the design of internal alignment clamp for pe pipe … ho 2016.pdfthe design of internal alignment...

The Design of Internal Alignment Clamp for PE Pipe Fusion

IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan

The Design of Internal Alignment Clamp

for PE Pipe Fusion

HO Chun Yiu, Alan

Engineer

Technical Development Section, Distribution Operation Department,

The Hong Kong and China Gas Co. Ltd.



Abstract :

Electrofusion is one of the common methods for joining Polyethylene (PE) pipes to lay new

pipeline and rehabilitate aged metallic pipes. However, it is now suffering some limitations to

strive for excellent electrofusion quality by utilizing the existing strap clamp which is used to

hold the position of pipes and couplers when undergoing electrofusion process.

To eliminate these limitations for PE pipes electrofusion, an innovative equipment naming as

“Internal Alignment Clamp” (IAC) has been developed. It aims to improve the joint quality and

reliability as well as enhance gas safety by rectifying the pipe geometry imperfections actively,

especially in the fusion zones, when performing electrofusion regardless of the external

congested condition of the coupler.

This paper introduces the working principle, design features of this equipment and functional

verifications are shown to support its improvement beyond traditional strap clamp.



1. Introduction :

Similar with other international cities, Hong Kong has a high urban density, commercial and

residential buildings and congested underground utilities everywhere (Fig. 1). Due to this

congested underground situation, Electrofusion becomes the predominant joining method to

lay new pipeline and rehabilitate aged metallic pipes. As Hong Kong is densely populated, even

single accident cannot be tolerated and could be a disaster; the community could be benefited

from enhanced safety through pursuing a more qualitative and reliable electrofusion solution

by the gas company.

Fig. 1 The high urban density situation in Hong Kong

Having a detailed insight of the basic principle of Electrofusion process and the worsening

factors of joint quality is essential to understand the inspiration of developing the Internal

Alignment Clamp.

1.1 Principle of Electrofusion

Electrofusion (Fig. 2) is a method to join Polyethylene (PE) and other plastic pipes using

electrofusion coupler that have built-in electric heating coils which are used to weld the joint

together.

The pipes to be joined has to be cleaned and scraped, and then inserted into the electrofusion

coupler properly and fixed by clamp, after that a voltage is applied for a fixed time depending

on the coupler in use. The built-in heating coils then melt the inside of the coupler and the

outside of the pipe wall, the molten PE will flow and fill in the gap between the pipes and

coupler, which weld together to produce a very strong homogeneous joint. The assembly is

then cool down for a specified time. The electrofusion process is then completed.



Fig. 2 Principle of Electrofusion Process

1.2 Worsening factors of the electrofusion joint quality

The strap clamp is currently implemented to help maintain pipes in position with the coupler

when performing electrofusion. Both pipe ovality and misalignment do not favor electrofusion

jointing, while the use of traditional strap clamp is unable to control and rectify these potential

jointing imperfections. In addition, the congested underground environment also hinders the

use of strap clamp. These may lead to an inferior joint.

1.2.1 Geometry imperfections of pipes

Fig. 3 PE pipe deformation induced by pipes storage



Few geometry imperfections of the PE pipe might be induced through transportation

and storage (Fig. 3), such as Oval-shape-deformed and Locally flattened. Ovality is a

measure of the out-of-roundness of the pipe (Fig. A in Appendix), the larger the ovality

value, the larger the variation in the annular gap between the pipes and coupler (Fig. 4).

Fig. 4 Difference between pipes with ovality and perfectly circular after inserted into coupler

1.2.2 Misalignment of pipes and coupler

Both Angular and Parallel Misalignment (Fig. 5) would induce a large variation in the

annular gap between the pipes and coupler as well, due to the improper installation

process despite of having perfectly circular pipes. It might be caused by (a) improper

tightening force applied to the strap clamp which varies with different pipe size and the

alignment condition and (b) workmanship inconsistencies due to different jointers

operation.

Fig. 5 Angular and parallel misalignment of pipes and coupler

1.2.3 Congested environment outside the coupler

In some situations, the traditional strap clamp is not applicable, such as (a) limited space

in trench at pedestrian road and (b) congested trench which full of other underground



utilities (Fig. 6). It is a physical limiting factor of the external environment which hinders

the implementation of strap clamp.

Fig. 6 Congested trench situation

1.3 Design change incubated by disruptive innovation thinking

An innovative equipment “Internal Alignment Clamp” (in short, IAC) has been developed (Fig. 7)

to tackle the mentioned challenges of PE pipes electrofusion. It aims to improve the joint

quality and reliability, for instance, 1) improve the geometry of PE pipes in fusion zones actively,

i.e. auto-reround oval-shape-deformed pipes; 2) ensure proper alignment of pipes and coupler

automatically; 3) enable adaptability to different pipe sizes; 4) eliminate limitations of

congested environment outside the coupler; 5) lower the workmanship inconsistencies caused

by different jointers operation. Therefore, it can facilitate a good quality and reliable PE jointing

as well as enhance gas safety significantly.

