Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21)
Prague, Czech Republic Virtual Conference – August, 2021
Paper No. ICMIE 109
DOI: 10.11159/icmie21.109

Design, Manufacturing and Testing of Pipe Fittings
M. Evren Toygar1, Selin Kirdiş2, Mustafa Yegin1, Elvan Pehlivan1, Umut Doğan1, Özkan Deniz1, MustafaÇoban1
Dokuz Eylul University, Mechanical Engineering Department
Tınaztepe Campus, Izmir, Turkey
evren.toygar@deu.edu.tr; selin.kirdis@metu.edu.tr
2Middle East Technical University, Graduate Program of Biomedical Engineering
Ankara, Turkey1

Abstract - Fasteners have a very significant place in machine design, and they are the indispensable elements of many sectors such as
automotive, electrical electronics, metal industry. Pipe fittings are one of the basic types of fasteners, and the most significant feature ofpipe fittings is that they provide impermeability. In the first part of the study, pipe fittings were designed and manufactured. In the second
part of the study, experiments were conducted to analyze the effect of the surface roughness, fluid pressure and material type on the pipe
fitting’s sealing performance with the help of the measured torques that prevent leakage. In the following sections, this torque is referred
to as sealing torque. Experimental results are consistent with mathematically calculated results and SolidWorks Simulation results.
Additionally, it is thought that the result of the performed experiments in this study can help the pipe fitting manufacturers in terms ofmaterial and surface roughness selection.
Keywords: Fastener; pipe fitting; surface roughness; sealing

1. Introduction

Fasteners are used in most machines, electronic devices and furniture. Since these products consist of more than onepiece, they usually need to be connected with fasteners. Pipe fittings are one of the basic types of fasteners, and the mostsignificant feature of pipe fittings is that it provides impermeability. Impermeability is achieved by preventing leakage fromthe pipe fitting. Fernando and Karabelas [1] state that the effect of sealing is found by observing the amount of liquid leaking.
Fluid leakage between statically contacting surfaces depends on various parameters that can directly affect the sealingperformance. These parameters are; fluid pressure, fluid viscosity, contact pressure (CP) and surface mechanical behaviour,texture and topography [2]. In the paper written by Li et al. [3], the effect of design parameters, such as the conical angle andthe conical ring’s displacement, on the contact pressure was examined. Moreover, a procedure was developed by Fernando
and Karabelas [1] to examine the sealing performance, and they found contact pressure distributions using this procedure.
In this study, our aim is to design and manufacture pipe fittings and determine the sealing performance of the fitting indifferent conditions with the help of experiments and simulations. The sealing performance was investigated in terms of fluidpressure, material type and surface roughness with the help of conducted experiments. The effect of these parameters on
sealing was interpreted via measuring the bolt tightening torque which is called sealing torque for this study.

2. Design and Production

The designed connection element, which can be seen in Fig. 2.1, consists of three basic parts. These parts are the body,nut and ring. Body and ring parts were produced by using CNC machining, and the nut part was purchased.

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Fig. 2.1: Designed pipe fitting

In this study, our design is based on the pipe fitting standard ISO 8434-1 [4]. Basic factors such as the taper angleof the ring part, which was determined as 240 using ISO 8434-1 [4] were preserved. Screw and nut connection waspreferred M18 x 1.5 fine thread in accordance with ISO 68-1 bolt standards [7]. An additional screw hole was drilled in
the body part, suitable for the connection of standard nozzle types. Moreover, similar designs were examined during thedesign process [5], [6].
The main problem encountered in the designed screw fastener is the leakage problem. As long as there is a gap
between the two environments, a material passage can not be prevented, and impermeability can not be achieved. Sealing
is important not only for the liquid inside the pipe to leak out but also to prevent dust and dirt from mixing with theliquid inside the pipe from the environment. Dust could impair the liquid purity and block the nozzle hole.
Leakage can occur from two surfaces in the screwed pipe fittings [3]. The conical ring, which is in direct contact
with these two surfaces, provides sealing by applying pressure to the body element’s conical surface with the help of anut. Therefore, the ring’s material type and surface roughness are significant. So, testing the effect of the conical ring’s
material type and surface roughness is sufficient for our experiments. In accordance with this information, the brass andthe aluminium ring was produced in three different roughness classes and the copper ring in two different roughnessclasses for the experiments. Manufactured parts of the pipe fitting and experimental setup can be seen in Fig 2.2.
Designations of the materials are Cu-ETP for copper, CuZn39Pb3 for brass and 6082 for aluminium.

