indian journal of science and technology, doi: 10.17485

AbstractBackground/Objectives: Saddles are one of the important parts of vessel as they support the vessel. In this study, how Mode II type crack propagated inside the junction of saddle and vessel connection would spoil the entire setup of the vessel was investigated. The main intention of this work was to avoid the repeated failures of saddles during operation in energy development industries and wherever it is used. Methods/Statistical Analysis: Two different types of saddles were considered and fabricated using IS2060 Grade B material. The saddle parts were welded as per the code rule of API. Findings: Normally, welding in inclined saddle is difficult in comparison with straight saddle. This may be reason; the failure rate of inclined saddle is high in comparison with straight saddles during operation and loading conditions. The other possibility of failure is the gap formation inside the weld during joining the plates. This is due to non-deposition of weld materials. The gap would grow during operation and loaded conditions. To avoid these types of failures, external and internal crack inspections were done. Once the inspection was done, it was examined the load carrying of the fabricated saddles using FEM. Then the solid works software was used to simulate the solid model which it’s developed similar like original saddle fabricated for estimating the load carrying capacities. The obtained results of NDT and FEM were presented and the design recommendations based on investigation and study are also suggested. Applications/Improvements: The obtained results of NDT and FEM were presented and the design recommendations based on investigation and study are also suggested.

Design and Crack Analysis of Pressure Vessel Saddles Using Finite Element Method

A. M. Senthil Anbazhagan and M. Dev Anand

Department of Mechanical Engineering, Noorul Islam Centre for Higher Education, Kumaracoil - 629 180, Thuckalay, Kanyakumari District, Tamilnadu State, India; [email protected], [email protected]

Keywords: Pressure Vessels, Saddles Finite Elements, Inspection, Support Structure.

1. Introduction to Pressure Vessels and Saddles

A pressure vessel is a container which is designed closed for holding gases or liquids at a pressure considerably dissimilar from the ambient pressure. Classification of pressure vessels are of various types like Cylindrical, Rectangular, and Spherical. Cylindrical and Rectangular types can be further classified into Horizontal and Vertical type vessels. Horizontal vessels normally placed on sad-dle supports and vertical vessels placed on skirt support. Since these types are based on process requirements, sometime in these vessels would place inclined position. Placing inclined vessel is a difficult task as we require inclined saddle. As we mentioned in synopsis, this proj-ect, we considered only horizontal and inclined saddles for cylindrical type vessels for design and development.

Saddles are supports which hold the vessels. The bottom portion of the saddle is normally welded or bolded to the ground or wherever it is mounted. As far as horizon-tal vessels are concerned, straight and inclined saddles are used for placing the vessels. Normally, horizontal vessels are supported using two numbers of saddles. However, the no of saddles can be vary based on the length of the cylinder. Sometimes, if the vessel length is too long we may require three to four numbers of saddles for placing the pressure vessels.

2. Design of Saddles

2.1 Design of Inclined and Horizontal Saddles

Saddles contain Base plate, Web, Ribs and Wear Plate. The wear plate is used to carry the pressure vessel and has

*Author for correspondence

Indian Journal of Science and Technology, Vol 9(21), DOI: 10.17485/ijst/2016/v9i21/90567, June 2016ISSN (Print) : 0974-6846

ISSN (Online) : 0974-5645


Indian Journal of Science and Technology2 Vol 9 (21) | June 2016 | www.indjst.org

the internal diameter same as that the outer diameter of vessel. The total weight of the pressure vessel is directly distributed to wear plate and then transferred to the based plate through web and rip plates. The web and ribs are designed to carry or support the wear plate. They are located bottom of the wear plate and above the base plate. Wear, Web and Ribs are welded on the base plate. This base plate is fixed on the bottom. Please refer Figure 1 shown for reference.

