are located or extended more than 2.25 m above grade shall be provided with safety cages. Ladders that rise more than 5 m shall have an intermediate rest platform.
For equipment requiring operational control or normal maintenance during plant operation:-
Platforms or ladder access not less than those specified herein shall be furnished for equipment, located more than 3.6 m above grade and 2.1 m above another platform and include the following means of access:
Where regular access is required, a minimum clear aisle width of 0.75 m and overhead clearance of 2.3 m shall be provided.
Groups of valves at battery limits in elevated pipe racks and grade pipe sleepers shall be provided with permanent platform access. The type of valves (gate, plug, ball, etc.) shall be taken into account when locating such platforms.
Exceptions: Flanged nozzles on vessels, block valves in pipe racks (not requiring operation except for infrequent isolation) metal temperature measuring points in piping, and orifice flanges in lower pipe racks shall NOT be provided with permanent means of access.
Elevated platforms shall have sufficient space as defined herein for maintaining equipment; tall columns shall be provided with davits for removing covers, relief valves, blinds, etc. and the same shall be located such that these can be lowered safely to ground level.
Plant Layout Design Rules for Manual operation of valves
Valves requiring operation during plant operation or in an emergency shall be located as follows, otherwise, such valves shall be equipped with chain operators or extension stems:
Horizontally installed valves 6″ (150 mm) and smaller – the bottom of the handwheel shall not be higher than 2.25 m or the maximum height to the centerline of the handwheel shall be 2.3 m above grade or platform, whichever governs.
Horizontally installed valves 8″ (200 mm) and larger – maximum height to the centerline of the handwheel shall be 1.95m.
The preferred height to the centerline of all valves shall be 1.5 m above grade or platform.
Horizontally installed wrench-operated plug, ball, or butterfly valves shall be positioned so that the wrench movement arc is no higher than 2.3 m above the grade or platform.
Equipment Clearance and Access Guidelines
Layout and Safety Design Rules for Furnaces and Fired Heaters
Several furnaces in the same or different services and part of the same process unit or facility, together with associated close-coupled equipment, may be located in a single area and shall be segregated within that area only as required for operational and maintenance requirements.
To avoid a hazard, a furnace and close coupled equipment or a furnace area shall be located not less than 15m and preferably upwind (prevailing) from other equipment containing flammable fluids, except as follows :
The distance shall be measured from the outside of the nearest of furnace walls to the nearest point of the equipment considered.
Not less than 15 m from air coolers, containing flammable fluids.
Gas or liquid reforming furnaces, as used in ammonia and similar plants, may be located at a minimum distance from associated process equipment consistent with operating design and maintenance requirements.
Reforming and desulphurizing furnaces may be located at a minimum distance from their reactors and feed/effluent exchangers, consistent with operating and maintenance requirements.
Not less than 15m from switch rooms, un-pressurized control houses, and the compressor or pump house containing equipment in hydrocarbon service. These distance requirements shall generally be governed by statutory / TAC regulations.
Furnaces shall be located at a maximum practical distance from process equipment containing liquefied petroleum gas or similar materials in accordance with applicable Tariff Advisory Committee (TAC) rules with a minimum distance of 15 m.
Integral-type fired heaters such as start-up heaters shall be considered exceptions.
Fired furnaces of the following types that are used only for planned intermittent and start-up service may be located at a minimum practical distance from the equipment which they serve and not less than 6 m from other equipment, including air coolers containing flammable fluids.
Furnaces having welded coils and no header boxes.
Furnaces with header boxes facing away from other equipment.
Vertical cylindrical furnaces.
Areas for tube pulling shall be as shown on the plot plan and may extend over roads that are peripheral to the unit and not required for access to other plot areas.
Furnaces shall be provided with platforms for operation and access as follows:-
Platforms for maintenance of soot blowers and dampers.
Platforms for burner operation when inaccessible from grade or in accordance with client requirements.
Platforms for access / observation doors except that when the doors are located less than 3.6 m above grade or another platform, access shall be by ladder only.
Platforms for header boxes containing removable plug fittings.
Platforms for decoking / swing elbow connections.
Plant Clearance and Access Considerations for Heat Exchangers, Air Coolers & Cooling Towers
Shell and tube heat exchangers at gradeshall generally not be stacked more than two units high, with a maximum bundle weight of ten tonnes.
Permanent steel or reinforced concrete structures with monorail beams shall be provided for supporting bundles during pulling and lowering to grade if any of the following conditions apply :
When specified available mobile equipment is not suitable.
Shells stacked more than two units high.
