and welcome to this series of lectures on principles of construction management where
we are talking about different aspects related to construction project managements in the
last class we talked about the introduction an introductory aspects of quality in project
management basically construction projects and today in the first lecture following that
we are going to talk about quality in construction as related to welding so what had happened
last time was that we had said that the thought process of the quality control is closely
linked to standardized test methods and specifications and test methods lay down a detailed procedure
for almost all this steps involved in a test especially for tests that are considered important
from the point of view of results we had also said that engineers in the field are sometimes
required to interpret the provisions in a method or create a new test method itself
for a unique situation at that particular site
for that particular material and so on we would also said that this decision in terms
of interpretation of the provisions or when you create a new test method it cannot be
arbitrary and must be based on principles of known and relevant tests and the required
performance of the produce that is the product or the process involved we are also re iterated
that the purpose of these tests could be to ascertain the performance of a product or
process and therefore determine its acceptability or it could be to compare two or more products
or processes we had clearly stated that issues relating to quality control will be examined
using case studies or taking up examples of simple processes from the field the effort
will be to carry out exercises that will help in understanding the issues involved and how
they are addressed in a quality assurance quality control kind of a framework basically
let me remind you that the discussion is not so much about the provision that exists but
what are the considerations that may prevail for those provisions and must be provided
for
so with this background which is largely a recap of what we have talked about in the
last class lets move forward and try to interpret or understand the process of welding and a
issues relating to quality control as far as this very important industrial process
is concerned now what is welding it is a fabrication technique that involves joining materials
together by heating them to a suitable temperature by applying heat with or without the use of
pressure and or additional filler material so what we are basically doing or what we
do in welding is to have these two plates which need to be joined at this place so there
are different ways of doing it as far as welding is concerned one of the methods is to create
this v here and deposit some material here and this is basically the welding process
the other option could be you take two plates you put another plate on top another plate
on bottom and try to drive rivets or bolts through these joints so there are different
methods which are used and we are concentrating on welding so in certain cases there is an
external material involved that is the deposition of the electrode material as we will see later
or it could be a situation where the material in these two plates or reinforcing bars or
whatever it is fuses and that of course also implies or requires heating at the joint what
we have to be obviously careful is if we apply heating here
what are the implications of that heating as far as the main body of the material is
concerned till what point from the joint is the properties effected those are the kind
of things that go on in the background in the engineers mind when we decide about what
technique to use what are the kind of quality control procedures we will use and so on continuing
further this heating is generated through various sources electric arc gas flame laser
electron beam friction current resistance and so on these are these are different technologies
that have been developed over the years and we have methods which are available to us
all of them have their own pluses and minuses as far as heat application at the joint is
concerned some of the methods of welding which are commonly used are stick shielded metal
arc welding gas tungsten arc welding gas metal arc welding flux cored arc welding and electro
slag welding
so this is of course not a discussion on a not a d type class in welding and and we just
understand what the physics of the operation is and then move on to quality control issues
so this picture here shows the basic arc welding operation so as we can see here this is a
work work and the way it is shown is that we are trying to do a welding operation let
say for these two plates and this joint runs in this direction this is the region where
arc has been generated and heating will take place and this is the electrode which in detail
looks like this there is a core which is covered by a sheath and this core consists of alloying
materials flux that slag formers and so on this material from the core gets deposited
as we move the arc along the joint so now please remember that is movement along the
joint involves the electrode becoming shorter so basically what the welder has to ensure
is that as he moves the electrode there is a feed that goes in towards the job accounting
for the loss of electrode material and it has also to move along the direction of the
joint so there are two components to the motion of the welders hand these are some of the
common welding types that we use in structure engineering in civil engineering butt joints
lap joints t joints edge joints and corner joints and you can see how they look like