2.2 Design Methodology of Horizontal and Inclined Saddles

Our saddle designs are based on the assumption of the cylindrical vessel diameters 16” and 12” as shown I Figure 2. It is assumed 16” diameter vessel is sitting on the inclined saddle and 12” diameter vessel is sitting on the horizontal saddle which designed and manufactured. The methodology of design calculations are as follows. Since shortfalls of design code guidelines, so necessary to follow L.P. Zicks1 method to design the saddles. L.P. Zick method is very much suitable for our horizontal saddles. But applied his method for both horizontal and inclined saddles. The method of calculation to fix the Web, Rib, Base and Wear ticks are as follows as based on the2-15.

2.3 Design of Inclined SaddleA TA2885A-0000-C-00116 is the formal written document describing mechanical calculation procedures, which provides direction to the pressure vessels designer for making sound and quality production components as per the code requirements. The purpose of the document is to guide designer to the accepted procedures so that repeatable and trusted techniques are used. A TA2885A-0000-C-001 is developed for each material alloy and for each type used. Specific codes and/or engineering soci-eties are often the driving force behind the development of a company’s TA2885A-0000-C-001. Based on that, it is designed for vertical and inclined saddle and the summary of entire things are indicated in Table 2 to 10.

Figure 1. Horizontal saddle support.

Figure 2. Horizontal inclined saddle support.

Table 1. Inclined saddle results

Inclined Saddle Results Actual AllowableLong. Stress at Top of

Midspan 51.77 137.90 N/mm²

Long. Stress at Bottom of Midspan 53.52 137.90 N/mm²

Long. Stress at Top of Saddles 52.71 137.90 N/mm²

Long. Stress at Bottom of Saddles 52.60 137.90 N/mm²

Tangential Shear in Shell 1.46 110.32 N/mm²Circ. Stress at Horn of

Saddle 0.81 172.38 N/mm²

Circ. Compressive Stress in Shell 0.07 137.90 N/mm²

Table 2. Summary of Loads

Vertical Load (Including Saddle Weight)

802.36 Kgf

Transverse Shear Load Saddle 37.93 KgfLongitudinal Shear Load Saddle 7.62 Kgf

Table 3. Summary of Dimensions

Base Plate Length Bplen 420.0000 mmBase Plate Thickness Bpthk 10.0000 mm

Base Plate Width Bpwid 180.0000 mmNumber of Ribs (Inclined

Outside Ribs) Nribs 2

Rib Thickness Ribtk 10.0000 mmWeb Thickness Webtk 10.0000 mmWeb Location Webloc Center


Indian Journal of Science and Technology 3Vol 9 (21) | June 2016 | www.indjst.org

Table 4. Results for Saddle Ribs, Web and Base Plate

Y A AY IoShell 13 92 124855 225

Wear Plate 32 23. 75200 243.Web 166 26. 431235. 8628

Base Plate 301 18. 541800 16310.Total 513 160 1173090. 25405.

Table 5. Moment of Inertia of Saddle

Y A AY AY2 Io

Rib 102.0 16.9 172686.0 0.0 480.4

Web 102.0 19.7 201246.0 0.0 3.3

Values 102.0 36.7 373931.9 0.0 483.6

Table 6. Outside Rib Inertia of Saddles

Y A AY AY2 IoRib 102.0 16.9 172686.0 0.0 480.4Web 102.0 19.7 201246.0 0.0 3.3

Values 102.0 36.7 373931.9 0.0 483.6

Table 7. Straight Saddle Design ResultsResults Actual Allowable

Long. Stress at Top of Midspan 40.10 137.90 N/mm²Long. Stress at Bottom of Midspan 42.68 137.90 N/mm²

Long. Stress at Top of Saddles 41.61 137.90 N/mm²Long. Stress at Bottom of Saddles 41.27 137.90 N/mm²

Tangential Shear in Shell 1.71 110.32 N/mm²Circ. Stress at Horn of Saddle 0.97 172.38 N/mm²

Circ. Compressive Stress in Shell 0.06 137.90 N/mm²

Table 8. Results Ribs, Webs and Base Plate

Base Plate Length Bplen 375.0000 mmBase Plate Thickness Bpthk 10.0000 mm

Base Plate Width Bpwid 180.0000 mm

Number of Ribs (InclinedOutside Ribs)

