1. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
CSWIP PLANT INSPECTOR LEVEL 1 WEEK 1
COURSE NOTES
CONTENTS
SECTION SUBJECT
01 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
Section 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.
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2. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
• 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
Then
Just keep on coming back to it. Again and again
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3. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
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 02
Plant Inspection/QA in Context
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4. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
• 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 inspection
There 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:
FEP
FUNCTION
SAFETY
SERVICE
LIFETIME
MECHANICAL
PERFORMANCE
QUALITY
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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5. 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 03
Inspection safety
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6. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
Inspectors 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. Rusting
2. Nitrogen purging 5. Free-flowing solids
3. Limestone/chalk + water =co2 6. Chemical residues
Precautions to be taken for confined space entry include:
1. Safe systems of works 8. BA if required
2. Effective isolation 9. Emergency procedures
3. Cleanliness 10. Harness
4. Good ventilation 11. Communication system
5. Gas test 12. PTW system
6. Special tools 13. Rescue equipment
7. 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 tests
Pressure 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°C
2. Stand clear 7. Use the correct blanking flanges etc
3. Calibrated gauges with the correct scale 8. Check the test pressure carefully
4. Check screwed fittings and plugs carefully 9. Double-check the units
5. 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 systems
Permit-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 hazards
Many 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 04
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9. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
Section 05
Legislation, 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 regulation
PUWER : Provision and use of work equipment regulation
PSSRs : Pressure system safety regulation
CDM : Construction and design management
One 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 plant
And 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 REGULATIONS
The 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 reports
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10. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
Reg. 10 : Report situations of ‘imminent danger’
Written schemes of examination (WSE)-summary sheet
Written schemes of examination (WSE)-summary sheet
What 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/or
Draw 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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11. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
Section 06
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 effectively
Some guidelines to the effective use of ITPs are:
1. First draft. 3. Timescales
2. Marking up 4. Witness points
• A typical ITP for pressure equipment
Step
No.
Operation
Inspection Point Certificate
Requirements
Comments
M C TPI
1
2
3
4
5
6
Boiler header tube
Transfer of marks
Mechanical tests
Chemical analysis
Hydro test
Tube NDT
Documentation review
W
W
W
W
W
W
R
W
W
W
W
R
W
W
W
W
W
R
EN 10 204(3.1A)
certificates
Note any
NCR’s in this
column
1
2
3
4
Safety valve spindle
Mechanical tests
Chemical analysis
NDT
Documentation review
W
W
W
W
W
W
W
W
R
R
W
W
EN 10 204(3.1B)
certificates
1
2
3
Boiler structural steel work
Mechanical tests (sample)
Chemical analysis (sample)
Documentation review
W
W
R
W
R
W
R
R
R
EN 10 204(2.2)
certificate for plain
carbon steel
1
Steam pipe expansion joints
Documentation review W R -
Certification of
conformity
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12. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
NOTE: W= witness points M= manufacturing C= contractor TPI= third party inspector R= review
• A typical ‘welding’ ITP and interpretation
Step
No.
Operation
Reference
Document
Inspection
Points Certification
Requirements
Record No.
M C TPI
1 Weld procedures WPS/PQR R - - BS EN 288 XX/Y
2 Welder approvals BS EN 287 R - - BS EN 287 XX/Y
3 10% RT BS 2600 R R - Record sheet XX/Y
4 100% MT BS 6072 R R - Record sheet XX/Y
5 Visual inspection BS 5289 R W W Record sheet XX/Y
6 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
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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
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13. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
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?
These links help to provide an effective inspection “regime”
Link 1: responsibility
The responsibilities stated in the contract specification are used to pass the requirements for compliance
with standards down to subcontractors.
Link 2: decisions
The 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: costs
The costs of inspection activities often govern which of the specified tests a plant inspector can witness.
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Section 07
Inspecting materials
• 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 data
Alloy steels have various amounts of Ni, Cr, Mn or Mo added to improve properties.
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).
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Type %C (others) % Re (MN/m²) Rm (MN/m²)
Ni/Mn steel 0.4
0.85Mn
1.0 Ni
480 680
Ni/Cr steel 0.3
0.5 Mn
2.8 Ni
1.0 Cr
800 910
Ni/Cr/Mo steel 0.4
0.5Mn
1.5 Ni
1.1Cr
0.3Mo
950 1050
15. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
• 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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18. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
Non-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/m²
2. Zink alloys 200-360 MN/m²
3. Copper alloys 200-1100 MN/m²
4. Aluminium alloys 100-500 MN/m²
5. Magnesium alloys 150-340 MN/m²
6. Titanium alloys 400-1500 MN/m²
• The main ones in use are nickel alloys
No. Alloy type Designation Constituents (%) UTS (MN/m²)
1 Ni - Cu UNS N04400 (‘Monel’) 66Ni, 31Cu, 1Fe, 1Mn 415
2 Ni – Fe ‘Ni lo 36’ 36Ni, 64 Fe 490
3 Ni – Cr ‘Inconel 600’ 76Ni, 15Cr, 8Fe 600
4 Ni – Cr ‘Inconel 625’ 61Ni, 21Cr, 2Fe, 9Mo, 3Nb 800
5 Ni – Cr ‘Hastelloy C276’ 57Ni, 15Cr, 6Fe, 1Co, 16Mo, 4W 750
6 Ni – Cr (age Hardenable) ‘Nimonic 80A’ 76Ni, 20Cr 80-1200
7 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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Section 08
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 inspection
You 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 corrosion
1. Location : the vessel exterior
2. Extent : general corrosion over 100% surface
3. Depth : average 30% t, max. 50%
4. Scale : widespread over all critical stress areas
5. 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.
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20. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
Section 09
Visual 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).
Terminology
Weld joint arrangements
Fillet welded joints
Some of the more common welding imperfections
1. Root concavity
2. Lack of fusion
• Lack of sidewall fusion
• Lack of inter-run fusion
• Lack of root fusion
3. Undercut
4. Incompletely filled groove
5. Over-convexity
6. Arc strike
7. Spatter
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21. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
8. Slag inclusions (also causing lack of sidewall fusion)
Causes:
• Insufficient cleaning between passes.
• Contaminated weld preparation.
• Welding over irregular profile.
• Incorrect welding speed.
• Arc length too long.
9. Cracks
A. 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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23. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
Material degradation and failure:
An introduction
Material strengths
When 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 fail
The 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.
Fatigue
Characteristics 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.
Creep
It 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.
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24. CSWIP PLANT NSPECTOR LEVEL I WEEK 1
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.
Glossary of creep terms
1. Creep
Creep 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 limit
An alternative term for creep strength.
3. creep rate
Creep 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 recovery
It is the rate of decrease in deformation that occurs when load is removed after prolonged application in a
creep test.
5. creep rupture strength
It is stress required to cause in a creep test within a specified time (stress rupture strength).
6. creep strength
Maximum stress required to cause a specified amount of creep in a specified time (creep limit).
7. creep test
This 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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