CSWIP 3.1_2009

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WELDING INSPECTION of STEELS

Section Title

1) Duties & Responsibilities 2) Welding Terms & Definitions

3) Welding Imperfections

4) Mechanical Testing

5) Welding Procedures/Welder approval

6) Materials Inspection

7) Codes and Standards

8) Welding Symbols on Drawings

9) Introduction to Welding Processes

10) Manual Metal Arc Welding

11) Tungsten Inert Gas Welding

12) Metal Inert/Active Gas Welding

13) Submerged Arc Welding

14) Welding Consumables

15) Non Destructive Testing

16) Weld Repairs

17) Residual Stress & Distortion

18) Heat Treatment of Steels

19) Oxy-Fuel Gas Welding/Brazing and Bronze Welding

20) Thermal Cutting Processes

21) Welding Safety

22) Weldability of steels

23a) The Practice of Visual Welding Inspection 23b) Visual Welding Inspection Practical Forms

All Notes Written and Produced by:

Anthony (Tony) Whitaker

Inc’ Eng. M Weld I. EWE. IWE. EWI.IWI.LCG

Principal Lecturer/Examiner

TWI DXB FZ

GSM Tel: 00971-50-6426453

[email protected]

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WIS 5

Preparatory for CSWIP 3.0/3.1

Section 01 Duties & Responsibilities

Of a Welding Inspector

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Welding Inspection of Steels WIS 5

Section 01 Duties & Responsibilities

Rev 09-09-08 Copyright 2009 TWI Middle East

1.1 WORLD CENTRE FOR

MATERIALS JOINING TECHNOLOGY

Welding Inspection

An Introduction:

In the fabrication industry it is common practice to employ Welding Inspectors to ensure

that fabricated items meet minimum specified requirements and will be suitable for their intended applications. Employers need to ensure that Welding Inspectors have appropriate abilities, personal qualities and level of job knowledge in order to have confidence in their work. As a means of demonstrating this there are a number of internationally recognised schemes, under which a Welding Inspector may elect to become certified.

The purpose of this text is to provide supporting WIS 5 (Welding Inspection of Steels course number 5) reference notes for candidates seeking qualification in the Certification

Scheme of Welding and Inspection Personnel CSWIP 3.1/3.0 Welding Inspectors examinations.

A competent Welding Inspector should posses a minimum level of relevant experience,

and as such there are strict pre-examination experience requirements for the various examination grades. Each prospective CSWIP candidate should ensure their eligibility by evaluating experience requirements prior to applying for any CSWIP examination against the published document CSWIP–WI–6–92. (Requirements for Certification of Welding

Inspectors) All experience claims should be recorded on an independently verified CV.

A proficient and efficient Welding Inspector would require a sound level of knowledge

in a wide variety of quality related technologies employed within the many areas of the fabrication industry. As each sector of industry would rely more on specific processes and methods of manufacture than others, it would be an impossible task to hope to encompass them all in any great depth within this text, therefore the main aim has been to generalise, or simplify wherever possible.

In a typical Welding Inspectors working day a high proportion of time would be spent in

the practical visual inspection and assessment of welds on fabrications, and as such this also forms a large part of the assessment procedure for most examination schemes.

BS EN 970 (Non-destructive Examination of Fusion Welds - Visual Examination) is a

standard that gives guidance on welding inspection practices as applied in Europe. The standard contains the following general information:

 Basic requirements for welding inspection personnel.

 Information about conditions suitable for visual examination.  Information about aids that may be needed/helpful for inspection.  Guidance about the stages when visual inspection is appropriate.  Guidance on what information to include in examination records.

It should always be remembered that other codes and standards relating to welding inspection activities exist and may be applied to contract documents.

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THE WELDING INSTITUTE

MATERIALS JOINING TECHNOLOGY It could be generally stated that all welding inspectors should:

 Be familiar with the standards, rules and specifications relevant for the fabrication work being undertaken. (This may include National standards, Client standards and the Company's own 'in-house' standards)

 Be informed about the welding processes/procedures to be used in production.  Have high near visual acuity, in accordance with the applied scheme or standard.

This should also be checked periodically. (Normally 6 months)

Important qualities/characteristics that proficient Welding Inspectors would be expected to have include:

 Honesty

 A good standard of literacy and numeracy  A good level of general fitness

Welding Inspection is a job that demands the highest level of integrity, professionalism, competence, confidence and commitment if it is to be carried out effectively. Practical experience of welding inspection in the fabrication industry together with a recognised qualification in Welding Inspection is a route towards satisfying the requirements for competency.

A Welding Inspectors job is not unlike a judge in a court of law, in that it falls upon the Inspector to interpret the written word, and which on occasions can be a little grey. A balanced and correct interpretation is a function of knowledge and experience, but it must be remembered that it is not the inspector’s job to re-write the code/specification. The scope of work of the Welding Inspector can be very wide and varied, however there are a number of topics that would be common to most areas of industry i.e. most fabrications are produced from drawings, and it is the duty of the welding inspector to check that correct drawings and revisions have been issued for use during fabrication. The Duties of a Welding Inspector are an important list of tasks or checks that need to be carried out by the inspector, ensuring the job is completed to a level of quality specified. These tasks or checks are generally directed in the applied code or application standard. A typical list of a Welding Inspectors duties may be produced which for simplicity can be initially grouped into 3 specific areas:

1) Before Welding 2) During Welding

3) After Welding (Including repairs)

These 3 groups may be expanded to list all the specific tasks or checks that a competent Welding Inspector may be directed to undertake whilst carrying out his/her duties.

