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Copyright 2005, TWI Ltd World Centre for Materials Joining Technology 1

EXAMINATION

Examination in 5 (or 8) Parts(Each part has a 70% pass mark)

1. Technical Paper (1h 15min) 6 Questions given (4 answers required) Question #1 must be answered Answer 3 other questions from the remaining 5 questions

2. Interpretation of Welding Symbols (1h) Engineering drawing has welding symbols for 12 joints Interpret the symbols & comment on any errors or inconsistencies

3. Fracture Face Examination (1h) Examine fracture faces of 2 specimens & interpret modes of failure

4. NDT Reports (1h) Scrutinise 3 NDT Reports & list all errors and all omissions

5. Oral (~ 10 to 15 min) 1 Question: - subject will be related to supervision of welding

inspectors or to safety matters

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EXAMINATION

Examination in 5 (or 8) Parts(Each part has a 70% pass mark)

If a candidate for the Senior Welding Inspector Examination does nothold a recognised qualification in Radiographic Interpretation(a CSWIP or PCN Certificate) he is required to sit 3 additionalexamination parts, namely: -

6. Radiographic Interpretation (1h 30min) 6 dense metal welds - steel

7. Multi-Choice Radiographic Theory Paper (30min) 30 questions

8. Radiographic Density & Sensitivity (1h) Densitometer calibration using a Density Strip Sensitivity calculations for 5 welds

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THE SENIOR WELDING INSPECTOR

A Senior Welding Inspector may be Senior through beingput in charge of a team of Welding Inspectors.

In this role he may have a predominantly managerial rolethat requires organising and supervising their work and so

may have title of Team Leader or Supervisor.

In other circumstances he may have a more technicallydemanding role that requires detailed knowledge ofparticular activities.

The CSWIP Senior Welding Inspector Course is intended tocover aspects of both these roles.

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TYPICAL REQUIREMENTS - TECHNICAL KNOWLEDGE

Welding Technology

(Welding Inspector . plus)

NDT Techniques

( ability to carry out / interpret)

Codes/Application Standards

(ability to interpret)

Planning Systems

(ability to understand and also supply inspectionscheduling to project schedule)

Quality Assurance

(ability to plan & carry out some auditing)

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LEADERSHIP / SUPERVISION

A Supervisor is a person who has been given authority andresponsibility for: -

planning the work of others

controlling this work

A Supervisor is a man in the middle between operators andmanagement and subject to pressures from both directions

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LEADERSHIP

Is leadership an ability that a person is born with orcan it be acquired !!!!!! ?????

Personality is very influential - hence leadershipsometimes considered to be in the genes and a personreferred to as a born leader

Ability to be a good leader can be improved byexperience & from knowledge of managementtechniques through training

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TYPICAL REQUIREMENTS - LEADERSHIP SKILLS / ABILITY

Complex mixture of skills & attitudes - such as

being prepared to accept responsibility

willing to direct the work of others willing, and able, to delegate tasks to others

having a commitment to ones staff

able to solve / overcome problems (from greater & wider experience)

able to do all (or most of) the work done by ones staff

able to communicate - downwards & upwards within the Company

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What Makes a Good Leader / Supervisor ?

Qualities that are associated with a Good Supervisor are: -

has good technical skill & knowledge and good at solving problems

has ability to quickly determine priorities

is intelligent and confident shows good judgement

has enthusiasm for work and is usually cheerful & optimistic

sets a good example at work - high standards - leads by example

has no favourites and able to apply discipline fairly

is approachable - good listener - and prepared to consult staff

informs staff of important decisions affecting them and backs his team

is able to identify needs of team and obtain equipment and training

good at planning and delegation

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PRODUCTION PLANNING

PRESSURE VESSEL FABRICATION

T 1 T 2 T 3 H 1 H 2 N1

N2

N3

W 1 W 2

S1 S2

T = TierH = Head

N = Nozzle

W = Wrapper plate

S = Saddle

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PRODUCTION PLANNING

PRESSURE VESSEL: Typical Production Sequence

1. Prepare drawings & material list

2. Order materials - plate

3. - fittings

4. - heads

5. - weldingconsumables

6. Mark out, cut & roll shell plates7. Weld longitudinal seams

8. Fit & weld - T 3 to H 2

9. - T 2 to (T 3 H 2 )

