The Design of Internal Alignment Clamp for PE Pipe Fusion IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 1 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.
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The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 1
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.
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 2
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.
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 3
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.
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 4
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
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 5
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
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 6
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
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 7
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
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 8
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
The Design of Internal Alignment Clamp for PE Pipe Fusion
IGEM Young Persons Paper Competition 2016 (Far East District Section) HO Chun Yiu, Alan Page 9
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