Fig. 2.2: Manufactured parts of the pipe fitting and experimental setup

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The roughness classes decided for the conical ring are: N5-N7 range, N7-N9 range and N9-N10 range. The copper ring
was not produced in the N9-N10 roughness class range because of the machining problems caused by the copper’s highductility nature. Moreover, surface roughness measurements were performed in Dokuz Eylul University Materials
Engineering Tribology Laboratory to prove the rings’ roughnesses are consistent with required roughnesses. The surface
roughness measurement results were shared in Table 2.1, Table 2.2. and Table 2.3.
Table 2.1: Surface roughness measurement results of copper rings

Arithmetical Mean
Height (𝑅𝑅𝑎𝑎 )Root Mean SquareDeviation(𝑅𝑅𝑞𝑞 )The Total Height ofProfile (𝑅𝑅𝑡𝑡 )Maximum Height ofProfile (𝑅𝑅𝑧𝑧 )Roughness Class

COPPER 1

COPPER 2

0,57 μm

2,69 μm

0,70 μm

3,21 μm

3,26 μm

14,03 μm

3,02 μm

12,36 μm

N5-N7 range

N7-N9 range

Table 2.2: Surface roughness measurement results of aluminium rings

Arithmetical
Mean Height(𝑅𝑅𝑎𝑎 )
Root MeanSquareDeviation(𝑅𝑅𝑞𝑞 )The Total
Height ofProfile (𝑅𝑅𝑡𝑡 )Maximum
Height ofProfile (𝑅𝑅𝑧𝑧 )RoughnessClass

ALUMINIUM 1

ALUMINIUM 2

ALUMINIUM 3

1,03 μm

4,33 μm

6,51 μm

1,13 μm

3,91 μm

7,70 μm

4,67 μm

15,05 μm

31,36 μm

4,12 μm

13,96 μm

28,44 μm

N5-N7 range

N7-N9 range

N9-N10 range

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Table 2.1: Surface roughness measurement results of brass rings
BRASS 1BRASS 2
BRASS 3
Arithmetical
Mean Height
0,97 μm
5,52 μm7,03 μm(𝑅𝑅𝑎𝑎 )
Root Mean
Square1,18 μm
6,58 μm
8,37 μm
Deviation(𝑅𝑅𝑞𝑞 )The Total
Height of
6,42 μm
25,70 μm
33,62 μm
Profile (𝑅𝑅𝑡𝑡 )Maximum
Height of
9,44 μm
24,49 μm
30,45 μm
Profile (𝑅𝑅𝑧𝑧 )Roughness
N5-N7 range
N7-N9 range
N9-N10 range
Class

3. Method

3.1. Experimental Setup
Experiment conditions were determined in line with the needs since the regulation of the test conditions could not
be found in the standards for the data desired to be obtained.
Pratissoli Plunger Pump KE28H was used to pump water to the nozzle connected to a 12 mm pipe. Jetting-Vacuum
Truck was used to control water, and Pakkens MH100 Pressure Gauge was used to measıre pressure. Measurements ofsealing torques were taken via Norbar 100 Torque Wrench. The schematic representation of the experimental setup canbe seen in Figure 3.1. The realization of Fig 3.1.B was shown in Fig. 2.2 with the subtitle ‘’Experimental Setup’’.

Fig. 3.1: Schematic representation of the experimental setup

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3.2. Procedure
Experiments were performed to determine the sealing performance of the fastener. Experimental variables are material,surface roughness and fluid pressure, and the effect of these variables on the sealing performance was examined bycomparing the sealing torques in static and dynamic conditions separately. In the experiments, the nut was tightened with atorque wrench, starting from 20 Nm and increasing 1 Nm until the sealing was achieved and the sealing torques in different
conditions was examined.
During the experiments, it was observed that, in the case of dynamic load(such as turning the nut by hand, hitting theconnection element), the body disconnected from the ring and further disconnected from the pipe.
Table 3.1: Experimental Conditions
Experiments

