cswip 11-01 - plant inspection- week 1 cours

CSWIP PLANT NSPECTOR LEVEL I WEEK 1

CSWIP PLANT INSPECTOR LEVEL 1 WEEK 1

COURSE NOTES

CONTENTS

SECTION SUBJECT01 Roles and duties of the plant inspector (week1 & wek2)

02 QA/inspection in context

03 Inspection safety

04 Inspection background: basic skills

05 Legislation, rules and regulations

06 Inspection and test plans(ITPs)

07 Inspecting materials

08 Visual inspection skills

09 Visual examination of welds

10 Inspection and basic NDT

11 Corrosion: an introduction

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1Section 01

Roles and Duties of a Plant Inspector (week1)&Roles and skills of the plant inspector (week2)

The basic types of inspection: Shop inspection: is involved with inspection of equipment either during manufacture or repair. In-service inspection: inspection of equipment that is already in use.

Other peoples’ view of the plant inspector:Some opinions of the plant inspector (which of these are true):1. Inspectors are fault-finders who love to find problems, so everybody dislikes them.2. Inspectors are nit-pickers and like to exploit suppliers and operations/maintenance people.3. Inspectors are arrogant and think they know everything.4. Inspectors are decisive (true)

In-service inspection:Sites carry out in service shutdown inspections because:1. It is precise legal requirement (not strictly true).2. It is sort of a legal requirement, and anyway, other companies do it (true).3. It saves money and increases plant availability (absolutely debatable).4. As form of self-protection (true).

Shop/vender inspection:This deals with new equipment or repairs.What are you trying to achieve during a shop inspection:1. To get value for money?

Yes, but through technical assessments. Inspectors do not generally get involved in commercial issues.2. To monitor ’quality’?

It is very difficult to define what’ good quality’ actually means. It is best not to confuse plant inspection with QA.

3. To drive suppliers into the ground (because they all properly deserve).

Some guidance on doing plant inspection work

1. Make sure you have the correct technical information:You should need basically the following:

The equipment specification. The acceptance and/or guarantee requirements. The relevant documents (codes & standards) raised by the contract specification.

2. Keeping your focus: Focus means keeping sight of priorities. The various parties present at a plant inspection may each have

different focus on events but, even though their technical objectives are broadly the same. This gives potential for time delays and extra costs. (*)

Subjects such as material traceability, testing techniques, workmanship, painting and packing, and weld specifications and many others develop as side issues of the main theme.

Commercial issues and questions of interpretation also appear to further complicate the arguments. Under such conditions you have to be very careful to keep your focus on the main issues.

Inspection focus: the 10-minutes loop Good inspection involves managing these different foci (look at how it works in practice). Under such conditions the side issues can become very effective at blocking your focus on FFP. Side issues are often more interesting, and easier to discuss, than FFP.

Get a clear focus on FFP of 23


Then

Just keep on coming back to it. Again and again

This is a loop, and it is a good idea to make it a ten-minute loop. This means that you can play a full part in side issue discussions but every ten minutes you need to bring the subject of the discussion back round to your FEP focus.

3. Asking and listening: A good technique to master, which will serve you in all kinds of inspection situations, is the chain

questioning.The precision of the questions need to have two main properties:

You must be accurate in what you ask. The questions must be chained.

Chain questions This is a very effective way of getting at the truth. The technique involves spending most of your time

(upwards of 80% of the time you spend speaking) asking questions; not in suspicious or confrontational manner, but asking, just the same.

The questions must ‘chained ’- each one follows on from the last answer. Note that it is essential you obtain verification of a previous answer before developing the next question. In most situations, a mixture of closed and open-ended questions seems to work best.

4. Making decisions: Making decisions is one of the things that you will have to do frequently during plant inspections. It is wrong to expect that all decisions will be simple accept-or-reject choices. Keep it simple so that everyone will know what you mean.

Non-conformance and corrective action reports: The main mechanisms used by the plant inspector when the equipment does not meet requirements are the

non-conformance report (NCR) and the corrective action (CA). In practice they are often linked closely together.

