WELDING DETAILS

For Hydraulic gates Manufacture

By N. Kannaiah Naidu

Technical Adviser

Welding processes are mainly three viz, metal arc welding, Gas and

submerged welding, and submerged arc welding. Each provides a means of

melting the metal at the joint to be welded and generally, a means of adding

additional metal to the joint. This paper discusses in general the welding and

related processes for the installation of anchors and other embedded metal

parts gate leaf for the hydraulic gates and its handling equipment.

Most widely used process throughout most industries is metal are

welding. Nearly all metals, ferrous and non- ferrous can be welded.

The main features of this process are as follows:

➢Immediate heating.

➢Depth of fusion and heating is fixed by electrode type size and current and

can be controlled some what but not closely, by the operator.

➢Nearly all metals can be welded.

➢Welding can be carried out in all positions.

➢Wide range of thickness can be welded.

Specification:

Welding shall be carried out in accordance with the specifications

mentioned in some of the codes:

1. IS – 813 – 1986: Scheme of symbols for welding

2. IS – 814 – 1981: Covered electrodes for metal are welding of

structural steel.

3. IS – 816 – 1969: Code of practice for use of metal arc welding for

general construction in mild steel.

4. IS – 822 – 1970: Code of procedure for inspection of welds

5. IS – 9595 – 1996 : Code of metal arc welding of carbon manganese

steels

6. Some of the precautions to be borne in the mind while welding are

Preparation of Base Material:

The grooves may be prepared by machine flame cutting. All

oil, grease, paint, loose scale etc., shall be removed from the vicinity

of the weld prior to welding. Notches or other surface defects

resulting from preparation shall be ground smooth before joint is

welded.

Shearing of plates shall only be permitted on edges of

secondary material which will be welded all edges of primary material

must be machine flame cut or if sheared, must be planned to a depth

of 6mm.

Material thicker than 40mm and up to 60mm shall be

preheated to 65C before flame cutting or welding.

Material thicker than 60mm shall be preheated to 104C before

flame cutting and or welding.

Assembly :Assembly of gate parts shall be carried out as per the

drawings. Wherever temporary welds are used the same are to be

removed and grounded wherever necessary. If braces are required to

support the flanges of girders during assembly and handling

temporary welds must not be used to attach the braces to the flanges.

Welding Processes :The welding shall be carried out as per the code of practices of

IS standards and the methods finalized with the in house expertise.

The most widely used welding process in sites is shielded

metal arc welding (SMAW).

Weld Consumables :

Welding of Carbon steel to carbon steel :E7018 low hydrogen electrodes, confirming to specification CSA W48.1

must be used.

Welding of Carbon Steel to stainless steel :

(IS 2062 to IS 1570 / 30Cr13)

E 308 – 16 or E 308L – 16 Stainless steel electrodes

confirming to specification CSA 48.2 must be used.

Alternatively E 309 – 16 or E 309 L – 16 stainless steel

electrodes can be used for Ni – 8 to 10 steel.

Welding of Stainless steel to cast steel:

E 308 – 16 or 308 L – 16 Stainless steel electrodes confirming

to specification CSA W48.2 must be used.

An electrode comparison chart is enclosed. The

consumption of electrodes per meter length for fillet and butt

welds is also enclosed.

Storage of Electrodes :

All electrodes are to be handled as explained below:

➢ All electrode containers arriving at the site shall be

examined for damage. Damaged containers shall be

returned to the supplier.

➢ Immediately upon opening each can of electrodes the

contents shall be placed in a holding oven held at a

temperature of 90 to 120C

➢ When electrodes have been out of the holding oven for a

period of time exceeding 4 hours they shall be returned

to the holding oven for a minimum soaking period of 4

hours before again being withdrawn.

a ) DOWN HEAD b) V

c) H d) O

Welding Position:The different weld positions are shown in fig.1:

Welding Defects

Their Causes and Prevention

Welding Objectives :The main objective is to obtain sound defect free welded joints.

Normal welds always contain minute slag inclusions or porosity

as revealed in non – destructive testing. Such small imperfections

which cause some variations in the normal average properties of the

weld – metal are called discontinuities.

When discontinuity is large enough to affect the function of the

joint, it is termed as defect.

Defects are caused by :

➢Substandard welding consumables.

➢Inefficient workman ship.

➢Lack of cleanliness.

➢Un favourable properties of the base metal.