10. - N 1 + H 1

11. Fit & weld - N 1 + H 1

12. Mark out, cut & roll wrapper plates

13. Weld W 1 & W 2 to shell plates

14. Fit & weld nozzles N 2 & N 3

15. Cut, assemble & weld saddles S 1 & S 2

16. Fit & weld S 1 & S 2 to W 1 & W 2

17. Carry out all final inspection

18. Pressure test

19. Blast & paint

20. Deliver

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A Preliminary Welding Procedure Specification (pWPS) is written for each test weld required

Welder makes a test weld in accordance with the pWPS Welding Inspector records all welding details used for making the test weld (as -run details) (EN standard states that an Independent Examiner or Examining Body or a Third PartyInspector may be required to monitor the qualification process)

Welding Procedure Qualification Record (WPQR) prepared giving range of qualificationallowed by the Welding Standard (EN or ASME IX) WPQR package submitted to Independent Examiner for endorsement (& usually to Client)

Test weld subjected to destructive testing according to specified methods Application Standard or Client may require additional tests such as impact tests, hardnesstests (for some materials - corrosion tests)

Finished test weld is subjected to NDT by the specified methods(EN Standard requires visual, MT or PT & RT or UT)

Welding Procedure Qualification

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Destructive Testing

pipe diameters> 323.9mm

1 2 3 4 5

678

1211

10 9

SPECIMEN TYPE POSITIONS

macro + hardness 1, 9, 11transverse tensile 2, 8, 10, 12Charpy weld metal 3, 5, 6Charpy fusion line 4, 7

WELD PROCEDURE QUALIFICATION TESTING (example)

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Destructive Testing

QUANTITATIVE TESTS & QUALITATIVE TESTS

QUANTITATIVE TESTS

for measuring a quantity ( quantity = a mechanical property )

typical mechanical tests - tensile test

- hardness test- Charpy V-notch test (& CTOD)

QUALITATIVE TESTS

for assessing joint quality (quality = good fusion & free from defects)

typical qualitative tests - bend tests- macro examination(micro examination for some metals)

- fillet fracture & nick-break tests

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Destructive Testing

Tensile Testing - Transverse Tensile Test

gaugelength

weld

TEST OBJECTIVETo measure the Tensile Strength of the welded joint

RESULTSSatisfactory if Tensile Strength greater than min. specified for base metal

(Some standards accept 95% of base material Tensile Strength)

Position of failure not usually in weld metal but in base material or HAZ

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Destructive Testing

Tensile Testing: All-Weld Tensile Test

TEST OBJECTIVETo measure Yield Strength & Tensile Strength of weld metal(% Elongation also measured & usually also % Reduction of Area)

RESULTSSatisfactory if all values are not less than minimum specified for basemetal (or required by desig) at ambient or at elevated temperature

from WPQ test piece electrode classification test piece

gauge length: all weld metal

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Destructive Testing

MECHANICAL TESTING: Charpy V-notch Test Positions

weld metal (surface)

weld metal (root)

fusion line + 2mmfusion linefusion line + 5mm

For each notch position 3 specimens are tested . May need to take testpieces from weld metal, fusion line, fusion line + 2, fusion line + 5 from bothweld faces and from root - total of 36 tests

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Destructive Testing

MECHANICAL TESTING: Charpy V-notch Impact Testing

TEST OBJECTIVE

To measure the impacttoughness of eachregion of the weld joint(weld metal, HAZ &

base metal) at aspecified temperaturethat is related to theservice conditions

RESULTS

Satisfactory if allvalues are not less theminimum specified bythe ApplicationStandard

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Welding Technology

HAZ toughness transitiontemp. has shifted to ahigher temperature

(caused by high heat inputwelding)

HAZ TOUGHNESS

unweldedfine grained

steel

no significantchange in HAZ

toughness ifmoderate heatinput used

Toughness Charpy

V-notch energy

(Joules)

Impact Test Temperature design temperature

good toughnessin steel atdesign temp.

low toughnessin HAZ atdesign temp.

