Start-Prof can estimate the support loads and stresses caused by slug flow loads using the static method.
Additional dynamic loads caused by the slugs hitting the bends and tees must be considered. It can lead to the dropping of piping from the supports, exceeding the allowable nozzle and pump loads, etc.
One of the methods for calculating the effect of slug flow loads is the static method. Vertical, horizontal, and resultant forces F can be determined by the formulas:
where
θ – bend angle (90 degrees, 45 degrees, etc.) ρ – fluid density v – slug velocity at the moment then it hits the bend A – internal pipe cross-section area DLF – dynamic load factor. For the static method recommended value is DLF=2 For straight tees load is calculated the same as for a 90-degree bend. Calculated forces should be applied to the bends that the slug heats step by step.
A=p∙(D-2t)²/4 = 3.14159∙(0.219-2∙0.016)²/4 = 0.027465 m² Loads on bend 2 will be: F=DLF*ρ*v*v*A*(1-cos 90)=2*0.001*40*40*274.65*(1-cos 90)=8790 N=879 kgf F=2*1000*12.65*12.65*0.027465*sin 90=8790 N=879 kgf Loads on bend 3 will be: F=DLF*ρ*v*v*A*(1-cos 90)=2*1000*12.65*12.65*0.027465*(1-cos 90)=8790 N=879 kgf F=2*1000*12.65*12.65*0.027465*sin 90=8790 N=879 kgf Loads on the bend 4: F=DLF*ρ*v*v*A*(1-cos 60)=2*1000*12.65*12.65*0.027465*(1-0.5)=4390 N=439 kgf F=2*1000*12.65*12.65*0.027465*sin 60=7610 N=761 kgf The smaller the angle of the bend, the less the load on the bend, because the direction change angle of the slug is smaller.
Using operation mode editor we should create one main operating mode (1) and three additional modes that will model slug loads on bends 2,3,4 (1.1, 1.2, 1.3). The mode type should be occasional.
In the picture below three load modes are shown:
To apply loads we should add an additional node near bend 2 and apply calculated loads:
The same for bend 3:
And for bend 4:
Piping stress caused by slug impact at the bend 3:
Support loads caused by slug impact at the bend 3:
In order to prevent the piping from falling from the supports, reduce the support loads, and reduce the stresses, you need:
Add limit supports (limit stop supports with a gap, sway brace, and snubber), that will take the huge dynamic loads
Stress Analysis of Buried or Underground piping seems to be difficult for many stress engineers due to the complex soil-pipe interaction. But the software Caesar II easily handles that part. In this article, we will learn the various buried piping analysis methods that are available in Caesar II. The points that will be covered in this article are:
The various analysis method of Underground piping
Overview of Soil Classification
Discuss the current practice of Underground pipe modeling & analysis
Examine the data inputs for buried piping and pipeline stress analysis
Make a suggestion for sound input data, especially where information is not known or available
Learn the inputs, generate some results & conclusions
Fig. 1 below provides the soil classification for the most basic soil types used for underground piping stress analysis.
The most basic classification of soil is based on grain size.
Soils with large grains are called “gravel” and soils with small grains are “sand”.
Internationally it is defined that sand contains grains larger than 0.063 mm and smaller than 2 mm.
Gravel contains grains with sizes between 2 mm and 63 mm.
Grains smaller than 0.063 mm are called “silt”.
Grains smaller than 0.002 mm are called “clay”.
Fig. 1: Soil Classification
Shear Stress in Soils
The ability to resist shear stresses depends on friction and cohesion.
When cohesionless soils are poured to the ground from above they will spread due to gravity. Because of friction, the area of spread is limited creating an angle of repose (φ) at the balanced state.
From this experiment, the friction force that resists the shear loads may be calculated and the internal friction coefficient (µ) of the soil may be determined:
f = µ ⋅n = µ ⋅w⋅cosϕ —-where f=wsinϕ
µ = tanϕ
The friction resistance (s) of any soil in any plane is then expressed as Sliding force ( s ) + Cohesion ( c )
s = n⋅tan(ϕ) + c
The angle (φ) is also called the soil angle of internal friction.
