Welding Defects

Question 1

Metal components can be formed/shaped in 4

ways:

Answer 1

Metal components can be formed/shaped in 4 
ways:
 Machining
 Casting
 Forging
 Fabrication
Components inspected subsea are mostly 
formed

Question 2

Define what a weld is

Answer 2

Welding is the term used to describe the joining
of two or more materials by fusing them
together with heat, pressure or both, so that the
atoms are brought into such close contact that
atomic bonding takes place.
 It’s difficult to guarantee that a weld is free
from all faults.
 Welds are constantly inspected to ensure
they’re not about to fail.

Question 3

What are the main ways to weld

Answer 3

There are 35 welding processes.
These are classified into 7 groups:
 Solid Phase
 Thermo-chemical
 Electric-resistance
 Radiant energy
 Unshielded Arc
 Flux-Shielded Arc
 Gas-Shielded Arc

Question 4

Explain Flux Shielded Arc Welding

Answer 4

Flux Shielded Arc Welding is the most widely
used process.
 An arc is struck between a consumable electrode &
the work
 This generates heat which melts the joint & the
electrode, which provides the filler metal
 The electrode is covered with a flux that melts &
provides slag & a gas shield, which protects the weld
pool from contamination

Question 5

Manual Metal Arc (MMA) is an example of Flux Shielded Arc Welding

Answer 5

Manual Metal Arc (MMA)
First developed in the late 19th century using
bare wire consumables.
 A simple process in terms of equipment
 Can be used with AC, DC+ or DC- current
 Demands high skill from the welder
 Widely used throughout the welding industry

Question 6

What are common faults with MMA

Answer 6

Common Faults

1) Overlap
2) Porosity
3) Slag inclusions
4) Excessive spatter
5) Lack of fusion
6) Crater cracks
7) Arc strike
8) Undercut
9) Excessive penetration
10) Incomplete penetration

Question 7

Explain Metal Inert Gas/Metal Active Gas MIG/MAG.

Answer 7

Metal Inert Gas/Metal Active Gas MIG/MAG.
Developed in the USA, 1940’s for welding
aluminium alloys.
Latest EN Welding Standards refer to it by the
American term GMAW (Gas Metal Arc Welding).
 It uses a continuously-fed wire electrode.
 Weld pool protected by a separately supplied
shielding gas.
 Classified as semi-automatic but may be fully
automated.
 The wire can be bare, solid wire or flux-cored hollow
wire.

Question 8

What are common faults with Metal Inert Gas/Metal Active Gas MIG/MAG.

Answer 8

Common Faults:

1) Porosity
2) Excessive spatter
3) Lack of fusion
4) Cracking
5) Arc strike
6) undercut
7) Excessive penetration
8) Incomplete penetration

Question 9

What is Tungsten Inert Gas (TIG)

Answer 9

Developed in the USA during WW2 for welding
aluminium alloys.
 Uses a non-consumable tungsten electrode.
 Requires a high level of welder skill.
 Produces very high quality welds.
 Slow compared to other arc welding.

Question 10

Common faults with TIG welding

Answer 10

Common Faults:

1) Arc Strikes
2) Burn Through
3) Porosity
4) Undercut
5) Tungsten Inclusion
6) Oxide Inclusion
7) Excessive Penetration
8) Incomplete Penetration

Question 11

Submerged Arc Welding (SAW)

Answer 11

Submerged Arc Welding (SAW)
Developed in The Soviet Union during WW2 for
welding thick section steel.
 The process is normally mechanized.
 Uses amps between 100 to over 2000,
producing deep penetration & high dilution
welds.
 Powdered flux is supplied separately via a flux
hopper.

Question 12

Name and describe 5 joints

Answer 12

1) Butt Joint (don’t confuse with a butt weld) - 2 plates fitted together at an angle of between 135° & 180°. Used offshore for circumferential & seam welds
2) ‘T’ Joint - 2 plates fitted together at an angle of between 5° & 90° such as the joint between two tubular members in a node
3) Lap Joint - 2 plates fitted one on top of the other the angle between them is between 0° & 5°
4) Corner Joint - 2 plates connected at the edges to make a joint at an angle of between 30° & 135°
5) Cruciform Joint - A joint at which 2 flat plates are welded to another flat plate at right angles & on the same axis

Question 13

Name 2 types of welds

Answer 13

1) Butt Weld - A tension resisting weld, in which, the bulk of the weld metal is contained within the planes
or thickness of the joined parent metals

2) Fillet Weld - The bulk of a fillet weld is contained outside the planes or thickness of the parent metal. Fillet welds tend to have less strength.

