Introduction
Oxy-Acetylene is still commonly used throughout the motor industry e.g. brazing exhaust pipes, removing them and removing stubborn bolts. Caution should be taken as misuse of heat from oxy-acetylene could result in distortion or fracture of metal or even result in injury or death.
Nowadays oxy-acetylene is no longer used in the repair of vehicle bodies.
The Health and Safety at Work Act requires employers and self employed people to provide and maintain plant, equipment and systems of work that are safe and without risk to health.
This document is a guide to the safe use of the common cylinder gases used in industrial applications. It does not apply to all types of gases in all applications.
Detailed information on individual gases is available on separate material safety data sheets.
These can be obtained from:  

• BOC Service Centres
• BOC Agents
• BOC Customer Services Centre (Freephone 1890 35 53 55)

Whilst proper care has been taken in the preparation of this document, no liability for injury or damage resulting from its use can be accepted.
To meet the requirements of legislation and codes of practice you must know and understand the properties of any gas you use as well as have a working knowledge of the equipment being used. Safety is the responsibility of all concerned. Your safety may depend on what you know of the gases and the equipment you use. for more detailed information please seek specialist advice.

 

This document gives what is considered to be best practice in accordance with current British and European Standards and Codes of Practice for working safely with industrial gases supplied in cylinders. It has been compiled from a variety of sources, including:

• BOC Gases
• British Compressed Gases Association (BCGA) Codes of Practice
• British (BS) and European (EN) standards

Standards
Most British Standards relating to gas welding and cutting equipment have been superseded by new European Standards. Where applicable the current European Standard (EN number) is used. Any equipment marked with the former British Standard and still in use may be acceptable provided its age condition and serviceability meet the requirements of the relevant BCGA codes of Practice. 

 

For information and advice on special gases or products not contained in this publication contact:
BOC Gases on:
1890 355 255 (Republic of Ireland)                                               

0800 111 333  (Northern Ireland) or your gas supplier                                                                                                               

 

1.0 Oxy-Acetylene Brazing Principles
1.1 Brazing
Brazing is used extensively throughout the panel beating trade as a quick means of joining sheet metal panels and other automobile parts. Although a brazed joint is not as strong as a fusion weld, it has many advantages which make it useful to the panel beater. Brazing is not classed as a fusion process, and therefore cannot be called welding, because the parent metals are not melted to form the joint but rely on a filler material of a different metal of low melting point which is drawn through the joint. The parent metals can be similar or dissimilar as long as the alloy rod has a lower melting point than either of them. The commonly used alloy is of copper and zinc, which is, of course brass. Brazing is accomplished by heating the pieces to be joined to a temperature higher than the melting point of the brazing alloy
A joining process in which the molten filler metal is drawn by capillary action between two closely adjacent surfaces to be joined. The filler metal is a non ferrous metal or alloy with a melting point above 500°C (932°F), but lower than that of the metal being joined. It is a process more comparable to soldering than to welding.
Brazing has the advantage that less heat is required and so there is less risk of deforming the work-piece. A joint clearance of between 0.04 and 0.20mm is required for the capillary action to draw the liquid filler material between the mating surfaces. Good brazing is dependent on well designed close fitting joints. Most metals including copper and aluminium can be successfully brazed.
The length of overlap in the join should be between 3 to 5 times the thickness of the materials being joined.
After careful cleaning, the correct flux for the materials being joined is applied. A soft neutral flame is used to heat the joint evenly, so that the entire area reaches the temperature required at the same time.

Once the joint is heated reduce the acetylene to give an oxidizing flame. The filler material, although heated in the flame must be melted by the metals being joined and not by the flame. If too much heat is applied to the filler material the zinc or copper will be lost and the joint will have a red or coppery colour appearance and may cause porosity in the joint.

2.0 Brazing Techniques
2.1 Braze Welding
Braze welding is performed in a similar way to forehand (leftward) welding and requires greater heat than brazing. At ambient temperature the joints can be practically as strong as fusion welded items, and are therefore commonly used in the manufacture of tubular steel sections used in furniture etc.
For brazing steel the joint should be heated to a dull red and the flame kept moving over the surface to ensure it is evenly heated. The width of the weld material will be determined by that, which is preheated to the melt temperature of the filling material.
Brazing rods melt quickly and it will be found that the torch will be a little further from the metal and progress faster than during a fusion weld. It is also recommended that a smaller rod is continually dipped rather than a larger rod, which could deposit too much material.
Braze welding joints should have the sharp edges remove prior to welding.
As with brazing the correct flux should be selected and the joint well cleaned prior to applying the flame. Care must again be taken to ensure the filler rod is not destroyed due to leaving it in the flame and burning off the zinc or copper. Flux may be applied by dipping the heated rod into the flux and applying to the heated joint and mixing with water and painting the joint.
The melted flux reacts with the base metal and cleans it. The melted filler rod should flow freely enabling a build up to the desired thickness. Maintain the temperature by continuing to play the flame onto the joint.   
Soft and Hard Soldering Methods
Brass- With the aid of flux, the melted alloy flows between the parts to be joined due to capillary attraction and actually diffuses into the surface of the metal, so that a strong joint is produced when the alloy cools. Brazing, or hard soldering to give its proper name, is in fact part fusion and is classed as a skin fusion process.
Brazing is carried out at a much higher temperature than that required for soft soldering process. A borax type of powder flux is used, which fuses to allow brazing to take place between 750°C and 900°C. There are a wide variety of alloys in use as brazing rods, the most popular compositions contain copper in the ranges 46 - 50 and 58.5 - 61.5 per cent, the remaining percentage being zinc.    
2.2 The Brazing Process:
Comprises the following steps:

• Thoroughly clean the metal to be joined.
• Using a welding torch, heat the metals to a temperature below their own critical or melting temperature. In case of steel the metal is heated to a dull cherry red colour.
• Apply borax flux either to the rod or to the work as the brazing proceeds, to reduce oxidation and to float the oxides to the surface.
• Use the oxy-acetylene torch with a neutral flame, as this will give good results under normal conditions. An oxidizing flame used for materials having a high percentage of brass content will produce a rough-looking brazed joint, which nevertheless is slightly stronger than if brazed with a neutral flame.

• Use only a small amount of brazing rod; if too much is used this weakens the joint.
• The two pieces of material to be brazed must be either lapped or carefully butted after edge preparation and must fit tightly together during the brazing operation. Iron, steel, copper and brass are readily brazed and metals of a dissimilar nature can be joined. Typical examples are as follows:

Copper to brass                                                                  Copper to steel                                                                 Brass to steel                                                                       Cast iron to mild steel                                                        Stainless steel to mild steel                                             coated materials like zinc-plated mild steel can be better brazed than welded.

• Carefully select the types of metal to be joined. Although dissimilar metals can be joined by hard or soft soldering, corrosion may occur due to the electrolytic action between the two dissimilar metals in the presence of moisture. This action is an electric cell, and results in one or other of the two metals being corroded away.

2.3 Main Advantages of Brazing

• The relatively low temperature (750 - 900°C) necessary for a successful brazing job reduces the risk of distortion.
• The joint can be made quickly and neatly, requiring very little cleaning up.
• Brazing makes possible the joining of two dissimilar metals for example, brass can be joined to steel.
• It can be used to repair parts that have to be rechromed. For instance a chromed trim moulding which has been badly scratched can be readily filled with brazing and then filed up ready for chroming.
• Brazing is very useful for joining steels which have a high carbon content, or broken cast iron castings where the correct filler rod is not available.

3.0 Welding Techniques
3.1 The Leftward Technique of Gas Welding
When you have mastered the technique of lighting the blowpipe and adjusting the neutral flame correctly, you will be ready to practice the leftward technique of gas welding. This will usually involve some practice, under supervision, on scrap pieces of material.
The first stage is to deposit a straight bead of weld on a single piece of material and then, when you have perfected this, to practice joining two pieces. The ultimate aim is to achieve a standard of weld quality that will enable you to produce the required test pieces, if you want to become a qualified welder.
The leftward method of gas welding is used for welding steel plate up to 5 mm in thickness. It can also be used for welding non-ferrous metals.
When the blowpipe is held in the right hand, the weld travels from right to left, with the filler rod in front of the nozzle. The inner cone of the flame, which should be in the neutral condition for welding mild steel, is held close to the metal but not touching it. 

The rightward technique is shown in figure 3. Some of the advantages of this method on thicker plate are as follows:

• It is faster and uses less filler rod, so it is less expensive.

2.   There is less expansion and therefore less contraction.
3.   The flame remains over the deposited metal, giving an               annealing action.
4.   A better view of the molten pool is obtained, allowing for greater control of the welding operation.

Gas welding can be used for positional welding (welding in the vertical and overhead positions). These notes cover the flat position only, as you will need to prefect this technique thoroughly before you can learn positional welding.

 

 

         

 

3.2 Torch Angle
Figure 4: Types of Joints

Note: All the joints in above examples are being produced by the leftward technique. The rightward technique can also be used for all these joints

3.3 Welding Positions


Butt welds in mild steel 5 to 8 mm (3/16 to 5/16 in.) thick.

 

4.0 Oxy-Acetylene Brazing Selection & Assembly

4.1 Equipment Assembly
Stand both cylinders vertically either in a cylinder trolley or in cylinder stands; if these are not available secure the cylinders upright against a wall with a length of chain. Cylinders should never be used lying on the floor.

4.2 Oxy-Acetylene Welding Components
A complete oxy-acetylene welding set consists of the following:

• Oxygen cylinder
• Oxygen regulator
• Blue oxygen hose
• Acetylene cylinder
• Acetylene regulator
• Red acetylene hose
• A blowpipe and set of rechargeable nozzles or tips
• Trolley to carry the cylinders
• Keys and spanners to fit the equipment
• Filler rods and fluxes
• Personal protection for the operator, i.e. Gloves, goggles, apron etc.

