Electrolock is a boltless restrained joint system with a double chamber socket to be used in Ductile Iron (DI) pipelines. It uses the same gasket as the normal push-on joint. The second chamber accommodates mechanical anchorage provided by specially designed locking bars or plates. It locks with a weld bead made on the jointing spigot. Electrolock joint Ductile Iron (DI) pipes are supplied with compatible Electrolock type Ductile Iron (DI) Fittings. Restrained joints are designed and tested as per the provisions of ISO 2531, EN 545 and ISO 10804.

Before the advent of Ductile Iron( DI) Pipes and Fittings (DI) pipes with boltless restrained joint, the older restrained joint design required cumbersome bolting arrangements with a separately cast follower gland, to serve the purpose of physically restraining the joint. However, in the new ‘Electrolock’ design no bolting is required to do the restraining. The advantages are manifold:

• Easier to assemble and disassemble
• Faster jointing
• Lesser excavation at joint since no bolting is required
• No separate follower gland is required
• As there is no extended part, it can be used for trenchless laying of DI pipe

The thrust force developed in a Ductile Iron (DI) pipeline is dispersed along the calculated restraining length with the help of:

• Passive soil resistance
• Skin friction between the pipe and the surrounding soil

The concept is explained with a sample force diagram showing the thrust force and resistance forces at horizontal bend -

Where,
P: Thrust force developed by internal pressure
A: cross sectional area of pipe
R_s: Unit bearing resistance / Passive soil resistance
F_f: Unit frictional resistance / skin friction
L: Restrained length

• Execution of project is faster. Concrete thrust block needs much longer time to install and cure.
• Very useful where there is no space for thrust block.
• Ideal for soils with low bearing capacity where a concrete thrust block can sink.
• Eliminates chance of destabilization due to future excavation.
• It is a more economical solution than conventional concrete thrust block.
• There is further savings in terms of lesser manpower and machine engagement, lesser excavation and land acquisition cost.
• No chance of third party interference
• It is technically advanced and is a more sustainable solution having lesser carbon footprint compared to concrete thrust blocks

The Electrolock restrained joint comprises of two chambers. It uses the same gasket as the normal Ductile Iron (DI) pipe push-on joint in the inner chamber to provide leak tightness. The second chamber accommodates mechanical anchorage provided by specially designed locking bars or plates. It locks with a weld bead made on the jointing spigot of the Ductile Iron (DI) pipe.

• All pipes in the pipeline need not be restrained
• All bends, reducers, end blocks and tees are to be with restrained joints.
• All joints on both sides of the fitting within the restraining length are to be restrained.
• The length to be restrained depends on soil type, backfill compaction level, pipeline profile and working pressure.
• Non-cohesive or sinking soils with low bearing capacity and lower friction angles require longer lengths of restrained pipes.

Some of the areas of application of Electrolock joint in a Ductile Iron(DI) Pipeline are –

• As a replacement for concrete thrust blocks
• Where there is not enough space to construct a thrust block
• In inclined hilly terrain where putting up of thrust block is difficult
• Where pipes are to laid very quickly
• Pipe systems for snow-making facilities
• Turbine penstock pipelines
• Underground fire-extinguishing pipes
• Pipes to be laid inside a culvert
• Trenchless laying and Horizontal Direction Drilling (HDD) application

Since there is no cumbersome bolting is involved in this type of restrained joint, Ductile Iron (DI) pipe and Fittings with Electrolock joints can be disassembled by removal of rubber blocks followed by unlocking the locking bars/plates and by removing them through the front slot one by one.

The unique quality of Ductile iron (DI) pipe restrained joint system is, it retains the joint flexibility, while providing physical restraint against axil pull and prevents longitudinal joint separation. Joint flexibility means that the jointing pipe can be deflected from a straight line by certain angle of deflection, as declared by the manufacturer. The allowable angular deflection for Electrolock joint is given below:

In a typical Ductile Iron (DI) pipeline with restrained joints, the thrust force is calculated and then a system of restrained jointed components, comprising a restrained jointed Ductile Iron (DI) fitting and a requisite number of restrained joint pipes on the upstream and downstream side of the DI fitting are installed to combat the thrust force. The length of pipeline to be restrained is calculated based on the pipeline pressure, type of fittings, surrounding soil parameters and backfill compaction level, as per the provision of ISO:21052.