 As fillet welds are not used for structural joints
that must withstand high stresses.
 The butt weld will be the type of weld most
frequently inspected offshore.
 All nodes, including safety critical nodes on the
structure, will be constructed using butt welds.

Question 14

How do defects in welds usually occur

Answer 14

Defects, such as porosity, often arise in welds due to gas penetrating the weld pool protection.
Gases that are likely to be present in a weld are hydrogen, nitrogen & CO2.
These are derived from:
 The atmosphere
 Water
 Hydrocarbons (grease or oil)
 Other oxides present in the weld vicinity, Due to a lack of care in preparation

These products get into the arc & provide a supply of gas that can be dissolved in the liquid metal weld pool.
 On cooling, the gas comes out of solution to form bubbles trapped in the weld metal.
 Sometimes, the gas may diffuse into the parent metal.
 Hydrogen diffusing into the HAZ will cause hydrogen embrittlement, which may lead to cracking.

Question 15

What effects does cooling have on the weld

Answer 15

The different temperatures in the regions around the weld cause differential expansion.
 On cooling, if cracking does not immediately occur, the material is put under a permanent stress, unless a stress relieving procedure is specified.
 This is referred to as residual stress.
 Normal working stress is imposed on top of this, giving an in-service stress higher than the design.
 Residual stress may cause a reduction in the fatigue life of the joint.

Question 16

Plate preparation terms

Answer 16

1) Double V butt weld - A butt weld in which the prepared faces will form two opposing V’s in section,
welded from both sides.
2) Included angle of a butt weld - The angle between the prepared faces.
3) Included angle of a fillet weld - The angle between the parent plates.
4) Parent plate - The metals that are to be joined by the weld.
5) Prepared angle, weld prep - The angle of bevel between the prepared face and the perpendicular.
6) Prepared face - The bevelled portion of the parent plate prior to welding.
7) Root gap - Separation between the parent plates to be joined.
8) Root face - The un-bevelled portion of the parent plate adjacent to the root gap.
9) Single bevel butt weld - A butt weld that has only one prepared face, welded from one side only.
10) Single V butt weld - A butt weld in which the prepared faces will form a V in section, welded from
one side only

Question 17

Terms defining weld features

Answer 17

1) Cap, face of the weld - Visible face of the completed weld.
2) Excess weld metal - Weld metal lying outside the line joining the weld toes.
3) Toe of the weld - Junction between the cap and the parent plate.
4) Root - Point where the back of the weld intersects the back face of the parent plate.
5) Weld zone - Area containing the weld and both HAZs.
6) Heat affected zone (HAZ) - Part of the parent plate that has been affected by heat from the welding process but which has not melted.
7) Throat thickness Total thickness of the weld metal.
8) Effective throat thickness (design throat thickness) - Weld thickness for design purposes, usually a line between both toes and the root.
9) Weld width - Shortest distance between the toes of the weld.
10) Toe blend - Transition between the weld material and the parent plate.
11) Leg (of a fillet weld) - Distance from the root of the weld to the toe of the weld.

Question 18

Welding process terminology

Answer 18

1) Filler rod - Filler metal for a weld in the form of a rod 440mm long used in MMA welding.
2) Filler bead - When the weld is made up of more than one pass of a filler rod the successive passes are called filler beads.
3) Run or pass - Weld metal laid down in a single pass from a filler rod.
4) Weldment - An alternative term to describe the weld zone.
5) Fusion zone - The edge of the parent plate along the prepared face and the root face along which the weld metal fuses with the parent plate.
6) Root bead - Weld bead laid into the root that protrudes beyond the back wall of the parent plate.
7) Run out length - The specified maximum lengths of weld run for a particular rod type.

Question 19

Describe planar defects

Answer 19

Planar Defects:
 May be caused in-service.
 Have a large surface area but small volume – e.g. cracks & laminations.
 They are essentially 2-Dimensional.