➢Low ambient temperature and humid atmosphere.

Every fabricator must strive to prevent the occurrence of weld

defects in the first instance and to rectify them if they have occurred.

Rectification welding defects increases fabrication costs considerably.

Typical Defects which can occur in arc Welds :

1.Incomplete Penetrations :

Incomplete penetration in a single Vee butt weld

In a weld adequate root penetration is ensured by using :

▪ Correct size of electrode.

▪ Sufficiently high current.

▪ Directing the arc towards the root during deposition of the root pass.

Rectification of this defect is a very costly proposition because it

requires removal of the entire thickness of the weld and re welding.

This defect occurs at the root of the joint when the weld metal fails to

reach it or weld metal fails to fuse completely with the root faces of the

joint. As a result, a void remains at the root zone which may contain

slag, inclusions. In a fillet weld, poor penetrations at the root zone can

give rise to cracking of single butt weld.

2. Lack of Fusion :LACK OF FUSION is defined as a condition where boundaries removal

of the entire thickness of the weld metal and base metal or between

adjacent layers of weld metal.

This defect is caused by the presence of :

❖ Scale ((rusting)

❖ Dirt

❖ Oxide

❖ Slag

❖ Other non metallic substances which prevent the underlying metal

from reaching metallic temperature.

To prevent the occurrence of this defect, the following steps should be

taken :

❖ Keep the joint surface clean

❖ Use adequate welding current

❖ De slag each weld pass thoroughly

❖ Place weld passes correctly next to each other

Lack of fusion is rectified in the same way as lack of prevention.

3. Undercut :This defect appears as a continuous or dis - continuous

groove at the toes of weld pass and is located on the base metal.

Undercut in the vertical leg of a horizontal and vertical fillet weld.

It occurs prominently on the edge of a fillet weld deposited in the

horizontal position.

This defect is usually caused by :

❖ Excessive welding current

❖ Too high speed of arc travel

❖ Wrong electrode angle or excessive side manipulation

❖ Also causes due to damp or improperly formulated

electrodes.

Note : In the case of statically loaded structures the

presence of small and intermittent under cutting will reduce

fatigue endurance of the welded joint and hence it should not

be permitted.

Rectification :

The defect is rectified by filling up the under cut groove

with weld pass. If under cut is deep and contains slag, it

should be clipped away before re welding. If the rectification

being carried out on thick joints and on high tensile seals, the

welding procedure including pre heating should correspond

to the recommended procedure for particular steel.

Over lap :

The defect occurs at the toes of weld and consists of weld –

metal which has over flowed on the base metal surface without

actually fusing to later. It can be isolated intermittent or

continuous. It occurs more often in fillet welds and results in

an apparent increase in the weld size.

Cause :

▪ It is occurred by an incorrect manipulation of the electrode,

where by the weld metal flows away from the fusion zone.

▪ Use of too large an electrode in relation to the welding position,

and excessive current coupled with a too low welding speed also

promote its occurrence.

▪ When a single – pass fillet larger than 7.5mm in leg length is

made in the horizontal position, the molten metal tends to sag

and causes overlapping in at the toe of the horizontal member as

shown in the figure.

Overlap in a horizontal-vertical fillet weld

Rectification :

Slight and intermittent over lapping may be ignored in

statically loaded structures, but it should not be permitted in

dynamically loaded structure as over laps act as stress – raises,

overlap is rectified by grinding, chipping or gouging out the excess

infused weld metal. Care should be taken to leave the smooth

surface.

5. Slag Inclusions :

Slag inclusions in a single-Vee butt weld

Slag inclusions are detected by the normal non

destructive testing methods. While non – metallic inclusions are

observed in the weld micro structure at high magnification.

Non metallic particles of comparatively large size entrapped in

the weld metal are termed as slag inclusion.

Causes :

Slag inclusions usually occurs in multi pass

weld due to imperfect cleaning of the slag between the

disposition of successive passes as shown in the figure. It

may also be caused by heavy mill scale, loose rust, dirt, grit

and other substances present on the surface of base metal.

Slag trapped in under cuts or between uneven preceding

runs may give rise to elongated lines of included slag when a

subsequent weld pass is deposited.

The melting characteristic of the welding

consumables and particularly the viscosity of the rusting

slag has an important bearing on inclusion. The molten slag

should float freely to the surface of the weld pool and easily

removable on solidification.

Prevention :❖Use proper welding consumables.