Fig. 7 Design Change from Traditional Strap Clamp to Internal Alignment Clamp



2. Internal Alignment Clamp :

IAC is a set of pneumatic actuated device which expands in 2-stages; clamps and rectifies the PE

pipes dimension and alignment when undergoing electrofusion process. The whole system is

shown in (Fig. 8). It consists of (a) the Internal Alignment Clamp, (b) Control Unit, (c) Pneumatic

Multi-Core Tubing, (d) Power Cord and (e) Wire. IAC is connected to a control unit with a multi-

core pneumatic cable. And CCTV (Closed-Circuit Television) system and lighting are equipped

for transmitting real time video wirelessly to provide feedback of the clamps operating status.

Therefore, the operator can remotely control the IAC by the control unit.

Fig. 8 The whole setup of the Internal Alignment Clamp

IAC is designed and simulated by CAD (Computer Aided Design) (Fig. 9) software and some precise

parts are fabricated by CNC machine for the sake of fulfilling tight tolerance requirements.

Fig. 9 Computer Aided Design and Simulation of the Internal Alignment Clamp



2.1 Mechanism of the clamp

Fig. 10 Mechanism and component list of the Internal Alignment Clamp

IAC is a set of pneumatic actuated device that transforms forces from 2 pneumatic cylinders to

both 4-plates pressing clamp or expander through 8 sets of linkage (Fig. B in appendix). Most of

the machined parts are made of Aluminum (AL-6061 and AL-7075) and rods are made of steel.

All parts are simulated (Fig. 9) before fabrication, verified and optimized to ensure its safety

factor is larger than 10 during normal operation. (Fig. 11)

Fig. 11 Parts are verified to ensure its Safety Factor > 10 in normal operation



Refer to the (Fig. B in appendix) for the details of forces transformation from pneumatic

cylinder to individual press plates pressing force. And (Fig. C) for the comparison between

Simulated requiring force and Calculated providing force for pipe deformation. It shows that

the IAC could provide sufficient forces to rectify the ovality from 1.5% to 0 for all Dn315, Dn355

and Dn400 pipe.

2.2 Operating Procedures

There are 5 steps of the operating procedures shown in Fig. 12 :

1) Insert the IAC into the rear pipe. Expand the Rear Clamp (1st stage) to lock its position

with the rear pipe and rectify the geometry of rear pipe fusion zone to become circular

2) Install the electrofusion coupler to the rear pipe

3) Insert the front pipe to the coupler

4) Expand the Front Clamp (2nd stage) of IAC to lock its position with the front pipe and

rectify the geometry of front pipe fusion zone to become circular

5) Retract both 1st and 2nd stage of IAC after undergoing the electrofusion and cooling

stages, then withdraw the IAC from the pipe and the whole operation is completed

Fig. 12 Internal Alignment Clamp operating procedures (Cross-Sectional View)



2.3 Special Features (Quick change for adapting various pipe sizes)

IAC is designed to apply for 3 majority pipe sizes for the Electrofusion: Dn315mm, Dn355mm

and Dn400mm PE pipe. It can be transformed easily to fit different pipe configurations by

changing the specified press plate which is locked by a quick lock.

The press plates are made of Polyformaldehyde (POM) (Fig. D in appendix) material which has

the advantage of low coefficient of friction, wear resistance, low heat conductivity and

relatively higher Young Modulus than PE. Press plates for different pipe sizes are all machined

by CNC machine precisely, but only the curvature is distinguished to fit with specified pipe ID.

Fig. 13 Fabricated POM Press plates and the engineering drawing highlight

2.4 Control Unit

The control unit (Fig. 14) of the IAC system is the essence of the system which is the control

interface between the IAC and the operator. Though it is important, it is simple and user-

friendly, there are 2 handles to control the Front and Rear clamp and a power button could be

accessed by the operator. And 3 pressure gauges for displaying the source, Front and Rear

Clamp compressed air pressures. It converts electrical power to energy stored inside

compressed air which transmitted through a multi-core pneumatic cable to expand and retract

both Front and Rear Clamp. Refer to (Fig. 14) and (Fig. K in the appendix) for pneumatic

components arrangement and the pneumatic diagram for the system respectively.



Fig. 14 Pneumatic components inside the Control unit

Fig. 15 Multi-Core pneumatic cable and power cord connection is located at aside of control box

2.5 Real Time Video Feedback

The CCTV and lighting (Fig. 16) on the IAC captures the real time video and transmits it

wirelessly via Wi-Fi signal to the operator monitor or cell phone. It provides feedback of both

clamps real-time situation to the operator.