 

 

4.3 Welding Equipment

Acetylene supply in cylinders (painted maroon) or pipeline.
Oxygen supply in cylinders (painted black with white band/pipeline).
Acetylene pressure regulator.
Oxygen pressure regulator.
Flashback arrestor, oxygen and acetylene.
Blowpipe with a range of nozzles.
Two lengths of gas hose, red for acetylene , blue for oxygen. To conform with international standards (ISO).
Each hose fitted with saffire hose check valve and regulator connecting nut.
Set of spanners and a cylinder valve spindle key for each cylinder.
Welding goggles and a spark-lighter.
Welding rods and fluxes.
Cylinder trolley or cylinder stands.

Note: All the above equipment is available from BOC.  

 

4.4 Gas Cylinders
Many gases are considered harmless at normal atmospheric pressure and temperature. However, if they are subjected to high pressure or temperature changes they are potentially hazardous.
A good example is air; it is perfectly safe until pressurized, when its stored energy can make it hazardous.
Cylinders used for storing gases under pressure are designed and built to a high specification and are subjected to regular pressure tests.
The supplier of the gas in the cylinder has a legal duty under the Pressure Systems and Transportable Gas Containers Regulations 1989 to inspect and test the cylinder regularly.
How often the cylinder needs to be tested will depend on:

• The gas contained in the cylinder – fuel gas cylinders are tested more frequently than compressed air cylinders for example.
• The working pressure the cylinder is subjected to – different gases are stored at different pressures.

The supplier can establish when the cylinder is due for test from stampings on the neck of the cylinder and by using shaped and coloured ‘test rings’ fitted around the neck of the cylinder. Each colour and shape of the test ring will determine in which year the test is to be carried out. This test ring is for the suppliers use and need not concern the users of the cylinder.
Cylinders are filled to different pressures dependent on the characteristics of the gas and the capability of the cylinder. They are made of steel or aluminium alloys. All cylinders are manufactured to meet European and British Standards and / or Home Office Specifications.
Although some cylinders are welded most are solid drawn from a single steel billet. This gives them strength and robustness.

In addition some cylinders have bursting disc to vent the gas quickly and reduce pressure should the cylinder be subjected to heat for example.
Most cylinders do not have a bursting disc. If the pressure increases abnormally, the cylinder normally splits or peels open to release its contents rather than fragmenting. However, it does depend on circumstances and the reasons for failure. The golden rules of cylinder safety are:

• Never tamper with cylinders
• Never re-paint, change markings or identification or interfere with threads
• Never disguise damage to a cylinder or valve. Contact the supplier
• Never attempt to repair a cylinder
• Never mix gases in a cylinder
• Never transfer or ‘decant’ gas from one cylinder to another
• Never scrap a cylinder you do not own
• Never subject cylinders to abnormally high or low temperatures
• Never try to refill a cylinder
• Never use them as rollers or supports
• Never pick them up by magnetic lifting

 

 

4.5 Gas Cylinders
A portable steel container for storing and transporting industrial gases, such as compressed oxygen or dissolved acetylene.
The steel cylinders are painted black with a white band on top; the usual sizes are 120ft³, 180ft³ and 240ft³.
The pressure of the gas in the cylinder is potentially the greatest hazard:

• Mild steel cylinders are charged to pressure of 1980 lb/in²
• Alloy steel cylinders to 2500 lb/in²
• Operating pressure readings on gauges: Oxygen 30 lb/in²

 
       

 

Oxygen right-hand threads (turn clockwise).
4.6 Acetylene Cylinders
Cylinders of varying sizes are used to transport acetylene. The acetylene cylinder is made of steel with a concave bottom, which is protected from wear by a welded steel band. The illustration shows a cutaway view of a standard acetylene cylinder.
After the acetylene cylinder is built, a wet cement mixture of various materials, such as asbestos or charcoal, is packed into the cylinder. The cylinder is then baked, and the mixture forms a porous, sponge-like mass. Under pressure, dissolved acetylene is safe, but free acetylene over 15 psi pressure is unsafe. For safety, then, it becomes necessary to dissolve the acetylene.
Acetone initially dissolves about 25 times its own volume, and as the temperature increases, so doss the amount of absorption. About 40% of the cylinder volume is filled with acetone, and, as the cylinder is charged with acetylene, the acetone absorbs the acetylene and swells up in the porous material.
The acetylene cylinder can be charged to 250 psi. In each cylinder are fuse plugs, consisting of steel bolts tapped into the cylinders. These are drilled and filled with a low melting alloy that melts between 203° and 207° F. In case of fire, the gas escapes through the melted fuse plugs, so a torch flame should be kept away from all cylinders. Most fuse plugs are on the top and/or bottom of the cylinder.
The cylinder should always be placed up­right during use since the liquid acetone can run through the regulators and into the hoses if the tank were placed on its side.
Cylinders are charged to pressure of 225 lb/in²
Operating pressure is 15 lb/in²

 

4.7 Summery - Acetylene C2  H2  (dissolved)
Produced from:          Calcium carbide and water
Cylinder Colour:         Maroon
Characteristics:            Colourless
Odour:                        Garlic like
Specific Gravity:          Lighter than Air: 0.9 (air = 1)
Inside the cylinder is a porous mass known as Kapok or Charcoal. Its purpose is to break up the internal volume of the cylinder into a number of small compartments.
This is a safety precaution because should the acetylene start to decompose or become unstable within the cylinder, it is impossible for the reaction to spread throughout the whole mass.
    