degraded HAZ

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Welding Technology

THE HEAT AFFECTED ZONE (HAZ)

unaffected basematerial

tempered zone

grain growth zone

recrystallised zonepartially transformed zone

MaximumTemperature solid-liquid transition zonesolid

weldmetal

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Destructive Testing

MECHANICAL TESTING: Hardness Testing

HARDNESS TEST METHODS

Vickers example 248 HV10Rockwell example Rc 22Brinell example 220 BHN-W (not usually used on macro sections)

TEST OBJECTIVE To measure the max. hardness in the weld joint(always in HAZ for steels)

RESULTS Satisfactory if no values are above the max.specified by the Application Standard

usually the hardest region

HAZ

fusion line(fusion

boundary)HAZ

~1.5 to 3mm

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Welding Technology

HAZ Hardness of Carbon-Manganese Steels

intermediate heat-input willgive satisfactory hardness

Rate of Cooling of HAZ

HAZHardness

high heat-input

welding tends togive a softer HAZ

low heat-inputwelding tendsto give a highHAZ hardness

fast slow

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Welding Technology

HAZ Hardness of Low-Alloy Steels

(such as the higher Cr-Mo grades)

Time to Cool

HAZHardness

low heat-input welding

fast cooling slow cooling

high heat-input welding

HAZ hardness always high (> ~ 400 HV)

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Destructive Testing QUALITATIVE TESTS: Bend Tests

full thickness of joint in tension = side bend

for joint thicknesses> ~ 12mm

face in tension = face bend root in tension = root bend

for joint thicknesses< ~ 12mm

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Destructive Testing

Tests are used instead of radiography or ultrasonic examination to show

that satisfactory fusion has been achieve

that the weld is has no defects

QUALITATIVE TESTS: Fillet Fracture & Nick Break Tests

force

fracture from root

machined slotmachined slot

FILLET FRACTURE NICK-BREAK

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PWHT

Steels are given a PWHT to reduce residual stresses caused by

welding [and also to temper (soften) the hardest regions of the HAZ] The main benefit of reducing residual stresses is to improveresistance to brittle fracture - explained as follows: -

Residual stresses can be higher than the max. allowed design stressand are powerful driving forces for propagating flaws (usually cracks)

In the as-welded condition, the steel joint has a lower tolerance toflaws that may become initiation points for brittle cracks

A crack that could cause brittle fracture is called a critical crack

The size of a critical crack depends on the material toughness and

total stress that the crack experiences in the joint (design + residual) An as-welded joint may only be able to tolerate a small critical crack- possibly so small that it could be missed by RT or UT

When residual stresses are removed, a critical crack should be so bigthat it could not be missed during NDT and so would be repaired

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PWHT

Removal of Residual Stress

Temperature (C)

100 200 300 400 500 600 700

YieldStrength(N/mm 2 )

100

200

300

400

500 Cr-Mo steel - typical

C-Mn steel - typical

At PWHT temp. the yieldstrength of steel reduced sothat it it is not strong

enough to give restraint. Residual stress reduced tovery low level by straining(typically < ~ 0.5% strain)

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PWHT

The toughness of the HAZ may be improved - particularly for the morehardenable low alloy steels & improves brittle fracture resistance

Removal of residual stress will give steels resistance to stresscorrosion cracking in certain media - for example in sour oil/gas, inammonia or in contact with nitrates and chlorides

It enables a welded component to be machined to accurate tolerancesthat may otherwise be impossible due constant re -balancing of tensileand residual stresses when metal is removed during machining. Thismay be referred to as a stabilising* PWHT

(* not to be confused with stabilised when referring to stabilising stainlesssteels by alloying additions of Nb or Ti)

Other Benefits of PWHT

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PWHT

PWHT Procedures - Basic Requirements

A PWHT should specify the following: -

The max. heating rate

usually from 300 or 400C depending on Code or item to ensure temp.gradients are not excessive (up to ~ 200C/h max. may be allowed)

large temp. gradients cause high stresses which may give cracking ordistortion

The soak temperature

depends on steel type and usually specified by Code (~550 to ~750 C )

The soak time

to ensure full thickness, and whole item, is at soak temp.

