basic welding

BASIC WELDING

• COMMON WELDING PROCESSES

• WELDING TERMINOLOGY

• WELD SYMBOLS / JOINT CONFIGURATION

• WELDER RELATED

• WELDING SAFETY

BASIC WELDINGCommon Welding Processes

Listed below are some of the more common welding processes used :

• SMAW -Shielded Metal Arc Welding (stick)• GMAW -Gas Metal Arc Welding (mig)• GTAW -Gas Tungsten Arc Welding (tig)• SAW -Submerged Arc Welding


• SMAW- Shielded Metal Arc Welding uses the heat of an electric arc between a covered metal electrode and the work (pipe, plate, etc). Shielding comes from the decomposition of the electrode flux coating. Filler is supplied by the electrode core wire and covering (iron powder and alloys).This process is usually done manually. The basic equipment is a power source, an electrode holder, a work clamp and the electrode. Electrodes operate variously on alternating current, direct current electrode positive (reverse polarity) or direct current electrode negative (straight polarity).


• SMAW welding metallurgy– Weld is strengthened by adding alloying elements and by

incorporating iron powder in the electrode covering(flux). Some ingredients in the covering may attract and hold moisture (a source of hydrogen) which causes cracking in certain welds. A group of electrodes specifically formulated to result in weld deposits having very low levels of hydrogen are referred to as “Low Hydrogen” electrodes. These have identification numbers ending in 5,6 or 8. Once removed from containers they require electrically heated storage in a vented oven capable of holding the electrodes between 250 – 350 deg F. (Low hydrogen electrodes should be stored in their original containers until ready for use)


• SMAW ELECTRODE IDENTIFICATION SYSTEM

E X X X X

STRENGTH

POSITION

COATING / OPERATING CHARACTERISTICS

Strength- Tensile strength (I.E. 70, or 60) 70,000 psi / 60,000 psi

Position: 1= all positions. 2= flat and horizontal fillet position only

Example: E-7018, E-6010


• SMAW limiting factors

All of the welding manipulations are controlled by the welder, such as electrode inclination, arc length and travel speed. The welder must set the proper current and select polarity if direct current.

• Discontinuities

Almost any discontinuity can be produced, but the most common is porosity, and slag inclusions.


• GMAW- Gas Metal Arc Welding, sometimes call Mig uses the heat of an electric arc between a continuous bare wire filler metal electrode and the work. Shielding is obtained entirely from an externally supplied inert gas (argon or helium) or reactive gases (C02 o 02) or a combination thereof. This process can be semi-automatic or automatic. GMAW process deposits the weld metal in the joint by one of the following modes: spray transfer, globular transfer and short circuiting transfer.


• GMAW MODES:• Spray Transfer – Spray transfer occurs with high current

and voltage combinations. Spray transfer mode best defines the arc and the pool for the welder. Due to high heat capacity this mode is best suited for flat and horizontal welding.

• Globular Transfer – Occurs at low currents compared to spray transfer. Low current at the tip produces large irregular drops without much direction which results in increased amounts of spatter compared to spray mode.


• GMAW MODES• Short Circuiting Transfer (GMAW-S) – The short

circuiting mode is a rather “cold process” and its misapplication may result in incomplete fusion. It is mainly used for very light gauge sheet metal welding. Most refineries and petrochemical plants do not allow the short circuiting mode of transfer in their welding specifications to weld on pressure retaining equipment.


• GMAW Welding ChemistryShielded gases protect gas metal arc welds from the atmosphere. Fluxes are not used in this process. All deoxidizers and alloying elements are incorporated into the electrode wire.

• Limiting Factors

The semi-automatic features of gas metal arc welding simplify the training of the welder and should make work more consistent, however the short circuiting mode may lead to incomplete fusion.