its the butt joint here its a lap joint a t joint edge joint and a corner joint of course
as structural engineers we know that
if we do joints like this it introduces certain eccentricity as far as a transfer a force
is concerned so this portion may or may not remain the way it is and it might deform as
far as action of stress is concerned that is certainly not a major matter of concern
as far as we are concerned today so moving forwards this picture here gives you the different
types of but joints single v single u double v so you can see that we are trying to divide
these types of joints depending on how much and where is the material being deposited
and also what kind of edge preparation we do as far as getting the joint ready is concerned
so this picture here again on the right hand side shows you the double u the single bevel
double bevel single j and double j and these are used in different forms at different locations
depending on whatever structural engineers or whatever designers suggest so this here
shows a picture of a fillet weld and we see that this is the material which is been deposited
and in welding terminology we call a leg root face toe and throat so as far as the stress
transfer is concerned the structural engineers know as to what kind of stresses act when
it comes to a welded area here which will be subjected to shear stresses and how they
are computed what is the shear strength of the weld and so on
so that is something which is pure structure engineering but this is something which is
important for us to understand even when we go into a quality control issues similarly
there are issues related to the butt welding and this picture here shows a butt welded
joint similar pictures of butt welded joints are given here and then i must introduce to
you the concept of a multiple pass weld what this multiple pass weld is it is used in cases
when the thickness of the plates is very large and we cannot deposit the material in a single
pass so if we look at this picture here we find that i will leave it to you to identify
what is the kind of joint that we have proposed here that is we have a joint when the edge
preparation has been done like this and since this thickness is very large the weld material
cannot be deposited in a single pass and therefore what is being proposed to be done is to deposit
material in several passes what we must remember is that this picture essentially represents
a joint being carried out on a plate which actually looks like this
so as we are moving forward this is the kind of edge preparation we have done and we are
either going to move this way or we are going to move this way which is a (( )) it is convenient
whichever way it is decided and as we go in this direction this is what is called a pass
and here what we have is a multiple pass system where the first pass is done and the second
pass is done the third pass fourth pass fifth pass sixth pass come back here do the seven
eight and nine then complete the ten and eleven on the top so this is the method by which
multiple pass welds are done and this joint becomes a monolithic joint for two plates
which are shown here where the issues involved n this kind of a welding process could be
the thickness of the pass obviously there is a pass thickness which is involved and
the voltage required depending on the kind of welding that is being done or the kind
of conditions under which the welding is being done the welder may choose to set the voltage
of the machine similarly the wire should not be positioned closer to one diameter from
the wall of the joint
this picture here is that of a plate girder which is very commonly used as far as civil
engineering is concerned we have the bottom flange the top flange and the web and these
are stiffeners that we know about that could be a horizontal stiffener here somewhere but
the important this as far as welding is concerned is that the web and the flange are connected
through a weld here the stiffener is connected to the web through a weld here and the top
flange is connected to the web plate through a weld here of course if we are not doing
a welded connection then we will have to use the web plate like this your flange is like
this and you will have to go through angles to connect the flanges in the web so we are
talking about welding is an option and we will see that remove these connecting members
connecting angles also tends to also helps us reduce the dead weight of the structure
having seen a civil engineering example let say in pipe lines this picture here is one
of those examples where a pipeline is being welded similarly here the welding is being
done inside the pipe that is the welder is basically working under fairly confined spaces
continuing this is another picture of a pipe line and we can see these kind of filler material
which is being used or which has been put in place to keep the alignment of the two
pipes at a desired level
so this is something which is very very important to ensure that after the welding has been
done there are no residual stresses arising out of misalignment continuing with this we
have a position here the welder has to lay down below the pipe and do the welding i hope
it is clear to you that these welding positions pose a very difficult challenge and call for
extra expertise on part of the welder so the position of welding is a very very important
aspect of the entire welding operation these are very awkward welding positions but from
an engineering point of view what has to be done going back to the discussion as far as