Axial Soil Resistance
Frictional Force on the Top of the Pipe and at the Bottom Of the pipe are different
In the case of an idealized model the axial resistance (f) can be determined by the following expression:
Fig. 2: Axial Soil Resistance equations
Lateral Soil Resistance
Lateral Soil Resistance is divided into 3 parts viz. Upward, Downward and Sideways
Upward Resistance (Fig. 3):
Upward soil resistance can be described by the application of the “soil prism theory” also known as “Marston’s load theory”! This theory states that the soil resistance is determined by (a) the weight of a soil prism above the pipe and (b) the shear forces exerted on either side of the prism. ! The shear conditions depend on the installation layout of the pipe and soil, but in this case, negative shear will be assumed. ! Next to the soil prism, the weight of the pipe needs to be taken into consideration as well.
Shear stresses can be found by integrating the friction along both side surfaces of the prism.
Let’s assume cohesionless soil (c=0, e.g. sand); ϕ is the friction angle of the soil.
q = ρDH + 2H (c + 0.5 ρ H Ka tanФ) + Wpipe = ρDH + ρH2 Ka tanФ
Downward Resistance (Fig. 3):
When the pipe moves downwards the soil resistance can be determined from the “vertical bearing capacity”.
Detailed geotechnical evaluation is required to determine the vertical bearing capacity.
For a general idea, the downward resistance can be roughly estimated to be as twice the horizontal resistance. ! The vertical bearing capacity is the vertical load required to break the soil underneath the pipe over the full width of the pipe.
Horizontal Resistance (Fig. 3):
When a pipe moves horizontally, it experiences
Passive Force from Front
Active Force from Back
Active force is ineffective as the pipe moves and a void is created.
qh = ½* ρ (H+D)2 tan2 (45 + Ф/2)
For cohesive soil (clay) ф = 0, hence less resistance
Fig. 3: Upward, Downward and Horizontal Resistance
How Caesar II models soil?
Soil is modeled as a ‘Bilinear Spring’ having ‘initial stiffness, ultimate load, and Yield Stiffness’
Ultimate load: Maximum load on the soil beyond which load does not increase but displacement can.
Ultimate loads are different in axial, lateral, and vertical directions
Modeling Soils in Caesar II
Caesar II simulates the soil surrounding the pipeline using springs of varying stiffness as shown in Fig. 4.
Fig. 4: Modeling Soils in Caesar II
About CII Buried Pipe Modeler
Refer Fig. 5
Fig. 5: Underground modeling in Caesar II
CAESAR-II Basic method by LC Peng
Fig. 6: Caesar II Basic Buried Model
American Lifelines Alliance-ALA
Fig. 7: Caesar II American Lifeline Alliance Buried Model
ALA method with 31J
B31J provides a set of calculations for revised SIFs and flexibility factors, as defined in the upcoming revision to ASME B31J. By using these revised SIFs and flexibilities, your stress analyses produce more accurate results. B31J provides the “more applicable data” referenced in recent editions of the piping codes.
Result Comparison with Various method:
Fig. 8: Caesar II Results Comparison for the same model
Conclusions
Results obtained by ALA Method are more reliable
ALA considers more variables based on published data
Better method if the soil is changing through the run
Peng’s Method gives a very good understanding of the subject and gives quick results for non-critical
If the buried pipe is modeled just as a reference in the Above ground Piping Analysis then suggested going for the ‘CAESAR II Basic Model’
For Pipeline analysis use ‘ALA Method with user-defined stiffness input
You can attend an online course on buried/underground pipe/pipeline stress analysis that covers the underground pipe stress analysis details using a practical case study by clicking here.
Author: This presentation is prepared by Mr. Deepak Sethia who is working in ImageGrafix Software FZCO, the Hexagon CAS Global Network Partner in the Middle East and Egypt. He has extensive experience in using Caesar II and PV Elite software and troubleshooting.