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MATERIALS JOINING TECHNOLOGY It is the duty of all Welding Inspectors to ensure all operations allied to welding are carried out in strict accordance with written and agreed code, practice, or specifications.

This will include monitoring or checking a number of operations including:

Before welding:

Safety:

Ensure that all operations are carried out in complete compliance with local, company, or National safety legislation (i.e. permits to work are in place) etc.

Documentation:

Check specification. (Year and revision) Check drawings. (Correct revisions)

Check welding procedure specifications and welder approvals

Validate certificates of calibration. (Welding equipment & inspection instruments) Check material and consumable certification

Welding Process and ancillaries:

Check welding equipment and all related ancillaries. (Cables, regulators, ovens, quivers etc.)

Incoming Consumables:

Check pipe/plate and welding consumables for size, condition, specification and storage.

Marking out preparation & set up: Check the:

Correct method of cutting weld preparations. (Pre-Heat for thermal cutting if applicable) Correct preparation. (Relevant bevel angles, root face, root gap, root radius, land, etc.) Correct pre-welding distortion control. (Tacking, bridging, jigs, line up clamps, etc.) Correct level and method of pre heat which must be applied prior to tack welding All tack welding to be monitored/inspected. (Feathering of tacks may also be required)

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During welding: Monitor

Weather conditions. Mainly for site work, welding is generally halted when inclement. Pre-heat values. (Heating method, location and control method)

In-process distortion control. (Sequence or balanced welding)

Consumable control. (Specification, size, condition, and any special treatments)

Welding processes and all related variable parameters. (Voltage, amperage, travel speed, etc) Welding and/or purging gases. (Type, pressure/flow and control method)

Welding conditions for root, hot pass, filler and capping runs. Inspect inter-run cleaning.

(The Root/Hot pass are normally inspected prior to filler runs to reduce costly repairs)

Minimum and/or maximum inter-pass temperatures. (Temperature and control method)

Check Compliance with all other variables stated on the approved welding procedure

After welding:

Carry out visual inspection of the welded joint. (Including dimensional aspects) Check and monitor NDT requirements. (Method, qualification of operator, execution) Identify repairs from assessment of visual or NDT reports. (Refer to repairs below) Post weld heat treatment (PWHT) (Heating method and temperature recording system) Re-inspect with NDE/NDT after PWHT. (If applicable) + Hydrostatic test procedures. (For pipelines or pressure vessels)

Repairs:

Excavation procedure. (Approval and execution)

Approval of the NDT procedures (For assessment of complete defect removal) Repair procedure. (Approval of re-welding procedures and welder approval) Execution of approved re-welding procedure. (Compliance with repair procedure) Re-inspect the repair area with visual inspection and approved NDT method

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MATERIALS JOINING TECHNOLOGY To be fully effective, a Welding Inspector requires a high level of knowledge, experience and a good understanding of the job. This should in turn earn some respect from the welder. Good Welding Inspectors should carry out their duties competently, use their authority

wisely and be constantly aware of their responsibilities.

The main responsibilities of a Welding Inspector are:

To observe all relevant actions related to weld quality throughout production. This will include a final visual inspection of the weld area.

To record, or log all production inspection points relevant to quality, including a final map and report sheet showing all identified welding imperfections.

To compare all reported information with the acceptance levels/criteria and clauses within the applied application standard.

Submit a final inspection report of your findings to the QA/QC department for analysis and any remedial actions.

To Record

To Compare

To Observe

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WIS 5 Section 1 Exercises:

1) List 4 other areas that would generally be covered by a non-destructive examination (NDE) inspection standard for welding?

1_

Basic requirements for welding inspection personnel

_________ 2_______________________________________________________________ 3_______________________________________________________________ 4_______________________________________________________________ 5_______________________________________________________________

2) List other desirable characteristics that all welding inspectors should possess? 1_K

nowledge_______________

__________________________________ 2_______________________________________________________________ 3_______________________________________________________________ 4_______________________________________________________________ 5_______________________________________________________________

3) List 5 other areas of knowledge with which a proficient welding inspector should be familiar with?

1

_Welding Processes_____________________________________

2 _______________________________________________________________ 3 _______________________________________________________________ 4 _______________________________________________________________ 5 _______________________________________________________________ 6 _______________________________________________________________

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4) Define your duties as a Welding Inspector to your nominated code of practice. Target Volume: Approximately 300 words (1.5 – 2 sides of A4 paper) Target Time: 20-30 minutes

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WIS 5

Preparatory for CSWIP 3.0/3.1

Section 02

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Section 02 Terms & Definitions

1

2:1 WORLD CENTRE FOR

Terms and Definitions:

A Weld:

______________________________________________________ _______________________ _

A Joint:

______________________________ _________________________

A Union of Materials Caused by Heat and/or Pressure

i.e. “The Process of Welding”

A Configuration of Members

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2

Types of common welds

Butt Welds

Fillet Welds

Spot/Seam Welds

Plug/Slot Welds

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3

Types of common joints

Butt Joints

T Joints

Lap Joints

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4

Weld Preparations

When welding it is generally required to fuse and fill the entire area across the faces of both members, therefore it may also be a requirement (depending on the process) to

prepare or remove metal from the joint allowing access for the welding process and fusion of the joint faces. Flame/arc cutting, machining or grinding may be used for this

operation however grinding is required on some steels after flame/arc cutting/gouging.

