The document provides information on weld repair, including the types of defects that can occur during manufacturing, the steps involved in deciding when repairs are needed, and how to execute welding repairs. It discusses inherent, processing, and service defects and their causes. The key steps in repair decision making are evaluating operating conditions, inspection history, reasons for failure, defect location using visual and NDT methods, and re-evaluating the need for repairs based on design calculations. When repairs are needed, the document outlines preparing the repair procedure, executing the welding according to qualified procedures while monitoring parameters, and inspecting the completed repair.

1. P R E S E N T E D B Y : R A G H A V E N D R A D A R J I ( 3 8 5 )
M . E . - P A R T I I ( W E L D . T E C H . )
G U I D E : M R . M . N . P A T E L
D E P T . O F M E T A L L U R G Y A N D M A T E R I A L S E N G I N E E R I N G ,
F A C U L T Y O F T E C H N O L O G Y A N D E N G I N E E R I N G ,
T H E M . S . U N I V E R S I T Y O F B A R O D A .
2 8 T H J A N U A R Y - 2 0 1 5
A presentation on
“Weld Repair”
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2.  Contents:
 Requirement of weld repair,
 Type of defects and its causes during manufacturing of any welded component,
 Steps involved in the decision making for repairs,
 Sequence for the detection of defects,
 Execution of welding repairs,
 Marking of defects,
 Systematic Approach to Weld Repairs,
 Acceptance Criteria for the defects,
 References
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3.  Requirement of weld repair:
 Repair and maintenance of parts and components is a major activity in
any process industry. Repair welding can be carried out as a logical
procedure that “ensures the part is usable and safe.”
 If repairs are done with proper care or precautions, it “can avoid
premature failures, large warranty claims, safety of property and
personnel and result in satisfied customers.”
 Failures of pressure vessels are still observed, which result in a costly
down time of production and product losses also sometimes it results in
environmental hazards and unsafe working conditions or disasters.
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4.  Defects:
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Defects
Inherent
Processing
Service

5.  Type of defects and its causes during manufacturing of any
welded component:
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 Inherent Defects:
 When materials are produced,
molten metal solidifies into
ingot form producing what is
known as inherent discontinuities.
 Such discontinuities then
can be rolled, forged and
section along with the
material in its subsequent
processing operations,
eg. Lamination.

6.  Inherent defects:
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 Cold shut:
Location : Surface or sub surface.
Cause : two streams of liquid metal that do not fuse.
 Porosity:
Location : Surface or Subsurface.
Cause : Entrapped gases during solidification of metals .
 Inclusion:
Location : Surface or Subsurface.
Cause : Contaminant introduced during the casting process.

7.  Primary Process Defects:
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 Discontinuities those originate during hot or cold forming are said to be
primary processing discontinuities.
 The processing of a wrought product by rolling, forging, casting or
drawing may introduce specific discontinuities into the product and
inherent discontinuity that were at one time undetectable or
insignificant may propagate and become detrimental.

8.  Processing Defects:
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 Porosity / (Cluster porosity):
Location : Surface or Subsurface
Cause : Vaporized constituents in the molten weld metal are entrapped during
solidification.
 Slag Inclusion:
Location: Subsurface
Cause : Improper cleaning of previous weld pass and mixing of oxides on the
base metal surface into the weld pool.
 Lack of Penetration:
Location: Surface or Subsurface.
Cause: Inadequate penetration of the weld joint root by the weld metal.

9.  Processing Defects:
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 Lack of Fusion:
Location: Subsurface
Cause : Failure of filler metal to fuse/ join with the base metal.
 Suck Back:
Location: Surface or Subsurface
Cause: where the weld metal has contracted as it cools and has been drawn up
into the root of the weld.
 Undercut(Internal and External):
Location: Surface
Cause: Under sized weld pool (related to excessive amperage, travel speed and
electrode size.)

10.  Processing Defects:
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 Offset/ Mismatch:
Location : Surface
Cause : where two pieces being welded together are not properly aligned.
 Cold or Hot Cracking:
Location: Surface or Subsurface.
Cause: A combination of atomic hydrogen, hardenable material and high
residual stress.
 Incomplete weld reinforcement:
Location : Surface.

