In this month’s blog post, we share how to join pipes by means of the recognised oxyacetylene, silver soldering and copper joining methods – competently to specifications given in this element, applicable to domestic / small plant refrigeration systems.

Safety Precautions

Safety is very important. Carelessness can cause accidents, so it is necessary that at all times great care must be taken to act and work safely to prevent harming yourself and others. You must familiarise yourselves with all safety rules, as well as obey and apply them!

Protective Clothing

  • All parts of your body must be covered when welding.
  • You must wear:
    • Overall that fasten up to the neck with long sleeves and legs that fit properly.
    • Cloth Skull Cap that covers your head and hair.
    • Leather gloves.
    • Leather apron.
    • Leather puttees or shoe covers (SPATS).
    • Safety shoes or boots.
    • Welding helmet when ARC welding.
    • Goggles when chipping or grinding.
    • Safety glasses when working near welders – dark or coloured.
    • Dark welding glasses when using oxyacetylene equipment.

Safety Signs

Familiarise yourself with these standard safety signs, and watch out for them at all times. These signs are used to prevent accidents happening by making you aware of the dangers and precautions to take. They must be OBEYED, so for your own safety, do not ignore them.

Working Area

  • The working area or workshop must be kept CLEAN and TIDY at all times.
  • Tidy your workshop at the end of the day.
  • Pick up paper, rags and scrap metal.
  • Place all rubbish in the bins provided.
  • Coil gas hoses and welding cables neatly.
  • Do not leave any items lying about.
  • Do not balance any items on top of each other.
  • Keep your floor space clear, clean and dry.
  • Do not weld in wet places.
  • Do not weld in confined spaces unless there is adequate fresh air to breath.
  • Do not weld near inflammable materials.

General

  • Wear your protective equipment at all times.
  • Always wear good overalls and good boots.
  • Avoid loose sleeves when working with machinery.
  • Avoid wearing oily or greasy clothes when performing welding and cutting operations.
  • Be careful when chipping. Flying chips may injure yourself or others.

Welding Equipment

  • Welding equipment is expensive and can be dangerous if not treated properly.
  • Always look after equipment.
  • Do not touch electrical connections.
  • Do not touch moving mechanical parts such as gears or rollers.
  • Do not examine equipment unless it is switched off at the wall.
  • Do not use damaged and broken equipment.
  • Do not use frayed electrical cables and damaged gas hoses.
  • Check gas connections regularly for leaks – ONLY USE SOAPY WATER.
  • Do not weld on gas cylinders.
  • Keep gas bottles and hoses away from heat and flames.
  • Do not drop or knock over gas cylinders.
  • Do not oil gas connections.
  • Turn off gas supplies when not in use.
  • Only use gas cylinders that are standing upright.
  • Do not roll gas cylinders along their sides.
  • Do not smoke near gas or gas cylinders.
  • Do not play with the equipment.

Act Sensibly and you will Not get Hurt

  • If Unsure, ASK!
  • Do not take risks.
  • Use safety precautions when using oxyacetylene equipment.

Safety Precautions when using Oxyacetylene Equipment

  • Keep oil and grease away from oxygen fittings.
  • Inspect oxygen and acetylene hoses periodically to see that it is free form cuts, cracks, burnt or worn places.
  • Do not test for leaks on oxygen or acetylene fittings with a naked light or flame. Escaping acetylene can be detected by its peculiar smell, or soapy water should be applied with a brush to connections to test for leaks.
  • Do not cut or weld on tanks or other vessels, which may have contained petrol, oils, spirits, paint or any inflammable or explosive material.
  • Remember sparks that are caused by welding, and particularly form oxyacetylene cutting, can travel a considerable distance. Such work should be carried out in a safe place or in a safe manner to prevent all risk of causing fires.
  • When flame cutting or welding painted or galvanised plates etc., wear an approved respirator.

IMPORTANT! Operators affected by fumes from this work should see a doctor without delay.

Safety in the use of Compressed Gas

  • If on opening the valve of a dissolved acetylene cylinder the gauge shows a pressure exceeding 4100 kPa OR
  • If the cylinder is heated accidentally or becomes unduly warm due to backfiring from the use of faulty equipment or other causes OR
  • If there is any sign of smoke or an unusual smell with the gas discharging from it OR
  • An explosion occurs in the regulator or hose.

They Must Be Dealt with Promptly, as follows:

  • If at all possible immediately move the cylinder into the open.
  • Close the valve and detach the regulator.
  • Open the cylinder valve fully to allow the gas to escape freely.
  • Immerse the cylinder in water or apply water with a hose from a safe distance to cool the cylinder.
  • Notify your supervisor immediately.
  • Special attention is drawn to the label attached to the neck of the cylinder: SAFETY PRECAUTIONS are printed on the reverse side of the label.