• GMAW ELECTRODE IDENTIFICATION CHART

E R X X S - X

ELECTRODE ROD

STRENGTH

SOLID WIRE

CHEMICAL COMPOSITION


• Discontinuities GMAW may result in any of the common

discontinuities with the exception of slag inclusions.

Porosity which is caused by gas trapped in the weld, is often the discontinuity found in this process.

Incomplete fusion is possible especially in welds made in the short circuiting transfer mode.


• GTAW – Gas Tungsten Arc Welding (TIG) uses an electric arc between a non consumable electrode (tungsten) and the work. Shielding is obtained from an inert gas or inert gas mixture. Filler metal is added as needed. Welds may be made with or without filler metal as required.

• The most significant feature in GTAW is that the electrode (tungsten) used is not intended to be consumed. Only the filler metal is consumed


• Welding ChemistryThe tungsten electrode contributes neither deoxidation nor fluxing, so it is fortunate that the melting is essentially slow and that most of the gases can escape from the weld pool before it freezes. The filler rod contains the needed deoxidizers. The slow heating and lower temperatures combined with slower cooling rates in GTAW will result in improved weld metal and heat affected zone mechanical properties.


• Limiting Factors

The outstanding factor of GTAW is the exceptional cleanliness that can be obtained in the weld, producing crack free welds in alloys that are difficult to weld in other process. However the limiting factor is the high skill level necessary to produce high quality welds is acquired by long experience in manipulating the electrode and feeding the filler wire when used.


• Discontinuities

All of the common types of discontinuities are possible with the exception of slag inclusions. Porosity is a common discontinuity due to the processes low tolerance for contamination. Tungsten inclusions may also result from accidental touching (dipping ) of tungsten into the molten weld pool.

WELDING TERMINOLOGY

LISTED BELOW IS SOME COMMON WELDING TERMS:

• AIR ARC(ARC GOUGE) – The process of removing metal by means of a carbon arc rod (electrode) connected to a welding machine and air

• BACKWELD – The process of completely welding the one side of a component, and then back grinding or back gouging the other side and applying a weld from that side

• BACKING WELD – The process of applying a weld pass to the back side of the weld to provide a backing. And then completely welding out the opposite side

• BACKING PLATE OR STRAP – The installation of a plate, strip of plate, usually of the same material as base metal to the back side of the weldment to aid in welding up large root openings in a weldment

WELDING TERMINOLOGY• Cap- The finished portion of the weld (last pass)

• Consumable insert – A type of spacer that is installed in the root spacing of a pipe or plate to keep the specified root opening and is made of the same material as the base metal. This insert acts as the filler metal for the root and is melted (consumed) with the welding process normally with GTAW.

• Discontinuity – an imperfection in the weld

• Defect – a discontinuity of sufficient size, length, type that will render that particular object unsuitable for intended service base on a criteria in an applicable code

WELDING TERMINOLOGY

• Destructive testing- a sampling of the weld that is actually taken from the weldment and is subjected to a bend, tension, or other form of test that usually destroys the test coupon.

• Essential variables- are those which a change, is considered to affect the mechanical properties of the weldment and shall require requalification of the WPS

• Filler metal- The consumable electrode that is used in most welding processes to fill the weld groove

• Flux- The coating on welding electrodes that when decomposes during welding forming a shielding gas around the weld.

WELDING TERMINOLOGY

• Heat Affected Zone (HAZ)- The portion of the base metal that has not been melted, but whose mechanical properties or microstructure have been altered by the heat of welding and cutting

• Preheat- the process of applying heat to a weldment before welding. This process reduces the thermal gradients within a weldment and slows down the cooling rates, resulting in a more ductile structure with lower residual stress. Preheat also aids in removing moisture and helps remove hydrogen.