❖Keep joint surfaces (especially gas cut surfaces) and bare filler

wires perfectly clean and clean the base metal thoroughly before

welding.

❖Avoid under cuts and gaps between deposited perfectly clean

and clean the base metal thoroughly before welding.

❖Avoid under cuts and gaps between deposited passes.

❖Clean the slag thoroughly between weld passes.

The strength of welded joint may be considerably reduced if large

irregular inclusions or elongated lines of inclusions at the weld

junction are present. These sometimes give rise to radiating hair line

cracks. The presence of small, isolated globular inclusion may not

however, seriously affect the static strength of a joint and these may

normally be disregarded.

Rectification :

The portions of weld metal which contain slag inclusions must be

removed and then filled with sound weld metal.

Porosity :

The presence of a group of gas pores in a weld caused by the

entrapment of gas during solidification is termed as Porosity.

The pores are in the form of small spherical cavities either

clustered locally or scattered through out the weld deposit.

Sometimes entrapped gas gives rise to single large cavity, which is

termed as a blow hole. In some rarer cases, elongated or tubular gas

cavities are presented these are referred to as piping or worm holes.

The gases are evolved by the chemical reactions in the

welding are these gases may have high solubility in the molten weld

metal, but as the metal solidifies and cools, their solubility decreases

rapidly and they are revolved from the metal, sometimes if the weld

metal solidification and cooling is too rapid, the gas gets entrapped

in the form of Porosity.

Causes :❖ Chemically imperfect welding consumables for example deficient in

deoxidizers

❖ Faulty composition of the base metal or electrode wire for example,

high sulphur content.

❖ Oil, grease moisture and mill scale on the joint surface.

❖ Excessive moisture in the electrode coating or submerged – are

flux.

❖ Inadequate gas shielding or impure gas in a gas shielded process.

❖ Low welding current or too long an arc.

❖ Quick freezing of the weld deposit.

Puddling of the weld metal and use of preheat or

higher current allow sufficient time for the dissolved gases to escape

from the weld metal. Presence of small, finally dispersed porosity is

normally not expected to affect the static and even dynamic properties

of a welded joint. However excessive porosity blow holes or piping

must be guarded against as they seriously impair these properties.

Their presence is detected by the conventional NDT methods. The

defective portions must be removed and re-welded.

7. Crack :Crack is defined as a discontinuity caused by the

tearing of the metal while in a plastic condition (hot crack) or by

fracturing of the metal when cold (cold crack). It represents a failure

under stress of a metal when it is behaving in a brittle manner ie., it is

inclined to fracture without deformation.

Cracking can occur in the weld metal, at the fusion line or in the base

metal. Cracks may be classified according to location and direction of

line and they may range in size from large cracks which can be seen by

the naked eye (called macro cracks) to extremely small fissures which

are detected with the aid of a microscope (called micro cracks). Typical

cracks occurring in a welded joints are as shown.

Hot Cracks :These cracks occur at temperatures above 540C and

when observed under the microscope are seen to have traveled across

the boundaries between the grains (inter granular). If the cracks has

extended to the surface, the fractured surface is found to be coated

with the blue scale or possibly black scale.

3

2

1

4

5 6

7

8

Classification of cracking according to location in a weldment :

❖ Weld metal crater cracking.

❖ Weld metal transverse cracking.

❖ Base metal heat affected zone transverse cracking

❖ Weld metal longitudinal cracking

❖ Toe cracking

❖ Underbead cracking

❖ Fusion line cracking

❖ Weld metal root cracking.

Shrinkage stress

Shrinkage stress

Hot cracking occurs in a solidifying metal at the end of the

solidification range, when this last portion is still liquid and the

mass of the metal is unable to deform without cracking. At this stage

when vibrational or contraction stresses are imposed on the metal a

fissure forms. Figure shows how a hot crack initiates in a heavy fillet

weld when it is subjected to high localized contraction or shrinkage

stresses indicated by arrows.

Stage 1 Stage 2

While hot cracking propensity increases with

increasing joint restraint, it is really the presence of

certain undesirable low – freezing compounds formed

by stray elements which promotes the phenomenon.

Causes :

The hot cracking tendency caused by

phosphorous, sulphur and silicon increases with

carbon and alloy content of the steel and hence high

tensile steels must have lower percentage of these

elements than in the case of mild steel. This applies as

much to the weld metal as the base metal.

THANK

YOU