Nribs 2

Rib Thickness Ribtk 10.0000 mm

Web Thickness Webtk 10.0000 mm

Web Location Webloc Center

Table 9. Moment of Inertia of Saddle

Y A AY IoShell 13 89 120051 216

Wear Plate 32 23 75200 243

Web 148 22 331155 5842

Base Plate 265 18 477000 12642

Totals 459 153 1003406 18942

Table 10. Results outside Ribs

Y A AY AY2 IoRib 102.0 16.9 172686.0 0.0 480.4

Web 102.0 17.5 178296.0 0.0 2.9

Values 102.0 34.4 350982.0 0.0 483.3

2.4 Design of Straight SaddleNo external loads and moments considered for this •saddle design.This saddle design is only based on the internal • pressure of the vessel.Developed stresses are within the allowable limit, •so saddle is safe for the considered 150bar design pressure.

3. Fabrication of Saddles

3.1 Fabrication of Saddles Inclined and Straight Types

This section explains how the saddles were fabricated and tested. The saddle consists of a base plate, web plate, two ribs and a wear plate in top. These plates were cut from

Figure 3. Horizontal straight saddle support.



the raw material and welded as per the manufacturing drawing which we prepared. The API code rules for welding were followed to join the plates.

3.2 Fabrication of Straight SaddleThe straight was fabricated based on the dimensions mentioned in the Table 11. These dimensions were obtained from our baseline line calculation. Dimension of all the straight saddle plate are given Table 11.

The above mentioned plate dimensions were cut from a standard plate which we bought it from mar-ket. They were cut by oxy- acetylene welding. During cutting, iron oxides formed on the edges of the work pieces, those are called as slag. Slag formation was because of the reaction between the atmospheric air and iron. Normally, at an elevated temperature, oxy-gen in atmosphere air would start react with ferrous material. As a result, they form as iron oxide and got deposited on the edges of welding. While cutting the material by oxy- acetylene welding, the material reach melting point and separated into two halves. Due to this, the edges would not be in a proper shape and it was rough. Hence, the edges were machined with 5 mm clearance. The machining was done in the Vertical Milling Machine and the subsequent machined materi-als were removed layer by layer with the help of rotary cutters. In every pass 1-2 mm was removed with respect to the sizes required. Similarly, all plates were machined and the required dimensions were acquired.

Wear plate was taken in to roller machine and rolled for required diameter. Cold rolling was selected and done under the re-crystallization temperature. Cold roll-ing consists of three rollers and they were arranged in to two rows. One roller was located at upper row and the other two rollers were in bottom rows. The plate (Wear) was inserted in between these rollers. By reducing the gap between the rollers, accurate diameter could obtain in the plate. Suitable template was made with the radius of 210 mm. The pre stated radius is the outer radius of the vessel. The plate was inserted in to the rollers often getting the template dimension which we made. There were several

insertion were done for obtaining the exact shape. And the process was repeated and attained the required shape. The base plate and the ribs were also ready after complet-ing the machining process. The web was cut at the top, to the outer diameter of the wear plate. Hence the wear plate was kept on the web and positioned accordingly. With the help of scriber the portion was marked and punched. Then the portion was cut by oxy-fuel welding then machined with the help of Hand grinding machine. The (height wise) edges were cut to 2 degrees to make the ribs inclined.

Once all the machining processes were over, the plates were joined by welding. The required grooves were taken in the plate. Bottom portion of web and ribs were provided with 2 mm double V groove and the ribs was provided with 4 mm single V groove at the top. Grooving was done by using Vertical Milling machine with the help of angle cutter. Then the plates were taken to weld-ing shop for welding. The type of weld was chosen based on the advantage, availability, cost, and strength and slag formation. Arc welding and Gas welding were usu-ally form slag on the weld surfaces and meantime it will reduce the strength of the weld but it is very economic. TIG welding is costlier than arc and gas welding but it won’t produce slag on the surface and the strength vise it is good. Hence TIG welding was chosen. For Mild steel material, Carbon steel (T-70S2) were chosen as filler rod. The web was kept on the base plate and adjusted accord-ing to the markings made. And the tri-square was used to keep the web vertically and the welding was made on 3 to 4 points. This was done to set the working pieces in accordance with the position required. Then the ribs were kept on its places and welded. Similarly the wear plate was also joined with the ribs and web. The required saddles were fabricated fully as per the drawing as shown in Figures 4-13. The weld joints were cooled after the fabrication was done.