For Shell centreline, more than 3.6 m above grade and Bundle weight exceeds ten tonnes
Platforms shall only be supplied where required for operation.
Although platforms shall not be provided for access to exchanger’s heads, the layout shall be arranged to facilitate maintenance.
Bundle removal of elevated air coolers may be over adjacent equipment where suitable cranes are available, otherwise, crane accessways shall be provided for removing bundles.
Access shall be provided for the maintenance of fan drives and headers as appropriate.
Proprietary plate type, double pipe, or multiple heat exchangers installed at grade will not be provided with handling or tube pulling facilities.
Air-cooled exchangers may be located at a grade above other equipment or structures, or above overhead pipe racks, subject to the effects of other equipment or structures on air cooler performance and as stated in the below paragraph
Air-cooled exchangers containing flammable fluids shall NOT be installed directly above control rooms, MCC rooms, transformers, and other major switchgear.
Water sprays shall be provided over equipment in the following services located directly beneath air-cooled air exchangers containing flammable fluids.
Pumps handling flammable fluids with an operating temperature above the auto-ignition temperature or 260°C (560°F) whichever is less or,
Pumps handling light hydrocarbons with a vapor pressure greater than 3.5 kg/cm² at 38°C (100°F) or with a discharge pressure in excess of 35 kg/cm² or
Compressors in flammable vapor service.
Equipment adjacent to cooling towers should be located at a sufficient distance downwind as determined by each season’s prevailing winds from cooling towers, to minimize detrimental effects during fog-creating seasons.
The location of cooling towers with respect to roads should be considered carefully as the fog created under certain conditions of temperature and humidity presents a serious driving hazard. If necessary, roads should be provided on both sides of critically located cooling towers; public highways should be located at min. 45 m from cooling towers.
Reactors, Towers, and Vessels: Monorail beams shall be provided for charging reactors only when the use of a crane is not feasible.
Design Rules for Structure Clearance and Access
Ladders shall generally be arranged for the side exit. Step-through ladders may be used for runs from grade up to a height of approximately 6 m or for elevated runs of approximately 3 m.
Where ladders are not provided for access between platforms, intermediate steps shall be provided where the difference in elevation is more than 0.35 m.
Handrailing shall enclose all stairways and platform areas where the clearance between the equipment and the edges of flooring is greater than 0.3 m. Toe plates only shall be provided around floor openings for permanent equipment where the clearance to the edge of the flooring is greater than 50 mm but less than 0.3 m. Handrails shall be provided at the periphery of tank roofs adjacent to access stairways and dip hatches.
Sheds for pumps, compressors, and other equipment, if provided, shall be as follows.
Where compressor sheds (or utility sheds) are provided they shall be open-sided steel frame structures, sheeted from roof eaves level down to a maximum height of 2.45 m above the compressor house floor level, with ventilation by means of natural draught.
Where pump or equipment sheds are provided they shall be steel framed with sheeting as described in (a) above.
Compressor houses shall be provided with suitable facilities for handling the heaviest machine component during normal maintenance including the following (but excluding motor drivers):-
A laydown area and suitable road access for this area shall be provided adjacent to the compressor house.
The compressor house ground floor shall be designed to carry the internal parts of the machines, but not the top halves of casings, during maintenance.
The design of structures containing equipment shall not provide for the removal of equipment, not considered a normal maintenance requirement, except as follows :
To provide access to mobile equipment.
To provide clearance within the structure
To provide for the removal of sections of the structure where specified.
Facilities for breakdown maintenance of vital equipment, the failure of which would seriously affect plant certification and/or production, e.g. Standby Generators / Power units.
Layout rules for Pumps and Compressors
Where permitted by the equipment design, the provision shall be made to allow the removal of the pump internals or driver without dismantling the piping or removing the isolation valves. For this purpose, a flanged spool piece or strainer on the pump nozzle shall be considered satisfactory.
Pump isolation valves shall be located in the pump area as close as feasible to the pump and operable from grade. Valve hand wheels shall be oriented to leave clearance over a pump for maintenance and to permit operation without leaning over the pump.
Pump / Compressor isolation valves shall be located near the equipment in such a fashion that no excessive loads are transferred to the Pump / Compressor nozzles.
In general, the drive ends of groups of similar pumps in process and utility plant areas shall line up. In offsite areas, the pump ends of the plinths of groups of pumps shall line up. Large pumps may be orientated parallel to a pipe rack or passage.
The alignment bellows for pumps shall not be mounted directly on pump nozzles. A flanged spool piece of sufficient length shall be installed and anchored between pump nozzles and the bellows.
