Shaft Alignment Methodology for Compressor and Driver

Written by Anup Kumar Dey in Construction,Maintenance,Mechanical

Before connecting the process gas piping with compressor nozzles, the shaft alignment work for the compressors and driver shall be carried out to ensure their concentricity. This concentricity between the shaft and the driver is very important for the proper smooth working of the compressors. This article will explain the alignment methodology in brief.

Concentric Alignment

Stainless steel shims 3 mm thick shall be placed equally beneath the legs of compressors to be erected on the baseplate, and then the equipment shall be placed on the baseplate. This is applicable when compressors are separately shipped from the baseplate. Thereafter, each fitting bolt is tightened. Alignment shall be concentrated through the equipment closest to the driver by adjusting the shim thickness beneath each piece of equipment.

The alignment work shall be carried out from place to place according to the specified order. In this step, the alignment of all equipment shall be concentrated first on the adjustment of the shims so that the equipment falls within the tolerance specified in the cold alignment map.

Final Alignment

The driver and all powered equipment shall be aligned at a cold offset position considered normal for operation. The specified values of cold offset are met by means of increasing or decreasing the thickness of the shims beneath the legs of all equipment from the concentric alignment position.

Once all the equipment satisfies the specified values, it is necessary to prepare an accurate alignment map between the equipment concerned and to record the shaft distances and thicknesses of the shims beneath the legs. After the cold offset alignment is completed, record and file the alignment data, shaft distances, and shim thicknesses.

These records will serve as important data for correcting alignment in the future. The allowable misalignment under the above cold offset condition shall be within +/- 10/100 mm of the planned alignment value

Hot Alignment

If any problem such as high vibration occurs, hot alignment checking will be only effective and helpful as a troubleshooting aid and/or for finding the appropriate countermeasures to take. It is not recommended hot alignment checking by using dial indicators on coupling hubs or anywhere else after a few hours or more of running, because the temperature of the equipment will change very quickly after shutdown.

Typical operational experience data for the best hot alignment are as follows:

Vertical thermal expansion growth of all equipment shall be calculated based on actual temperature measurement at supports under normal operating conditions.
If optical alignment equipment and material are available, they will be used for checking the alignment under cold conditions and normal operating conditions.

Shaft Alignment method/Steps

Install the alignment jig also known as the Alignment fixture to shaft B and attach the dial indicator to the jig as illustrated in Fig. 1.
Turn Shaft B Once to check for normal contact between the dial indicator on Shaft A.
Slowly turn shaft B and take four readings at every 90 degrees (Refer to example 1 in Fig. 2)
Then turn Shaft A by 180 degrees, then with Shaft A at this position, turn Shaft B once to check for normal contact with the dial indicator on Shaft A. then bring a dial indicator at the top of the shaft and set it at zero.
Slowly turn Shaft B and take four readings every 90 degrees. Please bear in mind that the indicator reading at each 180-degree position on Shaft A (point 4) is important for correcting the runout of the coupling.
Remove the alignment jig from Shaft B and attach it to Shaft A. Set the dial indicator above shaft B and perform the same measurements as mentioned above (Refer to Example 2 in Fig 2)

If the readings are such as those shown in Fig. 2 last image, the alignment of Shaft A and of Shaft B is the arithmetical mean of each of the two corresponding figures.

The alignment jig used for this must be free of any deflection to minimize measurement errors.

Preparation of Alignment Map

Depict the position of the rotor, the driver supports, and driven equipment such as the steam turbine, and the compressor in a reduced scale on graph paper and plot measurements on it. By this graph, one can easily find the present position of each rotor and the thickness of the shims to be used for adjustment. (Refer to fig. 3)

Few Notes

The final alignment before connecting the process gas piping shall be carried out in accordance with the cold alignment map issued by the vendor.
If an unallowable misalignment exceeding the cold alignment map limitation is observed, correction shall be made by adding or removing the shims beneath the compressor leg supports.
During the alignment work, the distance between shafts shall be measured often and checked within a tolerance of +/-0.5 mm. If it exceeds the limitation, a re-adjusting shall be made by moving the compressors.
While the shaft end distance is measured, each shaft should be moved towards the active side thrust bearing to put it at the expected operating position.