3.3 Fabrication of Inclined SaddleInclined saddle needs of 5 plates with 10 mm thickness. Dimension of all the plates are given Table 12.

Table 11. Straight Saddle Dimensions

Base Plate 375 X 180Rib Plate 488 X 150Web Plate 370 X 488Wear Plate 545 X 235

Table 12. Straight Saddle Dimensions

Base Plate 420 X 180Rib plate 517 X 150Web plate 386 X 488Wear plate 615 X 235



Figure 4. Ribs Plates of Inclined Saddle.

Figure 5. Ribs Plates of Inclined Saddle.

Figure 6. Web Plate of Straight Saddles.

Figure 7. Web Plate of Inclined Saddles.

Figure 8. Wear Plates before Rolling.

Figure 9. Wear Plates after Rolling.

Figure 10. Grooving of Plates in Vertical Milling Machine.

Figure 11. Fabricated Saddles (Front View).

Figure 12. Fabricated Saddles (Side View).

Figure 13. Fabricated Saddles (Inclined and Straight).



As stated previously, the plates were cut from a standard dimensioned plate by oxy-acetylene welding and machined with the help of milling machine. A tem-plate was made to the radius of 243 mm. The pre stated radius is the outer radius of the vessel. And the rolling was done on the plate according to the template made. The difference between straight saddle and inclined sad-dle is that the wear plate of the inclined saddle will be kept 5 degrees from the axis whereas the wear plate of the straight saddle is kept straight and coincides with the axis. To make this inclination the ribs were cut for 5 degrees widthwise. Cutting was done by oxy-fuel welding and machined by using Vertical Milling machine. Web plate was also grinded a bit to accommodate the wear plate. Once it was done then the plates were grooved as stated above and then welded properly. At this instant, both straight and inclined saddles were made according to the procedure and API weld guidelines. After fabricating the saddles, they must be checked for cracks, defects, etc. These defects might have occurred during operation or heavy loaded conditions. For testing these saddles, NDT methods were chosen to do the surface and internal crack checking’s.

4. NDTNon-Destructive Test (NDT) is defined as the method of testing the materials for surface cracks and internal cracks without damaging the parent material. The terms Nondestructive Examination (NDE), Nondestructive Inspection (NDI) and Nondestructive Evaluation (NDE) are also commonly used to describe the Non-Destructive Testing. NDT tests are widely used by the quality depart-ments by sampling basis for a batch of products or 100% checking of the materials for defects occurred while manu-facturing. This system is very helpful for production quality control system to monitor the deviations in products that occur due to improper manufacturing techniques. In a manufacturing unit products are manufactured as a batch and the batches may contain defected products. As per the acceptance sampling method or by other sampling meth-ods the batch will be checked for defects by taking some samples. To conduct this sampling test, NDT method will be used. It also widely used by the maintenance depart-ment in each mechanical company for detecting internal and external cracks. Hairline cracks and internal cracks occurred in a machine part cannot be found by naked eyes and it can be detected only by NDT methods.

4.1 Applications of NDT InspectionRaw materials which are used in the construction of •the product.Fabrication processes which are used to manufacture •the product.Finished product before it is put into service.•

4.2 Methods of NDT InspectionThe NDT technique uses various principles and different methods. There is no single procedure depending upon which the result are produced. The various methods of NDT are given below.

Dye Penetrant Test.•Magnetic Particle Inspection.•Ultra Sonic Testing.•Visual Inspection.•Oil and Chalk Process.•Eddy-Current Method.•Radiography Method.•Acoustic Emission Testing.•Leak Testing.•Infrared and Thermal Testing.•

From the above methods, dye penetrant and magnetic particle inspection were chosen to find the surface cracks and ultra-sonic and radiography tests were chosen to find internal cracks of saddles.

