Welding

Question 1

What metals can you use a Oxy-Acetylene welder on?

Answer 1

You can use this on any metal due to the flame burning unto 3300 degrees C. The two touching edges melt causing a bond. A filler rod can also be used.

Question 2

Describe oxygen cylinders?

Answer 2

The are made out of steel and are painted black. The can hold up to pressures of 150Bar. Oil and grease should never be in contact as there is a risk of it catching fire.

Question 3

Describe Acetylene cylinders and their risks?

Answer 3

The cylinders are painted red and pressure is stored at 17 Bar. When using the Acetylene, it should never be used at a pressure more than 1.03 Bar as it becomes highly unstable.

it its a extremely flammable gas and in the right conditions it can decompose quickly and explosively.

For this reason the cylinder does not contained compressed or liquefied acetylene, they however contain acetylene dissolved in acetone onto a porous mass within the cylinder. This will slow down or inhibit and decomposition.

Therefore great care should be taken and all acetylene cylinders must be clearly marked on the vessels safety plan.

Question 4

What is difference between a single stage and two stage regulator?

Answer 4

Two stage can supply a more constant pressure, more heavy duty, require less maintenance and can be identified by their second pressure chamber.

Question 5

How can we ensure the correct regulator goes on the correct cylinders?

Answer 5

Oxygen regulators have a right hand thread whereas acetylene and other furled gases have a lefthand thread.

Question 6

What colours are welding hoses in regard to their use?

Answer 6

Oxygen is blue,
Acetylene is red,
Propane is orange

Question 7

What standard should welding hoses comply with?

Answer 7

BS 5120:1987

Question 8

What is stated in the BS 5120:1987 regarding welding hoses?

Answer 8

• Good quality and resist kinks and abrasion
• Supplied in 20m lengths with fittings attached
• Oxygen fittings have plain nuts and right hand threads
• Gas fittings have grooved nuts and left hand threads
• Thread sizes to be different to air tools
• Non return valve fitted at the torch end
• Flash back arresters fitted at gas manifold
• inspect regularly for chafing, splitting or cracking.
• Leak test monthly with compressed air or nitrogen

Question 9

Why are check valves used?

Answer 9

To ensure that the mixture of fuel and oxygen happen only at the torch mixer or the torch tip and not in the hoses or regulator.

Question 10

What is a flash back arrestor and what does it do?

Answer 10

It is connected at the torch or regulator and contains a trap that is spring loaded. This cuts off the gas flow in the event of a flash back.

Question 11

List the advantages and disadvantages of Oxy-Acetylene?

Answer 11

Advantages of Oxy-Acetylene:
- It’s relatively easy to learn
- The equipment is cheaper than most other types of welding rigs
- The equipment is more portable than most other types of welding rigs
- The equipment can also be used to “flame-cut” large pieces of material
- Temperature of the flame can be controlled depending on the thickness and type of the material being welded
- Can be used as a heat source for general maintenance/brazing

Disadvantages of Oxy-Acetylene:
- Weld lines are much rougher in appearance than other kinds of welds, and require more finishing if neatness is required
- Welds have large heat affected zones
- The carriage and storage of the cylinders
- Not suitable for thick and high melting point materials

Question 12

What are the 3 types of Oxy-Acetylene flame and the meanings?

Answer 12

• Neutral
  The ratio of oxygen to acetylene is almost one to one, meaning there will be no chemical effect on the metal.
• Excess Acetylene
  Also know as carburizing, this is when there is more acetylene. When used on steel it will cause an increase in carbon content of the weld metal.
• Oxidizing
  This is when more oxygen is used than required. It will oxidise or burn some of the metal being welded.

Question 13

Explain TIG welding?

Answer 13

An arc is formed between a non-consumable tungsten electrode and the metal being welded. Gas is fed through the torch to shield the electrode and molten weld pool. If filler wire is used, it is added to the weld pool separately.

Question 14

List some bullet points about TIG welding?

Answer 14

• Uses a non-consumable tungsten electrode during the welding process
• Uses a number of shielding gases including helium (He) and argon (Ar)
• Is easily applied to thin materials
• Produces very high-quality, superior weld,
• Welds can be made with or without filler metal
• Provides precise control of welding variables (i.e. heat)
• Welding yields low distortion
• Leaves no slag or splatter

Question 15

What the 4 most common types of TIG Welds?

Answer 15

• Butt Joint
• Lap Joint
• T-Joint
• Fillet Joint

Question 16

What are the 3 gases used in TIG Welding and what metals would they be used on?

Answer 16

• Argon, This operates at a higher arc voltage for an easier start. It is used to weld mild steel, Aluminium and Titanium.
• Helium, This provides a higher heat input that allows to increase welding speed and weld penetration. It is used on mild steel and titanium.
• Argon/ Helium mixed. This creates a hotter arc in welding aluminium and aluminium alloys. It is used by auto welding machines.

Question 17

What are the downsides of TIG Welding?

Answer 17

• TIG requires greater welder dexterity than MIG or stick welding,
• TIG yields lower deposition rates,
• TIG is more costly for welding thick metal sections.

Question 18

Explain MIG Welding?

Answer 18

An arc is formed between the wire electrode and the workpiece. As the electrode melts with the arc it is deposited into the material. The shield gas produced protects the weld during solidification and assists in stabilising the arc. This providing a smooth transfer of metal between the weld wire and weld pool.

Question 19

What gases can be used in MIG Welding and on what metals?

Answer 19

• Argon CO2 blend is normally used to weld mild steel, aluminium, titanium, and alloy metals.
• Helium is used to weld mild steel and titanium in high speed process and also copper and stainless steel.
• Carbon dioxide is most often used to weld carbon and low alloy steels

Question 20

List the advantages and disadvantages of MIG Welding?