5.0 Identification, Care and Storage of Gas Cylinders
Cylinders containing gases are manufactured user strict government regulations. A colour code (B.S.349:1932) is used to indicate the contents of each cylinder.

Colour	Gas
Black with White Band	Oxygen
Maroon	Acetylene
Red	Coal gas and Hydrogen
Dark Grey with Black Neck	Nitrogen
Grey	Air

To prevent the interchange of fittings between cylinders containing acetylene and oxygen gases, the valve outlets on acetylene gas cylinders are screwed left-handed and they will have a groove cut around the circumference as shown.
 

                                                                              

5.1 Safe Storage of Gas Cylinders                                       

Oxygen and acetylene cylinders should never be stored together. They should be stacked as in the diagram, with the bottom layer well chocked to prevent rolling, or stored upright with a securing chain to prevent them falling over. The full cylinders should be stored separately from empty ones and used up in rotation as received. The storage area should be cool and dry, protected from direct sunlight, frost, rain and corrosive conditions. There should be prominent signs indicating the presence of fire risk and No Smoking signs should be strictly observed.

Cylinders should never be handled roughly or allowed to fall from a height. When using cranes, etc., to lift cylinders, a protective mat or cradle should be used. Cylinders should never be used as rollers. If a cylinder has been damaged in any way it should be labelled accordingly, and the suppliers should be notified when it is collected. When moving cylinders that are in use and have regulator valves attached use a proper trolley. The cylinder valves should be turned off, using the correct key, before the cylinders are moved, and care must be taken to protect the regulators from knocks and bangs.

 

5.2 Acetylene Cylinders in Fire
Acetylene becomes unstable as pressure increases so acetylene cylinders involved in a fire can be extra dangerous. After the fire is extinguished treat any acetylene cylinders as follows:

Other Cylinders
Spray with water from a safe position and keep checking until steaming from the cylinder surface stops. Contact BOC Gases regarding disposal and removal of cylinders. If safe to do so remove the cylinder to a safe position outside.
5.3 Labelling
All cylinders must carry a label. The label is the only sure means of identifying the gas inside the cylinder. It may also give the pressure the gas is stored at and outline basic safety requirements in accordance with the Carriage of Dangerous Goods (Classification, Packaging and labeling) and use of Transportable Pressure Receptacles Regulations 1996, and the Chemical (Hazard information and Packaging) Regulations 1994. The label should be complete and be attached to the cylinder.
Always check the cylinder is correctly labeled before use that its contents can be positively identified.
           

5.4 Regulators
The pressure of the gases obtained from cylinders is much higher than the gas pressure used to operate the welding torch. Since the pressure of the gases must be reduced between the cylinder and the welding torch, special reducing valves called regulators are required.
Regulators are precision instruments containing machined components which need to be handled with care. Avoid rough treatment which could damage sensitive springs, diaphragms, valve seals, safety valves etc.
Most regulators are constructed with two gauges. One gauge shows the pressure (amount) of gas being delivered to the torch.
Regulators are being manufactured to new European (EN) Standards. BS EN ISO 2503: 1998 sets out the standard for design and testing of regulators operating at pressures of up to 300 bar.
The pressure of gas in an oxygen cylinder is 19801b/in² and the pressure of gas in an acetylene cylinder is 2251b/in²
Pressure readings on gauges are up to:
Oxygen 301b/in²
Acetylene 151b/in²

 

5.5 Automatic Pressure Regulators
These are fitted to the oxygen and acetylene cylinders to reduce the pressure and control the flow of the welding gases. They are fitted with two pressure gauges. One indicating the gas pressure in the cylinder, and the other indicating the reduced outlet pressure.

5.6 Pressure Regulators

 

Always treat a pressure regulator as a precision instrument. Do not expose it to knocks, jars or sudden pressure surges caused by the rapid opening of the cylinder valve. Always open the cylinder valve slowly and smoothly using the special Spindle Key. Periodically check the bullnose seating on the pressure regulator. If the seating is damaged, it will leak gas. The pressure regulator should be replaced immediately.
Never use a pressure regulator with other than the gas for which it was designed. Release pressure using the pressure adjustment screw when shutting down, after cylinder valves have been closed and pressure in the hose has been released.
If gauge pointers do not return to zero when the pressure is released, the mechanism is faulty and the regulator should be replaced.
If the regulator "creeps" (passes gas when the pressure adjustment screw is released, or builds up on the low pressure side when the blowpipe valve is shut) it should be replaced. Ask for details of the BOC Service Exchange Scheme for safety and economy.
Do not attempt to repair regulators.