the feed is concerned you can imagine that in this case the feed has also to incorporate
the curvature of the joint when we are joining plates its a horizontal plate being joined
we have talked about this jointing of plates enough and we know that when plates are been
joined basically we are having a pass in this direction but there is no change in the position
of the plate but in this case the feed has to incorporate not only the consumption of
the electrode but also the change in the curvature of the pipe continuing further there are very
special environments such as under water where sometimes welding has to be carried out
please remember that we have talked about the fact that construction operations are
not necessarily carried out in green field environment that is not something which is
new at times construction operations involve repair and rehabilitation of the structures
and installations and in that case work has to be done under very challenging conditions
and this is one of those situations where we are talking about under water welding so
its the technology is already available the technology is not the subject of discussion
the point is to understand and appreciate that what standards we should use what will
be the methods of quality control we can draw inspiration from environmental welding that
is welding carried out under normal conditions and then drop (( )) specifications as far
as under water is concerned i do not mean to say that there are more specifications
that exists for quality control of underwater welding but the subject of discussion today
is to create an awareness in you on understanding what goes on when creating those specifications
or test methods you should understand the environment you should understand the conditions
and then try to ensure that in your protocol of doing things all those things are adequately
addressed
now obviously quality control has a very important component n non destructive testing so even
though thats not our subject primarily but its interesting and its important for us to
know some of the tests which are commonly used for non destructive testing of welds
faulty welds could lead to disastrous problems depending on the items being welded so non
destructive testing is essential to ensure that the defects are detected prior to the
system being putting used we must remember that quality control and quality assurance
of a larger project has several steps so we can talk in terms of a pipeline saying that
ok this is a pipeline saying that ok this is the pipeline which has these joints and
the first step would be to ensure that this is welded properly the next step would be
that well we will have a pipeline which has lets say several of these joints and we will
test this pipe line as a system as part of our quality control procedures so we will
probably talk about another example of pipelines and how we must drop a proper protocol for
quality control of a pipeline project but for the time being lets move on and try to
see the different methods which are available so visual testing is one of the most simple
and the most common thing that comes to our mind using magnifying glass hand held mirror
pocket rule weld gauge etcetera to inspect the weld
i would like to draw your attention to using the magnifying glass and a hand held mirror
please remember that this testing is carried out by an inspector so the inspector goes
to the site to inspect the welds and this inspection is part of a non destructive testing
protocol so the what does this inspector do and what are the kind of tools that he has
been used to look at the welds he could use a magnifying glass to see there are any obvious
abrasions on the surface and so on then there is a mirror because sometimes as we have seen
when the welder was doing the operation the weld may not be visible to the inspector so
easily so he has to use a mirror at different places to see the weld so there is something
like if you see certain security protocols you will realize that if you look at into
a car sometimes the bottom of the car is inspected using a mirror which is inserted through a
very strange looking contraption under the car so thats how we do visual testing continuing
with this easiest and most effective method but requires a very experienced operator coming
to the radiographic testing which is the next step utilizes x rays and radiographic isotopes
to determine the internal soundness of the weld now here we are talking about internal
soundness which is simply not possible to inspect through a visual inspection if we
recall the picture of a fillet weld for example or it could be any other weld what we have
is a deposit of material here now visual inspection can help us do any kind o inspection on the
surface when it comes to internal soundness whether there are some defects or voids which
have been trapped inside the weld which is quite possible in the case of multi pass welding
that requires something like a radiographic testing
it is highly valued versatile and widely accepted as the test method in welding magnetic particle
testing is another method and it is utilized to identify defects such as cracks at or near
the surface of ferromagnetic materials like nickel cobalt alloys if there no cracks then
the magnetic lines pass through the metal but due to cracks the field lines leave the
surface and the leakage field occurs and that is detected by magnetic particles so these
references that are given at the end of this slide those of you are more interested to
go to some of these references and try to understand the physics and how these methods
