DIY: Deterioration – Rot, Corrosion, Fatigue, etc

PATH: REFITTING & REPAIR » DIY » Fundamentals »


PAGE CONTENTS:
^ Rot.
^ ^ Decomposition.
^ ^ ^ Dry Rot.
^ ^ ^ Wet Rot.
^  Corrosion.
^ ^ Redox.
^ ^ Corrosion and Rusting.
^ ^ Galvanic Corrosion.
^ ^ ^ Anodic Index.
^ ^ ^ Galvanic Corrosion Simplified.
^ ^ ^ Stainless Steel.
^ Fatigue.
^ ^ Reverse Bending Fatigue
^ Forum Posts, Tech Notes & Tech Tips.
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Deterioration of marine materials are often natural processes Including rot and corrosion that tends to return these materials to their original natural state. Deterioration due to fatigue is also covered in this article. Deterioration due to wear, abrasion, and impact are covered in 15.3.1.3 – DIY: Troubleshooting, Failure Analysis,+ and in other articles specific to the material and equipment.

Rot

Rot and rotting in the marine environment most often refers to decomposition of organic matter through the processes of Dry Rot or Wet Rot.

More from Wikipedia.

Decomposition

In general, decomposition is the process by which organic substances are broken down into a more simple organic matter. The process is a part of the nutrient cycle and is essential for recycling the finite matter that occupies physical space in the biosphere. Bodies of living organisms begin to decompose shortly after death. Animals, such as worms, also help decompose the organic materials. Organisms that do this are known as decomposers. Although no two organisms decompose in the same way, they all undergo the same sequential stages of decomposition.

More from Wikipedia.

Dry Rot

Dry rot is wood decay caused by certain species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resulted in a darkly colored deteriorated and cracked condition. Dry rot is very destructive to the wood aboard ships. Dry rot cannot survive and flourish in the presence of saltwater, hence the swabby’s duty was to soak the decks in saltwater to kill the fungus and prevent dry rot. That is why freshwater was not used for this purpose. Fungus thrives in freshwater saturated wood. Why is it called “Dry” rot? Because dry rot leaves the wood looking cracked, dehydrated and dusty due to the lack of lignum (the heart of the wood)  which the fungus devours. The dust is fungus poo.

The life-cycle of dry rot can be broken down into four main stages. Dry rot begins as a microscopic spore which, in high enough concentrations, can resemble a fine orange dust. If the spores are subjected to sufficient moisture they will begin to grow fine white strands known as hyphae. As the hyphae germinate they will eventually form a large mass known as mycelium. The final stage is a fruiting body which pumps new spores out into the surrounding air.

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Wet Rot

Wet rot is a generic term used to define a variety of fungal species, such as Coniophora puteana (otherwise known ascellar fungus). Wet rot fungi obtain their food by breaking down the cell walls of wood cells resulting in a loss of strength of the wood. This can cause problems in the structural integrity of structures.

More from Wikipedia.


Corrosion

Corrosion in the marine environment is most often the result of one or both of the following processes: Redox and Galvanic Corrosion.

More from Wikipedia.

Redox

Redox (short for reduction–oxidation reaction) is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a reduction process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between chemical species. The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in simple terms:

Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.

Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

As an example, during the combustion of wood, oxygen from the air is reduced, gaining electrons from carbon which is oxidized. Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, oxygen is not necessarily included in such reactions, as other chemical species can serve the same function.

Corrosion and rusting

The term corrosion refers to the electrochemical oxidation of metals in reaction with an oxidant (such as oxygen). Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion; it forms as a result of the oxidation of iron metal. Common rust often refers to iron oxide, formed in the following chemical reaction:

4 Fe + 3 O2 → 2 Fe2O3
Four Iron atoms combine with three oxygen molecules to form two iron oxide molecules.

The reaction can occur relatively slowly, as with the formation of rust, or more quickly, in the case of fire. There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), and more complex processes such as the oxidation of glucose (C6H12O6) in the human body.

Corrosion involving iron alloys such as Stainless Steel can be a very complex process due to the oxidation of chromium and the galvanic interaction with other metals (see next section).