Answer 20

Advantages

• The ability to join a wide range of metals and thicknesses
• All-position welding capability
• A good weld bead
• A minimum of weld splatter
• Easy to learn

Disadvantages

• MIG welding can only be used on thin to medium thick metals
• The use of an inert gas makes this type of welding less portable than arc welding
  which requires no external source of shielding gas
• Produces a somewhat sloppier and less controlled weld as compared to TIG

Question 21

Explain Stick Welding or Shield Metal Arc Welding (SMAW)?

Answer 21

As an arc is struck between the electrode and the workpiece it creates a weld pool. This also melts the flux coating on the rod which forms a gas and slag to protect the weld pool.

Due to the rods length the weld lengths are short. Penetration is low and quality depends on the welder.

Question 22

What metals can a Stick Welding be used on?

Answer 22

Mild steel, Cast Iron and Stainless Steel

Question 23

Benefits of Stick Welding?

Answer 23

• Equipment used is simple, inexpensive, and portable
• Electrode provides and regulates its own flux
• Lower sensitivity to wind and drafts than gas shielded welding processes
• All position capability

Question 24

Regarding Stick Welding, what discontinuities may occur and what are the meanings behind them?

Answer 24

• Incomplete Fusion - A weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads
• Undercut - A groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal.
• Overlap - The protrusion of weld metal beyond the weld toe or weld root
• Underfill - A condition in which the weld face or root surface extends below the adjacent surface of the base metal.
• Incomplete Joint Penetration - A joint root condition in a groove weld in which weld metal does not extend through the joint thickness

Question 25

List 6 Stick Welding Problems?

Answer 25

• Arc Blow
• Arc Stability
• Excessive splatter
• Incorrect weld profile
• Rough surface
• Porosity

Question 26

List 7 different types of Weld Cracking?

Answer 26

• Toe crack
• Heat affected zone crack
• Weld interface crack
• Root crack
• Root surface crack
• Underbead crack
• Weld metal crack

Question 27

Explain Resistance Spot Welding (RSW)?

Answer 27

It uses both electrical current and mechanical pressure to creat a weld. By raising a sufficient amount of heat to a small volume of metal to a molten state. As it cools under pressure the metals will join.

Current density and pressure must be sufficient for the weld, as too high will expel molten metal from the weld zone.

Question 28

List the benefits and limitations of Resistance Spot Welding?

Answer 28

Benefits

• High speed welding
• Suitable for high rate production
• Economical
• Low distortion

Limitations

*Low tensile & fatigue strengths
* Lap joints add weight
* Not suitable for many applications

Question 29

What is Hydrogen Embrittlement and when will it take place?

Answer 29

Takes place within the heat affected zone (HAZ) of the weld. It can become a fracture at a low applied stress.

For failure to occur it is necessary to have;
a) Hydrogen (from wet plate and/or electrodes)

b) High heat affected zone hardness (from high C.E. and/or rapid cooling rate arising from thick material)

c) Applied and/or residual stress (high restraint on the joint)

Question 30

Explain an overview of Brazing with some advantages and disadvantages?

Answer 30

The use of a bronze or brass filer rod coated with flux with an oxyacetylene torch to join two piece of steel together. It melts the rod rather than the base material.

Advantages
- Allows to join dissimilar metals
- Minimize heat distortion
- Reduce extensive pre-heating
- Elimination of stored up stress found in fusion welding.
- Extremely important for repairs on large castings.

Disadvantages
- Loss of strength when subjected to high temps
- Cannot withstand high stresses

Question 31

Explain Bronze Welding?

Answer 31

By using a bronze rod similar to stick welding. the two edges of the metal are heated below there melting point and the bronze is melted to cause a flow over the edges to join them. Creating a strong and ductile union between the two high melting point metals.

Question 32

Explain the two different types of Fluxes?

Answer 32

Type FL 10: These fluxes contain hygroscopic chlorides and fluorides, especially lithium compounds. The residues are corrosive and must be removed by washing or scouring.

Type FL 20: These fluxes contain non-hygroscopic fluorides. The residues are not corrosive and may remain on the work piece.

Question 33

Explain Explosion Welding?

Answer 33

Explosion welding is a joining process in which explosive energy is used to propel the component metal parts together to form a metallurgical bond. A thin layer is stripped from both colliding surfaces and is ejected as a molten metal jet. This jet contains the surface contaminants and oxides that would otherwise prevent bonding. The two surfaces are in intimate contact under extreme
pressure enabling the bond to be formed.

Question 34

What is the material used for Explosion Welding and what does it consist of?

Answer 34

Know as Kelocouple, It was designed to produce a
continuous, crevice-free joint of high strength and low
corrosion rate, which provides an easy method of joining
aluminium alloy to steel.

It is made up of,
* A low-carbon manganese steel substrate;
* Aluminium alloy cladding;
* Commercial purity aluminium interlayer.

Question 35

List some good shipyard practices when carrying out Explosion Welding?

Answer 35

• Thickness of the transition joint should be 4-times the thickness of the aluminium
• Welding is performed using MIG. In the case of aluminium, the shield gas is argon.
• A type NG6 electrode is recommended for the aluminium weld with an approved 0.12% carbon content steel electrode for the steel weld.
• The steel should be welded first, using conventional fillet weld techniques. The weld should be completed in several short passes to ensure the interface temperatures are kept to a minimum.
• It is recommended that if a transition joint is to be bent, the radius should not be less than 8-times the joint width in the horizontal plane.
• If a corner is required and there is not enough room to bend the joint in the recommended way, the joint should be mitred.