Stainless Steel. What every boat owner should know. OTB 129.
We look at Stainless steel and some of the things you should know if you own a boat.
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Closed Captions (CC):
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stainless steel what every boat owner
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should know
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in this video we'll be explaining why
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all stainless steels are not created
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equal we'll be telling you how stainless
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steel has properties that make it weak
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how it can actually corrode
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and how stainless steel can leave you
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right in the doodoo when it friction
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welds we'll also be looking at the
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welding of stainless steel and what you
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need to do in order to make it last
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we'll also be looking at the build-up of
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stainless steel and what you need to do
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to ensure components are really good
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stainless
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make sure you watch to the end to find
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out what you should be using on your
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boat
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[Applause]
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[Music]
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stainless steel comes in all shapes and
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forms it can be extruded or drawn into
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rods box sections or tubes
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it can be hot forged into bars and rods
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it can be bent
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shaped
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punched drilled and machined into all
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sorts of shapes
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but not all stainless steels are equal
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they're not all the same chemical makeup
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and it's very important in the marine
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industry that you get the right type of
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stainless let's look at some of the
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basic characteristics of stainless steel
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but before we do remember that stainless
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steel is actually an alloy like brass
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and bronze and types of aluminium it's
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made up from different metals
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stainless steels have the following
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characteristics they're corrosion
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resistant they have reasonably high
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tensile strength and are very durable
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they're temperature resistant easily
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formed and fabricated their low
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maintenance attractive impairments
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environmentally friendly well they're
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recyclable phoretic martensetic and
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duplex stainless steels are classified
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as magnetic whereas austenitic is
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classified as non-magnetic well what
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does that mean
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304 is the most common type of stainless
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steel it contains 18 by weight of
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chromium and about 8 by weight of nickel
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and therefore is often referred to as 18
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8. it is used for many applications
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including cutlery kitchen equipment food
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processing equipment automotive and
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aerospace structural components and
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marine fasteners
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but leave it outside in a marine
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environment for just a couple of days
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and you'll see why it's not the right
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type of steel for you
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so what is the right type of stainless
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steel for us to use on a boat
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well generally it's this middle one
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three one six
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now i'm going to insert a caveat to that
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there are actually many types of
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stainless steel and they range in their
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properties and they're all known by
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different names or numbers but generally
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316 is what you want to use on your boat
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and as a general rule 316 is
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non-magnetic or austenitic so why do you
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need to know that well when you go
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looking for your fixings fastenings and
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stainless steel bits and bobs
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take a magnet with you
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stainless steel has some weaknesses too
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and we'll describe all of them in a
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minute
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but they're quite important
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considerations
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the resistant to ferro oxide formation
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commonly called rust or rusting results
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first from the presence of chromium in
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the alloy specifically from the
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propensity of the exposed chromium atoms
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to form an invisible
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adherent chromium-rich oxide film that
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displayed the further characteristics of
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being able to self-heal
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reform in other words
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in the presence of atmospheric oxygen
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after it's been disturbed i.e scratched
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a variety of modifications to the
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content of stainless steel can improve
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corrosion resistance
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even further and these include
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increasing chromium above the levels of
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eleven percent the addition of eight
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percent or higher amounts of nickel and
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the addition of molybdenum
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which improves the resistance to pitting
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corrosion
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what does that mean in layman's terms
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well generally stainless steel has to be
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clean and polished in order for it to
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form a surface that is impervious to the
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salty sea environment
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to do this it needs to have oxygen
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or air which contains roughly 19 oxygen
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saltwater also contains sufficient
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oxygen to do this provided the water is
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moving that is or can move around it and
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not stagnate
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once the oxygen is used up all the water
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stagnates the oxygen is used up in the
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formation of this impervious barrier
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where there is a lack of oxygen or
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stagnated water the lack of oxygen
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allows the stainless to corrode for
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example in this picture here we call
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this crevice corrosion it has a distinct
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appearance of black pitting of the
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material and may have black liquid
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around it the pitching can be quite deep
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if left unattended it can literally
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corrode right through a bolt fixing or
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flange or fitting
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and note that this is not galvanic
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action
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and can occur in fittings and fixtures
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well above the water line and this is
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one reason that washing your boat down
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every now and then with cold clean fresh
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water will help to preserve the
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stainless steel fittings and fixtures
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and it's another reason why rigging
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chain plates turnbuckles fixtures and
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cotter pins need to be regularly
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inspected regardless of their age
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let's have a look at an example of
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crevice corrosion
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and some of you would have seen the
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video that we did on this volvo water
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muffler before while the outside of this
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device looks lovely and shiny the
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internal starts to rot away from the
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first days used
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many of you will have seen the telltale
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rusty streaks in the bilge if you happen
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to have one of these fitted
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or had to replace it within a certain
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period and that usually is within two to
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three years the causes the worlds on the
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inside are unpolished and untreated and
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crevice corrosion under the clamping
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bands or jubilee clips where they join
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the stainless steel end caps in both
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instances the lack of oxygen causes
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crevice corrosion either in the end cap
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or
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in the worlds and premature failure of
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this component it's not really the right
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material for such a thing to be built
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from
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when we challenged volvo about this they
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said it's a consumable part despite it
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costing 600 euros for you to change at a
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dealer if you want to see the video in