This article is intended to serve as a guide in the development of equipment layout and piping layout for centrifugal compressors and their associated equipment, with the goal of producing safe, operable, economical, and maintainable installations.
Compressors are machines, which are used to increase the pressure of a gas by mechanically reducing its volume within the compressor casing.
Compressor Types
Positive Displacement Compressors
Reciprocating compressor
Screw Compressors
Centrifugal compressors
Pipeline compressors
Type of Compressor Drives
Following are the various types of Compressor drives:
Electric Motor Drives
AC Squirrel Cage Induction Motor
Synchronous AC Motor
Gas Turbines
Steam Turbines
Variable Speed Drives
Variable Frequency Drive
Variable speed (Hydraulic Coupling) Drives
Auxiliary Equipment’s
Lube Oil Cooler (Supplied by Compressor Vendor)
Lube Oil / Seal Oil Console (Supplied by Compressor Vendor)
Surface Condenser
Condensate Pump
Inlet Air Filters (Supplied by Compressor Vendor)
Suction Scrubber (Upstream of Compressor)
Air Cooler (Downstream of Compressor)
Discharge Scrubber (Downstream of Air Cooler)
Compressor Layout
When locating compressors, consideration must be given to accessibility, maintenance, and loss prevention requirements.
There must be a Vehicular (Crane / Fork Lift Truck) Access-way on at least one side of the installation. Refer Fig. 1
Fig. 1: Figure showing the requirement of Crane Access
A compressor is generally located inside Shed with the provision of a Mono-Rail or EOT Crane for Maintenance. The capacity of the crane is to be decided based on 150% of the highest weight of the component to be lifted. To be checked with the compressor vendor.
A compressor can be installed in a Series and Parallel arrangement.
The minimum Distance between two Adjacent Compressors shall be 10m.
Generally, Compressors are Grade Mounted (Fig. 2). But Process criteria/requirements will decide if it should be grade mounted or elevated
Fig. 2: Grade-mounted Centrifugal Compressor
Compressor Piping Layout
Suction & Discharge Piping (Fig. 3)
Compressor Suction Piping Shall be as Short as Possible.
Compressor Suction Piping should have Inlet Filter / Strainer. It can be Temporary or Permanent
Suction Piping should be sloping/free draining towards Inlet Scrubber
Suction lines require a minimum straight run of piping upstream of the suction nozzle which varies between 3 and 8 times the normal pipe size. (Vendor requirement)
All operating valves must be readily accessible, preferably from grade.
All lines to the Compressor shall be provided with break-up flanges for Maintenance.
Compressor Suction Line Flowmeter: Suction routing shall be such that Upstream and Downstream straight lengths shall be sufficient for the performance of the Flowmeter
Anti-Surge Valve Is Designed and Supplied by Compressor Vendor.
Input to Compressor Vendor for Designing / Sizing the Anti-Surge Valve is given by piping, by providing suction and discharge length.
Anti-Surge Valve is located on the Anti-Surge line which is basically a by-pass / recirculation line between Compressor Suction and Discharge Piping for Surge control
Anti-Surge Valve shall be located at Highest Point and shall be free draining on both side
Lube Oil Cooler & Piping (Fig. 4)
Lube Oil Cooler Shall be Accessible from Road.
Lube Oil Cooler Shall be located as close to Compressor as Possible.
Lube Oil Cooler Piping Should Not Interfere with Access and Maintenance space.
Lube Oil Cooler line must be Free Gravity flow requirements.
Lube Oil Cooler Piping Should have Break-up Flanges for Maintenance purposes.
Lube Oil Cooler Isometric should also have noted for “Pickling and Passivation” i.e. Chemical cleaning of Lines before commissioning.
Supporting Compressor Piping
The first support from Compressor Suction and Discharge nozzle is either Spring support or Adjustable support for Alignment during Construction / Erection.
Fig. 4: Lube Oil Cooler
Compressor piping should never be supported by the Compressor foundation. Pipe supports must be provided with independent foundations to avoid transmission of vibration.