4.2.1 Dye Penetration TestDye penetration test is one of the NDT methods, which is used to find the surface cracks (Flaws which are open to surface). This method is widely used because of its sim-plicity and low cost. The main principle of this method is capillary action due to surface tension. Here a penetrant is first applied on the material and allowed to penetrate for a particular time. Capillary action causes this penetration. Then a developer is applied to enhance the visibility which shows the crack in contrast color with a light background. Thereby the location of the crack is found. Before conduct-ing any costly tests such as ultrasonic, radiography, dye penetrant is used. Hence if any surface crack is found, the material can be rejected without wasting money for high end tests. This method can be used for ferrous and non-ferrous metals and cannot be used for porous materials. To find surface discontinuities on non- ferrous materi-als, magnetic particle inspection cannot be used. Hence



the only possible way to find surface discontinuities on non-ferrous martial is by Dye penetrant inspection.

ASME Section 5 Article 6 SE 165.ASTM E 165 – 02 for liquid penetrant test.

Dye penetrant test is conducted on saddles to find the defects in welded joints. The detailed procedure of dye penetrant test is given below.

A clean surface is essential for successful dye penetration inspection. Hence the welded part of the saddle is first cleaned with the help of lint free cloth thoroughly as sown in Figure 13. All the foreign mate-rial, dirt, welding flux, slag, etc are taken out, since they may absorb the dye and may show a false indication of crack. Then a cleaning solvent is applied on the parts and wiped out with a cloth. The solvent used for cleaning is Magno flux cleaner. Cleaning is one of the important tasks in this test because inadequate cleaning may result in poor sensitivity of Dye penetrant test. Now the saddle is ready for applying penetrant. There are three methods to apply penetrant. They are: 1. Spraying, 2. Brushing and 3. Dipping.

For small components spray method is sufficient. But for larger components spraying will consume more time hence they are dipped. Here the saddle is of smaller size so spray method is chosen. The penetrant used in this process is ORION-115 P and red in colour as shown in Figure 14. The penetrant is sprayed at a distance of 300 mm from welded parts and moved slowly on the welded joints. After applying penetrant thoroughly, dwell time is given for penetration. Dwell time is the time taken by the penetrant for capillary action to take place. This dwell time vary with respect to the hardness of the material. Hard materials require lengthy dwell times. The dwell time usually vary from 10 to 30 minutes. Here the sad-dle is given around 30 minutes of dwell time. During the dwell time the penetrant must have penetrated through the cracks.

After giving enough dwell time, the surplus dye must be removed from the surface. Dye is removed with a lint free cloth and all the penetrant is wiped out. This cleaning must be done uni-directionally. Cleaning in different directions may take out the penetrant from cracks. Cleaning should be de done repeatedly until the penetrant is totally wiped off from the surface. Residual penetrant on the surface may give false or irrelevant indications.

Developer is applied, after cleaning the surface thoroughly. The developer used in this process is ORION-115D as shown in Figure 15. This contains white powder mixed with evaporative liquid. When it is sprayed, the white powder is deposited on the surfaces and the liquid is dried off. Before applying developer, the can is shook thoroughly to make the white powder to dispense with liquid. A fine and even coat of developer is given on the surface and moved along the weld. Heavy coat on the surface may give blurred indication of crack. Now dwelling time is given for the developer to absorb the penetrant from cracks. This dwell time varies from 7-10 minutes.

The saddle is taken out to the sun light, after sufficient duration for developing; the saddle was inspected with naked eyes. Complicated areas were inspected using mag-nifying glass is as shown in Figure 16. In case of defect (flaw), it will appear as red colour in white background. During inspection, no such indications of flaws were found

Figure 13. Surface preparation is done with the help of cleaner and lint free cloth.

Figure 14. Penetrat is Applied with the Help of ORION 115P.

Figure 15. Developer is applied on the Saddles.



on the welded parts. As per the ASME standards the above inspection on the weld parts are found satisfactory.

Depending only upon the dye penetrant test, the result cannot be concluded. Hence the saddle is checked for defects by using magnetic particle inspection.