Fig. 16 Real time video signal is captured by the CCTV on the IAC and transmitted wirelessly

3. Functional Verifications :

3.1 Dimensions verification

Fig. 17 Comparison between the PE pipe ID before and after implementing the IAC

The dimensions verification is performed to check whether the pipe ovality is rectified under

implementing the IAC. In general practice of electrofusion jointing, the largest acceptable pipe

ovality is 1.5%. Only for this verification, 0.5% more additional requirement is added for

providing margin, thus, pipes are deliberately deformed to around 2% ovality are tested.

The results are acceptable and matched with simulation closely that the ovality of all Dn315 ~

Dn400 pipes are largely reduced. It is confident to ensure 1.5% ovality can be rectified to

around 0 by implementing IAC.

Item Norminal OD Norminal ID Status Remarks

Dn ID1 ID2 Ovality (%) ID1 ID2 Ovality (%)

1 351.4 357.8 1.81 354.2 355 0.23 Accept

2 352.3 356.9 1.30 354.3 354.5 0.06 Accept

3 349 359 2.82 353.3 355.7 0.68 Ignore org ovality 2.82% > 2% , Out of range

4 312.1 317 1.56 314.4 314.9 0.16 Accept

5 311.4 317.3 1.88 314.3 315.1 0.25 Accept

6 312.6 316.9 1.37 314.6 314.7 0.03 Accept

7 276.7 281.7 1.79 279 279.5 0.18 Accept

8 276.3 282.2 2.11 278.5 280 0.54 Ignore org ovality 2.11% > 2% , Out of range

9 277 281.4 1.58 279.1 279.3 0.07 Accept

355

315

314.66

279.2

Before After

Comparison between the PE pipe ID before and after using the Internal Alignment Clamp

400 354.55



3.2 Electrofusion Joint Quality verification

By benchmarking the peel test results (Fig. 18) of same badge of joints by implementing IAC and

strap clamp under a few extreme conditions and referring to the simplified peel test results (Fig.

19), it is observed that joints by IAC are performing better than joints by strap clamp. Please

refer to (Fig. E in appendix) for the detailed peel test results.

Fig. 18 An example of the Peel Test comparison between using Strap Clamp and IAC

Fig. 19 Simplified Peel Test results (Strap Clamp vs Internal Alignment Clamp)

4. Conclusion

Incubated by disruptive innovation thinking and utilized precision computer-aided design and

simulation, this first-of-its-kind equipment helps solve difficulties during electrofusion with its

special features.

The Internal Alignment Clamp is designed to aid for improving the joint quality and reliability as

well as the gas safety. Various benefits can be realized by using this equipment when

comparing to strap clamp,



Equipping with (a) the Auto-Rerounding function and (b) Alignment Correction, IAC

helps to tackle the ovality problem and misalignment of PE pipes when undergoing the

electrofusion process

2-Stage expansion for front and rear clamp mechanism

Press Plates are quick-changeable for adapting various pipe sizes

Limitation of the external congested environment can be minimized

This application, Internal Alignment Clamp, is not only beneficial to the gas industry, but also

has potential to extend to the water industry.

Fig. 20 Internal Alignment Clamp advantages : Auto-Rerounding and Alignment Correction

- THE END -



Appendix :

Fig. A Interpretation of the Ovality [1]

Fig. B Forces transformation from pneumatic cylinder to individual press plates pressing force



Fig. C Comparison between Simulated required force and Calculated provided force for pipe

deformation



Fig. D POM material - Mechanical properties

Fig. E Detailed Peel Test parameters and results (Strap Clamp vs Internal Alignment Clamp)

Size Clamp

Side

L R L R L R L

S5 -3.8 400C 6.24 6.7 399.15 399.3 3.36 3.3 Strap Pass -

S6 -5.1 400C 5.93 5.87 398 399.12 4.5 3.17 Internal Pass -

S11 28 315C 2.5 5 315.75 315.81 1.65 1.44 Internal Pass -

S12 29 315C 4 4.5 315.83 315.85 1.44 1.24 Strap Fail L9 (76%), L12 (100%), R12 (77%)

S13 25 315C 2.5 2 316.05 316.07 1.58 1.4 Strap Fail R12(45%)

S16 25 315C 3 2 315.5 315.9 2.84 2.37 Internal Pass -

Nominal

Dia.

Avg GapODSample

No.Temp/C

Peel Test ResultsPipe Gap

PT Result Fail LocationOvality



Fig.F Simulation results of rectifying 1.5% Ovality to 0

Fig. G Simulation results of rectifying 2.5% Ovality to 0.53%

Fig. H Machining parts verification to ensure Safety Factor > 10



Fig. I Example of the engineering parts drawing for the press plate

Fig. J Example of the engineering assembly drawing for the press plate assembly



Fig. K Pneumatic diagram of the pneumatic circuit in the control unit

Reference :

[1] Ovailty: http://www.cmrp.com/dompdf/ovalitycalc.php

http://www.cmrp.com/dompdf/ovalitycalc.php

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