5.7 Flashback Arrestors

Flashback arrestors are fitted to the regulators on both the oxygen and acetylene cylinders. The purpose of these is to prevent flames getting back into the cylinders in the event of a backfire or similar accident. There are two types of flashback arrestors - a disposable type and a re-settable type.
5.8 Hoses
These carry the gases from the regulators to the blowpipe. They are rubber, backed with canvas reinforcement. The oxygen hose is blue in colour with right-hand threads on all connections. The acetylene hose is red with left-hand threads on all connectors.
One end of the hose is connected to the flashback arrestor at the cylinder end, while the other end is connected to a hose check valve at the welding blowpipe end.

 

The correct hose bore size, pressure rating, length and colour coding are essential for safety. European Standard BS EN 559 (formerly BS 5120) sets the requirements for the manufacture of hoses, including their colour for different gases:

• Blue       -  Oxygen

• Red        -  Acetylene and other fuel gases (except LPG)

• Black      -  Inert and non-combustible gases

• Orange   -  Liquified Petroleum Gases

Never use hoses that are longer than necessary. Never use equipment while hoses are wrapped around the cylinders or trolley

 

5.9 Hose Check Valves
Hose check valves, or hose protectors, are fitted between welding blowpipe and the hoses. They are marked "fit to blowpipe" or with a directional arrow to ensure that they cannot be fitted incorrectly. Should they be fitted incorrectly, i.e. attached to the regulator, no gas will flow through them. Basically they are spring loaded non-return valves designed to close in the event of a backfire taking place in the welding blowpipe.
6.0 High Pressure Blowpipe
This is designed to mix the gases and deliver them to the nozzle. As the two gases delivered to the blowpipe at equal pressure the injection principle as used in the low pressure blowpipe is unsuitable for us on the high pressure system. There are several makes of gas welding blowpipes on the market all of which are
supplied with detachable nozzles of different sizes. These numbered nozzles indicate the approximate consumption of gas in litres per hour. Usually they are numbered 1-2-3-5-7-10 etc. The greater the number the larger the hole size. Therefore the larger the nozzle the greater the amount of heat can be achieved. The blowpipe is simply a mixing device to supply approximately equal volumes of oxygen and acetylene to the nozzle, and is fitted with regulating valves to vary the pressure of the gas, as required.
6.1 Ancillary Equipment
A spindle or bottle key is used to open the valves on both cylinders. Each valve should only be opened approximately ½ turn and during use the key should be left in the position on the acetylene cylinder, so that it can be turned off immediately in the event of an emergency.
Spark lighters are used to ignite the gases. Do not use matches or cigarette lighters as these could constitute a hazard.

6.2 Flash Back

This is the appearance of a frame beyond the blowpipe and even into the regulator. 
Back fire
This is the appearance of a flame in the neck or body of the blowpipe.
Back Fire may occur when there is:

• A dirty nozzle tip
• Wrong pressure for nozzle being used
• Touching plate or weld pool with nozzle
• Overheating of blowpipe (cool down in water. Make sure that the gas is passing through nozzle)

 

 

6.3 Blowpipes for Special Purpose
The use of blowpipes for cutting is, in the main, restricted to the cutting of ferrous materials, as the process is one of oxidizing the metal.
It is also possible to cut stainless steel by feeding iron powder into the flame, but this requires the use of a powder hopper and compressed air system, in addition to an attachment which fits on the head of a cutting blowpipe. Other means for cutting stainless have, in the main, superseded this method and the equipment is no longer generally available in the UK.
Steel mills prepare billets by scarfing the surface of the material prior to rolling. This requires the use of a special blowpipe designed to produce high flows of oxygen at low pressure, similar in many respects to flame gouging. To enable quick starts to be made a mechanism to feed a mild steel rod into the flame is an integral part of these blowpipes. Due to the low demand, they are not generally available in the UK and have to be imported.

6.4 Blowpipes
High-pressure blowpipes for use with dissolved acetylene are of the mixer pattern. Both gases must be supplied to the blowpipe at pressures appropriate for the blowpipe nozzle.

 

 

 

6.5 Nozzle Size and Gas Velocity
The power of the blowpipe is measured by the amount of acetylene gas that is used per hour. Blowpipe manufacturers have various ways of showing this:

• By the quantity of gas passed per hour, in litres.
• By the diameter of the hole in the nozzle.
• By a number corresponding to the plate thickness that can be welded by that nozzle.