Compressor Suction / Discharge Piping should be routed in such a way that it has enough flexibility to accommodate Thermal Expansion and Reduce the Nozzle Load.
Compressor Suction / Discharge Piping should be adequately supported as per Stress Engineers’ Support requirements.
Process Should be consulted for any possibility of two-phase flow/slug flow and the line should be supported accordingly
As compressors are meant for Gaseous fluid, the Hydro-test load on supports may be very high for big bore lines. Hence we can recommend Temporary supports to be erected during Hydro-testing with the help of a Stress Engineer.
Utility Requirements
The following are the utilities required for the Compressor:
External Fuel gas for seal gas system
Instrument Air for the Instruments/Control system/Seal gas system
External loads on static equipment nozzle flange joints must be assessed in order to comply with code requirements. In general, except for the flanged joints at high temperatures, the external forces and bending moments have little effect on the joint integrity of a properly assembled joint as long as the loads are within allowable design stress levels. It is a standard engineering practice to limit the external loads on flanged joints. So, selecting an appropriate method for assessing the effect of piping bending moments and external loads during the design phase becomes a task in trying to set a limit that encourages good piping design. There are various methods available for assessing the effects of external loads on nozzle flanges. In this article, we will discuss some of those methods. The points that will be covered in this article are:
ASME Interpretation BPV VIII-1-16-85
ANSI Flange Pressure Reduction Options In PV Elite
Code Case 2901
What Code Interpretation BPV VIII-1-16-85 States
This interpretation states that if you have external loadings acting on a nozzle you have to consider them on the flange too.
In 2013, however, PVP2013-97814 was written to address this issue. But many users complained that their jurisdictions did not/would not accept such a published (peer-reviewed) paper by a reputable author, because it did not have the approval of the ASME Boiler and Pressure Vessel Code Committee.
Compliance With ASME VIII-1, Paragraph UG-22:
Internal and external design pressures are not the only criteria used when designing pressure vessels. ASME VIII-1, paragraph UG-22, requires that all external loads acting on the pressure vessel be taken into account as well.
These include forces and moments that arise from attached piping and equipment, the weight of the vessel and its contents, liquid static head as well as wind and seismic induced reactions.
ANSI Flange Pressure Reduction Options:
Select a method for ANSI flange pressure reduction. Several methods are available to de-rate the flange MAWP based on external loads. If flanges are externally loaded they have the potential to leak. To keep this from occurring, it might be necessary to choose a heavier class of flange than one that is good for the design pressure per the B16.5/47 standard.
At the time of this writing (November 2017), the ASME Code has no rules on a particular method to use. They do however state (in a Code Case) that the external loadings must be considered.
Methods Available in PV Elite:
Kellogg Method
PVP Method
50% Stress Method
DNV Method
Assessing the flange MAWP reduction method in PV Elite:
Kellogg Method –
The Kellogg method is well-known and conservative. The axial load and moment are used to compute an equivalent pressure that is then deducted from the flange rating from the B16/47 table.
PVP Method –
This method is taken from the paper: ‘Improved Analysis of External Loads on Flanged Joints’ PVP2013-97814 by Dr. Warren Brown delivered in Paris July 14-18 2013 published by ASME. MAWP of the flange is adjusted so that the following equation is observed:
Sustained forces and moments must be entered for those results to be meaningful. Otherwise, the computed flange rating is zero.
50% Stress Method –
If the computed stress/allowable stress is < 0.5 on the pipe wall, then the allowable pressure is the full rating from the ANSI/ASME standard. If the stress ratio is >= 0.5, then the full equivalent pressure based on the Kellogg method is subtracted from the flange rating. This method looks at the stress in the nozzle wall to determine the MAWP. These are the data:
DNV Method –
The DNV method is considered to be a bit unconservative. It is essentially 1.3 times the flange rating minus the equivalent pressure based on the Kellogg method. The idea is that because the flanges will be a hydro test at elevated pressure and because there will loading applied (flanges in the piping system), then their rating can be elevated using the above equation. Most piping is tested to 1.5 times the design pressure, but we use a factor of 1.3 for conservatism because 1.3 is the factor used in Division 1 for hydro testing pressure vessels.