actually operate next in the line of testing of welds is liquid penetrate testing which
is called lt the material is cleaned thoroughly and coated with dye solution which seeps in
by capillary action here again we are trying to understand if here is any capillary action
as a result of pores or defects in the weld the dye is then removed and a developer is
applied to draw the dye out of any defects and used where magnetic particle testing cannot
be done
there is an ultrasonic method for testing of welds and uses high frequency sound waves
to detect imperfections in the metals and both the surface and subsurface defects can
be detected located and measured and its a fairly accurate method this again is the reference
which has been used to put this material together on these testing methods and now i think we
have prepared enough ground to understand the requirements of quality assurance quality
control inspectors what is the background that the instructor must have in wanted to
be able to carry out a fair and a thorough inspection of welding works obviously knowledgeable
about applicable codes it is obvious that there are applicable codes or there will be
applicable codes what we have insisted in doing today is to not go into the coral provisions
if you in fact go through this discussion that we are having today and then read the
codes you will find that the codes actually address some or all of those issues which
are being talked about so an inspector must know what codes are applicable in a particular
case he should have a thorough understanding of the non destructive testing and interpretation
of its results non destructive testing is like a pathological tests and its the physician
who has to interpret it somebody who carries out the test is carrying out
the test as given y the manufacturer of that testing equipment what are the limitations
of that test how the test should be actually interpreted is being left to the inspector
and that something which the inspector and the engineer must really understand ability
to understand weld symbols and complex fabrication plants we did not get into it but there are
all kinds of symbols which are available which are used in drawings to indicate the different
kind of welds and the first thing that has to be seen is whether the welding has been
done as prescribed by the designer or as required by the designer and given on the drawing so
in fact the drawing itself also gives a very important clue as far as the quality of design
that has gone on as far as welding is concerned knowledge about common defects in various
types of welding and how to avoid them so the inspectors job is also sometimes to educate
the welders and tell them what kind of precautions can be taken so that a particular defect is
avoided and excellent communicative skills is just a soft skill which all inspectors
must have as a matter of a all engineers must have now before we go into the disadvantages
lets first go through the advantages of welding which will put a lot of our discussion in
prospective as no hole is required there is no reduction in area we talked about
the fact that we want to join two plates and we make wholes in these plates in order to
put a plate and then we are going to use rivets or bolts what i am trying to show you is a
situation something like this where there are these two plates being jointed through
rivet or bolts these holes reduce the cross sectional area of this plate and that is what
is something which a structural engineers are not happy about they would like to avoid
that and therefore welding comes to a rescue and we can make do without any hole been drilled
into the plates filler plates gusted plates and connecting angles are not used and that
leads to a reduced overall weight of the structure the efficiency of a welded joint is more then
that of a riveted joint welded joints look better than the bulky riveted or butted joints
speedier and more silent fabrication those of you had some experience with realize that
riveting and bolting is a very noisy operation
sometimes and welding is relatively more silent and of course it is faster complete rigid
joints can be provided alterations and additions to existing structures are easy and required
less work space in comparison to riveting now having said that what are the disadvantage
welded joints are more brittle and therefore their fatigue strengths is less than the members
jointed and that something which we are aware of and the designers keep that in mind when
they prescribe welding due to uneven heating and cooling of the members during welding
the members may distort resulting in additional stresses there is heating of the joint so
if you have this plate being joint with this plate we have already talked about the fact
that this area will get heated now obviously if there is a heating the joint will also
cool and this heating and cooling at this location could result in distortions and additional
stresses both these aspects heating and cooling in certain cases need to be addressed through
pre heating of the joints and ensuring that the cooling happens at a certain rate a skilled
labor and electricity are required for welding no provisions for expansion and contraction
is kept in welded connections inspection is more difficult and costlier than that of riveting
works
this is actually the bottom line as far as quality control and quality assurance procedures
in welding is concerned defects like internal air pockets slag inclusion and incomplete
penetration are difficult to detect and that is why we need very very thorough inspection
procedures which are the only way to ensure good quality construction now the first thing
