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Understanding Copper

With awareness about copper’s benefits increasing, Gurmit Singh Arora, MD, Rajco Metal Industries Pvt Ltd, highlights the key technical aspects of copper plumbing.

Copper plumbing basically comprises of two aspects – Copper tubes and Copper fittings. At present copper tubes in our country are specified for water, gas and sanitation under BS2871.
 

An Indian Standard will be out very shortly. As some of us are aware, the British standards have now merged with the European specifications and copper pipes are now specified under the BS EN 1057.

Similar to the A-B-C specifications for GI, wall thicknesses in copper is specified under Tables X, Y & Z. Table X is the medium quality used in 90% of installations worldwide. It gives the sizes, thickness and pressures for 15mm to 35mm OD.

As you can see from Table X, a 15mm tube which is equivalent to a ½” GI pipe has a working pressure of 841 PSI and a burst pressure of 3480 PSI. When subjected to such high pressures a copper tube will only burst above 3400 PSI.

Copper tubes are supplied in various qualities, hard, half hard or soft. Hard tubes are not recommended for bending. In fact, half hard tubes are also available for bending.

I can say so confidently with my company having already supplied over 10,00,000 m of bendable copper tubes of size 12mm OD x 0.6mm WT to the Mahanagar Gas project for its entire internal gas pipelines. It is highly impossible for somebody to hydraulically or pneumatically pressure test 100% of the tubes in 10’ lengths.

However, in lieu of this pressure test, Eddy Current testing has been prescribed as per ASTM E 243.

Tubes subjected to Eddy current are 100% leak-proof and any tube with any internal micro blow hole or defect which may rupture or leak is rejected by this test. It is therefore an absolute pre-requisite to specify copper tubes for plumbing only after this test.

Moreover, plasticity and ductility of material are only derived by proper chemical composition and use of right raw materials. The minimum percentage of copper in a tube is required to be 99.9% with a phosphorus level of 0.015% to 0.040%.

Elongation in half hard tubes is required to be minimum 30%. It is only then that the expansion on the outside surface and the contraction on the inside surface of a bent tube are uniform and free from wrinkles or kinks. It is very important for you to buy a proper quality product & specify eddy current tubes only.

Moreover, if tubes are having an oxide layer in the ID, they would corrode within a short time. I am quoting a paragraph from the book ‘Copper Tube in Domestic Water Services’ issued by the Copper Association of UK.

“Attack on copper tubes occurs when a thin film of carbon is formed within the bore of the tube during the manufacturing process. The cleaning process now used by major manufacturers ensures that the tubes meet the requirement of BS2871 concerning the absence of deleterious films in the bore. The requirement of BS2871 and the manufacturers’ warrantee provides adequate safeguard against this type of failure or pitting corrosion.”

Fittings are specified under the BS864 Part II for water & gas applications, now newly specified under BS EN 1254. What are the quality determinations that are required when you use these fittings especially for water services? As we all know most of us have no control over the supply of water in India.

In some areas water quality is hard, while at some places it is soft. It may also contain various constituents above WHO standards (Like the total dissolved Solids which are required to be less than 500 mg/lt, calcium content which is required to be less than 75 mg/lt, PH required between 6.5 & 8.5, and hardness – as CaCo3 – required below 300 mg/lt).

So, does our water supply meet the WHO standards, and if not what is the level of precaution we as responsible contractors have taken to ensure leakage proof installations.

Copper fittings for water services are required to be manufactured in dezincification resistant materials. Let me first explain to you the meaning of dezincification and then the necessity of dezincification resistant fittings.

Dezincification is an aggressive complex corrosion which is a form of attack which occurs on ordinary, duplex or uninhibited brass. In some areas the presence of otherwise harmless constituents in potable waters leaches the zinc leaving a mass of porous copper.

I would like to quote from a paper issued by Copper Development Association, Johannesburg, South Africa. “Recent test over a five year period sponsored by the Water Research Commission show that even with reef supply waters dezincification in ordinary or uninhibited brass may take place resulting in component failure within as little as three months. Use of dezincification resistant fittings approved by South African Bureau standards will give the assured service required.”

The materials which are dezincification resistant basically are copper because copper does not contain zinc, gun metal and a recently developed brass alloy CZ132 called dezincification resistant brass.

All dezincification resistant fittings of gun metal bear the GM mark which indicates its chemical composition and all dezincification resistant fittings bear the presence of the DR mark – a genuine mark of resistance to dezincification. These fittings also bear the BSI Kite mark.

The other detrimental factors could be the quality, size, dimensions and forging stock of these fittings itself. In Jamnagar, people cast fittings and then forge them. Basically casted fittings have a complex grain structure due to overheating and are not approved or recommended for plumbing applications especially for potable waters.
 

The casting process before forging must involve a process called shell moulding and then forging to give the fitting proper hardness, elongation and more important a uniform grain structure. Moreover, there are various fittings which are not as per the dimensions required under EN 1254 Part I. The neck of the fitting has to be of a specified length to allow the tube to easily and comfortably sit in the fitting.

Male threads of fittings must be tapered as per international BSP threads and female threads of fittings must also be BSP. This is necessary for a lock-in to occur between the male and female thread so that you get a tight leak-proof joint. If female and male threads are both parallel, you keep on tightening till it reaches the end of the thread and when you over tighten it cracks.

The third important aspect is the use of solder wire and flux. Lead-free solder wire is specified under BS 219 and EN 29453 to be 99% tin and 1% copper. You can also have a tin silver solder wire; however it is more expensive.

Solder wire must be absolutely lead-free as lead can result in contamination. Solder wire must have a melting point of approximately 230°C so that capillary action would occur when it changes from a solid to liquid state. Flux should be non corrosive. It should be used in proper recommended amount and excess flux if any, should be wiped out after the joint is made and allowed to cool normally.

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