Question 20

Describe Volumetric Defects:

Answer 20

 Caused during fabrication.
 Have a large volume compared to surface – e.g. Porosity undercut & lack of penetration.
 They are 3-Dimensional.

Question 21

Describing a defect

Answer 21

Describing a defect
BS EN ISO 5817 Defines 6 categories of weld defects:
 Cracks.
 Cavities.
 Solid Inclusions.
 Lack of Fusion & Penetration.
 Imperfect Shape.
 Miscellaneous.
C.C.S.L.I.M.

Question 22

What is a crack

Answer 22

Cracks are linear discontinuities produced by fracture.
They may be reported as:
 Longitudinal.
 Transverse.
 Crater.
 Centreline.
 Toe (Fusion zone).
 HAZ.

Question 23

What causes cavities

Answer 23

Causes:
 Loss of gas shield
 Damp electrodes
 Contamination
 Arc length too large
 Damaged electrode flux
 Moisture on parent plate
 Welding current too low

Gas pore <1.5mm
Blow hole >1.6mm

Question 24

Describe Solid Inclusions

Answer 24

Volumetric defects caused by non-metallic inclusions
which are trapped in the weld pool before it solidifies

Causes:
 Inadequate cleaning.
 MAG & TIG can produce silica inclusions.
 TIG & MAG can produce Tungsten & Copper inclusions

Question 25

Lack of Fusion/Penetration

Answer 25

Causes:
 Poor welder skill.
 Incorrect electrode manipulation.
 Arc blow.
 Incorrect current or voltage.
 Incorrect travel speed.
 Incorrect inter-run cleaning.

Question 26

Imperfect Shape

Answer 26

Poor cap profile & excessive cap reinforcement may lead to stress concentration points at the weld toes & will also contribute to overall poor toe blend

Eg. Undercut An irregular groove at the toe of a weld run in the parent metal
Causes:
 Excessive amps/volts
 Excessive travel speed
 Incorrect electrode angle
 Excessive weaving

Overlap
An imperfection at the toe or root of a weld caused by metal flowing on to the surface of the parent metal without fusing to it.
Causes:
 Contamination.
 Slow travel speed.
 Incorrect welding technique.
 Current too low.

Question 27

Miscellaneous

Answer 27

Stray flash or arc strike - Burn marks on the parent metal caused by striking arcs with the welding rod off
the line of the weld; can sometimes be caused by arcing of the weld supply cable if the insulation is damaged.
Excessive dressing - Grinding away too much weld metal and leaving the weld below the level of the surface of the parent plate.
Grinding mark - Grooves or marks on the parent plate caused by poorly controlled grinding or surfacing tools.
Tool mark - Marks indented into the parent plate caused by chipping hammers or similar hand tools.
Hammer mark - Obvious damage caused by a hammer blow.
Torn surface - Surface irregularity caused by breaking off temporary attachments, colloquially known, though not always accurately, as dog scars see below.
Surface pitting - Small depressions on the weld or parent plate.
Spatter - Spots of weld metal thrown out from the weld pool and attaching themselves to
the parent plate.
Dog scar - colloquial term, see above - A welding scar left over after removal of a dog, (a temporary metal fixing used to stabilise the parent plates during the welding process).

Question 28

What does a diver generally report

Answer 28

As diver inspectors are concerned with in-service inspections, volumetric defects will seldom be
identified.
 Planar defects may be observed, as these could be caused by stress or fatigue failure.
 This type will be of most concern in the toe of the weld, which is also where it is most likely to be found.

Question 29

What is the general format for reporting

Answer 29

1) Type of Defect.
Describe with correct terminology.
1) Location.
2) Clock &/or tape position relative to a known datum - HAZ, the toe, the weld cap or the parent plate.
3) Dimensions.
4) Start/stop position - If a crack, is it continuous or intermittent.
5) Description.
6) If a crack - is it branching - orientation of the branches.

During fabrication, the weld dimensions are checked & verified against the weld design specifications to ensure that it is fit for purpose.
Weld Inspectors will confirm that the welds meet these requirements & for the visual elements of the inspection, a number of measuring gauges are used.