4.2.2 Magnetic Particle InspectionMagnetic particle inspection is one of the Non-Destructive testing methods, which carried out to find the surface cracks (cracks which are open to surface). It can also be used to detect the sub surface cracks on work pieces up to 6 mm thickness. Here the Ferro-magnetic particle is sprinkled over the surface and the part is magnetized. These particles will be accumulated at the flaw and gives an indication of crack.

The time required for conducting this test is very low and sensitivity of this test in finding surface cracks is higher than that of Dye penetrant test. Dye penetrant test requires more time, since the surface has to be cleaned, penetrant and developer should be applied and dwelling time must be given for penetrant and developer. It con-sumes lot of time. But the magnetic particle test can be conducted within a very short time. In some instances, Dye penetrant test may give false indication. But the probability of giving false indication in Magnetic particle test is very low.

ASTM E - 709ASME Section 5

This test is conducted on the saddles to find the surface cracks and the detailed procedure is as shown in Figure 17.Magnetic particle inspection is depends upon the principle of Magnetic Flux Leakage. A straight piece of magnetic material will have poles at each ends known as South and North Pole. As we know similar poles repel each other and different poles attract each other (north and south pole attracts and north and north poles repels).

Magnetic flux lines flow from South to North Pole inside the magnet and north to south around the magnet. When a crack begins on a surface, it will be open to the surface and the surface will be separated into two halves. These two separated parts will be taken as two bar magnets and two poles are created at each ends. Now the magnetic flux lines will get distorted due to the discontinuity and starts flow from North to South Pole in air gap. These flux leak-age will attract the Ferro-magnetic particles sprinkled on them. Since these poles are different in nature, they start to attract each other. Hence the strength between these poles will be higher and they will attract the Ferro-magnetic particles sprinkled over the surface. Thereby the defect can be found easily.

Magnetic particle testing equipment consists of a Magnetizing Yoke, Ferro-magnetic particles (Dry, Wet, and Fluorescent) and Ultra-Violet light in case of Fluorescent magnetic particles is as shown in Figure 18. The Yoke is used to magnetize the material. Magnetization can be done by either circular or longitudinal. In this experiment, longitudinal magnetization is done on the saddles. The Ferro-magnetic particle used is of fluorescent type.

Before testing magnetic particle inspection on saddles, the equipment is calibrated with a gauge known as Pi-Gauge. The pi-gauge has a known defect on its sur-face, which is invisible to naked eyes. Magnetic particle inspection will be carried out on the Pi-gauge and it has to give the indication of crack. Thereby the equipment is calibrated. The pi- gauge was magnetized by yoke and flu-orescent magnetic particles were sprayed on the pi-gauge as shown in Figure 19. The ultra-violet ray light is now focused on the pi-gauge. It is found that the magnetic par-ticles were accumulated at the defect place. The crack was indicated by a white shiny colour in metal background.

Figure 16. Diagram shows the different procedures involved in dye penetration inspection.

Figure 17. Leakage fields between two pieces of a Broken Bar Magnet (a) with Magnet Pieces Apart, and (b) with Magnet Pieces Together (Simulating Flaw). (c) Leakage Field at a Crack in a Bar Magnet.



Hence the equipment is calibrated and the test is now can be conducted on the saddles.

Before conducting magnetic particle test on saddles, pre-cleaning has to be done. The saddle surface was cleaned with cloth and all the foreign materials were removed. Now the saddle is magnetized using yoke in each joint and the fluorescent particles were sprayed from Mangnaflux bottle. Since the size of the yoke is small, magnetization cannot be done for the whole saddle at a time. Hence saddle is divided into number of parts, and each part is magnetized separately. Now the fluorescent magnetic particles were sprayed on the saddle in each part. The ultra-violet ray light was focused on each part of the saddle and checked for cracks. No crack or defects were found on the saddle during inspection. Hence the weld done on the saddle was found satisfactory.