WELDING TERMINOLOGY• Post Weld Heat (PWHT)- also known as stress relieving

in carbon and low alloy steels. The metals temperature is raised to just below the lower transformation temperature and held for a prescribed time and allowed to cool at a controlled rate. This process is done to help eliminate the residual stress in metals and to reduce the hardness of the weld and adjacent HAZ after welding to back within acceptable limits, thereby reducing the possibility of cracking

• Porosity- a discontinuity in a weld when gas is trapped in the solidifying metal which is caused by gas released in the welding process or gas released from chemical reactions occurring during the welding process.

• Repair – any rework on a completed weld that requires re-welding to correct a fault discovered by visual or non-destructive testing and is beyond the standard limits of acceptability

WELDING TERMINOLOGY

• Root Bead- The first or stringer bead that initially joins two sections of pipe, plate or fitting

• Welding Procedure Specification (WPS)- a written procedure (recipe) prepared to provide direction for making production welds to a code requirement. It is supported by a PQR (procedure qualification record) which is a record of actual variables used in the welding of the test coupon.

• Procedure Qualification Record (PQR) –documentation of what occurred during welding the test coupon and the test results of the coupon

JOINT CONFIGURATION

Butt Weld• 1= Groove Face

• 2= Root Opening

• 3= Groove Angle

• 4= Root Face

• 5=Plate thickness

• 6=Bevel Angle 1 2

3

4

5

6

JOINT CONFIGURATION• Root Opening – A separation at the joint root between the

two work pieces• Root Face – The portion of the groove face adjacent to the

joint root• Groove Face – The surface of a joint member included in the

groove• Groove Angle – The total included angle of the groove

between the two work places• Bevel Angle – The angle formed between the prepared edge

of a member and a plane perpendicular to the surface of the member

• Groove weld size – The joint penetration of a groove weld• Plate thickness – The thickness of the base metals to be

welded

JOINT CONFIGURATION

Parts of a butt weld

Weld Face

Weld Root

Toe of Weld both side

Face or Weld Reinforcement

JOINT CONFIGURATION

• Parts of a butt weld

Heat Affected Zone (HAZ)

Weld Metal

Groove FacesCap

Root

Base Metal

WELDING SYMBOL

Arrow side

Other side

R

F

A

(E)S L-P

(N)

Finish symbol

Contour symbol

Groove angle

Root opening

Length of weld

Pitch (center to center )

Weld all around symbol

Reference line

S

I

D

E

S

B

O

T

H

The weld symbol both sides or one side

Groove weld size

Depth of bevel

Arrow connecting reference line to arrow side member of joint or arrow side of joint

Number of spot, seam or plug welds

Tail omitted when reference not used

WELDING SYMBOL

• Examples: Single V Butt Weld

1/8

1/8 root opening

1/875 deg

75 deg

75 deg. groove angle

WELDING SYMBOL

• Staggered intermittent fillet weld

3-10

3-10

Fillet weld side view

10”

3”

(3/8)

(3/8)

3/8”

WELDING SYMBOL

Single V Groove

Double V Groove

Single Bevel Groove

Double Bevel Groove

WELDER RELATED• A Welder Performance Qualification test is given to

determine the ability of the welder or welding operator to make sound welds.

• When a welder has not welded with a process for a period of 6 months or more his qualification shall expire, unless within the six month period prior to his expiration date, the welder has welded using a manual or semiautomatic welding process for that process for which he was qualified. (Recommend to use a welder continuity sheet)

• Or when there is specific reason to question his ability to make sound welds.

WELDER RELATED• Welder test positions for pipe• 1G- Pipe is horizontal and rotated , welding flat on

or near top of pipe• 2G- Pipe or tube is vertical and not rotated during

welding, welding is horizontal• 5G- Pipe or tube is horizontal fixed, and not

rotatated, weld is vertical, flat and overhead• 6G- Pipe is inclined fixed at a 45 deg angle and

not rotated during welding

WELDER RELATED

• Welder test positions for plate• 1G- Plate is horizontal weld position is flat• 2G- Plate is vertical axis of weld is horizontal

weld position is horizontal• 3G- Plate is vertical and axis of weld is vertical

weld position is vertical• 4G- Plate is horizontal weld position is overhead

WELDER RELATEDCommon Discontinuities • IP- or inadequate penetration without hi-low is defined as

the incomplete filling of the weld root. Inadequate penetration due to hi-low is the condition that exists when one edge of the root is exposed or un-bonded because the adjacent pipe or fitting are misaligned.