Few more Useful Resources for you..

Shaft Alignment Methodology for Compressor and Driver
Connection procedure (Alignment) of Process Piping with Rotating Equipments: An Article
Alignment Check Methodology in Piping Stress Analysis using Caesar II
Few articles related to Pumps
Piping Design and Layout Basics

Shell & Tube Heat Exchanger Piping | Online Course on Drums/Exchanger Layout & Stress Analysis

Written by Anup Kumar Dey in Piping Design Basics

Shell & Tube Heat Exchangers are the most frequently used Heat Exchangers in Process Plants. The purpose of this presentation is to provide guidelines for Shell & Tube Heat Exchanger Piping Layout. Click here to get a preliminary idea about shell and tube heat exchangers.

Use of Shell & Tube Heat Exchangers

All Heat exchangers are used to transfer heat from one fluid to another. They are generally named as coolers, chillers, condensers, heaters, reboilers, waste heat boilers, steam generators & vaporizers in the process plant.

Types of Heat exchangers

The most commonly used types of heat exchangers are

Shell & Tube heat exchanger
Air-cooled heat exchanger
Plate-type heat exchanger
Spiral heat exchanger
Double pipe heat exchanger

Shell & Tube Heat Exchanger Construction (Fig. 1)

Diagram showing construction of a typical Shell and Tube Heat Exchanger — **Fig.1:** Diagram showing the **construction of a typical Shell and Tube Heat Exchanger**

These heat exchangers are generally designed, fabricated, inspected, and tested as per API 660 / EN-ISO 16812 / TEMA. The DEP for the design & construction of the shell & tube heat exchanger is DEP 31.21.01.30 – Gen.

General Guidelines for selection for tube side & shell side fluids:

Clean fluid through the shell & dirty fluid through tubes.
Corrosive fluid through tubes as it is easy for cleaning & allows the use of carbon steel for the shell.
Water through shell & process liquid through Only seawater through the tube side.
High-pressure fluid through tubes which allows for min. the wall thickness of the shell.

The layout of shell & tube heat exchangers other than in banks

As per the exchanger positions in a process plant, the following general classification can be made:

Exchangers which should be next to other equipment: e. g. Vertical Reboiler
Exchangers which should be close to other equipment: e. g. Overhead condenser
Exchangers located between other process equipment: e. g. The exchanger with process lines connected to both the shell & tube side
Exchangers located between process equipment and the unit limit:e.g. Product coolers

Establishing elevations for the exchanger

Where process requirement dictates the elevation, it is usually noted on the P&ID/PEFS
The grade is the best elevation from an economic point of view
Located in structures where gravity flow is required or connected to pump suction which has specific NPSH requirement e.g. overhead condenser

The layout of Shell & Tube heat exchanger in banks

Arrangement of exchangers (Fig. 2):

**Fig. 2: Typical arrangements of shell and tube heat exchangers**

Various types of Exchanger orientation are possible as mentioned below:

Sample exchanger orientation (Fig. 3)

**Fig.3: Figure showing Heat Exchanger Orientation**

Single and Paired Exchangers (Fig. 4)

**Fig.4: Single and Paired exchanger orientation**

Parallel Exchanger Installation (Fig. 5)

Series Exchanger Installation (Fig. 6)

Stacked exchanger installation

Two exchangers in series or parallel are usually stacked. Refer Fig. 7

Nozzle arrangement for better piping (Fig. 8)

Structure-mounted exchanger installation (Fig. 9)

Supporting shell & tube heat exchanger piping

No special guidelines for supporting
Pipe stress analysis is required to be carried out for the exchanger inlet & outlet lines
Fixed saddle support near the tube bundle head, sliding support near the rear head

Heat exchanger maintenance

Tube bundle extractors (Fig. 10)

Online Course on Drums/Exchanger Layout & Stress Analysis

To learn more details about the Drums/Exchanger Layout & Stress Analysis method We suggest the following online Course:

Drums/Exchanger Layout & Stress Analysis: The Complete course covers most of the Layout & Stress Analysis related concepts, step by step modeling in Caeser-II has been defined which every piping engineer should understand.