The simple guide is this: The more taken out then the more that must be replaced.

The function of the root gap is to allow penetration where optimum dimensions lay between zero and up to 10mm depending on the process and application.

The function of the root face is to control the level of penetration by removing excess heat in acting as a heat sink. Generally the higher the energy of a process then the wider becomes the root face and narrower becomes the root gap.

Included angle

Bevel angle

Root face

Root gap

Root radius

Root landing

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5

Single Sided Butt Weld Preparations

Single Bevel

Single V

Single J

Single U

Single sided preparations are normally made on thinner materials, or when access from both sides is restricted.

The selection may be also influenced by the capability of the welding process and the position of the joint, or the positional capability of available welding consumables, or the skill level available.

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6

Double Sided Butt Weld Preparations

Double Bevel

Double V

Double J

Double U

Double sided preparations are normally made on thicker materials, and when access from both sides is unrestricted. They may also be used to control the effect of distortion, and in controlling economics, by reducing weld volume in thicker sections.

It should be noted that it is not uncommon to find weld preparations that are of a

compound or asymmetrical nature. Values & applications given below are only typical:

a) An asymmetrical preparation (1/3 + 2/3) may be used to control/reduce the effects of contraction stresses and distortion when access to both sides is restricted.

b) A compound angle preparation, used to reduce weld metal costs in thicker section.

c) An asymmetrical bevel preparation, sometimes used in positional welding. 2G/PC

a. 1/3 2/3 60º 60º 45º 15º c. b. 35º 20º

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7

Welded Butt Joints

A Butt Welded Butt Joint

A Fillet Welded Butt Joint

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8

Welded T Joints

A Fillet Welded T Joint

A Butt Welded T Joint

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9

Welded Lap Joints

A Fillet Welded Lap Joint

A Spot Welded Lap Joint

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10

Welded Closed Corner Joints

A Fillet Welded Closed Corner Joint

A Butt Welded Closed Corner Joint

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11

Welded Open Corner Joints

An Inside Fillet Welded Open Corner Joint

An Outside Fillet Welded Open Corner Joint

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12

Terms used in a Butt Welded Butt Joint

A & B =

Excess

Weld Metal

(Excess to the Design Requirement or DTT)

Fusion Zone

1.2.3.4. = Weld Toes

1 3 4

A

B

2

Weld Face

Weld Width

Design Throat Thickness

Fusion Boundary

Or Weld Junction

Actual Throat Thickness

HAZ

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13

Terms used in a Fillet Welded T Joint

In visual inspection it is usually the leg length that is used to size fillet welded joints. It is possible to find the design throat thickness easily by multiplying the leg length by 0.7

The excess weld metal can be measured by taking the measurable throat reading, then by deducting the design throat thickness calculated above.

Example:

If the leg length of a convex fillet weld is measured at 10 mm, then the design throat thickness = 10 x 0.7 which is 7mm

If the actual measured throat thickness is 8.5 mm then the excess weld metal is calculated as: 8.5 – 7mm = 1.5mm excess weld metal

Vertical Leg Length

Horizontal Leg Length

Weld Face

Excess Weld Metal

Design Throat Thickness (DTT)

Actual Throat Thickness (ATT)

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14

Design Throat Thickness (DTT)

Nominal and Effective

Equal Leg Lengths

z

“a”

= A ‘Nominal’ design throat thickness (DTT)

“s”

= An ‘Effective’ design throat thickness (DTT) (Deep penetration fillets welds) When using deep penetrating welding processes with high current density it is possible to create deeper throat dimensions. This added line of fusion may be used in design calculations to carry stresses and is thus a major design advantage in reducing the

overall weight of welds on large welded structures.

The basic effect of current density in electrode wires is explained graphically in Section

12 on page 12.9 of this text.

This throat notation “a” or “s” is used in BS EN 22553 for weld symbols on drawings as dimensioning convention for the above types of fillet welds throughout Europe.

s

a

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15

Fillet Weld Profiles

____________________

Concave fillet welds are the preferred profile for joints that are to be loaded in cyclic stress, as this

will minimise stress concentration and reduce possible sites for fatigue crack initiation.

In critical applications it may be a requirement of the welding procedure that the toes are lightly

ground or they may also be flushed in (dressed) using TIG (without additional filler metal) to

remove any notches that may be present. Peening or shot blasting will also improve fatigue life.

Concave

ATT = DTT

Mitre

ATT = DTT

Convex

DTT

ATT

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16

Welding Positions:

(As extracted from BS 499: Part 1: 1991

Figure 38

)

Graphical Representation for Butt Welds

UK (USA)

ISO/BS EN

1G Flat Position

(Rotated)

Flat Position

1G

PA

2G

Horizontal Vertical Position

2G

PC

PF

PG

3G

Vertical Position

3G

PF

Vertical up

PG

Vertical down

4G

Overhead Position

4G

PE

(

Pipe axis fixed horizontal)

PF

PG

5G

Vertical Position

5G

PF

Vertical up

PG

Vertical down

H-LO45

J-LO45

6G

Inclined Position

(Fixed)

6G

H-LO45

Vertical up

J-LO45

Vertical down

45°

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17

Graphical Representation for Fillet Welds

UK (USA)

ISO/BS EN

(Weld throat vertical)