Identification of Cylinders

Each compressed gas cylinder is clearly labelled with the name of the gas contained herein, and all cylinders must be colour coded. Users must refuse to accept any gas cylinder of which the contents are not clearly indicated by means of a label.

To prevent the interchange of the fittings between cylinders of flammable and non-flammable gases, the valve outlets are screwed left handed and right hand respectively. All Propane-butane (LP.GAS) equipment used in the workshops is marked with grey paint and suitably tagged with the wording “Use on L.P. gas only”.

NOTE: Never allow cylinders, valve threads, or marking to be altered in any way. Never attempt to mix gases in a cylinder. Never attempt to fill gas cylinders.

Transportation and Handling of Cylinders

  1. Although cylinders are strongly constructed they must always be handled with care.
  2. Do not allow cylinders to slide over or come into contact with sharp edges.
  3. Do not allow cylinders to overhang the sides of transport vehicle.
  4. Do not drop cylinders or allow them to come into violent contact with each other.
  5. Do not allow cylinders to be transported unless valve caps are firmly screwed on.
  6. Do not load or offload cylinder by means of electromagnetic cranes or chain slings.
  7. Do not lift more than one cylinder at a time unless use is made of a properly designed cradle.
  8. Do not use cylinders as roller beds for moving heavy articles.
  9. Do not, under any circumstances, roll acetylene or L.P. gas cylinder except on the base. Where possible, a trolley or hand truck should be used.
  10. Ensure that cylinders are safely stacked during transportation.
  11. Use a securely adjusted rope sling on the cylinder body for lifting single cylinders.
  12. Remove pressure regulators and equipment before transporting cylinders by means other than a specially designed cylinder trolley.
  13. Transport L.P. gas cylinders properly secured in the vertical position.

Selection of Equipment

Care in the selection of the correct type of equipment for the job in hand is an important safety factor and the following points are strongly recommended:

  • Cylinder pressures vary considerably with the different compressed gases, so be sure you select the correct regulator for the gas to be used. It is dangerous to use a L.P. gas regulator on an acetylene cylinders.
  • For cutting operations it is essential to select an oxygen regulator to give a sufficiently high rate of flow to ensure efficient operation. Low pressure oxygen regulators are available for welding applications.

Oxy-Acetylene Welding

This is a gas welding process wherein the welding heat is obtained from the combustion of oxygen and acetylene.

The system used today consists of the following equipment:

  • Supply of oxygen compressed into cylinders or from evaporators.
  • Supply of acetylene compressed into cylinders.
  • Acetylene pressure regulator.
  • Oxygen pressure regulator.
  • Two lengths of re enforced rubber hose – Red and Black or Blue.
  • Welding torch with various sized of nozzles.
  • Spanner and spindle key.
  • Welding goggles and spark lighter.
  • Welding rods and fluxes.

NOTE: Distinctive colours are used to distinguish oxygen equipment from acetylene equipment, i.e. black or blue hoses, righthand threaded fittings and black cylinders for oxygen and red hoses, left-hand threaded fittings and red cylinders for acetylene.

Acetylene

Acetylene is a colourless, flammable gas and is slightly lighter than air. Acetylene of 100% purity is odourless, but gas of ordinary commercial purity has a distinctly garlic like odour and will burn in air with an intensely hot luminous and smoky flame.

Acetylene gas is highly flammable and no naked flame should be held near a leaking cylinder, valve or connection. Leaks can be detected by smell or by the use of soapy water applied with a brush.

Oxygen

Oxygen is a colourless, odourless, tasteless gas that supports life and makes combustion possible. It constitutes about 21% of the atmosphere. As liquid it is transparent, pale blue and slightly heavier than water. All materials that are flammable in air burn much more vigorously in oxygen. Some combustibles, such as oil and grease, burn with near explosive violence in oxygen if ignited.

Oxygen escaping from leaking hose or connections will form an explosive mixture with oil or grease and will cause clothing and other material to take fire vigorously from a spark. Leaks can be detected by applying soapy water with a brush to fittings. Oxygen should not be inhaled from cylinders and pipelines, or used for ventilation.

NOTE: When repairing damaged hoses, “copper tubing” must not be used. Copper will cause a chemical reaction, which produces a very dangerous substance called copper acetylene, which can explode and cause fires.

CAUTION: The pressure on the acetylene regulator must not exceed 100 kPa because it is a very unstable gas and can cause an explosion.

Flames used for Oxy-Acetylene Welding

Successful welding will depend to a large extent on your ability to obtain the correct flame for the particular work you have to do. It is necessary to familiarise yourself with the appearance of the various types of flames. There are three different types of flames that are required in oxyacetylene welding and cutting, namely, the carburising, the neutral and the oxidising flame.

We will continue with adjusting the flames in the next issue.

Grant K Laidlaw

Grant K Laidlaw F.S.A.I.R.A.C.

References

ACRA