Note- The equivalent pressure is the pressure derived from the Kellogg Equation.
Analysis result-
ASME BPVC Code Case 2901:
Does Code Case 2901 available in PV Elite?
Yes, the PVP method in PV Elite is essentially the same thing as the Code Case.
ASME BPVC Code Case 2901-
The PVP MAWP Reduction Method-
What’s New in PV Elite 2019:
This presentation is prepared by Mr. Deepak Sethia who is working in ImageGrafix Software FZCO, the Hexagon CAS Global Network Partner in the Middle East and Egypt. He has extensive experience in using Caesar II and PV Elite software and troubleshooting.
Pipe reducers are vital components in piping systems. At its core, a pipe reducer is a type of pipe fitting designed to connect two pipes with different diameters. In other words, it enables the transition from a larger pipe size to a smaller one or vice versa. In this article, we’ll introduce pipe reducers, explaining their fundamental role in piping systems, their types, materials, applications, and dimensions.
What is a Pipe Reducer?
A pipe reducer is a type of pipe fitting that reduces the nominal bore from a bigger inner diameter to a smaller inner diameter. Piping and Pipeline Systems are not of uniform size and there is a requirement to reduce or expand the lines depending on process requirements, hydraulic criteria, or availability of material. Here comes the importance of a special pipe fitting called Pipe Reducers or Pipe Expanders.
Pipe reducers are manufactured following the ASME B16.9, DIN2615, JIS B2312, and ASME B16.11 standards and are highly reliable and compact components. Pipe reducers are usually made by a forging method known as the “outer dia method”.
Types of Pipe Reducers
Reducers in piping can be classified depending on various parameters as mentioned below:
Pipe Reducer Types Based on Construction Geometry
Types of Piping Reducers Based on End Connection
Pipe Reducer Categories Based on the Material of Construction
1. Types of Piping Reducers based on Construction Geometry
Pipe Reducers are one of the most extensively used fittings in the piping industry to reduce or expand the size of the straight part of the run pipe. Basically, there are two types of pipe reducers depending on the construction geometry:
Concentric reducers and
Eccentric reducers.
Concentric Reducers
As shown in Fig. 1, In concentric reducers the area reduction is concentric and the centerline of the pipe on a bigger end and smaller end remains the same. These styles are normally used for vertical lines. So in concentric reducers, the pipe axis remains the same. Reducers are reversible and can be used in any direction.
Fig. 1: Concentric Reducers
In Concentric Reducer, the size reduction from a larger to a smaller size is uniform at a constant rate over a specified length. A symmetry is maintained around the fitting keeping the same centreline. Joining pipe or tube sections of different diameters on the same centreline axis is made possible by using concentric reducers.
Eccentric Reducers
As shown in Fig. 2, in eccentric reducer there is an offset between the center lines of the bigger end and the centerline of the smaller end. This offset or eccentricity will maintain a flat side either on top or on the bottom side.
In an Eccentric Reducer, the reduction in the pipe size is achieved at a constant rate but maintains one side of the fitting horizontally. The use of eccentric reducers is also reversible and can be used as eccentric expanders. Eccentric reducers are not symmetrical about their centerlines.
Fig.2: Eccentric Reducer
This offset or eccentricity can easily be found by the following equation:
Eccentricity=(Bigger end ID-Smaller end ID)/2
Eccentric Reducer Installation
While using an eccentric reducer, the user has the option of orienting the flat side. Usually, for horizontal lines, eccentric pipe reducers are oriented with either the flat side up or down, and the same with deviation is mentioned in isometric.
Specific Uses of Eccentric Reducers
Normally eccentric reducers with the flat side down are preferred for the following cases on horizontal lines:
On Sleepers and Piperacks: To maintain the same BOP (Bottom of Pipe) for piping supports.
Control valve station: An eccentric reducer with a flat side down is required to get a constant flow through the control valve with less flow disruptions.