Galvanic Corrosion

Galvanic corrosion (also called bimetallic corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. Dissimilar metals and alloys have different electrode potentials, and when two or more come into contact in an electrolyte, one metal acts as anode and the other as cathode. If the electrolyte contains only metal ions that are not easily reduced (such as Na+, Ca2+, K+, Mg2+, or Zn2+), the cathode reaction is reduction of dissolved H+ to H2 or O2 to OH−. The electropotential difference between the reactions at the two electrodes is the driving force for an accelerated attack on the anode metal, which dissolves into the electrolyte. This leads to the metal at the anode corroding more quickly than it otherwise would and corrosion at the cathode being inhibited. The presence of an electrolyte and an electrical conducting path between the metals is essential for galvanic corrosion to occur. The electrolyte provides a means for ion migration whereby ions move to prevent charge build-up that would otherwise stop the reaction.

Nobility index
Most Noble (Most Cathodic) ⇒ Least Noble (Most Anodice)

Metal Index (Volts)
Most Noble (Most Cathodic)
Gold‚ solid and plated‚ Gold-platinum alloy −0.00
Rhodium plated on silver-plated copper −0.05
Silver‚ solid or plated; monel metal. High nickel-copper alloys −0.15
Nickel‚ solid or plated‚ titanium and its alloys‚ Monel −0.30
Copper‚ solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys −0.35
Brass and bronzes −0.40
High brasses and bronzes −0.45
18% chromium type corrosion-resistant steels −0.50
Chromium plated; tin plated; 12% chromium type corrosion-resistant steels −0.60
Tin-plate; tin-lead solder −0.65
Lead‚ solid or plated; high lead alloys −0.70
2000 series wrought aluminum −0.75
Iron‚ wrought‚ gray or malleable‚ plain carbon and low alloy steels −0.85
Aluminum‚ wrought alloys other than 2000 series aluminum‚ cast alloys of the silicon type -0.90
Aluminum‚ cast alloys other than silicon type‚ cadmium‚ plated and chromate −0.95
Hot-dip-zinc plate; galvanized steel −1.20
Zinc‚ wrought; zinc-base die-casting alloys; zinc plated −1.25
Magnesium & magnesium-base alloys‚ cast or wrought −1.75
Beryllium −1.85
Least Noble (Most Anodic)

NOTES: The nobility index of both active and passive (state) stainless steel can be found below under “Stainless Steel”.

More from Wikipedia.

Galvanic Corrosion Simplified

When two different metals find themselves in close proximity and electrically connected to each other, they are subject to galvanic corrosion if they are submerged in a common electrolyte. This can be illustrated by a beaker containing an electrolyte such as salty water. The sodium in the salt is actually a metal which makes the salt water a strong electrolyte. The illustration below shows two different metals submerged in the salt water. one of the metals is more noble then the other according to the Nobility Index chart above. Since the electrolyte is slightly positively (+) charged, it will try to attract negatively (-) charged sub-atomic particles  such as electrons from the metals. The most noble of the two metals will gladly give up some of its electrons to the salt water if it can recoup those electrons from the least noble metal immediately through the electrical connection. Unfortunately, this will cause those atoms in the least noble metal that gave up electrons to the most noble metal to become positively (+) charged which in turn will aggravate their neighbors into pushing them out from the least noble metal into solution with the salt water. Pretty soon, the least noble metal will start to look like swiss cheese. Just how quickly this happens depends on the voltage difference between the two metals (also shown in the chart above).

PIX of Beaker

More from Wikipedia.

If a third metal is introduced into the above illustration, what will happen depends on new metal’s voltage potential in relationship to the other two metals. If its potential is between the other two metals then the corrosion process remains the same and the third metal will not be affected. However, if the third metals potential is greater, that is to say that the potential is a higher negative (-) value, then the third metal becomes the new least noble and it will be the one that corrodes (wastes) away. We can use this situation to our advantage. By intentionally introducing a lesser noble metal as a sacrificial anode, we can protect what was the least noble metal from galvanic corrosion.

More from Wikipedia.

Alloys +

PIX of Beaker

A common application in a marine situation is illustrated below. A stainless steel propeller shaft which will have a high nobility value because of its chromium content will give up electrons to the salt water, but at the same time will recoup the lost electrons with electrons stripped from the zinc in the propellers bronze alloy resulting in dezincification which will make the propeller weak and brittle. The propeller will usually display a pinkish discoloration of the typically bright yellow bronze surface. The addition of zinc sacrificial anodes such as one or two zinc shaft collars or a zinc anode propeller nut cover can protect the propeller from such galvanic damage. Sacrificial zincs can be attached to the propeller shaft strut, bearing, etc. and the rudder and rudder bearings, etc. to protect each one independently. Or, If all the underwater machinery and steerage are bonded together, a single transom mounted zinc may be an option. For more about Galvanic Corrosion Protection Systems and DIY: Galvanic Corrosion Protection.