It is most important when making a weld that the correct blowpipe power is used. The two factors that mostly affect this are the velocity and quantity of gas which passes through the nozzle.
The capacity of a nozzle (the power) is recognised by the amount of acetylene it consumes per hour at the recommended gas pressures: this is usually expressed in cubic feet or litres. Manufacturers usually mark their nozzles with a number, indicating the capacity in cubic feet or litres.
Always check the manufacturer's recommended flame setting for specific nozzles.
For any metal, and welding technique employed, the flame required has a definite relationship to the type of metal and thickness.

PLATE THICKNESS		NOZZLE SIZE
INCHES	MM	FT3	LITRES
1/32	0.8	1	50
3/64	1.2	2	75
1/16	1.6	3	100
3/32	2.4	5	150
1/8	3.2	7	225
5/32	4.0	10	350
3/16	4.8	13	350

6.6 Nozzle Maintenance

Do not maltreat a nozzle. Do not use it as a hammer or lever.

To clean nozzle orifices, sets of special nozzle cleaning reamers are available form BOC. Should these not be available use a drill one size smaller than the orifice and work it up and down without twisting; the drill should be held in a pin vice. If the drill does not enter easily start with a smaller drill increasing in size until the correct diameter is attained. Effective preheat shape can only be maintained if gas orifices are sharp and square with the end of the nozzle. If the nozzle becomes damaged on the end, rub it down with a sheet of fine emery laid on a flat surface such as a sheet of glass taking care to keep the nozzle square with the rubbing surface. The orifice should then be cleaned out as described above. The nozzle has been designed to make this reconditioning possible and as much as 3mm (⅛) may be removed before a nozzle becomes unserviceable.

6.7 Connections to Cylinders

Manifold system of distributing gases
At the welding station (or at the cylinders) the high-pressure gases are passed through regulators to reduce to correct working pressure. Usually these regulators are screwed into the cylinder outlet valves. Regulators may be fitted with gauges on the high-pressure side to indicate cylinder gas pressure, and on the low-pressure side to indicate the gas-flow pressure.
Note: Copper pipe is never used for acetylene.

6.8 Fitting of New Cylinders

When you are fitting new cylinders you should remember the following safety points.

• Keep eyes clear  when cracking snifting cylinders
• Do Not Smoke
• Crack acetylene cylinder outside if possible
• Use open spanner (Do not over tighten)
• Blow out hoses before connecting up
• Turn cylinder key half turn
• Report any leeks to your instructor
• Rectify leaks immediately

6.9 Operator Safety
The cylinder valve is a safety mechanism, if dirt, grit, oil or dirty water gets into the cylinder, the valve may leak. It is extremely dangerous to attempt to repair cylinder valves. Never apply any form of lubrication or sealing compounds to threads. Any fittings and equipment used must be fit for its purpose and suitable for the gas in the cylinder.

• Never apply PTFE tape, jointing compounds or any other sealing materials to the valve in an attempt to achieve a gas tight seal. If a gas tight seal cannot be achieved metal to metal, replace the regulator or change the cylinder.
• Note: some regulator bullnose connections have ‘O’ ring seals. Check these are in a good condition. If not replace with an approved part, remove the plastic protection caps. 
• The cylinder valve or pipeline valve should be inspected for damage prior to opening.

 

6.10 Snifting
Before fitting equipment to cylinder valves make sure there are no particles of dirt or water in the valve outlet. ‘snifting’ is the term used to describe the means of removing fine particles of dirt and moisture from the cylinder valve outlet. Under no circumstances use sharp objects like screw drivers to clean cylinder valve seals.
   
Eye protection and gloves must be worn                          during snifting. Do not look into the cylinder valve while snifting

 

• Visually inspect the valve for damage, check the threads are clear and use a clean dry cloth to remove any large deposits.
• Fit the spindle key to the valve. Stand clear of the gas stream and on no account deflect the gas stream with your hand. Hold the cylinder securely with one hand and proceed to ‘crack’ open, then immediately close the valve.
• There is some noise associated with ‘snifting’, this is normal. The extent of the noise will depend on the pressure in the cylinder.
• When ‘snifting’ fuel gases ensure there is no possible source of ignition in the vicinity. When ‘snifting inert gases and oxygen ensure there is good ventilation.
• Never ‘snift’ hydrogen as it may ignite spontaneously.
• Never ‘snift’ toxic or corrosive gases.
• Instead carefully inspect the outlet and if there are any signs of dirt, blow it out with a jet of oil free compressed air or nitrogen.

6.11 Fitting of New Cylinders
1.
Blow out the cylinder valve socket by opening the valve about a ¼ turn. Close immediately.
This is called cracking open the cylinder valve
Figure 26

2.
Make sure valve socket is clean before screwing the regulator into the valve socket. Tap spanner sharply to ensure a gas- tight
3.
Slacken the regulator pressure control screw so that there is no pressure on the gauge.
Figure 28

 

Connecting to the Cylinder                                                                        
Connect the regulator to the cylinder valve (left hand for acetylene and other combustible gases, right hand for oxygen and other non-combustible gases), using the correct spanner and ensure a gas tight seal. Do not use any form of jointing paste or tape between regulator and cylinder valve. Check that the pressure adjusting screw of the regulator is fully released (turned fully anti-clockwise).