The purpose of NCR is to make statement on fitness for purpose of the equipment that you have inspected. Note that the purpose of a NCR is not to reject equipment. The objective of corrective actions is to bring the equipment to a condition where it meets fully the

fitness-for-purpose criteria that you have been set for it.

Expecting criticism: During plant inspections don’t be surprised if you are accused of being uninformed, ignorant or even

unreasonable. It is normal for your technical knowledge in specialist areas to be questioned.

Finally: THINGS NOT DO IT Get carried away with a sense of inspector’s self-importance. Become paranoid (convinced that everyone is telling you lies, all of the time). Believe every thing that manufacturers and plant operators tell you.

Section 02Plant Inspection/QA in Context

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Within the project structure at several levels are found plant inspection responsibilities and activities. These activities occur both during construction of the plant (work inspection) and during the operational

life of the plant (in-service inspection).

Woks inspection -v-in-service inspectionThere are both similarities and differences between the tasks and skills that are needed as shown below, note that the technical scope of the in-service inspector is slightly wider, incorporating corrosion and degradation mechanisms:

Work inspection In-service inspection Compliance with codes/standards

regulations Compliance with codes/standards

regulations Design appraisal Design appraisal Life assessment Life assessment Integrity of materials Integrity of materials Quality of manufacture Quality of manufacture Documentation records Documentation records

Corrosion assessment Fatigue & creep effects

Fitness-for-purpose (FEP)Plant inspection involves making decisions about FEP. FEP is about utility and there are essentially four elements to it:

1) Function Function is what the equipment does, or will it do it without the implications of extra cost or wasted

time. For example, a crane transforms electrical power into a capability to lift and move a load. By looking at

the nature of the specific transformation required, you can investigate the function of the equipment and get a precise view of its capabilities.

Equipment function is always linked to the circumstances of its integration into the process system. Further resolution can be carried out by looking at the cost implications of getting equipment to do what

is required. This helps FFP to come into focus.

2) Mechanical performance This about the mechanical strength of the component; the main aim is that equipment and components,

when in use, should be operating below their elastic yield stress with the required design factor of safety. You must assess the mechanical strength of a component in relation to its likely mode of failure. As in example, it is of limited use calculating static principles stresses in a pressure vessel if the vessel is

likely to fail by fatigue or creep –induced cracking, or because o dynamic stresses.

3) Service lifetime The engineering factors that influence lifetime are wear and corrosion.

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1 Wear is related mainly to moving parts; bearings, pistons, gears, any things where there is relative

movement between two components. Unwritten rules, empirical knowledge and accumulated experience all play a large part. Plant inspectors can however learn to concentrate on those areas that can be assessed, such as

materials, tolerances and assembly.

4) Safety and quality Plant inspection is a different discipline to quality assurance and safety; there are important links

between them, but also many differences. The main difference is that QA is about documents, systems and certificates where as inspection is more

about the physical and engineering. QA-certified plant manufacturers, contractors and users have produced, or operated plant and systems

are not fit-for-purpose. Plant inspection is part of QA inspection activities and often part of a company’s overall QA structure,

but remembers that the main function of the QA structure is administrative rather than technical.

Who know and does what in plant inspection? Large projects normally mean that there are several parties sharing responsibilities for plant inspection.

Section 03Inspection safety

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1Inspectors are often not familiar with those day-to-day hazards that exist at plants that they visit.

Accidents are caused by: Unfamiliarity (you are not doing it every day) Complacency Poor communication Simply doing the wrong thing

Confined space inspections Be careful with DP/MPI materials. (COSHH Regs) Before the gas-free certificate: keep your head out Remember the risk assessment for chemical content of tanks etc (cleaning before entry)

Lack of oxygen can be caused by:1. Steaming out 4. Rusting2. Nitrogen purging 5. Free-flowing solids3. Limestone/chalk + water =co2 6. Chemical residues

Precautions to be taken for confined space entry include:1. Safe systems of works 8. BA if required2. Effective isolation 9. Emergency procedures3. Cleanliness 10. Harness4. Good ventilation 11. Communication system5. Gas test 12. PTW system6. Special tools 13. Rescue equipment7. Good lighting 14. Back-up man

Note: these should all be included in the risk assessment form you sign it before entering the vessel.

