Ductile Iron Piping

ductile iron pipes

WHY USE DUCTILE IRON PIPING?

In most parts of the developed and undeveloped world Ductile Iron has for decades been the preferred piping material.

The product is favoured by Engineers, Municipalities, Water Authorities and Contractors for properties such as corrosion resistance, maintenance-free, long life, and robustness, ease of laying, no comebacks and overall economy of contract.

Due to the influence of past circumstances, the generic product Ductile Iron piping is currently not well known in South Africa. The shortcoming of this information often results in an incomplete knowledge of the available range of products that could be used to optimize water reticulation designs.

Some manufacturers of Ductile Iron Piping have recently established a presence in this country with regards to the availability of product as well as back-up technical support for designers and contractors. A BS EN 545:2006 specification currently exists to ensure compliance of the product quality. ISO 2351:1998 International standard.

Ductile means ductility as shown above. This is done by adding Magnesium into high quality base iron (cast iron) thus changing the molecules arrangement of cast iron which is present in flake form, rendering the material brittle, to small spheres eliminating any risk of crack propagation.

Jointing

On Ductile Iron Pipes there are many kinds of jointing methods available of which the most common and standard joint is the Push In Joint. By inserting the elastomer gasket and pushing the spigot into the socket you have made a watertight joint. No need for expensive mechanical machines one can train less skilled pipe layers to do the jointing process of which DZ Amanzi Pipeline Systems provides this training free of charge to the client.  Steel Pipes traditionally have to be welded which comes with high costs i.e. Skilled Coded Welders, X-raying of joints after welding Corrosion repairs internally and externally of the welded joints.

Fittings

Full range of fittings is available either socketed or flanged. Corrosion protection by means of  Zinc Rich paint and bitumen coated, internally cement mortar lined. This is generally determined by the Engineer’s needs. Following fittings are available: Ductile Iron can also be hybrid by use of Steel Specials and jointing by use of Klamflex (VJ) type couplings recommended. This gives the Engineers the freedom to design Steel Specials as the project requires. All these items are locally manufactured by Klamflex with the aid of their in house Engineers assisting in its design.

  • Bends. (Socketed or flanged)
  • Tees.  (Air valve tee. Scour valve tee. Equal tees)
  • Reducers
  • Reducing flanges & Blank flanges.
  • Straight fittings
  • Flanges Sockets / Spigots
  • Puddle pipes. Single or double flanged fittings.

 

 

Robustness

With regard to the design aspect, a pipeline may be (and often will be) subject to stresses brought about by later developments, which often could not have been foreseen at the design stage. High safety factors should therefore be included at the time of designing in order to limit possible risks, whose resultant cost could very rapidly outweigh the investment cost.

Ductile Iron Piping is the most robust pipe on the market and is exceptionally well suited to typical problems of South African installation conditions. It is generally accepted that it is not possible for the site engineer to supervise each and every individual construction action-taking place on a site. In this instance the robustness of Ductile Iron piping is his guarantee against pipe failures because of improperly constructed pipe beddings, backfill that was not properly compacted or pipe jointing that leaks. Ductile Iron Pipes is classed as a semi ridged pipe which makes it reliant on its own pipe material for ring stiffness where traditionally steel pipes would require careful compaction to aid with its ring stiffness resulting higher cost of installation.



Safety Margins

 All piping systems have built in safety margins.

Only Ductile Iron however has a large enough margin that could effectively cope with totally unforeseen circumstances.

The following graph illustrates the safety margin of Ductile Iron Pipes with regards to internal water pressure ratings.

K9 Pipes Operating Pressures
Versus Bursting Pressures

 

As an example, a DN 500 pipe is designed to withstand a maximum permissible pressure of 32 Bar. In reality bursting tests carried out on these pipes show that bursting pressures close to 130 Bar are obtained, i.e. an effective safety factor of 4. Whereas steel will only give you a limited wall thickness to suit the pressure required for a specific project leaving you with very little room of a safety factor.

The resistance to unforeseen external loads is another special attribute of Ductile Iron Pipes. This not only allows the pipe to be laid in rocky or heaving soil but also affords a large margin of safety when future construction machinery and traffic loads have to be accommodated.

As a bonus a safety feature is that Ductile Iron is one of the most difficult pipes to which illegal water connections could be made.

Mechanical Properties

The materials Ductile Iron and Steel have a major advantage over synthetic pipe materials, as they do not deteriorate with age. Ductile Iron again has an advantage over steel because of its unique corrosion resistance, which ensures a long and useful life span.