As you are aware that heat exchangers & drums are an integral part of any plant. This full course is divided into two parts: The Heat exchanger piping layout consists of the following five modules:

Module 1: Classification of Heat Exchanger: Covers various types of heat exchangers
Module 2: Constructional and Operating features for all Type exchangers
Module 3: Layout Aspects to design the layout of
- Shell and Tube exchanger
- Spiral Exchanger
- Plate type Exchanger
Module 4: Layout Aspects: 3D Pictorial Views
Module 5: Interesting facts: Optimizing Layout

It will cover all aspects of Piping layouts for Heat exchangers/Drums

The Stress Analysis part will cover the following:

Various concepts related to Stress Analysis keeping in view the Exchangers/Drums piping have been captured and explained in detail.
Actual modeling in CAESAR II is done and explained in detail w.r.t. industry practices and various codes & standards.

The major topics that the course covers are provided in Fig. 11 below:

**Fig. 11: Heat Exchanger Piping Layout and Stress Analysis**

So, simply click here to join the course at an amazing price

Few more resources for You..

Basics of Shell and Tube Heat Exchangers: A brief presentation
An article on Plate Heat Exchanger with Steam
A typical Check List for Reviewing of Shell & Tube Heat Exchanger Drawings
A brief presentation on Air Cooled Heat Exchangers
Basic Considerations for Equipment and Piping Layout of Air Cooled Heat Exchanger Piping
Reboiler Exchanger and System Type Selection

Hydrostatic Field Test of GRP / GRE lines

Written by Anup Kumar Dey in Construction,Engineering Materials,Maintenance,Pipeline

Considerations for Hydrostatic Field Test of GRE lines

The hydrostatic field test or hydraulic test on the GRP/GRE line, or on the section of it, is required to verify the hydraulic sealing of the system at the testing pressure and then, indirectly, its structural integrity. The liquid used for hydraulic testing is generally water (γ = 1); in particular cases, the liquid could be seawater (γ = 1.025).

Before proceeding with the filling of the line, check that the same can be pressurized, i.e. complete vents, drains, valves, and/or blind flanges, and every fitting or accessory required by design documents. If the line is above ground, check that the bearings have been executed correctly and that the thrusts due to the hydraulic internal pressure are all correctly sustained.

If the line is underground, check that this is completely ballasted and that the thrusts due to the hydraulic internal pressure are all sustained by the soil or by thrust anchoring blocks.

The joints will be visible, in order to allow the inspection unless otherwise stated by the Client or its representative.

It is preferable to test lines, or segments of the line, whose length doesn’t exceed 1000-1500 m.

Hydrostatic Field Testing Pressure

The hydrostatic testing pressure is generally 1.5 times the design pressure in the lowest point of the section of the line being tested.

gre pipe — **Typical GRP/GRE pipes in Plants**

Instrumentation for the Test

All the equipment and the instruments that are required to perform the testing will have to be available and connected to the GRP piping system.

Connect the metering and recording instruments to the line, possibly in the lower point (X point) of it. Otherwise, for the evaluation of the pressure, consider the geodetic gradient of the gauge compared to the X point and the specific weight of the fluid used for the testing (sweet water or seawater) in order to adjust the reading of the same. The value of the pressure of testing will be:

Pp = Pm ± ΔH

where:

Pp Testing pressure
Pm manometric pressure
ΔH geodetic gradient
γ specific weight of the water
± higher/deeper gauge compared to X point

NB: the instruments must be set before and after the test.

Liquid Filling on the Line for Test

The filling of water will be performed after the cleaning of the line.
Verify that suitable pumps are available for the filling of the line and for its pressurization.
Verify that all the vents have been opened.
Fill the line slowly, possibly from the lower part, in order to facilitate the escape of the air through the vents.
When the line is completely full, be sure that all of the vents and the valves are well closed. Ascertain furthermore that there aren’t any leakages, by doing a visual control along the run of the line. In case a leakage is found, empty the line if necessary and make the repair. Then fill the line again as above.