• Hi-Low- is the mismatch of either the root or the OD surface of the pipe, plate or fittings

• Slag Inclusion- is a non metallic solid entrapped in the weld metal or between the weld metal and parent metal

• Burn Thru- is defined as a portion of the root bead where excessive penetration has caused the weld puddle to be blown into the pipe

WELDER RELATED

Common Discontinuities cont.• Concave Root – a root bead that is properly fused to and

completely penetrates the sides of the pipe or plate wall thickness along both sides but whose center is somewhat below the the inside surface of the ID wall

• Porosity- can be cluster, wormhole etc. Porosity is entrapped gas pockets inside the weld

• Undercut- A discontinuity at the edge or toe of the welds where a groove is created by welding too hot or traveling too fast during welding.

WELDER RELATED

• Tungsten inclusion- is cause when the welder accidentally dips his tungsten electrode into the weld puddle, and the tip of the tungsten electrode breaks off and is left un-fused in the weld metal.

• Incomplete fusion- due to cold lap is defined as an imperfection between two adjacent weld beads or between the weld metal and base metal that is not open to the surface (condition where the two passes or base metal and weld metal are not fused together)

WELDING SAFETY

• SAFETY IS AN IMPORTANT CONSIDERATION IN ALL WELDING, CUTTING AND RELATED WORK

• THE MOST IMPORTANT COMPONENT OF AN EFFECTIVE WELDING SAFETY PROGRAM IS LEADERSHIP SUPPORT AND DIRECTION. MANAGEMENT MUST CLEARLY STATE OBJECTIVES AND SHOW IT’S COMMITMENT TO WELDING SAFETY

• Management must be certain that only approved welding, cutting, equipment are used. Such equipment includes torches, regulators, welding machines, electrode holders, and personal protective devices.

• Proper use and maintenance of the equipment must be taught• Personnel in areas next to welding and cutting must also be protected

from radiant energy and hot spatter

WELDING SAFETY• Where arc welding or cutting is regularly performed next to painted

walls, the walls should be painted with a finish having a low reflectivity of ultraviolet rays

• Open flame, electric arcs are a ready source of ignition. The best protection against fire is to do welding and cutting in specially designated areas or enclosures made of non combustible materials

• Welding helmets containing the appropriate filter plates must be used by welders and nearby personnel when viewing an arc.

• Sturdy shoes, boots and heavy clothing should be worn to protect the body from flying sparks, spatter and radiation burns. (cuff less pants and covered pockets are recommend

• Durable leather gloves or other suitable material should be worn

• Sparks or hot spatter in the ears can be serious, properly fitted , flame resistant earplugs should be worn whenever such risk is present

• Ear plugs should be worn when performing air arc gouging

WELDING SAFETY• Personnel should be protected from fumes and gases

performed during welding, cutting etc. Protection from this exposure is usually accomplished by adequate ventilation

• Where exposure would exceed permissible limits, with available ventilation, suitable respiratory protection must be worn

• Last, do not forget x-ray (gamma ray) radiation safety. Obey all x-ray barrier signs. Do not go into these areas when radiography is taking place (normally magenta and yellow tape)

REMEMBER, WELDING SAFETY IS A VERY IMPORTANT PART OF WELDING

WELDING WRAP UP

• This presentation was only a brief overview of welding, and was intended to only give a general understanding and familiarization of some of the more common processes, safety concerns and terms.

• If you have any questions I will try to answer them now, if I cannot I will research and look up. I can be reached at ext. 4083

Thank you for your attendance