4.2.3 Ultra Sonic TestingUltra sonic testing is one of the NDT methods, which is used to evaluate the internal conditions of the material i.e. used to find the internal cracks in the material particularly in sound conducting materials. It is one of the classical method and it is been used for the past 5 decades. It can also used to find the thickness of the material. In this method sound is used to find the defects. The Ultrasonic instrument uses the principles of sound propagation to detect and locate defects such as cracks, porosity, deterioration, corrosion, lamination and foreign

inclusions found in material. Using this method the size and shape of the defect could be found out which will be very helpful in fracture mechanics. Depending upon the size and shape of the flaw, the maximum safe stress can be calculated. Ultra sonic testing uses the principle of sound propagation. A short pulse of ultrasound is generated by means of an electric charge applied to a piezo electric crystal, which vibrates for a very short period at a par-ticular frequency is as shown in Figure 20. This frequency varies from 1MHz to 6MHz. These vibrations or sound waves have ability to travel through elastic materials. The Ultrasonic waves propagated through the material will be reflected on reaching an interface (such as defect, flaw, hole, back wall). These reflections will be detected by the piezo electric crystal. These oscillations are transferred to the CRT screen to acquire the result.

An Ultrasonic flaw detector consists of a CRT screen, Pulse generator, and Pulse receiver is as shown in Figure 21. A pulse generator is an electronic device that can produce high voltage electrical pulses. These electrical pulses are then given to the transducers. A pulse receiver is used to receive the electrical pulses from the transduc-ers. The CRT screen converts these electrical signals into visible format in a digital display. The result of any test can be obtained from the CRT screen only.

Probes are used to convert the electrical pulses into ultrasonic waves. Different types of probes are used in ultrasonic testing. Selection of proper probe is depending

Figure 18. A Yoke, Ultra-Violet Lamp and Ferro Magnetic Particles.

Figure 19. The Pi-Gauge.

Figure 20. Ultrasonic testing schematic setup.

Figure 21. The probe and the ultrasonic flaw detector are shown above.



upon the thickness of the material and type of material. The different types of probe used are:

Straight-Beam (Single Transducer).•Straight-Beam (Thru-Transmission).•Angle-Beam.•

Sound waves from the straight beam are transmitted through the work piece by a transducer and reflected back by the other side surface of the test object. These reflected waves will be received by the same transducer. Hence the transducer acts as both receiver and generator of ultra-sonic waves. Here the transducer will have separate sound transmitter and receiver. The ultra-sonic waves will be transmitted by a separate transmitter and the waves are received by a separate receiver. The angle-beam (Shear Wave) technique is used for testing sheet, plate, pipe and welds. This technique is used where the beam has to be transmitted at an angle. The different angles of probes available are 45, 60 and 70 degrees.

It is used to transfer the ultrasonic sound waves form the probe to the work piece. It used to be in the form of liquid or paste. Oil, Grease, etc. It can be used as a coupling medium.

To inspect the saddle, Angle probe is selected. Selection of probe angle depends upon the formulae given below.

Probe angle = 90 – T

Where, T - Thickness of the material to be inspected. Hence the angle for the probe selected is 70 degree. At the fore most the Ultrasonic equipment is checked for calibration.

Here the probe was made to move on the calibration block to find the known defects. First the thickness of the material is checked and then the defects were checked for calibration. The ultrasonic equipment was able find the defects. Hence the equipment is calibrated is as shown in Figure 22.

Now the saddles are checked for internal cracks. First the coupling is poured on the surface of the saddle. The coupling used in this test was oil. Now the probe is moved on the surfaces nearer to the weld joints and checked for defects on the CRT screen. The CRT screen shows the echoes on the screen and if echoes are found then the saddle can be declared as defected one. This procedure is repeated for both the saddles is as shown in Figure 23. During the test echoes were found at the thickness of 10.2-10.6. Hence it is assured that the defect available on

the saddle was “undercut”. And some other echoes were found at the thickness of 6.3-8.2. These are welding defects caused due to insufficient filling of filler material. Since this saddle was a structural member the welding could not penetrate properly throughout the joints. The defects were marked on the material and test was completed.