GRP Line Stabilization

This phase of the testing procedure is required to allow the complete thermal and mechanical stabilization of the pipeline.
In this phase insert the measuring and recording tools. The pressure will have increased up to reaching the value of the design pressure.
The increase of pressure won’t be greater than 1 bar every 10 minutes for ND>500mm, or 1 bar every 5 minutes for ND ≤ 500mm.

Acceptance Criteria

Once the required pressure is achieved, maintain the pressure until its stabilization, up to a maximum of 12 hours if no visible leakages are found. Possible pressure drops can be balanced by switching on the pumping system
Pressure drops are due to temperature change, entrapment of air, settlement of the soil or of anchoring blocks, or expansions of non-rigid joints. Periodically check the vent valves if automatic, or open them to let the air escape.
The stabilization phase can be considered finished when pressure variations do not occur for at least two hours, without water integration.

Non-Acceptance Criteria

The test will have to be considered invalid and will have to be stopped in the following cases:

ascertained leakage
clear deformation of the pipe’s supports and settlements in anchor blocks or in the soil, that are not becoming stable, and that can cause damage to the pipeline;
after 12 hours if it is not possible to maintain a steady pressure, without integration, for at least 2 hours.
After having repaired the possible damages that occurred to the piping and/or support system, submit again the pipeline for testing.
If it is not possible to find out the reason for the lack of pressurization, deeper investigations are required, for example, uncovering buried parts, checking the sealing of the valves, and where it is possible, inspecting the inside of the pipeline.

Pressure Testing

The pressure will be increased until one achieves the value of the pressure of testing. In this phase compile a minute of testing, reporting the values of pressure and temperature at the beginning of the testing.
The increase of pressure won’t be higher than 1 bar every 10 minutes for ND>500 mm and 1 bar every 5 minutes for ND≤ 500mm.
The line will be kept at this value of pressure for a time not lower than 2 hours.
At the end of this period verify the values of the measurements (pressure, temperature, etc.) and transcribe these final values on the minute of testing.

Acceptance Criteria and Conclusion of the Test

The hydraulic testing will be considered positive if, at the end of the 2 hours of testing, one of the following points is achieved:

During the period of the hydraulic test, the pressure will stay stable.
No leakages are visible at any point of the pipeline, or in the joints, or in the testing equipment.
The change of pressure between the beginning and the end of testing is due to the change in temperature of the testing water.
The change of pressure between the beginning and the end of testing is due to the presence of air in the line.
When the joints of the line are manufactured with elastomeric gaskets and there is a decrease in pressure, the initial pressure has to be restored by pumping an amount of water not greater than (from the Std. AWWA M 11 – Manual of water supply practice):

Q = 0.0001⋅D ⋅ L ⋅H

where:

Q amount of water (liters)
D diameter (mm)
L length of the line (m)
H test time = 12 hours

A combination of the above points.

Failed Test

In case of failure of the test, find the cause of the leakage, empty the line and start immediately the repair of the line or replace the defective pieces.
The pipeline can then be tested again according to the procedure.

Online Video Course of FRP/GRP/GRE Pipeline Stress Analysis using Caesar II

If you are interested in learning FRP/GRE/GRP Piping Stress Analysis using Caesar II software, you can have a look at the following online video course

FRP Piping/Pipeline Stress Analysis using Caesar II

Major Factors Affecting the Pump Performance

Written by Anup Kumar Dey in Mechanical,Process

A Pump or Pumping system is the major equipment in any process or power plant. So the equipment should operate properly to give the best output in terms of performance. However, there are many factors that influence the pump’s performance. Out of those, the main (major) factors which affect the performance of the pump are:

Impeller design
Improper priming
Insufficient NPSH
Reduced capacity
Wrong direction of rotation
Clogging of suction pipeline and impeller
Improper shaft alignment
Packing troubles
Noisy operation

This article will explain these points in short.

Impeller Design

Backward curved blades, β2<90°
Forward curved blades, β2>90°
Radial blades, β2=90°

The following table provides a guideline for pump performance with various blades.