 

Commencing Operation
Connect the downstream equipment and open the cylinder valve slowly. Check all joints for leaks using a 0.5% Teepol in water solution. The contents of the cylinder will register on the cylinder contents gauge and will decrease to zero as the cylinder empties. The contents are generally shown in the bars and Ibf/in² (1 bar = 14.5 Ibf/in²).
To set pressure, screw the pressure adjusting knob clockwise until the required outlet pressure registers on the outlet gauge. When gas is flowing, there maybe a reduction in pressure, and adjustments should be made. Purge the gas line before lighting the equipment.
Finish of Operation
When work has stopped, close the cylinder valve, vent gas from the system and unscrew the pressure adjusting knob.

 

                 Check for Leaks and Rectify Immediately
6.12 The Welding Flame
The following procedures should be followed when lighting and adjusting the blowpipe flame.

• Open all the blowpipe valves.
  
• Open cylinder valves slowly by one turn of the spindle.
  
• Set the regulators to the correct working pressure.
  Close blow pipe valves.
  
• Open the acetylene control valve on the blow pipe about ½ - ¾ of a turn.
  
• Using a pilot light or spark lighter, light the acetylene.
  (Ensure that the flame points away from you).
  
• Reduce or increase the gas supply by operating the blow pipe valve until the flame just ceases to smoke.
  
• Open the oxygen control valve on the blow pipe until the white inner cone in the flame is clearly visible.
  
  THIS IS THE CORRECT FLAME FOR WELDING MILD STEEL.
  
• To extinguish the flame, close the acetylene valve and then the oxygen valve on the blow pipe.

6.13 The Oxy-Acetylene Flame
Acetylene is composed of Hydrogen and Carbon, as are most fuel gases. It is mainly the carbon which provides the intense heat and very high flame temperature (3100°C) when burned with oxygen. If sufficient oxygen is not provided, then the carbon is given off into the air as black, sooty smuts.
Acetylene has a very high proportion of carbon in it and if the oxygen is turned down to provide a flame with excess carbon; the carbon is taken into the steel to provide a high carbon surface, used for hard surfacing operations.
A neutral oxy-acetylene flame burns equal proportions of oxygen and acetylene and is reducing in nature, thereby reducing any iron oxide to iron and taking up the oxygen; consequently there is no need to use a flux when welding steel. It should be noted that iron oxide is not refractory.

Figure 29: The Oxy-Acetylene Flame Showing the Various Zones.

 

 

6.14 Welding Demonstration 2 – The Structure of the Oxy-Acetylene Flame
AIM:                    
To demonstrate the three oxy-acetylene flame settings.
EQUIPMENT:
Oxy-acetylene welding equipment, including goggles and flint lighter.
THEORY:   
There are three distinct flame settings:

 

• Neutral Flame

This flame burns equal quantities of oxygen and acetylene. (In practice, it is advisable to have the slightest possible acetylene haze at the cone tip to begin with.)

Figure 30: Neutral Flame
Cone tip hottest part approx. 3100°C.

 

 

•      Carburising Flame

This flame has an excess of acetylene which results in a carbon- rich zone extending around and beyond the cone. Note: Both the Neutral and carburising flames are reducing in nature.

Figure 31: Carburising Flame

 

• Oxidising Flame

This flame has an excess of oxygen which results in an oxygen-rich zone just beyond the cone. This flame is obtained by setting to neutral and then turning the fuel gas down.
Figure 32: Oxidising Flame

 

Safety
With
Industrial
Gases
  
                   
6.15 Operator Safety
Daily Check List for Gas Control Equipment:
Leaks may develop in any part of a gas system but particularly at joints. It is important that all equipment is checked using an approved leak detecting solution and if necessary corrective action taken before use.
Always check that each cylinder is labelled correctly identifying Gas and Pressures.

• Before work, check that the gas cylinders are stored in an upright position and secured.                             

• Inspect pressure regulators for danger. Always use a regulator which is designed for the gas and pressure you are using (e.g. 230 bar regulator on new 230 bar cylinder). Never use an oxygen regulator for nitrogen or air. Regulators must be labelled to BS 5741/BS 7650.

• Inspect the condition of hoses for signs of deterioration. Always use hoses of the correct colour and quality – blue for oxygen, red for acetylene, orange for propane and black for inert gases. Hoses must be marked/labeled to BS 5120

• Ensure flashback arrestors are fitted to both oxygen and fuel gas systems. They must be labelled correctly for the gas and pressure being used, labelled to BS 6158.

• Ensure hose check valves are fitted to hoses at the torch end.

• Ensure there are no solvents, oil or grease present as high pressure oxygen reacts violently with these substances and may explode or ignite.

• Ensure there are no jointing compounds, lubricants or thread tape on any gas fittings or connections.

• Check all connections on hoses are crimp fittings.