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full i'll put a link in the description
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and at the end of this video
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stainless steel will stretch under load
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there are various tables available that
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can quantify this
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in the various types of steel
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but again in layman's terms as you talk
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the stainless steel bolt or nut
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and loads it will stretch
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as it settles it will not apply the same
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compressive force
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here's an example of that
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your kill bolts will probably be 316
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stainless grade a4 if they're actually
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stainless at all
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they'll be in the region of 24
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millimeters od or diameter
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just under an inch
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the initial torque setting for this size
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of fixing is 603 newton meters or 444.5
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feet pounds
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when dry fitted
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or
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543 newton meters or 400
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feet pounds when lubricated
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if you were to then go back and test the
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torque or check it at a later date the
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stainless steel will have stretched
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applying the same torque again will
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stretch the bolt further
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continue to do this over a period of
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time and the kill bolts will actually
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snap or be severely weakened
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the way around this
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do not re-torque stainless steel bolts
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or nuts
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if you suspect that they were never set
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correctly in the first place then only
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tighten them to sixty percent of their
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original setting from the data sheet or
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replace them entirely with bolts or nuts
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set to the right torque
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you should certainly not be re-talking
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kill bolts made of stainless steel if
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you do not know the history after all
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you wouldn't do it on a car cylinder
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head would you
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and it's the same principle that applies
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here only more so
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while a strong still
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stainless steel has a tendency to work
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harden becoming very hard and brittle
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under repetitive loads
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drilling stainless steel has to be done
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slowly under pressure
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and so that the cutting edge of the tool
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actually cuts
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any rubbing
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or a lack of cutting pressure will
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darken the still and it will work
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hardened to a point that it becomes
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locally harder than the standard high
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speed steel drill bit the trick is
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firstly to drill slowly with a sharp
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drill with a lot of force so that the
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bit cuts clean spirals or swarf from
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both the cutting edges of the drill bit
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use water or a water-based coolant to
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keep the drill bit and the steel cool
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but better still use paraffin or white
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spirit as a coolant and a lubricant if
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you can get hold of them
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use a cobalt bit
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these are extremely hard but they can be
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up to 10 times more expensive
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but these bits are ideal for drilling
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stainless steel but again being harder
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they are somewhat brittle
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when using stainless steel fixings or
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bolts the nuts under load can gall or
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friction world making the nut and bolt
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weld together
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before they are in their final position
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there is just about no cure for this
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other than cutting away the bolt or nut
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and replacing it if you're strong in the
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arm and weaken the head like me you can
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sometimes snap the nut or the bolt with
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lots of leverage
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but above 12 millimeter or half inch
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you'll need extremely long lever or very
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strong arms
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so how can we avoid galling well the
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first thing is to slow down your
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installation speed
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don't use bolts to pull joints together
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use a lubricant such as tef gel
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avoid damaged or dirty threads and use
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extra care with lock nuts
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if a fastener binds or begins to bind
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you should stop immediately
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so while we're actually outside the
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chandler's here these guys are great
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um
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ozaturq marin
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or east marine
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they're actually in our marina and
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they're really good they've got all the
12:11
stuff he sells a lot of second-hand
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stuff as well so you know when you want
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the odd bits and pieces
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he's quite often got a secondhand one
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but a couple of things that
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i wanted to show you this is
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a hose clamp
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and this is a you know a quality german
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hose clamp
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made
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it's actually stamped inside
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the stainless
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but look at this this is the bolt
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which tightens it up
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you can see that's just
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mild still
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possibly coated
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there's a galvanized one
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same thing and there's another one
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so
13:02
again
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this piece is stamped stainless steel
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but the
13:09
the bolt that goes through the center
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is just northern ordinary carbon steel
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so when you buy hose clamps or jubilee
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clamps make sure you take your magnet
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with you and make sure that the securing
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nut that tightens it up is not magnetic
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and it's not carbon steel
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the same thing applies when you're
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buying fittings or fixtures
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make sure you're getting what you're
13:33
actually paying for
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and the same with some fixings now some
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fixings can be very slightly magnetic
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especially if they're an a4 80 grade
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but talk to your supplier about this
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if they're reputable they won't mind you
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asking questions
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this is our local steel fabricator and
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he's very good
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he never throws anything away because he
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knows the value of good quality
14:00
stainless steel and when you want to go
14:03
and have something made he's usually got
14:05
something there which will fit the bill
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and may be able to be repurposed
14:11
everything that comes out of the
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workshop is extremely well polished and
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here he's making
14:17
some extension pieces for a fishing rod
14:19
holder for the frame we're about to look
14:22
at let's take a look at the welding on
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this frame
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so this is what a good stainless steel
14:29
world should look like
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they've been acid etched
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and then have a high polish
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these are really good worlds
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and this is the type of quality you
14:39
should be looking for if you're having
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welding done
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or you're approaching someone to do
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welding for you
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don't be afraid to ask for samples or to
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see samples of their previous work
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a good fabricator or engineering shop
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will only be too happy to show you the
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type of quality that they can turn out
15:00
the difference in world quality is
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pretty much self-explanatory what you
15:05
see is what you get on the left is a bad
15:09
world done with a mig welder and on the
15:11
right a good world with the tig welder
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the difference pretty plain to see what
15:18
you see is what you get
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metallogy is a really complicated
15:24
subject and there's lots more detail
15:26
that we could go into but not in this
15:28
video if you go to our website
15:31
and then scroll over to the technical
15:34
stuff you'll see that there's a pdf
15:36
version
15:37
of this video which you can reference or
15:40
use with your sailing club or just
15:42
general information
15:43
you can download it
15:45
for free along with lots of other bits
15:47
and bobs
15:48
pop over to svmpavidus.com
15:51
hopefully this video has been of use to
15:53
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