In horizontal gas, steam, or vapor piping, eccentric reducers are required to be installed with a flat side down, which allows condensed water or fluid to drain at low points.
Pump Suction Piping Reducer
Eccentric reducers with the flat side up are used for all pump suction lines (excluding pump handling slurry) on horizontal lines. This way one can avoid air getting trapped inside the pipeline during initial venting through the pump casing and will help in avoiding Cavitation.
However, the pipe reducers used on discharge lines are concentric type.
2. Types of Piping Reducers based on End Connection
Depending on the end connections of this fitting with a straight pipe, reducers are grouped as follows:
Butt-welded pipe reducers
The applicable pressure rating and dimensional and material standards for butt-welding reducers are the same as those applicable to butt-welding elbows.
Socket welded pipe reducers
As shown in Fig. 3, such reducers are available in concentric type only and in the form of pipe coupling with one end socket to fit larger diameter pipe and another end socket to fit smaller diameter pipe. Standards are the same as those applicable to socket weldingpipe elbows.
Fig. 3: Socket Welded Reducers
Screwed piping reducers
Available only in the concentric type and are in the form of coupling having one end to fit bigger pipe and another end to fit smaller pipe. ASME B16.11 is an applicable dimensional standard. Material standards, including pressure ratings, are the same as those of screwed elbows.
Fig. 4: Flanged and Screwed Reducer
Flanged pipe reducers
Their pressure rating, use, material, and dimensional standards are the same as those applicable to flanged elbows. Regardless of reduction, their face-to-face dimensions are governed by the larger pipe size.
3. Pipe Reducer Categories Based on the Material of Construction
Depending on the pipe reducer material of construction, there are two types of piping reducers:
Metallic Pipe Reducers, and
Non-metallic Pipe Reducers
The common materials used for the construction of such pipe reducers are explained below.
Materials of Pipe Reducers
Pipe reducers are made of various materials like Carbon Steel, Alloy, Stainless steel, and many more non-ferrous materials. As compared to the Stainless Steel Reducer, Carbon Steel Reducer possesses higher strength, high-pressure resistance, and wear resistance, but this can be easily corroded.
Carbon Steel material standards and grades used for pipe reducers are ASTM A234 WPB, A420 WPL6, MSS-SP-75, etc
Stainless Steel Pipe Reducer material grades are: ASTM A403 WP 304, 304L, A403, 316, 316L, 317, 317L, 321, 310 and 904L, etc.
Alloy Steel Pipe Reducer material grades include A234 WP1, WP5, WP9, WP11, WP22, WP91, etc.
Nickel Alloy: ASTM/ASME SB 336 UNS 2200 (NICKEL 200), UNS 8020 (ALLOY 20 / 20 CB 3, UNS 2201 (NICKEL 201), UNS 4400 (MONEL 400), UNS 8825 INCONEL (825), UNS 6625 (INCONEL 625), UNS 10276 (HASTELLOY C 276), UNS 6600 (INCONEL 600), UNS 6601 (INCONEL 601).
Copper Pipe Reducers
Brass Pipe Reducers
Non-Metallic Pipe Reducers
PVC Piping Reducers
Rubber Pipe Reducers
HDPE Pipe Reducers
Plastic Pipe Reducers
GRP/FRP Piping Reducers, etc
Piping Reducer Symbols
Reducer symbols help in the proper identification of the exact pipe fitting. Fig. 5 below provides the symbols for piping reducers that are used in P&ID and Isometric drawings.
The dimensions for butt welded piping reducers are provided by ASME B16.9. In Pipe Data Pro software, you can easily get the required pipe reducer dimensions. The following image provides part of the pipe reducer size chart as a reference.
Fig. 6: Pipe Reducer Dimensions
When to Use a Piping Reducer
Pipe reducers are essential fittings for adapting pipes of different sizes, offering solutions for various complex scenarios. They are particularly useful when adjustments in flow rates or pressure are required within a piping system. For instance, in systems where hydraulic conditions necessitate flow management, reducers play a crucial role in controlling these parameters. It is important to consider how a pipe reducer will impact the overall system, as it can affect both flow dynamics and pressure levels.