• Check that both hoses are equal length. Do not coil surplus hose around the cylinders or regulators.

• Set the correct gas working pressure and leak test all parts of the work station equipment using an approved leak detecting solution. (Diluted Teepol solution)

• Before lighting up ensure both hoses are correctly purged.

• Check that suitable fire precautions are taken and fire extinguishers are available. Always have BOC data and safety sheets for each of the gases used and stored on your premises.

 

Safety
BOC supplies equipment which is manufactured to the highest standards of quality and safety and will give first-class service for many years if operated correctly. The following notes will help to ensure your equipment is efficient and safe. Some suggestions for personal safety are also included. It is not intended to list every possible safeguard. These notes must be supplemented by caution and common sense on the part of the individual. Remember familiarity breeds over-confidence.
Safety precautions to be observed when using compressed gases with welding and cutting equipment are described in the companion booklet, "Safe Under Pressure" available from your nearest BOC branch or Cylinder Centre. Data Sheets and a Cylinder Identification Wall Chart are also available.

 

8.0 Hazards
8.1 Oxygen
Oxygen cylinders and the fittings attached to them must never be greased or oiled. Even small quantities of oil and grease, when mixed with oxygen, can react and cause an explosion. Oxygen has no smell and does not burn, but it will support and speed up combustion. It should never be used for ventilating enclosed spaces or for blowing clothes or other combustible material. Even a spark can, under these conditions, start a fire which may result in considerable damage or injury to personnel.
8.2 Acetylene
Acetylene gas has a noticeable smell, is highly inflammable and will ignite and burn very easily. Even a mixture of acetylene and air as low as 2% will give an explosive compound condition when in contact with metals and alloys, such as those containing copper and silver. Piping’s and fittings made of copper should never be used with acetylene gas.
Take extra care with both oxygen and acetylene cylinders to ensure that there are no leakages when assembling the equipment. Dirt should be blown clear of the valve seats by cracking the valves momentarily before attaching the pressure regulator.
NEVER: test for leakage with a flame. Soapy water should be brushed over the joint to test for leakage of gas. Always check, on completion of the job that no    glowing fragments or sparks are left.
REMEMBER: that even at some distance away from the oxy-acetylene flame the temperature is still very high and capable of starting a fire.

 

15.3 Oxygen
The commercial method of producing oxygen is to abstract it from the atmosphere by a process of distillation.
The composition of gases which make up the atmosphere is:
Nitrogen         75%
Oxygen           23%
Other Gases     2%                                                                                                                                                                                                     
                       100%                                           
In brief, the air is compressed, causing it to liquefy. In this state the oxygen separates from the nitrogen and can be filtered off.
Oxygen does not burn but supports combustion, i.e. it is essential that it is present for combustion to take place. Oxygen cylinders are coloured black and have right-hand threads as does all equipment associated with them.
Oxygen cylinders are hollow and when fully charged can be pressurized up to 175 atmospheres or 2,500 1bs/sq²
1        Atmosphere    =   101.3 Kn/M²
150    Atmosphere    =    15,195 Kn/M²
175    Atmosphere    =    17,727 Kn/M²

OXYGEN should never be used as an Air Blow off system.
Like most gases oxygen is colourless, odourless and tasteless. It is supplied in black cylinders with right hand connections. Oxygen is often referred to as O2.

Oxygen makes up approximately 20.9% of the atmosphere we breathe and is essential to life.

When we breathe in we inhale: 20.9% Oxygen                          78% Nitrogen                             1% Argon The remainders being trace gases in very small amounts.

 

 

 

 

 

Some 5% of the oxygen in the air we breathe is absorbed into the bloodstream with 5% carbon dioxide exhaled as a waste gas.

When we breathe out we inhale: *16% Oxygen                          78% Nitrogen                             1% Argon                              5% Carbon Dioxide * The reason mouth to mouth resuscitation is so effective

Oxygen is not flammable but   readily supports combustion. It   is only slightly heavier than air. If a leak occurred the atmosphere around the location could become oxygen enriched. Oxygen enrichment is a real hazard. Always test for leaks using an approved leak detector solution. Do not use soapy water.
Materials that readily burn in air, burn much faster and more intensely in oxygen enriched atmospheres. Propane for example will burn when mixed with air at approximately 1900 °C; when mixed with oxygen the flame temperature increases to approximately    2900 °C to 3200 °C. Material not normally considered combustible may burn in atmospheres where the oxygen content is above 20.9%
If clothing becomes impregnated with oxygen, ventilate them by walking in fresh open air for at least 15 minutes and avoid going near any sources of ignition.
IMPORTANT: High pressure oxygen reacts violently with oils, greases, tarry substances and some solvents. This includes things like soap, butter and some hand creams.

In some circumstances if oils and greases come into contact with leaking high pressure oxygen the oils may ignite causing very high temperatures and energy release. The energy release is rapid (similar to that of an explosion). All equipment, valves and cylinders must therefore be kept free from oil and grease.