1F Flat Position

Flat Position

(Rotated) 1FR

1F

1FR

L-45/PA

2F

Horizontal Vertical Position

2F

2FR

(Pipe axis horizontal)

2FR

2F

PB

2FR

PB

(Weld axis vertical)

PF

PG

3F

Vertical Position

3F

PF

Vertical up

PG

Vertical down

(Weld axis horizontal)

4F

Overhead Position

4F

PD

(Pipe axis horizontal)

5F

Vertical Position

5F

PF

Vertical up

PG

Vertical down

P G PF PG PF 45° 45° Pipe Rotated

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18

Summary of Weld and Joint Terms and Definitions:

A Weld:

A

Union of materials

, produced by heat and/or pressure

(The process of Welding)

A Joint:

A

Configuration of members

(To be welded)

A weld preparation:

Preparing a joint to allow

access & fusion

through the joint faces

Types of weld:

Butt. Fillet. Spot. Seam. Plug. Slot. Edge

Types of joint:

Butts. T’s. Laps. Open corners. Closed corners

Types of preparation:

Bevel’s. V’s. J’s. U’s

Single & double sided

Preparation terms:

Bevel angle. Included angle. Root face. Root gap.

Root radius. Root landing

Weldment terms:

Weld face

Weld root

Fusion zone

Fusion boundary

Heat affected zone (HAZ)

Weld toes

Weld width

Weld sizing: (Butts)

Design throat thickness (DTT)

Actual throat thickness (ATT)

Excess weld metal (Weld face)

Excess weld metal (Root penetration bead)

Weld sizing: (Fillets)

Design throat thickness (DTT)

Actual throat thickness (ATT)

Excess weld metal (Weld face)

Leg length

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19

WIS 5 Section 2 Exercises:

Complete the exercises below by inserting all information in the spaces as provided?

Insert the BSEN welding position as given into the diagram below:

PA

PB

PC

PD

PE

PF

PG

H-LO45

J-LO45

Insert the remaining terms for:

A Single U Preparation Butt Joint

Included angle

__ LO45

P__

P __

__-LO45

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20

A Single V Butt Welded Butt Joint

Identify and list 4 more types of common welds and joints:

Types of Weld

Types of Joint

1)

Butt Weld

1)

Butt Joint

2)

3)

4)

5)

1) A joint containing more than one type of weld is termed a _______________welded joint 2) A joint containing two of the same type of weld is termed a ______________welded joint

1 3 4

A

B

2

or Weld Junction

A + B =

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21

Insert the remaining terms that may be used in the sizing of a fillet weld:

State the main reasons for a weld preparation:

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WIS 5

Preparatory for CSWIP 3.0/3.1

Section 03

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Section 03 Welding Imperfections

Rev 09-09-08 Copyright 2009 TWI Middle East 3:1

Welding Imperfections:

What are welding imperfections?

Welding imperfections are discontinuities caused by the process of welding. As all items contain imperfections it is only when they fall outside of a “level of acceptance” that they should be termed as defects, as if present they may then render the product defective or unfit for its purpose. The closeness of tolerance in an applied level of acceptance depends upon the application or level of quality required i.e. “The Fitness for Purpose” As all fusion welds can be considered as castings they may contain imperfections associated with the casting of metals, plus any other particular imperfections associated with the specific welding process. Welding imperfections may be classified as follows:

1) Cracks 2) Gas Pores, Cavities, Pipes

3) Solid Inclusions 4) Lack of Fusion

5) Surface and Profile 6) Mechanical/Surface Damage 7) Misalignment

1)

Cracks

Cracks sometimes occur in welded materials, and may be caused by a great number of factors. Cracks are generally predictable and for any crack like imperfection to occur in a material, there are 3 criteria that must be fulfilled:

a) A Force b) Restraint c) A Weakened Microstructure

Typical types of hot and cold cracks to be discussed later within the course include:

1) H2Cracks 2) Solidification Cracks 3) Lamellar Tears

All cracks have sharp edges producing high stress concentrations, which generally results in a rapid progression, however this also depends on the properties of the metal. Cracks are classified as planar imperfections as they are 2 dimensional i.e. length and depth. Most cracks are considered as unacceptable and thus classified as defects, though some standards (i.e. API 1104) permit a degree of so called “Crater, or Star Cracking”

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2)

Gas pores, Porosity, Cavities and Pipes

Gas pores

These are singular gas filled cavities 1.5mm diameter, created during solidification of the weld and the expulsion or evolution of gases from solution in solidifying weld metal. They are generally spherical or ovular in appearance though they may extend to form

elongated gas cavities, or Worm holes depending on the conditions of solidification. The

term used to describe an areas of rounded gas pores is Porosity, which may be further classified by the number, size and grouping of the pores within the area (i.e. Fine, or coarse cluster porosity) Gases may be formed by the breakdown of paints, oil based products, corrosion or anti corrosion products that have been left on the plates to be welded. A singular gas filled cavity of >1.5mm diameter is termed a Blow hole. Porosity may occur during the MIG or TIG process by the temporary loss of gas shielding, and/or ingress of air into the arc column and may also be caused by an incorrect setting of the shielding gas flow rate. Gas pores/porosity may also break the welds surface where they are known as surface porosity. Porosity may be found in deep SAW or MMA welds due to damp fluxes or damaged MMA electrode coatings, or an incorrect welding technique. Porosity may be prevented by correct cleaning of materials, correct setting and shielding when using the TIG or MIG welding processes, and using dry undamaged consumables.