Here are some common scenarios where a reducer is appropriate:
Flow Rate Management: To adjust the flow rate by connecting a larger diameter pipe to a smaller one, which can be essential for controlling the speed and volume of the fluid or gas in the system.
Pressure Control: When reducing the pipe diameter, the velocity of the fluid increases, which can help manage pressure changes in the system. This is useful for optimizing system performance and preventing pressure loss.
System Design and Integration: To connect pipes of varying sizes in a complex system. For example, a large main pipe might need to connect to smaller branch pipes or equipment with different inlet or outlet sizes.
Space Constraints: In situations where space is limited, a reducer can facilitate the transition between different pipe sizes without requiring additional space for larger fittings or equipment.
Component Compatibility: When existing equipment or components have different connection sizes, a reducer helps integrate them into the piping system without needing to replace or modify the equipment.
The application of Pipe reducers is mentioned in the P&ID and accordingly, they are selected as per the sizes mentioned. As you can see in Fig. 7, the requirements of Piping Reducers are clearly specified.
Fig. 7: Piping Reducer Requirements in P&ID
Uses of Piping Reducers
Piping reducers or expanders are widely used in the piping, pipeline, and plumbing industries to change pipe size from a larger to a smaller diameter. Common industries where pipe reducers find extensive applications are:
Chemical and Petrochemical Industry
Water Treatment
HVAC Systems
Food and Beverage Industry
Mining and Construction
Oil and Gas Industries
Pharmaceutical Industry
Wastewater
Shipbuilding Industry, etc
In general, horizontal liquid reducers are always eccentric, with the flat side on top. This design helps prevent air bubbles from building up in the system. In pipe racks, the flat side is on the bottom to keep the pipe’s bottom position consistent and supported. Eccentric reducers are used on the suction side of pumps to avoid air accumulation, which could cause pump stalls or cavitation. Horizontal gas reducers are always eccentric, with the flat side on the bottom. This allows condensed water or oil to drain from the low points.
Reducers in vertical pipes are usually concentric unless the layout requires a different design.
Piping Reducer Ordering Information
The following information should be supplied to the vendor while placing an order for pipe reducers.
Pipe Size and Outer diameter
Governing standard (ASME B16.9, GB, HG, HGJ, SH, SY, DL, AN, SI, JIS, or DIN).
Differences between Concentric and Eccentric Reducers | Eccentric vs Concentric Reducers
A concentric reducer and an eccentric reducer are two different types of pipe reducers that are used to connect pipes of different sizes. The main differences between them are in their shapes and how they are used.
Fig. 8: Eccentric vs Concentric Reducers
A concentric reducer is a type of pipe reducer that has a conical shape with a symmetrical centerline. It is designed to reduce the pipe’s diameter uniformly and is commonly used in horizontal piping systems where there is no need to maintain the same elevation. With a concentric reducer, the centerline of the larger end of the reducer coincides with the centerline of the smaller end, which means that the fluid flow direction remains unchanged.
On the other hand, an eccentric reducer is a type of pipe reducer that has an asymmetrical centerline. It is designed to reduce the pipe’s diameter and shift the centerline of the pipe at the same time, which means that it is commonly used in horizontal piping systems where there is a need to maintain a constant fluid level. With an eccentric reducer, the centerline of the larger end of the reducer is offset from the centerline of the smaller end, which means that the fluid flow direction changes.
The major differences between an eccentric reducer and a concentric reducer can be summarized as follows:
Aspect
Concentric Reducer
Eccentric Reducer
Shape
The central axis remains aligned during the transition.
The central axis is offset, with one side flat.
Pipe Alignment
Aligns the centerline of the larger and smaller pipes. Concentric reducers provide an in-line conical transition between pressurized pipes of differing diameters. Thus, concentric reducers connect pipes of unequal size but have a common centerline. The same fitting can be used in reverse as a concentric expander.