that i would like to take up from the point of view of quality control is give you an
insight on welder qualification welder certification is based on specially designed tests to determine
a welders skill and ability to deposit sound weld metal the main part of the welders test
consist of welding one or more test coupons which are then examined using non destructive
tests and destructive methods so there are coupons and there are tests non destructive
and destructive to make sure that the welder has indeed deposited sound weld metal in the
joint as was required and this is the test for the welders skill and ability the welder
used at site should be qualified as per a set protocol i have listed amarican welding
society the aws or the american society for mechanical engineers which is asme but it
need not be american society it could be any society which is acceptable to the clients
but the idea is that not everyone should be allowed to weld a site is not a training place
when you come to the site its a professional job the training has to happen somewhere else
and you should have or the welder should have a proper certification which has been issued
or which has been granted by a authority or an institution which is mandated for that
purpose it could be a certificate issued by the indian institute of welders or any such
professional organization experience in hours is also very important
one might require that in this particular job we would like to have experienced welders
its like having experienced pilots so once you move from one category to another you
have to put in certain hours of flying in the same way here we have to put in a certain
amount of hours of welding before you can say that yes i am an experienced welder and
i can do more challenging job the welder should understand the material of welding position
in welding and the equipment to be used we can talk about horizontal vertical curved
surfaces over head and so on so the welder has to be competent to be able to do these
things there is of course the possibility that a welder is not qualified for over head
welding but is good enough for horizontal and vertical welding so
so be it the certificate should so its like the driving license you may be able to drive
a two wheeler but not a four wheeler a normal light vehicle but not a heavy vehicle so your
license or your certification should clearly say what are the conditions in which you have
been tested what are the kind of jobs that you are qualified to do now a few tips on
vertical welding quality control vertical and overhead is difficult because we are working
against gravity so some of the tips that experienced welders tell us is use a smaller electrode
small weaves and stringer beads are preferred to to wide weave passes point the electrode
straight into the joint and tip it slightly upwards only a few degrees n the direction
of travel to allow the arc force to control the puddle a triangular weave motion produces
the best results do not use a whipping motion or remove the electrode from the molten puddle
and keep amperage in the lower level of recommended range so these are some of the tips which
are available as far as experienced welding is concerned going forward with over head
welding quality control it again is one of the most challenging positions working against
gravity and here the tips are more less similar to retain a complete control of the molten
puddle use a very short arc and reduce the amperage as recommended the weight of the
cable itself could become difficult to handle
if you are doing overhead welding and to reduce arm and wrist fatigue he cable could be draped
over the shoulder when welding in a standing position avoid welding into very sharp angle
as too much angle could lead to a wondering arc and could leave some burn marks wear a
helmet because that is the way your head is protected against any smearing metal or spatter
what are the quality issues in welding quality of the materials used whether its a electrode
or their job preparation of joints and materials including pre heating of materials in joint
if required cleaning of joints alignment of members being jointed equipment used for the
purpose position of the weld environmental conditions cooling after welding if required
welder qualification and so on and all this has to be kept in mind when we are developing
an inspection protocol in terms of the method and frequency also other considerations such
as the criticality of the operation consequences of failure past record etcetera should be
kept in mind we must also keep a meticulous record of all welding operation at site that
becomes very very handy in case of any referral which is required after the operation has
been carried out
the records must clearly indicate the number of the weld the welder who carried it out
what were the qualifications of that welder who carried it out what were the conditions
that were prevailing when the welding was carried out and what if any for the test that
were carried out at that particular joint so now before i conclude the discussion today
on this welding let me also show you some pictures of robotic welding applications were
we have basically eliminated the use of a welder the human intervention has been removed
and that gives us consistency in quality faster and it conserves material with this let me
give you a list of references which i have used and you may find relevant to understand
the whole operation a little better and i look forward to seeing you in another case
study on quality operations in construction projects
thank you