Shrinkage Cavities

These are internal voids or cavities that are generally formed during the solidification of large single welds of high depth to width ratio (d:w) as with SAW or MIG/MAG. They may be defined as hot plastic tears caused by large opposing contractional forces in the weld and HAZ until the ductility of the hot metal is overcome resulting in a plastic tear. Shrinkage cavities can produce high concentrations of stress at their sharp edges, which may propagate cracks to the weld surface appearing around the weld centreline.

Crater Pipes

Occur at the end of a weld run, where insufficient filler metal is applied to fill the crater.

Surface Cluster Porosity Fine Cluster

Porosity

Blow Hole >1.5 mm Ø Hollow Root Bead (Elongated Gas Cavity)

Coarse Cluster Porosity Shrinkage Cavity

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3)

Solid Inclusions

Solid inclusions may be either of a metallic or non-metallic nature which may become trapped inside the solidified weld metal. The type formed is highly dependant on the

welding process being used, as when using processes that utilise fluxes to form a slag

such as MMA or SAW then non-metallic slag inclusions may occur. Deep inclusions may occur when slag traps such as internal undercut have been formed in the root area then not properly cleaned prior to deposit of the filler or capping runs. Slag traps and subsequent slag inclusions are mostly caused by incorrect welding technique. Welding processes such as MIG/MAG and TIG use silicon, aluminium and other elements to de-oxidise the weld in forming silica and/or alumina. These non-metallic compounds may again be trapped inside the weld through inadequate cleaning of previous runs. Tungsten inclusions are metallic inclusions which may be formed during TIG welding by a poor welding technique, an incorrect tungsten vertex angle, or too high amperage for the diameter of tungsten being used. Copper inclusions may be caused during MIG/MAG welding by a lack of welding skill, or incorrect settings in mechanised, or automated

MIG welding. (Mainly when welding aluminium alloys) Welding phenomena such as

“Arc Blow” or the movement of the electric arc by magnetic forces may cause solid

inclusions to be trapped in welds. The location of all inclusions is important as they may just occur within the centre of a deposited weld, or between welds where they also cause

“Lack of inter-run fusion”, or at the sidewall of the weld preparation also causing “Lack of side wall fusion” Generally solid inclusions may most likely be caused by:

1) Lack of welder skill. (Incorrect welding technique)

2) Incorrect parameter settings, i.e. voltage, amperage, speed of travel 3) Magnetic arc blow

4) Incorrect positional use of the process, or consumable 5) Insufficient Inter-run cleaning

Internal Solid Inclusion

Solid Inclusion (Also causing

a Lack of Sidewall Fusion)

Solid inclusions formed from base metal undercut (Slag trap) in the root run, or hot pass. They are known as “Wagon Tracks” when seen on a radiograph

Surface Breaking Solid Inclusion Internal Solid Inclusion

(Also causing a Lack of Inter-run Fusion)

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4)

Lack of Fusion

Lack of fusion may be defined as a lack of union between two adjacent areas of material and may occur either in the Weld Root, Inter-run or Sidewall where it may also be

surface breaking. Lack of fusion may also be found in the form of Cold Laps that may

occur on plate/pipe surfaces during positional welding and caused mainly by incorrect use of the process and the effects of gravity. A difference between the terms Cold Lap and Overlap is that cold lap is considered to occur between touching surfaces but with poor or no fusion, whereas overlap (Page 3.5) indicates movement of weld metal beyond a given point (normally beyond 90°) Though technically different these terms are often

misused even within specifications and may be taken to mean the same although the term

selected for reporting is dictated by that used within the applied standard. Lack of fusion may occur when using processes of high currents as arcs may be deviated away from the fusion faces by magnetic forces causing a lack of fusion, an effect known as “Arc Blow”. Lack of fusion may also be formed in the root area of the weld where it may be found on one or both plate edges when it may be accompanied by incomplete root penetration. (Page 3.6) Lack of sidewall fusion is commonly associated with dip transfer MIG caused mainly by the inherent coldness of dip transfer and the action of gravity, but may also be attributed to high inductance settings or lack of welder skill. Lack of Fusion is also often caused by the formation of solid inclusions between runs and faces. (Page 3.3) Like solid inclusions, lack of fusion imperfections may most likely be caused by:

1) Lack of welder skill. (Incorrect welding technique)

2) Incorrect parameter settings i.e. voltage, amperage, speed of travel etc 3) Magnetic arc blow

4) Incorrect positional use of the process, or consumable 5) Insufficient inter-run cleaning

Lack of Sidewall Fusion

(Also causing an Incompletely Filled Groove)

Cold Lap

Lack of Sidewall Fusion

Lack of Root Fusion Lack of Inter-run Fusion

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5)

Surface Profile

Surface profile imperfections are generally caused through poor welding technique. This includes the use of incorrect parameters, electrode/blowpipe size and/or manipulation and joint set up and may be weld face and/or root, as shown in groups A B and C below:

A:

Spatter though not a major factor in lowering the weldments strength it may mask other

imperfections and should therefore be removed prior to inspection. Spatter may also hinder NDT and be detrimental to coatings. It can also cause micro cracking or hard spots in some materials due to the localised heating/quenching effect.