Clearance and Spacing Rules for Buildings
Where practicable, central control rooms, MCC rooms, and substations shall serve several process units, utility plant, and offsite facility areas. Suitable isolation of utility supply shall be provided where required.
However, where impracticable, or as per the client’s operating philosophy, separate control/MCC rooms may be provided for utility and offsite areas.
Control rooms and switch rooms shall be located as follows:-
In an area which shall be at a safe distance from the nearest normal source of flammable hazard (Safe distance as per statutory or TAC rules) or,
When not located in a safe area shall be of pressurized design with the top of the air intake stack located in a safe area. In such cases, the construction may have to be blast-proof.
Design rules for Piping
In general, process lines, utility headers, and instrument and electrical cables in process and utility plant areas shall be routed on overhead pipe racks at established elevations and in offsite areas on pipe sleepers at grade level.
In general, lines to equipment in process and utility plant areas will be run overhead of maintenance and operating passages. However, short runs of pump suction and similar lines may be run at grade level where they do not obstruct maintenance access. Where the crossing of general walkways is unavoidable, walkover platforms shall be provided.
Offsite pipe racks/sleepers shall normally be located adjacent to storage tank dykes and roads.
Within dyked areas, lines shall be run by the most direct route, as limited by flexibility and tank settlement. Lines at grade serving tanks in a dyked area shall not pass through adjoining dyked areas.
Insulated lines passing through dykes shall be enclosed in sealed sleeves, and uninsulated lines shall be coated and wrapped. Insulated lines under road crossings, and all pressure lines beneath railroad crossings, shall be enclosed in sleeves unless they are run in culverts.
When located below grade, piping provided with protective heating and piping and services requiring inspection and servicing shall be in built-up trenches.
Cooling, potable, fire service, and similar water piping, shall generally be buried with the centerline of the pipe below the frost line, or be provided with means to prevent freezing.
Buried piping shall be provided with a protective covering of at least 0.3 m. In cases where heavy load traffic is expected, the minimum coverage may be 1.0 m with/without higher than the normal thickness of piping.
At all changes in direction piping requiring frequent (at least once a week) cleaning shall be provided with flanged fittings or with five diameters (minimum) bends. The run of pipe between flanged cleanout points shall be limited to 12 m for cleaning from one end, and 24 m for cleaning from both ends.
Lines that require occasional cleaning shall be provided with sufficient breakout flanges for dismantling.
Piping from pressure-relieving devices such as safety valves that discharge to a closed system shall generally be arranged to drain to headers without pocketing of lines and accumulation of condensates at the safety valves.
The flare headers outside process unit areas shall be elevated and self-draining to the flare knockout drum. Flare auxiliaries, such as the ignitor station and steam injection control valve, shall be located near the drum. The line between the flare and the drum shall drain to the drum.
Where practicable piping shall be designed to accommodate expansion without using such devices, such as expansion bellows, cold springing, etc. Line spacing may be based on anticipated line movements under normal operating conditions, if practicable.
Rules regarding Height for Atmospheric Discharge
The top of stacks and continuously operating vents discharging hazardous vapors shall be at least 3 m above any platform or flat building roof, within a horizontal radius of 21 m from the stack or vent. This vertical clearance may be reduced by the same distance that a platform or building roof exceeds 21 m. However, the height shall be governed by State Pollution Control Board regulations and the HAZOP/hazard studies.
The top of the outlet piping from relief valves and intermittent vents discharging hazardous vapors to the atmosphere shall be at least 3 m above any platform of a flat building roof within a radius of 15 m. This vertical clearance may be reduced by the same distance that a platform or roof exceeds is 15 m from the outlet piping.
The discharge of steam, air, or similar non-flammable vapors from relief valves and continuously operating vents, shall be located to prevent any hazard to personnel.
Minor vents, controlled by an operator, may discharge to the atmosphere local to the equipment vented subject to restrictions as noted above.
Guidelines for Flares
The location of flares shall be determined in accordance with client requirements, and vendor recommendations and in reference to the limitations of the ‘Guide for Pressure Relief and Depressurising Systems’ – API – RP.521.
It is desirable that the flare shall be positioned upwind of process units and tankages, to reduce risks of ignition of possible vapor leaks.
The safety zone around the flare stack shall be decided based on an acceptable radiation level at grade. This zone shall be isolated by means of a fence.