Material

Arithmetical Mean
Height (𝑅𝑅𝑎𝑎 ) ofConical Part of TheRingExperiment 1

Aluminium

1,03 μm

11,8 mmExperiment 2

Aluminium

1,03 μm

12 mm

Experiment 3

Aluminium

4,33 μm

12 mm

Experiment 4

Aluminium

6,51 μm

12 mm

Experiment 5

Brass0,97 μm

12 mm

Experiment 6

Brass

5,52 μm

12 mm

Experiment 7

Brass

7,03 μm

12 mm

Experiment 8

Copper

0,57 μm

12 mm

Experiment 9

Copper2,69 μm12 mm

The Diameter ofThe Pipe

Ring materials, surface roughnesses and pipe diameters used for the experiments can be seen in Table 3.1, and theleakage, drip and sealing torques measured in the experiments conducted under these conditions at different water pressures
are indicated in Table 4.1.

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4. Analysis and Results

The results of the experiments can be seen in Table 4.1. These results were measured in static conditions. It has
noticed that under any dynamic load (such as hitting the fastener, rotation of the fastener, etc.), the connection elementperform its function for these experiments. The reason is that the sealing torques specified in Table 4.1 are not sufficientthe pipe and ring to be squeezed until plastic deformation occurs.
Table 4.1: Experiment Results
10 BAR
30 BARTORQUE (Drip)(Nm)

SEALING TORQUE(Nm)

TORQUE (Drip)(Nm)

SEALING TORQUE(Nm)

TORQUE (Drip)(Nm)

SEALING TORQUE(Nm)

TORQUE (Drip)(Nm)

SEALING TORQUE(Nm)

70 BARTORQUE(Leakage) (Nm)50 BARExperiment 134445050535354-54Experiment 235444646535355

55

57

Experiment 3

30

4042-

4242

48

48

50

Experiment 430

3435-

35-

35-

35

Experiment 530

42

43

4344-

44-

44

Experiment 630

3741-

41-

41-

41

Experiment 7

30

3435-

35-

35-

35

Experiment 8

30

40

41

41

48

48

49-

49

Experiment 930

4041-

41

41

43-

45

EXPERIMENTS

Further experiments were performed to examine the dynamic characteristic of the pipe fitting. For dynamic conditions
at 70 bar, the sealing torques are 75 Nm, 60 Nm and 80 Nm for the copper, brass and aluminium ring, respectively.

5. Conclusion

The effects of material, surface roughness, and pressure are examined with experiments in this research.
Firstly, there is an absolute relationship between surface roughness and sealing performance. As the surface roughness
increases, the sealing torque decreases because the decrease in the contact area provides the same surface pressure with theless applied force. Therefore, the surface roughness of the conical ring is suggested to be high.
Secondly, the systems’ sealing torques, in which the brass rings were used, most of the time have the lowest values thanother systems. Thus, the brass material is the most suitable material for the conical ring since it would be appropriate tochoose the material which provides the lowest sealing torque.
Additionally, it has been observed that the increase in liquid pressure generally increases the sealing torque as expected.
The system in which the aluminium ring was used was more affected by the increase in liquid pressure than the otherexperimental systems. The system with the brass ring is the least affected.

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References[1] U. S. Fernando and G. Karabelas, “Analysis of end fitting barrier seal performance in high pressure unbonded flexiblepipes”, in Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2014,
doi: 10.1115/OMAE2014-23574.
[2] B. N. J. Persson, Sliding Friction: Physical Principles and Applications, 2nd Eds. New York, NY, USA: Springer, 2000.
[3] X. Li, X. Du, J. Wan, and H. Xiao, “Structure analysis of flexible pipe end fitting seal system”, in Proceedings of theInternational Conference on Offshore Mechanics and Arctic Engineering - OMAE, 2015, doi: 10.1115/OMAE201541718.
[4] Metallic tube connections for fluid power and general use — Part 1: 24° cone connectors, ISO 8434-1, 2018.
[5] A. Legris, “Pipe fittings, and in particular for high pressure fluid pipes,” United States Patent 4309050, Jan. 5, 1982
[6] H. Ko, “Water Pipe Connecting Structure,” United States Patent 5516155, May 14, 1996.
[7] ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads, ISO 68-1, 1998.

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