An Incompletely Filled Groove, or Under-fill will take the weld throat below the value

of the DTT (Design Throat Thickness) and if appearing on the side wall may also cause high stress concentrations to occur through a Lack of Sidewall Fusion. (Page 3.4)

Overlap may be caused by lack of welder skill i.e. an incorrect electrode/torch angle,

and/or travel speed etc. If contact is made with the base metal then Overlap may be also be accompanied by, or termed as Cold Lap within an application standard. (Page 3.4)

An Incompletely Filled Groove

Under-fill

Spatter

A

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B:

A Bulbous Contour is an imperfection as it causes sharp stress concentrations at the toes

of individual passes and may also contribute to overall poor toe blend.

Arc Strikes, Stray-Arc, or Stray Flash may cause cracks to occur in sensitive materials,

producing sharp depressions in the metals surface, causing stress raisers and corrosion sites. Arc strikes should be ground, crack detected and repaired as required.

Incomplete Root Penetration may be caused by too small a root gap, insufficient

amperage, or poor welding technique i.e. poorly dressed or un-feathered tack welds. It produces sharp stress concentrations, and reduces the ATT (Actual Throat Thickness) below that specified for the joint. Incomplete Root Penetration is always accompanied by a Lack of Root Fusion as technically there is no weld metal present to be fused.

Poor Toe Blend Bulbous Contour Arc Strikes

Incomplete Root Penetration + Lack of Root Fusion

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Effect of a Poor Toe Blend

A very poor weld toe blend angle

An improved weld toe blend angle

The excess weld metal height is within limits but the toe blend angle is unacceptable

Generally specifications tend to state that “The weld toes shall blend smoothly” This statement can cause many problems as it is not a quantitative instruction, and therefore very much open to individual interpretation. To help in the assessment of the acceptance of the toe blend it should be noted that the higher the angle at the toe then the higher is the concentration of stresses. When the toe angle reaches 30° - 40° the stress concentration ratio at the weld toe becomes > 2:1

A poor toe blend will always be present when the excess weld metal height is excessive or the weld profile is excessively bulbous, however it may be possible that the height is within the given limits, yet the toe blend is not smooth, and is therefore a defect, and unacceptable. It should also be remembered, that a poor toe blend in the root of the weld has the same effect. It can be clearly seen that any rapid change in the section will induce stress concentration and therefore the use of the term reinforcement to describe any amount of excess weld metal is very misleading and inaccurate, though this term is very often used in many application standards.

6 mm

80°

3 mm

30°

3 mm

90°

(41)

C:

An Irregular Bead Width is a surface imperfection, which is often referenced in

application standards as. “The weld bead should be regular along its length”

Undercut

Undercut can be defined as a depression or grove at the toe of a weld in a previous deposited weld or base metal caused by welding. Undercut is principally caused by an incorrect welding technique, including a high a welding current, or slow a travel speed in conjunction with the welding position i.e. 2F/2G or PB/PC. It is often found in the top toe of fillet welds when attempting to produce a leg length >9mm in one run. Undercut can be considered a serious imperfection, particularly if sharp as again it causes high stress concentrations. It is thus gauged in its severity by length, depth and sharpness.

Undercut (Base metal, “Top toe”) Undercut (Base metal)

(42)

Shrinkage Grooves

Shrinkage grooves occur on both sides of the root base metal caused by contraction

forces of the shrinking weld pulling on the hot plastic base metal. They are often wrongly identified as root undercut which may occur in the root but is caused mainly by gravity

i.e. G2/PC though being grooves they are all evaluated in length, depth and sharpness.

Undercut (Weld Metal)

Undercut (Root Run or “Hot Pass”)

(43)

Root Concavity. (Suck Back in USA)

This may be caused when using too high a gas backing pressure in purging. It may also be produced when welding with too large a root gap and depositing too thin a root bead, or too large a hot pass which may pull back the root bead through contractional stresses.

Excess Root Penetration

May be caused by using too high a welding current, and/or, too slow travel speed, too large a root gap, and/or too small root face. It is often accompanied by burn through, or a local collapse of the weld puddle causing a hole in the weld root bead. Penetration is

only excessive when it exceeds the allowable limit, as given in the application standard. Root Oxidation

Root oxidation may take place when welding re-active metals such as Stainless Steels or Titanium etc. with either contaminated or an inadequate purging gas flow.

Incompletely Fused Tack Welds and Stop/Starts

It is often a procedural requirement for tack welds or for the end of root run welds to be

feathered (Lightly ground and blended) prior to welding/re-striking. This requirement is

very dependent upon the class of work. Feathering should enable tack welds or previous welds to be more easily blended and any failure to achieve this correctly may result in a degree of lack of root fusion/penetration and/or irregularities occurring in the weld root.

Root concavity

Pipe Plate

Un-feathered

start

of run Un-feathered

root tack

Incomplete Penetration Irregular Root Bead

Un-feathered

end

of run

(44)

A Burn Through may be caused by a severely excessive root penetration bead followed by local collapse of the weld root in the effected area.

It may be generally caused by a combination of the following factors:

a) > welding current b) > root gap

c) < root face d) < speed of travel

Its occurrence is also very dependent upon the welding position and the effect of gravity.