Offsets the centerline of the larger and smaller pipes. An eccentric pipe reducer fitting is manufactured with the smaller outlet off-center to the larger end, which allows it to align with only one side of the inlet. The same fitting can be used in reverse as an eccentric expander.
Flow Characteristics
More suitable for vertical pipe systems
Better for horizontal pipe systems to prevent air pockets
Installation
Generally easier to install in vertical pipes
Often used in horizontal applications or where a smooth flow transition is needed
Application
Common in systems where the alignment of the pipes is critical
Preferred in systems where air or gas pockets may form
Cost
Typically less expensive
May be more expensive due to the complex design
Table 1: Differences between Concentric Reducer and Eccentric Reducer
In summary, the main differences between concentric and eccentric reducers are their shapes and their application. A concentric reducer has a symmetrical centerline and is used to reduce the diameter of the pipe uniformly, while an eccentric reducer has an asymmetrical centerline and is used to shift the centerline of the pipe while reducing the diameter.
Pipe Reducer vs Pipe Expander: What are the Differences?
A pipe reducer and a pipe expander are both used to transition between pipes of different diameters, but they serve opposite functions. A pipe reducer decreases the diameter of a pipe, typically featuring a conical or tapered shape that narrows from a larger to a smaller end, and is used to manage flow rates and pressure changes. In contrast, a pipe expander increases the diameter, often with a bell-shaped or tapered design that widens from a smaller to a larger end, facilitating the transition to larger pipes and accommodating varying flow rates.
While reducers help adapt systems to smaller pipe sizes, expanders are employed to upgrade or accommodate larger pipe sizes, and their installation requires careful alignment to ensure smooth flow and system efficiency. In general, it is related to the fluid flow direction. If towards the fluid flow the outlet size increases, it is called a pipe expander. Again when towards the fluid flow direction, if the pipe size decreases it is called a piping reducer.
Usually by using a pipe reducer the fluid velocity is increased and by using a piping expander the fluid velocity is reduced.
Flanged pipe bends or flanged elbows are piping elbows connected with flange fitting to fitting. This means there is no spool or pipe piece in between the elbow endpoint( weld point) and flange. Flanged elbows are widely used for piping connections requiring compact pipe routing. Flanged elbows are purchased as a pipe fitting. On the other hand, flanged bends are prepared when a flange (weld neck or any other type) is directly welded to a piping elbow.
Types of Flanged Elbows
Based on the number of flanges connected to the pipe elbow fitting, flanged bends are of two types:
Single Flanged Elbow and
Double Flanged Elbow
When one side of a pipe elbow is connected to a flange but the other side is connected to a pipe it is called a single-flanged elbow. Again when there are flanges on both sides of the elbows, it is called a double-flanged elbow. Refer to Fig. 1 for a typical example.
Fig. 1: Single and Double Flanged Elbow
Effect of Flanged Elbow or Flanged Bend
When the flanges are attached near elbows or bends (Near Control Valve assembly and equipment nozzles); they exert a severe restraining force on the flexibility of the bend, thus reducing the flexibility of the bend and increasing the force and moment in the nearby support or nozzle. ASME B 31.3/ASME B31J Code provides two correction factors C1 and C2 to take care of the same effect. So basically the single-flange and double-flange options provide the following impacts in a piping system:
In Caesar II software the effect of the flanged bend can be easily taken care of by modeling flanged elbows as mentioned below.
Sometimes dummy/trunnion attachments at the elbow also provide a similar effect which is why a few organizations have the practice of using a flanged elbow while modeling the trunnions from the elbow.
Single or Double Flange Option should be applied to Stress Analysis if there is any flanges or valves (heavy/rigid body) within two diameters (2D as per BS 806) of the ending weld point of the bend as shown in Fig. 2.
Fig. 2: Criteria for using Flanged Bend in Caesar II
The modeling steps for the flanged bend are shown in Fig. 3. Single flanged bend is indicated by selecting 1-Single Flange as shown in Fig. 3. Similarly Double Flanged Bend can be indicated by selecting the 2-Double Flange option.
Fig. 3: Caesar model showing the flanged bend application criteria