11.  Processing Defects:
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 Tungsten Inclusion:
Location : Subsurface
Cause : Molten weld pool or filler metal comes in contact with the tip of
tungsten electrode.
 Burn Through:
Location: Surface.
Cause : Too much heat causes excessive weld metal to penetrate the weld zone.

12.  Secondary Processing Defects:
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 Grinding Cracks:
Location: Surface
Cause : Localized overheating of the material due to improper grinding
procedures.
 Heat Treating Cracks:
Location: Surface
Cause : Uneven heating and cooling that produces stresses exceeding the
tensile strength of the material.
 Quench Cracks:
Location: Surface
Cause : Sudden cooling from elevated temperature

13.  In Service Defects:
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 Fatigue:
Location: Surface.
Cause: Component under cyclic load which is below Yield Strength.
 Creep:
Location: Surface.
Cause: Material under high temperature causes micro structural change .
 Stress Corrosion Cracking:
Location: Surface.
Cause: Due to Combine effect of Stress and Specific Corrosion environment.
 Hydrogen Induced Cracking:
Location : Surface.
Cause : Combined effect of applied tensile or residual stress and hydrogen enriched
environment.

14.  Steps involved in the decision making for repairs:
 Operating conditions, Inspection history, Material of construction of pressure
vessel.
 Reasons for failure.
 Location of the damaged area by visual inspection and evaluation by NDTs.
 Re-evaluate the need for repairs (Back to design calculations).
 Repair Methods, (For pressure retaining parts) .
 Preparation of repair procedures.
 Replacement of major components.
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15.  Operating conditions, Inspection history, Material
of construction of pressure vessel :
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 A careful study of the operating parameters and inspection history and properly
maintained internal inspection reports, materials of construction, “its
behaviour with the process fluid, welding techniques used during
construction, design consideration etc”, also gives an adequate confidence level
about the use of pressure vessel.
 Such information is also “useful for making the repair decision”. Carefully
selected material of construction and the fabrication procedures, welding
procedures as well as inspection and certification by the competent inspection
authorities during fabrication stage, always intend to give such information.

16.  Reasons for failure:
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 Premature failure of any component will occur because of the following
reason:
A. Faulty design,
B. Faulty workmanship,
C. Wrongly selected material of construction,
D. Wrong welding techniques.
 The normal service failures are attributed to corrosion, changes in the working
parameters, operation of the vessel for which it is not designed, impurities in
the operating fluids, metallurgical changes in the base metal etc.

17.  Reasons for failure:
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 Once the damage is identified the pressure vessels must be thoroughly
inspected to evaluate the extent of damage, need for repair and the repair
method.
 Thorough visual inspection of the pressure vessel can be supplemented by a
suitable NDT examination, to locate the defects and the extent.

18.  Location of the damaged area by visual inspection and
evaluation by NDTs :
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 The personnel may be required to stay (inside the component) for internal
inspection there could be possible repairs where hot work is involved, there
fore “a safe entry permit from a competent authority” i.e. from the safety and
operation departments. (LPT)
 “The external surface should be checked” for any corrosion below the
insulation, obvious leakages, structural attachments, connections, foundations,
leak proof tightness of pressure relief valves etc.
 “The identified damage can be supplemented by NDT for the extent, where by
decision for repairs can be taken confidently” , various NDT possible, are UT
thickness measurement, UT scanning, RT, MPI and LPT.

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20.  Re-evaluate the need for repairs:
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 Based on the NDT results obtained, the same can be “verified by the designer
and inspector by performing design calculations”, to ensure that the
remaining thickness is still safe, and whether the repairs are warranted or not.
 Location of defect is also important. “On base metal away from the weld
metal, a monitor thinning can be left unattended.” In event there are
borderline case the thickness can be recalculated by carrying our full RT and
thereby revising the Joint efficiency.
 Repairs shall be checked and verified by the Design Engineer.

21.  Re-evaluate the need for repairs:
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 Location of localized corrosion, such as on the base metal, away from L seam,
Away from C seam, on the weld joints, on crown portion of the head, etc.
thereby, “comparing the original design requirement”. e.g. by carrying out L
seam Radiography .
 Based on the remaining thickness corrosion rates are calculated and the MAWP
at the available thickness also calculated. “If the MAWP required is lower that
the calculated MAWP then the repairs are not warranted” provided the owner
user is ready to carry out internal inspection as per next scheduled interval.
 The Inspector should think out all such possibilities and advise the owner user,
so as to take a precise judgment on the repair.
 “MAWP: Maximum Allowable Working Pressure.”