Pressure testsPressure tests (normally hydrostatic tests using water) are a common feature of plant inspection.Pressure tests precautions:

1. Bleed all the air out 6. Temperature >7°C2. Stand clear 7. Use the correct blanking flanges etc3. Calibrated gauges with the correct scale 8. Check the test pressure carefully4. Check screwed fittings and plugs carefully 9. Double-check the units5. Raise the pressure slowly 10. Use water, unless the procedure specified otherwise

Note: there is a HSE guideline on pressure testing: document GS4 Pneumatic testing: is very dangerous and must be covered by special risk assessment.

Isolation and PTW systemsPermit-to-work (PTW) systems are in force on most plants. Make sure all equipment is ‘locked-out’ before you go near it and start touching anything.

Electrical spark hazardsMany plants have flammable environments, that means you cannot use most types of cameras, lights, inspection borescopes and spark testers etc, unless you have a special PTW.

Watch out for overhead hazards Cranes and lifting beams are the cause of lots of injuries to inspectors. You have to watch out for them.

Finally: “personnel protective equipment” (PPE) shall be used on all sites such as helmet, eye protection and safety shoes.

Section 04Inspection background: basic skills

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1Pressure measurement units

PSI Kg/cm² Bars N/mm² (MPa)PSI 1 0.0703 0.06895 6.895

Kg/cm² 14..223 1 0.9807 0.09807Bars 14.503 1.0197 1 0.1

N/mm² (MPa) 145.03 10.197 10.0 1Table (1): pressure unit conversions

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Section 05Legislation, rules and regulations

In-service inspection of pressure equipment is covered by a variety of regulations as shown below:

LOLER : Lifting operating and lifting equipment regulationPUWER : Provision and use of work equipment regulationPSSRs : Pressure system safety regulationCDM : Construction and design managementOne of the most important sets of regulations of relevance to the plant inspector is the pressure system safety regulation (PSSRs: 2000).

The pressure system safety regulation (PSSRs) 2000 The PSSRs are a requirement on the plant user/owner to:

Think about the risk of the plantAnd then

Have the plant inspected on a ‘planned’ basis

A bit of history The inspection of pressure equipment during its working life was originally initiated by engineering

insurance companies with the objective of reducing the number of accidents and, hence claims. The essence of the PSSRs is the concept that all included equipment is covered by a written scheme of

examination (WSE), and then that is inspected periodically by a ‘competent person’

Inclusions/exclusions from the PSSRs

Included in the PSSRs excluded in the PSSRs a compressed air receiver and the associated pipework

where the product of the pressure times the internal capacity of the receiver is >250 bar litres

an office hot water urn (for making tea);

a steam sterilising autoclave and associated pipework and protective devices; a machine tool hydraulic system;

a steam boiler and associated pipework and protective devices; a pneumatic cylinder in a compressed air system;

a pressure cooker; a hand held tool; a gag loaded hydraulic accumulator; a combustion engine cooling system;

a portable hot water/steam cleaning unit;

a compressed air receiver and the associated pipework where the product of the pressure times the internal capacity of the receiver is <250 bar litres;

a vapour compression refrigeration system where the installed power exceeds 25kw;

a pipeline and its protective devices in which the pressure does not exceed 2 bar above atm. pressure;

a narrow gauge steam locomotive; a portable fire extinguisher with a working pressure

below 25 bar at 60°c and having a total mass not exceeding 23 kilograms;

the components of self-contained breathing apparatus sets (excluding the gas container); a portable LPG cylinder;

a fixed LPG storage system supplying fuel for heating in a workplace. a tyre used on a vehicle.