Design Rules for Maintenance and Equipment Handling
Handling facilities shall be limited to the handling of working parts of equipment that require frequent or routine service and which are inaccessible to the handling facilities assumed to be available at the plant. Such facilities shall not be designed to handle heavy parts which normally are unaffected, such as the bedplates of rotating machines, rotating equipment, the bodies of compressors, machinery, frames, etc.
Special consideration must be made where major machines are involved (e.g. multi-case compressor trains) where heavy lifts are likely and laydown areas are required. Clear passages to workers are also required in such cases.
The design and installation of monorail beams, overhead traveling cranes, and hoist trestles shall be based on lifting the parts to be handled and transporting them or lowering them to specified maintenance areas or to grade. From these points, they are expected to be removed by skids or hand trucks to other areas which are more suitable for maintenance.
Requirements for Paving, Surfacing, and Grading
Paving shall be provided as shown on the plot plan. Walkways to buildings only and the following areas shall be paved subject to client’s discussions, on a contract-to-contract basis.
The areas below bottom oil-fired or combustible liquid-containing furnaces and under elevated structures support coke drums or catalyst-containing vessels.
The areas around groups of two or more pumps are located outdoors, extending approximately 1.2 m beyond the pump foundations with bunds on all sides.
The areas around process equipment :
Drainage facilities shall be provided to recover spilled materials or drain to the chemical/effluent system.
The areas around rail and road loading installations, additive and metering facilities, extending approximately 1.2 m around the facility with bund on all sides.
Areas below pressurized spheres and bullets.
Curbs, when required to retain spilled materials, shall normally extend from the bottom of the paving to a height sufficient to contain the full contents of the largest atmospheric tank in the area. Concrete surfaces normally exposed to acids or similar corrosive materials shall be provided with protective coatings such as acid/alkali-resistant tiling.
All paving shall be sloped towards drainage points, the minimum slope shall be 1 in 125 and the maximum fall shall be 150 mm, except for floors of control rooms, operator houses, and MCC room which shall be laid level. High points of paving shall generally be coincident with the finished floor elevation applicable to the area under consideration.
The type and surfacing of roads and access ways for maintenance vehicles access shall be as shown on the plot plan.
Unpaved areas within the battery limits of utility plant and process unit areas, administration and parking areas, shall be graded and surfaced with a minimum of 50 mm of gravel, crushed stone, or other suitable material.
Offsite areas such as tank farms inside bund walls, pipe racks, and areas alongside roads, will not normally be surfaced except where required for maintenance or as specified in statutory regulations.
Finished grade elevation of different plant areas or within the battery limits of an area, may be varied and established to permit adequate drainage.
Roads shall be ramped over piping at the intersection with grade-level pipe sleepers, if possible. If not, suitable culverts shall be provided for the passage of pipes.
Design Considerations for Pipe Trenches and Pits
In general, pipe trenches shall have concrete or brick side walls, open tops covered with grating or plate, and bottoms surfaced with crushed stone.
Paving with acid-resistant titles shall be furnished in acid or similar corrosive services, and shall be sloped for drainage, with a drainage sump at the lowest point.
The following items shall be considered :
Firestops shall be provided where trenches cross-unit battery limits, or to maintain separate areas, such as totally enclosed buildings, furnaces, or grouped equipment.
Pipe trenches located near fired heaters or any sources of ignition shall be backfilled with sand and be provided with sealed covers.
The minimum width of pipe trenches shall be 450 mm. A minimum clearance of 100 mm shall be provided between the outside of the pipe, flange or insulation, and walls, and 50 mm to the high point trenches bottoms.
Pipe trenches in paved areas shall be covered with plate or grating set flush with the top of the paving, and in unpaved areas shall be covered with a steel plate set 50 mm above the high point of adjacent grade. Trenches inside buildings shall be covered with MS / CI grating set flush with the floor. Trenches subject to vehicle traffic shall be provided with removable reinforced concrete covers set flush with the surface.
Where provided, pits shall have concrete/brick walls. Floor surfacing of pits shall be concrete. Pits shall have a sump for the collection of drainage. The pit floor shall slope towards the sump.
Access to pits shall be by ladders or ladder rungs cast into the walls. Stairways shall be provided for pits containing equipment such as vessels, pumps, and exchangers. Auxiliary exit ladders shall be provided if any point on the pit floor is more than 7.5 m from a main or auxiliary exit.
Open pits shall be provided with handrailing and 150 mm high curbs above the grade level.
Closed pits shall be provided with suitable removable covers set flush with paving in paved areas or 50 mm above grade in unpaved areas. Sealed covers, with a vent, piped to a safe location shall be provided for pits located near fired furnaces or similar sources of ignition.