Codes typically require 1h per 25mm of max. joint thickness

The max. cooling rate

usually to 400 or 300C - same reasons as for heating rate control

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PWHT

PWHT Procedures -Additional Considerations

Before a PWHT commences it is necessary to: -

Decide the number of thermocouple attachments and their positions

so that the temperature of the whole component is monitored

If the item needs to be given any additional support

to avoid distortion due to self-weight because it is relatively weak atthe soak temp.

For Localised PWHT

Need to also specify: -

The width of the heated band to ensure that residual stresses at a distance from the weld are removed

The width of the temp. decay bands beyond the heated zone

to ensure high stresses are not produced by large temperature gradients

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Post Weld Heat Treatment

Localised PWHT

PWHT procedures also need to also specify: - The width of the heated band

to ensure that residual stresses at a distance from the weld are removed

should be specified by Code

The width of the temp. decay bands beyond the heated zone to ensure high stresses are not produced by large temperature gradients

should be specified by Code - usually same width as heated band

The position of the thermocouples to monitor the width of heatedbands and the temp. gradient in the decay bands

pipeline weld

heated bandtemp.decay

temp.decay

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Cracking in Weld Joints

RE-HEAT CRACKING

Cracking that occurs when weld joints in certain steels when they arebeing heated to their PWHT temperature or are put into elevated temp.service without PWHT

( this gives this type of cracking the name re - heat )

Susceptible PWHT temp.range ~ 500 to ~ 650C or service 350 - 550 C

Cracking occurs in the HAZ - usually in the zone that has the largestgrain size (the grain growth zone nearest to the fusion line)

grain growth zone

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Cracking Mechanisms

RE-HEAT CRACKING

Re-heat cracking occurs because: -

some strengthening of the steel occurs during heating to the PWHTtemp. (or if in as-welded condition while in service at an elevated temp.)

strengthening occurs by carbide formation

- steels with Vanadium, Chromium and Molybdenum are mostsusceptible because these elements are strong carbide formers

the carbides & nitrides strengthen the grains so that relief of residualstresses takes place by all the strain concentrating at the weaker grainboundaries

if the steel contains certain levels of impurities (such as Tin, Arsenic& Phosphorus) they concentrate at the grain boundaries and reducetheir rupture strength

the presence of large grains in the HAZ means that the impurities aremore concentrated and such regions become the most sensitive tocracking

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Cracking Mechanisms

AVOIDING RE-HEAT CRACKING

The risk of re-heat cracking can be minimised by: -

using steel that has very low impurity levels

various formulas have been developed to relate sensitivity to crackingto levels of impurities

for particularly sensitive steels (usually those with higher Vanadium)ensure that: -

weld bead positions and heat input are controlled to give a finegrained HAZ (temper-beading)

avoid stress concentrations - poor fit-up and sharp weld toes

heat through the sensitive temperature range quickly during PWHT

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Quenched & Tempered Steels

Q & T STEELS

Steels that are strengthened by rapid cooling from an elevatedtemperature (quenching)

Quenching temperature depends on steel composition but typically~900C

Steels are very strong in the quenched condition but ductility and

toughness usually too low for any application Tempering reduces the as- quenched strength and gives usable ductility

and toughness

Tempering temperatures typically ~550 to 760C

Strengthening by quenching is achieved by certain alloying additions thatallow the stronger phases (martensite & bainite) to form (rather than theferrite)

The % of the alloying elements that allow strengthening must be highenough to allow the stronger phases to form through the full thickness

For some steels, the alloying levels need to be higher in thick sections toensure through - hardening

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Typical Mechanical PropertiesSTEEL TYPE C Si Mn Cr Mo Ni Nb V Yield / 0.2%PS

(N/mm 2)Tensile Strength

(N/mm 2)Elongation(% on 50m

water quenched & tempered at 595 to 480C(100mm round section)

AISI 4130UNS G41300W. Nr. 1.7218ASTM A 505, 646

-0.04

0.400.60

0.81.1 - - - 540 to 655 703 to 800 20 to 25

water quenched & tempered at 595 to 480C(100mm round section)