THE MAIN REGULATIONSThe main regulations of interest to the plant inspector are regulations 7, 8, 9 and 10:

Reg. 7 : Safe operating limits (sols)Reg. 8 : Written scheme of examination (WSE)Reg. 9 : Inspection and reportsReg. 10 : Report situations of ‘imminent danger’

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1Written schemes of examination (WSE)-summary sheet

Written schemes of examination (WSE)-summary sheetWhat is the WSE?It is a document containing information about selected items of plant or equipment that form a pressure system, operate under pressure, and contain a ‘relevant fluid’.

What is a ‘relevant fluid’? Compressed or liquefied gas

including air above 0.5 bar pressure. Pressurised hot water above 110°C. Steam at any pressure.

What does the WSE contain? Identification number of the item of plant or equipment; Those parts of the item which are to be examined; The nature of the examination required, included the inspection and testing to be carried out on any protective

devices; The preparatory work necessary to enable the item to be examined; The date by which the initial examination is to be completed (for newly installed systems); The maximum interval between each examination and another; The critical parts of the system which, if modified or repaired, should be examined by a competent person before

the system is used again; The name of the competent person certifying the written schemes of examination; The date of certification.

The plant items included are those which, if they fail, ‘could unintentionally release pressure from the system and the resulting release of stored energy could cause injury ’

Who decides which items of plant are included in the WSE? The user or the owner of the

equipment. The WSE must be suitable

throughout lifetime of the plant or equipment so it needs to be reviewed periodically and, when necessary, revised.

What is ‘A competent person’ ‘Competent person’ means a

competent individual person (other than an employee) or a competent body of persons corporate or unincorporated.

What does the ‘competent person’ do?Advice on the nature and frequency of examination and any special safety measures necessary to prepare the system for examination

And/orDraw up and certify as suitable the WSE prepared by the user or owner.Users/owners of pressure systems are free to select any competent person they wish, They should be ensuring that the competent person selected can actually demonstrate competence.

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Inspection and test plans

Inspection and test plans (ITPs) ITPs are key documents for the plant inspector. A large contract can have several hundred ITPs, using different formats and containing varying degrees

of detail. ITPs are almost the best mechanism for controlling and organising the various inspection activities.The purpose of an ITP The purpose is to provide a mechanism for organising inspection activities. ITPs are an excellent documentary record of the activities and commitments of the multiple parties

involved.Essential content of an ITP Some contract specifications will often include a specimen ‘pro-forma’ ITP to indicate the level of

information that is required.A check list of ITP content: A clear list of manufacturing and test steps for each manufactured component. Cross references to salient contract specification clauses. Detailed reference to which acceptance standards (or technical standards) are applicable to each

manufacturing and test step. Cross references to manufacturing’ more detailed working procedures. Indication of the records and certification requirements applicable to each step. A system of activity codes. These are useful for understanding which tests are being referred to (e.g.

under general NDT categories).

Using ITPs effectivelySome guidelines to the effective use of ITPs are:

1. First draft. 3. Timescales2. Marking up 4. Witness points

A typical ITP for pressure equipmentStep No. Operation Inspection Point Certificate

Requirements CommentsM C TPI123456

Boiler header tubeTransfer of marksMechanical testsChemical analysisHydro testTube NDTDocumentation review

WWWWWW

RWWWWR

WWWWWR

EN 10 204(3.1A) certificates

Note any NCR’s in this

column

1234

Safety valve spindleMechanical testsChemical analysisNDTDocumentation review

WWWW

WWWW

RRWW

EN 10 204(3.1B) certificates

123

Boiler structural steel workMechanical tests (sample)Chemical analysis (sample)Documentation review

WWR

WRW

RRR

EN 10 204(2.2) certificate for plain

carbon steel

1Steam pipe expansion joints

Documentation review W R - Certification of conformity

NOTE: W= witness points M= manufacturing C= contractor TPI= third party inspector R= review

A typical ‘welding’ ITP and interpretation of 23


Step No. Operation Reference

Document

Inspection Points Certification

Requirements Record No.M C TPI

1 Weld procedures WPS/PQR R - - BS EN 288 XX/Y2 Welder approvals BS EN 287 R - - BS EN 287 XX/Y3 10% RT BS 2600 R R - Record sheet XX/Y4 100% MT BS 6072 R R - Record sheet XX/Y5 Visual inspection BS 5289 R W W Record sheet XX/Y6 Document review - R R R - XX/Y