	Backward curved blades, β2<90°	Forward curved blades, β2>90°
No of blades	12-16	60
Blade angle, β2	40°	145°
Hydraulic efficiency	80%	70%
Power consumption	low	high
application	Changing operating condition	Fixed duty operation
losses	low	high

Improper Priming

All the air in the pipeline should be expelled completely

Precautions to eliminate trouble :

The pump should be primed completely before starting
The suction pipe should be 1m below the lowest water level
It should be completely airtight
Eccentric reducers should be used if necessary to avoid air pockets in the pipeline

Centrifugal Pump Performance — **A typical Centrifugal Pump**

Insufficient NPSH

NPSH= (P_atm-P_v)/ ρg – hs – hfs
NPSH depends on the temperature of the operating liquid
Variation in water level is considerable – The lowest level should be taken into account for NPSH determination
Frictional losses should be kept minimum by selecting a suitable diameter.
It is commonly accepted the static head in the pump will be maintained at 6.7m for water with a temperature of 10-20°c
NPSH available > NPSH required

Reduced Capacity

One of the main reasons for the reduced capacity is increased head
Total head > designed head
The pump or the impeller should be changed to obtain the rated capacity

Wrong Direction of Rotation

This cause the rated capacity and head will not be obtained
The pump fails often to operate
Remedy :
- arrow cast is indicated in the pump casing
- care should be taken while mounting the impeller

Clogging of Suction Pipeline

The suction pipe is clogged by some bricks, wood often
The strainer is clogged by paper, leaves
To rectify this pipeline should be inspected periodically

Improper Shaft Alignment

It is due to the misalignment of the motor and pump shaft
It results in vibration and noisy operation
To avoid this two shafts should be aligned properly

Noisy Operation

Air leakage in the pump
Shaft misalignment resulting in the vibration
Cavitations
They can be reduced by a proper dynamic balance of the shaft and impeller
The cavitations are reduced by properly designing the pump with suitable NPSH

Few more resources for you..

Pumps & Pumping Systems: A basic presentation
Cause and Effect of Pump Cavitation
NPSH for Pumps: Explanation and Effect
Water Hammer Basics in Pumps for beginners

What is Thermal Bowing?

Written by Alex Matveev in Caesar II,Piping Stress Analysis,Piping Stress Basics,Start-Prof

The thermal bowing phenomenon occurs when a horizontal pipe is filled partially by hot or cold fluid (LNG). Many thermal bowing occurrences cause unexpected damage to the piping or supporting structure. Since thermal bowing occurs mostly at transient conditions, such as during startup, the bowing phenomenon may go unnoticed until the damages are discovered.

It can also occur when one side of the pipe is exposed to the sun and the other side is in the shade.

This effect takes place when the temperature difference between the top and bottom of the pipe section is significant. It is called the thermal gradient. This thermal gradient causes pipe thermal strains that produce pipe curvature called thermal bowing.

Assumptions for thermal bowing

The following Assumptions are made for thermal bowing

Thermal strain distribution across the pipe section is linear
Applied only for horizontal pipes that meet “horizontal tolerance” criteria |DZ| / ( DX² + DY² + DZ² )^0.5 < Tolerance
Bowing is acting only in the vertical plane

Basics of Thermal Bowing

The thermal gradient can be different for each pipe element. And also it can be different in each operation mode.

**Temperature Distribution in Thermal Bowing**

The pipe curvature due to the thermal bowing effect:

r – curvature radius
D – outside diameter of the pipe
a – thermal expansion coefficient at operating temperature

T_top – the temperature at the top of the pipe
T_bottom – the temperature at the bottom of the pipe

Performing Thermal Bowing in Start-Prof

The thermal gradient (T_top-T_bottom) should be specified in pipe properties.

**Specifying Thermal Bowing in Start-Prof**

The thermal bowing effect should be switched on in Project Settings.