5. Finite Element SimulationFinite Element Technique (FEM) is a numerical technique to find fairly accurate solutions to boundary value prob-lems which utilizes variation methods (the calculus of variations) for minimizing an error function and create a stable solution. Analogous to the idea that linking many tiny straight lines could fairly accurate a larger circle, FEM includes all the methods for linking a lot of effortless element equations over numerous small sub-domains, named finite elements, for approximating a more complex equation over a superior domain. In this project, we used FEM to find out the load carrying capacities of the saddles which we fabricated material details are listed in Table 13 and the boundary condition are shown in Figure 24.

Figure 22. Calibration of the ultrasonic equipment.

Figure 23. Ultrasonic inspection on saddles.

Table 13. Materials of Vessel and Saddle

Items MaterialsVessel Material SA 516 Gr.70 (Assumed)Saddle Material IS 2026Gr-B



5.1 Loads Considered IncludesInternal and External design Pressures.•Weight of the Vessel.•Assumed Wind and Seismic Loads.•

Since this analysis is only to check load bearing capacity we didn’t consider all external loads.

5.2 Boundary ConditionsThe bottom portions of the saddle were arrested in all directions. And the top of the wear plat, we applied 150 bar uniform pressure load to check the maximum load bearing capacity of the saddle and we obtained the fol-lowing results. We checked, the obtained stresses are within the allowable stress limit of the saddle and we found that the obtained stresses are with the allowable and we concluded we can use these saddles up to 30 mm thickness vessels with maximum of 150bar internal pressure.

5.3 Allowable Limits of the MaterialAllowable Stress Limit of the Saddle Material in the com-bined loading condition = 204MPa

5.4 Analysis Remarks

Figure 25. Von-Misses and deflection of inclined saddle.

Figure 26. Strain of the inclined saddle.

Figure 27. Stresses in the straight saddle.

Figure 28. Strain and displacement of straight saddle.

Figure 24. Boundary condition of the saddle.

Figure 29. Strains in straight saddle.

6. Results and DiscussionBased on the results (Figures 25 to 29), it concluded that the developed stresses are within the allowable limit, so



the saddle is safe up to 150 bar uniform pressure loading condition. Also it holds up to 30 mm thickness pressure vessel with the operating pressure load up to 150 bar. So the load carrying capacity of the saddle is 150 bar.

7. ConclusionBased on our study in the areas of design, fabrication, NDT and FEM simulation, we concluded the followings for future development. Normally Zicks method appli-cable only for horizontal saddle design, but this work proved that Zick method also applicable for inclined saddles provided inclined saddle would undergo proper FEM simulation test.

Without FEM, the inclined saddle design based on Zicks approach would not help all the time for make sure, the saddle is safe.

There were no surface cracks identified during DPT, MPT testing. This was due to the suitable welding. So it is mandatory that quality checks need to be done on welds prior to use the saddle after fabrication.

There were no internal cracks identified in our UT testing. This was also due to suitable welding. Internal crack checks need to fix as mandatory for all the weld joints. Either UT or RT needs to be done for all the weld corners for ensuring, the design is safe.

The FEM simulation proved that saddles are good enough for withstanding 150bar internal pressure load. Always check the load bearing capacity of the saddles prior to erection using FEM.

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6. Brownell LE, Young EH. Process Equipment Design. New York: John Wiley and Sons Inc.; 1959.

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10. Mackerle J. Finite elements in the analysis of pressure vessels and piping, an Addendum: A bibliography (2001-2004). International Journal of Pressure Vessels and Piping. 2004; 82(7):571–92.

11. El-Abbasi N, Meguid SA, Czekanski A. Three-dimensional finite element analysis of saddle supported pressure ves-sels. International Journal of Mechanical Sciences. 2001; 43(5):1229–42.

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13. Khan SMA. Stress distributions in a horizontal pressure vessel and the saddle supports. International Journal of Pressure Vessels and Piping. 2010; 87(5):239–44.

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16. Available from: http://www.tormeneamericana.com.ar/public/TA2885A-0000-C-001 Data%20Book/Databook%20H-21002/TA2885A-0000-C-001%20-%20Mechanical %20Calculation /TA2885A-0000-C-001%20-%20AS%20Built.pdf

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