NOTE: W= witness points M= manufacturing C= contractor TPI= third party inspector R= review Part of a steam turbine ITP

COMPONENT

TENSILE

TESTS

IMPACT

TESTS

CHEMICAL

ANALYSIS

ULTRASONIC

MPI

DYEPENETRANT

DIMENSIONAL

CHECK

SPECIAL TESTS

Rotor forging Х Х Х Х Х Sulphur distribution ‘print’

Rotor after welding and machining Х Х Spectral analysis

Rotor wheels Х Х Х Х Х Х

Rotor and stator blades Х Х Х Х Х Hardness check (per batch of blades). Spectral analysis

Rotor after blade fitting Х

Other casing and valve chests Х Х Х Х Х Х

MPI on all excavations. Hardness test (on flange faces). NDT repeated after repair and heat

treatment

Blades carriers Х Х Х Х Х Х

Gland seal casings Х Х

Bearing pedestals Х Х Х Additional tensile tests for cast iron pedestals

Bearing shells Х Х Х Х Х Ultrasonic test of the white metal bond

to the backing materials. DP test for surface porosity.

How do the ITPs link with these other documents?

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These links help to provide an effective inspection “regime”

Link 1: responsibilityThe responsibilities stated in the contract specification are used to pass the requirements for compliance with standards down to subcontractors.Link 2: decisionsThe document hierarchy has operational links to the ITPs. This helps to ensure that the acceptance criteria shown in the ITPs are controlled and compliant with the actual contract requirements, not the manufacturers opinion of what they may be, or those that he usually use.

Link 3: costsThe costs of inspection activities often govern which of the specified tests a plant inspector can witness.

Section 07Inspecting materials

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It is essential to check the up-to-date version of the relevant British standards, euro-norm or equivalent when choosing or assessing a material.

The most common alloys used for mechanical plant are divided into the generic categories of plain carbon steels, low and high alloy steels, stainless steels and non-ferrous alloys.

Plain carbon steels - basic data

Type %C %Mn Yield, Re (MN/m²) UTS, Rm (MN/m²)

Low carbon steel 0.1 0.35 220 320

General structural steel 0.2 1.4 350 515

Steel castings 0.3 - 270 490

Alloy steel - basic dataAlloy steels have various amounts of Ni, Cr, Mn or Mo added to improve properties.

Type %C (others) % Re (MN/m²) Rm (MN/m²)

Ni/Mn steel 0.4 0.85Mn1.0 Ni 480 680

Ni/Cr steel 0.30.5 Mn2.8 Ni1.0 Cr

800 910

Ni/Cr/Mo steel 0.4

0.5Mn1.5 Ni1.1Cr0.3Mo

950 1050

Stainless steels – basic data Stainless steel is a generic term used to describe a family of steel alloys containing more than about 11%

chromium. The family consists of 4 main classes, subdivided into about 100 grades and variants.

No. Class Basic characteristics

1 Austenitic The most commonly used basic grades of stainless steel. They have 17-25%Cr, combined with 8-20%Ni, Mn, and other trace alloying elements. They have low carbon content, which make them weldable. They have the highest general corrosion resistance of the family of stainless steel.

2 Ferritic Ferritic stainless steels have high Cr content (>17%Cr) coupled with medium carbon. They have good corrosion resistance properties rather than high strength. They have some Mo and Si, which encourage the ferrite to form. They are generally non-hardenable.

3 Martensitic This is a high carbon (up to 2% C), low Cr (12% Cr). The high carbon content can make it difficult to weld.

4 Duplex

They have a structure containing both austenitic and ferritic phases. They can have a tensile strength of up to twice that of austenitic stainless steels. They are alloyed with various trace elements to aid corrosion resistance. They are as weldable as austenitic grades but have a maximum temperature limit, because

of the characteristic of their microstructure.