AISI 8630UNS G86300W. Nr. 1.6545ASTM A 322, 331, 505

0.280.33

0.150.30

0.700.90

0.400.60

0.150.25

0.400.70 - -

495 to 595 660 to 780 21 to 26

oil quenched & tempered at 650 to 540C(100mm round section)

AISI 4140UNS G41400W. Nr. 1.7225ASTM A 322, 331, 505, 519, 646

0.701.00

0.801.10

0.150.25 - - - 580 to 685 772 to 883 19 to 23

oil quenched & tempered at 650 to 540C(100mm round section)

AISI 4340UNS G43400W. Nr. 1.6565ASTM A 332, 505, 519, 547, 646

0.380.43

0.150.30

0.600.80

0.700.90

0.200.30

1.652.00 - - 786 to 1000 924 to 1138 16 to 20

EXAMPLES of Q & T STEELS

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Mechanical PropertiesSTEEL TYPE C Si Mn Cr Mo Ni Nb V N

OtherYield / 0.2%PS


(N/mm 2)Elongation(% on 50mm)

A 335-P91X10CrMoVNb9-1(steel number 1.4903)

0.080.12

-0.50

0.300.60

8.009.50

0.851.05

-0.40

0.060.10

0.180.25

0.0300.070

Al-

0.040= 415 585 = 22

12CrMoV11-1

(steel number 1.4922)

0.170.23 0.40

0.301.0

10.012.5

0.801.20

0.300.80

- 0.200.35

- - = 500 700 -850 = 16

A 335-P9110.100.13

0.100.30

0.300.60

8.509.50

0.901.10

0.200.40

0.060.10

0.150.25

0.0500.080

W0.901.10 = 440 = 620 = 22

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Typical Chemical Composition Typical Mechanical Properties (t=25mm)STEEL TYPE

C Si Mn Cr Mo Ni Nb V Ti Al OtherYield/0.2%PS


(N/mm 2)Elongation(% on 50mm)

WELDOX 700 -0.20

-0.60

-1.60

-0.70

-0.70

-2.0

-0.04

-0.09

-0.04

-0.015

N (min) 0.0015B (max) 0.005 = 700 780 - 930 = 18

WELDOX 900 -0.20

-0.50

-1.60

-0.70

-0.70

-2.0

-0.04

-0.06

-0.04

-0.018

N (min) 0.0015B (max) 0.005 = 900 940 - 1110 = 16

WELDOX 960 -0.20

-0.50

-1.60

-0.70

-0.70

-2.0

-0.04

-0.06

-0.04

-0.018

N (min) 0.0015B (max) 0.005 = 960 980 -1150 = 16

WELDOX 1100 -0.21

-0.50

-1.40

-0.80

-0.70

-3.0

-0.04

-0.08

-0.02

-0.020

N (min) 0.0015B (max) 0.005 = 1100 1250 - 1550 = 12

WELDOX is a registered Trade Name of SSAB Oxelosund

Chemical compositions and tensile properties of some HSLA steels used for structural applications

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Welding of Q & T Steels

Alloying additions used to achieve strengthening also will givehardening of the HAZ

Higher HAZ hardness give higher risk of cracking and the needto always use low Hydrogen welding processes and also theneed to use pre-heat for most grades

Higher HAZ hardness usually mean that many of these steelsrequire PWHT to improve resistance to brittle fracture

Careful control of heat input - not too high - may be needed forsome steel types to avoid softening of the HAZ and loss ofstrength

For the highest strength grades there may be difficulty inachieving matching strength weld metal that has goodtoughness and ductility

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Pre-Heat & Interpass Temperature

Pre-Heat Temperature

Applied to reduce risk of cracking - helps to allow H to escape fromthe weld joint and can reduce hardness of HAZ for some steels

Pre-heat temperature should be checked on both sides of the jointat a distance of at least 75mm from joint edge

Pre-heat should be checked on the other side from the pre-heatedside - if access allows

If hand held gas pre-heating is used, temp. should be checked ashort time after the heating torch has been removed

Interpass Temperature

This is the temp. at the position that the welder will re-startwelding in a muti-run weld

Temperature should be measured on the steel as close as practicalto the re-start position (it can be taken on the weldat that point)

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