Excess Root Penetration

(Beyond the specified limit)

Root Oxidation

(In Stainless Steel)

This may lead to a Burn Through

(A local collapse of the weld pool leaving a hole in the root area)

(45)

To summarise, surface/profile welding imperfections are as follows:

1) Incompletely Filled Groove/Lack of Sidewall/Root Fusion 2) Cold Laps/Overlap

3) Spatter

4) Arc Strikes. (Stray arcs) 5) Incomplete root penetration 6) Bulbous, or Irregular Contour 7) Poor Toe Blend

8) Irregular Bead Width

9) Undercut. (Weld and/or Base metal)

10) Root Concavity. Root Shrinkage Grooves/Root Undercut 11) Excess Penetration. Burn Through

(Comparatively measured as radiographic density in some line pipe standards)

12) Root Oxidation

Surface and profile imperfections are mainly caused by a lack of applied welding skill.

6)

Mechanical/Surface damage

Mechanical/Surface damage

This can be defined as any material surface damage caused during the manufacturing or handling process, or in-service conditions. This can include damage caused by:

1) Grinding 2) Chipping

3) Hammering 4) Removal of welded attachments by hammering 5) Chiselling 6) Using needle guns to compress weld capping runs 7) Corrosion (Not caused through welding, but is considered during inspection)

As with arc strikes the above imperfections are detrimental to quality as they reduce the plate or wall thickness through the affected area. They may also cause local stress concentrations and corrosion sites and should thus be repaired prior to acceptance.

(46)

7)

Misalignment

There are 2 main forms of misalignment in plate materials, which are termed:

1) Linear Misalignment 2) Angular Misalignment or Distortion

Linear Misalignment: can be controlled by the correct use/control of the weld set up

technique i.e. tacking, bridging, clamping etc. Excess Weld Metal Height and the Root

Penetration Bead must always be measured from Lowest Plate to the Highest Point of the weld metal, as shown below.

Angular Misalignment: may be controlled by the correct application of distortion

control techniques, i.e. balanced welding, offsetting, or use of jigs, fixtures, clamps, etc.

Hi-Lo is a term that is generally used to describe the unevenness across the root faces

between pipes found during set up and prior to welding. This unevenness is often caused by an un-matching and/or irregular wall thickness, or between pipes having any degree of ovality.

Angular Misalignment/Distortion measured in degrees

15

Hi-Lo

Linear Misalignment measured in mm

3 mm

(47)

Summary of Welding Imperfections:

Group

Type

Causes/Location

1) Cracks Centreline Weld Metal

H2 HAZ & Weld Metal

Lamellar Tears Base metal

2) Porosity/Cavities

Porosity Damp electrodes Un-cleaned plates/pipes

Loss of gas shield Gas pore 1.5mm 

Blow hole > 1.5mm

Shrinkage cavity Weld metal (high d:w)

3) Solid Inclusions

Slag MMA/SAW Poor Inter-run cleaning Undercut in hot pass. Arc blow Silica TIG/MAG (Fe steels)

Tungsten TIG Dipping tungsten in weld pool Copper (MIG/MAG) Dipping tip in weld pool

4) Lack of Fusion

Lack of side wall fusion

(Can be surface breaking)

Arc Blow

Incorrect welding technique Lack of root fusion Un-feathered tack welds

Cold lap/overlap Positional welding technique

5) Surface & Profile

Poor toe blend Incorrect welding technique Arc Strikes Poor welding technique Incomplete penetration < Root gap/Amps. > Root face Incompletely filled groove Incorrect welding technique

Spatter Damp consumables Bulbous contour Incorrect welding technique

Undercut: Surface and internal

Too high an amperage Poor welding technique Shrinkage groove (Root) Contractional stress

Root concavity Too high gas pressure Excess Penetration

Burn through

Too large root gap/amps Too small a root face Crater Pipes (Mainly TIG) Incorrect current slope-out

6) Mechanical damage Hammer/Grinding marks etc. Poor workmanship

7) Misalignment

Angular Misalignment () Poor fit-up. Distortion Linear Misalignment (mm) Poor fit-up

Hi-Lo (mm) Irregular pipe wall or ovality

Notes:

The causes given in the above table should not be considered as the only possible causes of the imperfection given, but as an example of a probable cause.

Good working practices and correct welder training will minimise the occurrence of unacceptable welding imperfections. (Welding defects)

(48)

WIS 5 Section 3 Exercises:

Observe the following photographs and identify any Welding Imperfections:

(As indicated within the ovals)

A A A A A A A A A _A 1) 2) 3) 4) A 6) Plate. Butt Weld Face

Pipe. Butt Weld Root

Plate. Butt Weld Root

Plate. Butt Weld Face

Pipe. Butt Weld Root 5)

A

(49)

Rev 09-09-08 Copyright 2009 TWI Middle East 3:16 A A A A A A A A A 7 8) 9) 10) A A

Plate. Butt Weld Root 12)

11)

A

7) Pipe. Butt Weld Root Plate. Fillet Weld Face

Plate. Fillet Weld Face Plate. Butt Weld Face

(50)

Rev 09-09-08 Copyright 2009 TWI Middle East 3:17 A A B B A A B B A A B B B A A B A A B 15) A B 13) A B 14) 16 17) 18) 16) A B

Plate. Butt Weld Root Plate. Butt Weld Face

Plate. Butt Weld Face Plate. Butt Weld Face

(51)

Record all welding imperfections that can be observed in photographs 19-24:

19) Pipe. Butt Weld Face

(52)

22) Plate. Butt Weld Root 21) Plate. Butt Weld Face

(53)

24) Plate. Butt Weld Root 23) Plate. Butt Weld Face

(54)

WIS 5

Preparatory for CSWIP 3.0/3.1

Section 04

(55)