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1Non-ferrous alloys basic – data This term is used for alloy materials that do not have iron as their base element. The ones used for mechanical engineering application, their UTS ranges, are:

1. Nickel alloys 400-1200 MN/m²2. Zink alloys 200-360 MN/m²3. Copper alloys 200-1100 MN/m²4. Aluminium alloys 100-500 MN/m²5. Magnesium alloys 150-340 MN/m²6. Titanium alloys 400-1500 MN/m²

The main ones in use are nickel alloysNo. Alloy type Designation Constituents (%) UTS (MN/m²)1 Ni - Cu UNS N04400 (‘Monel’) 66Ni, 31Cu, 1Fe, 1Mn 4152 Ni – Fe ‘Ni lo 36’ 36Ni, 64 Fe 4903 Ni – Cr ‘Inconel 600’ 76Ni, 15Cr, 8Fe 6004 Ni – Cr ‘Inconel 625’ 61Ni, 21Cr, 2Fe, 9Mo, 3Nb 8005 Ni – Cr ‘Hastelloy C276’ 57Ni, 15Cr, 6Fe, 1Co, 16Mo, 4W 7506 Ni – Cr (age Hardenable) ‘Nimonic 80A’ 76Ni, 20Cr 80-12007 Ni – Cr (age Hardenable) ‘Inco waspalloy’ 58Ni, 19Cr, 13Co, 4Mo, 3Ti, 1Al 800-1000

Material traceability Most of codes and standards for pressure equipment and similar plant make provision for quality

assurance activities designed to ensure that materials of construction are traceable. There are several ‘levels’ in use, depending both on the type of material and the nature of its final

application. The most common document referenced is the European standard EN10 204, it provides for two main

‘levels’ of certification: class ‘3’ and class ‘2’.

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Visual inspection skills

When you visually inspect something what are you trying to achieve in your report?1. Shirk responsibility?

Not uncommon. Plant inspectors can feel unsure about taking responsibility for hard technical conclusions.2. Show people how clever you are?

Again, Not uncommon, particularly in areas such as welding where plant inspectors often feel more comfortable.

3. Only make weak conclusions? Doesn’t give a good service to your client.

The difficulties of visual inspectionYou have to look carefully at the situation, and find out as much additional information as you can.Some rules of visual inspection

Try to ‘think around’ what you are looking at Ask other people about what you see …. (You might learn something). Concentrate on the engineering ….. It is all too easy to get sidetracked.

An example: inspection and reporting of corrosion1. Location : the vessel exterior 2. Extent : general corrosion over 100% surface3. Depth : average 30% t, max. 50%4. Scale : widespread over all critical stress areas5. Severity : severity level 2(scale 1-4)6. Criticality : criticality level 6(1-10)7. Compliance : non-compliance with clause xxx of API 510

Finally: the objectives of visual inspection are: Keep your eye open. Convey technical information. Make it logical and easy to read.

Section 09 of 23

CSWIP PLANT NSPECTOR LEVEL I WEEK 1Visual inspection of welds: revision

The best way is to use a check list. This will provide a clear and simple way to present your finding in the report.

Commonly used standards for visual inspection of welds are: BS 5289, EN 970 and EN 25817 (some of those do not include details of acceptance criteria).

TerminologyWeld joint arrangements

Fillet welded joints

Some of the more common welding imperfections1. Root concavity2. Lack of fusion

Lack of sidewall fusion Lack of inter-run fusion Lack of root fusion

3. Undercut4. Incompletely filled groove5. Over-convexity6. Arc strike7. Spatter

8. Slag inclusions (also causing lack of sidewall fusion)Causes:

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1 Insufficient cleaning between passes. Contaminated weld preparation. Welding over irregular profile. Incorrect welding speed. Arc length too long.