The linear coefficient of thermal expansion of the Ductile Iron is 11 x 10    m/m/ºC, a value virtually identical to that of the cement mortar lining 12 x 10    m/m/ºC, a thus eliminating the risk of crack formation through differential thermal expansion. With this in mind Ductile Iron pipe with standard push-fit joint system makes it an ideal pipe for above ground installation eliminating expensive expansion joints as required for steel pipes.

Mechanical Properties

The materials Ductile Iron and Steel have a major advantage over synthetic pipe materials, as they do not deteriorate with age. Ductile Iron again has an advantage over steel because of its unique corrosion resistance, which ensures a long and useful life span.

The linear coefficient of thermal expansion of the Ductile Iron is 11 x 10    m/m/ºC, a value virtually identical to that of the cement mortar lining 12 x 10    m/m/ºC, a thus eliminating the risk of crack formation through differential thermal expansion. With this in mind Ductile Iron pipe with standard push-fit joint system makes it an ideal pipe for above ground installation eliminating expensive expansion joints as required for steel pipes.

Ground Movement

Ductile Iron Pipes can accommodate the greatest amount of ground movement of all types of pipe materials. This is due to the angular deflection that the joints can undergo without leaking, combined the mechanical strength of the pipe itself. Thus making it perfect pipe in seismic conditions i.e. mines where there is regular blasting and shock waves causing damages to welded or ridged joints. As well as unstable soil conditions where there is a possibility of movement.

Ease of Laying

The robustness of the pipe together with the push-fit joint makes Ductile Iron one of the easiest pipelines to lay. All that is generally required is a mechanical machine to dig the trench, lower the pipe into the trench and with the back of the bucket, push the spigot end into the socket to achieve an absolute watertight joint. The pipe is ideal for South-African conditions since apart from foreman and the machine operator, local labor can be used to level the trench and assist with the laying and backfill. The sealing of the joint is extremely reliable. Destructive tests have shown that the joint never leaks or bursts. The joint furthermore has a very good resistance to internal vacuum conditions.

The Cost Factor

The question often arises:
“How do Ductile Iron Pipes compare to other materials on price?”
The answer is:
 Pipe to pipe, probably more expensive.

At the end the contract however, the customer has to pay for the whole contract and not only for the pipes. To make a fair comparison certain cost saving features has to be brought into the cost calculation.

Kindly consider the cost influence of the following items:

Ductile Iron Pipes never or seldom require:

  • Cathodic protection systems
  • On-site welding and reinstatement of linings and coatings.

The requirements for Ductile Iron Pipes are less than for any other pipe material as far as the following is    concerned:

  • The importation or construction of pipe beddings.
  • Selection or compaction of backfill
  • On-site repair work of coating and lining caused through handling.
  • Ductile Iron Pipes offer the biggest ID which will result better capabilities in result reducing pumping costs.
  • Ductile Iron Pipes can be laid above ground and never require expensive thermal compensators as this is taken with the spigot & socket joint system.
  • Highest safety margin to surges and water hammer related damages.
  • Quicker installation time on Spigot & Socket Pipes.” Time = money.”
  • Ductile Iron Pipes can offer different laying solutions without selecting different pipe materials on specific projects i.e. River crossings, Bridge crossings, Above Ground installation and unsuited soil conditions.

Laying Ductile Iron Pipes to follow horizontal or vertical curves and thereby omitting the cost of pipe bends and anchor blocks can achieve further substantial savings.

A factor which is harder to put a cost to, but which could be of major importance, is the reliability and longevity of Ductile Iron Pipes. The cost of replacing a failed pipeline would by far outweigh the additional cost of the initial specification of Ductile Iron Pipes.

DZ Amanzi Pipeline Systems Services.

DZ Amanzi Pipeline Systems offer free of charge to the client / buyer the following services.

  • Regular progress reporting of delivery schedule of purchase order.
  • Quality control at port of discharge and final delivery site.
  • Training to pipe laying contractor on handling, repairs and installation on initial start of project.
  • All quality factory certification at time of manufacture excluding independent third party inspection which will be for clients account.
  • All technical assistance is also offered to the Contractor and Design Engineer

For any further technical requirements please contact the following person.
Derrick Hall.

DZ Amanzi Pipeline Systems Pty Ltd.

Cell: 082-775-2102

Email: derrick@dhzamanzi.co.za

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