Section 04 Mechanical and Destructive Testing

Destructive/Mechanical Testing:

Destructive and/or mechanical tests are generally carried out to ensure that the required levels of certain mechanical properties or levels of quality have been fully achieved. When metals have been welded, the mechanical properties of the plates may have changed in the HAZ due to the thermal effects of the welding process. It is also necessary to establish that the weld metal itself reaches the minimum specified values. The mechanical properties or material characteristics most commonly evaluated include:

Hardness

The ability of a material to resist indentation

The opposite of Hard is Soft

Toughness

The ability of a material to resist fracture under impact loads

The opposite of Tough is Brittle

Strength

The ability of a material to resist a force. (Normally tension)

The opposite of Strong is Weak

Ductility

The ability of a material to plastically deform under tension

The opposite of Ductile is Un-ductile

To carry out these evaluations we require specific tests. There are a number of mechanical tests available to test for these specific mechanical properties the most common of which are:

1) Hardness testing. (Vickers/Brinell/Rockwell) 2) Toughness testing. (Charpy V/Izod/CTOD) 3) Tensile testing. (Transverse/All weld metal)

Tests 1 – 3 have units and are termed quantitative tests We use other tests to evaluate the quality of welds

4) Macro testing

5) Bend testing. (Side/Face/Root) 6) Fillet weld fracture testing 7) Butt weld Nick-break testing

Tests 4 – 7 have no units and are termed qualitative tests

Used to assess

Quality

Used to measure

Quantity

(56)

1)

Hardness tests.

(Used to measure the level of hardness across the weldment)

Types of hardness test include:

a) Rockwell scale (Diamond or steel/ceramic ball) b) Vickers pyramid. HV (Diamond)

c) Brinell. BHN (5 or 10 mm diameter steel/ceramic ball) d) Shore Schlerescope (Measures resilience)

Most hardness tests are carried out by (1) impressing a ball, or a diamond into the surface of a material under a fixed load, (2) then measuring the width of the resultant indentation and comparing it to a scale of units (BHN/HV etc.) relevant to that type of test. Hardness surveys are generally carried out across the weld as shown below. In some applications it is required to takes hardness readings at the weld junction/fusion zone. A Shore Schlerescope gauges resilience by dropping a weight from a height onto the surface then measuring the height of the rebound. The higher the rebound the higher is the resilience of the material. As resilience in materials may be directly correlated to hardness then the hardness may be read in any or all sets of units. Early equipment was cumbersome, but still far more portable compared to other hardness testing methods available. Equipment is now widely available similar in size of a ballpoint pen. This form of equipment may be used by the welding inspector to gauge hardness values on site, and is scaled in all of the common hardness scales.

(57)

2)

Toughness tests.

(Used to measure resistance to fracture under impact loading)

Types of toughness test include:

a) Charpy V. (Joules) Specimen held horizontally in test machine, notch to the rear. b) Izod. (Ft.lbs) Specimen held vertically in test machine, notch to the front.

c) CTOD or Crack Tip Opening Displacement testing. (mm)

There are many factors that affect the toughness of the weldment and weld metal. One of the important effects is that of testing temperature. In the Charpy V and Izod test the toughness is assessed by the amount of impact energy absorbed by a small specimen of 10 mm² during fracture by a swinging hammer. A temperature transition curve can be produced from the results.

The notch may be machined either in the Weld metal, Fusion zone or HAZ depending on which area/zone is to be evaluated during the test. The standard notch is 2mm deep,

0.25 mm root radius, and included angle 45  though other shapes of notches exist i.e.

“U” with all relevant dimensions given in the standard. Smaller scaled versions of this test are also available.

10 x 10 mm specimen Machined notch

The Charpy V test

2mm 45º

0.25r

Graduated scale of Joules absorbed energy

Specimen Release lever

Notch placed to the rear of the strike

Pendulum locked in position

(58)

A Ductile/Brittle transition curve for a typical C/Mn Structural Steel

The transition temperature of welded steels can be affected by many factors including:

a) Alloying (Chemical composition)

The curve can effectively be moved to the left by additions of manganese of up to 1.6 %

maximum as this has a positive effect on improving the toughness of plain ferritic steels

down to service temperatures of – 30°C. For toughness below this temperature a Nickel content of between 5 – 9% may be added for service temperatures down to – 175°C, however nickel is a very expensive metallic element and is thus only used where low temperatures are severe. For toughness down below – 175°C fully austenitic stainless steels are generally used as these alloys show measurable toughness down to – 270 °C.

b) Heat input

The above curve can effectively be moved to the right by using a high heat input or

thermal cycle during the welding, where Time at Temperatures spent around the Lower Critical Temperature of the steel promotes the occurrence of grain growth. Energy

required in fracturing a large or coarse grained steel is comparatively lower than finer

grained steel, hence on occasions where toughness is required the need to control heat

input and/or limit maximum inter-pass temperatures. A finer grain structure will move the curve to the left i.e. Increase the relative toughness values of a steel.

c) Chemical cleaning

The cleanliness of the weld metal will also greatly affect its level of toughness. Welding fluxes containing high amounts of basic compounds give much higher toughness &

strength weld metal values than welds made using lower amounts of these compounds.

-40 -30 -20 -10 0 10 20 30

Degrees Centigrade

Ductile fracture (Notch ductility)

Brittle fracture

Ductile/Brittle transition point

Energy absorbed (Joules) Temperature rangeC