22.  Repair Methods:
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 “Pressure parts” of the component must be repaired. Because ultimately they
are the parts which are going to be affected by pressure in service condition.
 “The cracks are gouged out or removed” and weld repairs can be carried out
from both sides, if approach is available,
 “The deep pits or localized corrosion can be weld built” to restore the original
thickness.
 The larger area, which cannot be welded by build up, “can be replaced”with
patch or a shell course or a head.

23.  Repair Methods:
23
 Any code requirements, contractual requirements or any statutory / regulatory
requirement must be complied during weld repairs.
 Original construction drawing, calculation data and inspection records are
important for repairs. If the original construction data is not accessible, then an
“analysis of the base material, including previous weld deposits, becomes
mandatory”.
 If dimensions require close tolerances or if flatness is critical, then benchmarks
that will aid the “repair without causing excessive and expensive damage to
the work piece must be established”.

24.  Repair Methods:
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 The crack in weld joint or a defect in the base metal can be repaired by
preparing a “U” or a “V” groove to “the full depth and length of crack” and then
fill up by weld metal deposit as described here.
 If the crack exists in the stress concentration region then consult a competent
pressure vessel design Engineer. “Corroded area may be restored by weld
metal deposition as described here.”

25.  Preparation of repair procedures:
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 The repair procedure should take care of the requirements of “the base metal,
welding consumables, sequential weld deposits, requirements of preheat, Inter
pass temperature, post weld heating, PWHT, impact test and the NDT
requirements”.
 If PWHT is required in original construction and it is not practicable or
advisable during repairs, then “the Inspector and the Pressure Vessel Design
Engineer shall review the reason for original PWHT of the equipment.”

26.  Execution of welding repairs:
26
 The repairer, under close supervision and surveillance of the Inspector,
executes actual repairs. “The written and qualified procedures are strictly
followed”.
 In case the Impact testing is specified, “the welding parameters are also
monitored” and ensured to be within the range at which the procedure is
qualified.
 Specified “NDE before welding repairs and after welding repairs” are carried
out and shall be approved by the Inspector.
 After repairs the inspection record and the history of equipment, giving details
of repairs, is updated and next inspection schedule shall be recommended to
the owner user.

27.  Marking of defects:
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28.  Is repair welding the right decision?
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 Is repair welding the right solution depends on the judgment factors that follow
“the earlier need for identification of the material in question”
 It may be found that “repair or rebuild is too costly”, or that a good repair is
not feasible.
 The relative strength of the weld and the base metal may be an important
consideration.
 A special consideration may be the effect of repeated repairs on the component.

29.  Systematic Approach to Weld Repairs:
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 Planning is essential before performing any welding repair operation.
 A large number of factors must be considered in deciding and planning the
most appropriate welding repair.
 Having a systematic approach to help ensure that all factors are considered can
be a substantial advantage
 There are two such approaches
 Welding repair planning checklist
 Welding repair decision model

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31.  Weld Repair Decision Model:
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32.  Weld Repair Decision Model:
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33.  Considerations during a repair:
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1. Repair procedure.
2. Welders qualified to repair procedure.
3. Repair correctly identified and marked (Shell# Nozzle CS).
4. Type of excavation (gouging / grinding).
5. Monitoring removal (LPT,UT).
6. Shape of excavation.
7. NDT on excavation. (LPT,UT).
8. Monitoring rewelding.
9. NDT on repaired area (as per original NDT)

34.  While carrying out the repair....
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 One should consider the following parameters after and during the
repair work:
 Shrinkage and distortion,
 Fit-Up,
 Thermal requirement,
 Preparation of the defect area,
 Part protection and Return to Service.

35.  Acceptance Criteria according to BS 4871: Part
1:1974 and BS 5500:1976
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36.  Acceptance Criteria cont……
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37.  References:
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 Paper from internet Titled “ Inspection and Welding Repairs of Pressure
Vessel, by S.V.Gupte.
 AWS Welding Handbook Volume 3 , Chapter 9 Materials and their Weld
ability.
 Presentation By P. Raghvendra on NDT and Defects, L & T HED, Hazira.
 Other Internet Sources ( Wikipedia, Google etc.)

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