The bending moment produced in the restrained pipe due to the thermal bowing effect:

E – pipe elastic modulus at operating temperature
I – the moment of inertia

The operating temperature should be equal to (T_top+T_bottom)/2

Some more Resources for You…

Stress Analysis using Start-Prof
Stress Analysis using Caesar II
Stress Analysis Basic Concepts
Piping Layout and Design

Introduction to EOT CRANES & HOISTS

Written by Anup Kumar Dey in Mechanical,Piping Design Basics

EOT (Electric Overhead Traveling) Cranes and Hoist are industrial machines that are mainly used for materials movements in construction sites, production halls, assembly lines, storage areas, power stations, and similar places.

Types of Cranes

Single girder cranes (Fig. 1A) – The crane consists of a single bridge girder supported on two end trucks. It has a trolley hoist mechanism that runs on the bottom flange of the bridge girder.

Double Girder Bridge Cranes (Fig. 1B) – The crane consists of two bridge girders supported on two end trucks. The trolley runs on rails on the top of the bridge girders.

**Fig. 1: Figure showing single and double girder cranes**

Selection of Cranes

Which Crane should you choose – Single Girder or Double Girder

Generally, if the crane is more than 15 tons or the span is more than 30m, a double girder crane is a better solution.

Components of Cranes (Fig. 2)

**Fig. 2: Figure showing Crane Components**

Essential Parameters for Specifying EOT Cranes (Fig. 3)

**Fig. 3: Parameters needed for specifying an overhead crane**

Codes and Standards for EOT Cranes

Electric Overhead Traveling cranes shall conform in design, materials, construction, and performance with the current issue of the following specifications, codes, and standards.

CMAA 70 Specification for Top Running Bridge & Gantry Type Multiple Girder Electric Overhead Traveling Cranes
AGMA American Gear Manufacturer’s Association
ASME HST-4 Performance Standard for Overhead Electric Wire Rope Hoists
ASME Y 14.1 Decimal Inch Drawing Sheet Size and Format
ASME B18.2.2 Square and Hex Nuts
ASME B30.2 Overhead and Gantry Cranes (Top Running Bridge, Single or Multiple Girder, Top Running Trolley Hoist)
ASME B30.10 Hooks
AWS D14.1 American Welding Society – Specification for Welding of Industrial and Mill Cranes
HMI 100-74 Hoist Manufacturer’s Institute – Specification for Electric Wire Rope Hoists
NEC 610-14 Determining Amperage Requirements for Cranes and Hoists
NEMA ICS 8 Industrial Control and Systems – Crane and Hoist Controllers
NFPA70 National Electrical Code
OSHA Occupational Safety & Health Administration
IBC International Building Code (This will eventually replace UBC)
UBC Uniform Building Code

Control Equipment (Fig. 4) for EOT Cranes

**Fig. 4: Typical control equipments for crane**

HOISTS (Fig. 5)

A hoist is a device used for lifting or lowering a load by means of a drum or lift wheel around which a rope or chain wraps.

**Fig. 5: Figure showing typical Hoists**

Hoist Selection Factors

The weight of the load to be lifted includes below-the-hook lifting, load-supporting, and positioning devices.
The physical size of the load.
Clearance Considerations
Lifting Speed Considerations
Hoist duty

Hoisting Equipment

Sheaves
Hook Assembly
Gear Assembly
Rope Drum
Ropes

Hoist Standards

ASME-HST-1 Performance Standard for Electric Chain Hoists
ASME-HST-2 Performance Standard for Hand Chain Manually Operated Chain Hoists
ASME-HST-3 Performance Standard for Manually Lever Operated Chain Hoists
ASME-HST-4 Performance Standard for Overhead Electric Wire Rope Hoists
ASME-HST-5 Performance Standard for Air Chain Hoists
ASME-HST-6 Performance Standard for Air Wire Rope Hoists
ASME-B30.7 Safety Standard for Base Mounted Drum Hoists
ASME-B30.16 Safety Standard for Overhead Hoists (Underhung)
ASME-B30.21 Safety Standard Manually Lever-Operated Hoists
OSHA (Parts 1910 and 1926) adopts or invokes the American Society of Mechanical Engineers

Few more resources of your interest..

Piping Design and Layout
Piping Interface
Piping Stress Analysis
Piping Materials

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