• Restrained joints are normally designed for underground application.
• All pipes in the pipeline need not be restrained
• All bends, reducers, end blocks and tees are to be with restrained joints.
• All joints on both sides of the fittings within the restraining length are to be restrained.

An Electrolock joint is a double chambered restrained joint, where the inner chamber of the joint houses the normal push-on joint gaskets of EPDM (Ethylene Propylene Diene Monomer) and it does the joint sealing

The length of Ductile Iron (DI) pipes to be restrained is calculated as per ISO 21052:2021-“Restrained joint systems for ductile iron pipelines — Calculation rules for lengths to be restrained”, where the calculation methodology is explained in details.

As per clause No. 11 of ISO 21052,… “Only in extraordinary circumstances, e.g. unstable soils, high internal pressure in combination with very shallow cover and exposed pipeline, the joint security is threatened. In these situations, the entire pipeline should be restrained and additional arrangements should be provided so that the angular deflection remains within the prescribed limits.”

The pressure bearing ability of a Ductile Iron (DI) restrained joint is declared by the manufacturer based on the type test of the joint conducted by the manufacturer. The table below gives value for allowable operating capacity of Electrolock joint.

Boltless restrained joint is preferred for trenchless laying mainly due to following factors –

• As it is boltless system with no extruded part like bolted follower gland, less frictional resistance is encountered during pull or push
• Absence of cumbersome bolted restrained joint fittings
• Being a self-restrained joint, it can effectively resist the pulling force exerted during trenchless laying

A properly designed, restrained pipeline uses the passive bearing strength of the soil and frictional resistance of the soil. Calculation of restraining length depends on certain parameters which are:

• Pipe size and pipe class
• Maximum working pressure of the pipeline
• Type of Fittings
• Trench type
• Depth of cover
• Soil type and characteristics
• Safety factors

Detailed calculation can be done as per the method explained in ISO 21052:2021-“Restrained joint systems for ductile iron pipelines — Calculation rules for lengths to be restrained”.

A sample cost comparison between supply and installation of Electrolock restrained joint pipes & fittings and supply and installation of socket and spigot joint pipes and fittings with construction of thrust blocks in 1.2 MPa design pressure (WT is at ground level) in cohesive–granular soil (depth of cover is 1m):

Therefore, it is found that the restrained joint option is cheaper when it is used in place of concrete thrust blocks in a Ductile Iron (DI) pipeline.
It may be noted that there will be further savings in terms of lesser manpower and machine engagement, lesser excavation, lesser land acquisition cost and also due to reduction of carbon footprint when Ductile Iron (DI) Pipelines are installed with Electrolock joint.

• Electrolock joints in a Ductile Iron (DI) pipeline are usually used in place of conventional concrete thrust block. Thrust blocks require cement and steel reinforcement. Production of cement and steel has very high carbon foot print.
• Installation of such Boltless restrained joints require lesser excavation during jointing. Thrust block construction requires larger soil excavation hence more man/machine engagement.
• Lesser disturbance of virgin soil indicates more environmental sustainability
• Faster execution of project means a more economic project execution and lesser carbon emission

Sample Calculation of total carbon emission of construction of a thrust block in Ductile Iron (DI) pipeline and equivalent value of CO2 emission:
Considerations:

• Weight of 1 cubic meter of M20 concrete:
  Quantity of cement required for 1 cubic meter of M20 concrete: - considering, 1440 kg/cum is density of cement, then cement quantity = (1/5.5) ×1.54m3 × 1440 kg/cum = 403 kg or around 8 bags of 50 kg of cement."
• Approximated CO2 emission per unit have been considered as per the literature review.
• Approximated Internal Carbon Price (ICP) has been considered as $50/MT of CO2 based on Carbon Disclosure Project, India.
• Approximated Voluntary Carbon Price has been considered as $5/MT of CO2 based on National Carbon Market.
• Carbon Footprint of DI Socket and Spigot pipes and DI Double Chambered Restrained Joint pipes are considered equal for this calculation.
• Design Pressure =1 MPa and Depth of Cover = 1 m

From the above calculation of carbon emission of conventional Socket and Spigot Pipes with concrete Thrust Block System, Ductile Iron( DI) Double Chamber Restrained Joint Pipes and Fittings will become the successor of Thrust Block day to day, due to lesser carbon footprint of Electrolock type Ductile Iron (DI) Restrained Joint Pipes and Fittings.