9. CracksA. Solidification cracks

Occurs during weld solidification process Steel with high sulphur content (low ductility at elevated temp.) Requires high tensile stress Occur longitudinally down the centre-line of weld

B. Hydrogen induced crack Requires susceptible grain structure, stress and hydrogen Hydrogen enters via welding arc Hydrogen source-atmosphere, contamination of preparation or electrode Moisture diffuses out into parent metal on cooling Most likely in HAZ

C. Lamellar tearing cracks Step like appearance Occurs in parent material or HAZ Only in rolled direction of the parent material Associated with restrained joints subjected to through thickness stresses on corners, tees and fillet Most common in steels with higher sulphur content >0.04% and/or high levels of non-metallic inclusions

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Material degradation and failure:An introduction

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CSWIP PLANT NSPECTOR LEVEL I WEEK 1Material strengthsWhen material is new, it has well-defined strength values. Material strength definitions and equivalent units in use in Europe and the USA are as shown below:

USCS (US Imperial)SI/European

Yield strength Ultimate tensile strength modulus

Fty (Ksi) or Sy (Ib/in²)Re (MN/m²)

Ftu (Ksi) or Sm (Ib/in²)Rm (MN/m²)

E (Ib/in²*106)E (N/m²*109)

Conversions are: 1Ksi = 1000 psi = 6.89MPa = 6.89MN/m² = 6.89 N/mm²

How materials failThe fracture of the material starts from the point in time at which a crack initiation occurs and continues during the propagation phase until the material breaks.

FatigueCharacteristics of fatigue failures are:

Visible crack-arrest and ‘beach mar’ lines on the fracture surface. Striations –these are the result of deformation during individual stress cycles. An initiation point such as a crack, defect, or inclusion, normally on the surface of the material.

CreepIt is a specialist subject, it is a degradation mechanism found in steels and other pressure equipment materials.

What is it dependent on? Creep is dependent on two parameters: temperature and time. For steels, creep occurs below about 390°C. Other factors such as corrosive atmospheres and fatigue conditions can act to make the situation worse.

What damage does creep cause? The main effect is a permanent that there is a reduction in tensile strength. The creep mechanism causes the metal structure to ‘flow’ leaving holes or voids in the material matrix. Structures under pressure stress therefore can deform, and then fail.

How is creep detected?Creep is detected using metallographic replication (often termed a replica), this is a non-destructive technique that enables a visual examination of the material’s grain structure as the following procedure: Prepare the metal surface using mechanical cleaning / grinding and a chemical etch. Bond a special plastic tape to the surface and allow the adhesive to cure. Remove the tape, transferring a replica of the metal surface to the tape. Examine the replica under low magnification and compare with reference microstructure pictures.Note that the results of replica tests are assessed in a qualitative way.If a material fails under this test, the next step is to perform full (destructive) tests for tensile strength on a trepanned sample taken from the component.

What is a typical creep resistant alloy? Main steams pipelines for fossil or gas-fired power stations containing superheated steam at 520°C+

commonly uses a DIN 14MoV63 alloy (or comparable 0.5%Cr, 0.5% Mo, 0.25% V material). This has documented creep-resistant properties up to 100000 hours of exposure.

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Glossary of creep terms

1. CreepCreep is defined as deformation that occurs over a period of time when a material is subjected to constant stress at constant temperature.The stages for the creep of the material:

A. Primary creep, starts at a rapid rate and slows with time.B. Secondary creep has a relatively uniform rate.C. Tertiary creep has an accelerating creep and terminates by failure of material at time for rupture.

2. creep limitAn alternative term for creep strength.

3. creep rateCreep rate is defined as the rate of deformation of a material subject to stress at constant temperature. It is the slope of the creep vs. time diagram obtained in a creep test (units are mm/hr or % of elongation /hr.).

4. creep recoveryIt is the rate of decrease in deformation that occurs when load is removed after prolonged application in a creep test.

5. creep rupture strengthIt is stress required to cause in a creep test within a specified time (stress rupture strength).

6. creep strengthMaximum stress required to cause a specified amount of creep in a specified time (creep limit).

7. creep testThis is a method of determining creep or stress relaxation behaviour. To determine creep properties, material is subjected to prolonged constant tension or compression loading at constant temperature. Deformation is recorded at a specified time intervals and a creep vs. time diagram is plotted (The slope of the curve at any point is the creep rate).

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cswip 11-01 - plant inspection- week 1 cours

Engineering