PIX of Underwater Machinery, etc.

More from Wikipedia.

Stainless Steel

In metallurgy, stainless steel, also known as inox steel or inox from French inoxydable (inoxidizable), is a steel alloy, with highest percentage contents of iron,chromium, and nickel, with a minimum of 10.5% chromium content by mass and a maximum of 1.2% carbon by mass.

Stainless steels are most notable for their corrosion resistance, which increases with increasing chromium content. Additions of molybdenum increase corrosion resistance in reducing acids and against pitting attack in chloride solutions. Thus, there are numerous grades of stainless steel with varying chromium and molybdenum contents to suit the environment the alloy must endure. Stainless steel’s resistance to corrosion and staining, low maintenance, and familiar luster make it an ideal material for many applications where both the strength of steel and corrosion resistance are required.

Stainless steels do not suffer uniform corrosion, like carbon steel, when exposed to wet environments. Unprotected carbon steel rusts readily when exposed to the combination of air and moisture. The resulting iron oxide surface layer (the rust) is porous and fragile. Since iron oxide occupies a larger volume than the original steel this layer expands and tends to flake and fall away exposing the underlying steel to further attack. In comparison, stainless steels contain sufficient chromium to undergo passivation, spontaneously forming a microscopically thin inert surface film of chromium oxide by reaction with the oxygen in air and even the small amount of dissolved oxygen in water. This passive film prevents further corrosion by blocking oxygen diffusion to the steel surface and thus prevents corrosion from spreading into the bulk of the metal. This film is self-repairing if it is scratched or temporarily disturbed by an upset condition in the environment that exceeds the inherent corrosion resistance of that grade.

The resistance of this film to corrosion depends upon the chemical composition of the stainless steel, chiefly the chromium content.

Corrosion of stainless steels can occur when the grade is not suited for the working environment.

it is customary to distinguish between 4 forms of corrosion: uniform, localized (pitting), galvanic and SCC (stress corrosion cracking).

Uniform corrosion takes place in very aggressive environments, typically chemical production or use, pulp and paper industries, etc. The whole surface of the steel is attacked and the corrosion is expressed as corrosion rate in mm/year (usually less than 0.1mm/year is acceptable for such cases) Corrosion tables provide guidelines

This is typically the case when stainless steels are exposed to acidic or basic solutions. Whether a stainless steel corrodes depends on the kind and concentration of acid or base, and the solution temperature. Uniform corrosion is typically easy to avoid because of extensive published corrosion data or easy to perform laboratory corrosion testing.

However, stainless steels are susceptible to localized corrosion under certain conditions, which need to be recognized and avoided. Such localized corrosion is problematic for stainless steels because it is unexpected and difficult to predict.

Acidic solutions can be categorized into two general categories, reducing acids such as hydrochloric acid and dilute sulfuric acid, and oxidizing acids such as nitric acid and concentrated sulfuric acid. Increasing chromium and molybdenum contents provide increasing resistance to reducing acids, while increasing chromium and silicon contents provide increasing resistance to oxidizing acids.

Sulfuric acid is one of the largest tonnage industrial chemical manufactured. At room temperature Type 304 is only resistant to 3% acid while Type 316 is resistant to 3% acid up to 50 °C and 20% acid at room temperature. Thus Type 304 is rarely used in contact with sulfuric acid. Type 904L and Alloy 20 are resistant to sulfuric acid at even higher concentrations above room temperature.

Concentrated sulfuric acid possesses oxidizing characteristics like nitric acid and thus silicon bearing stainless steels also find application.

Hydrochloric acid will damage any kind of stainless steel, and should be avoided.

All types of stainless steel resist attack from phosphoric acid and nitric acid at room temperature. At high concentration and elevated temperature attack will occur and higher alloy stainless steels are required.

In general, organic acids are less corrosive than mineral acids such as hydrochloric and sulfuric acid. As the molecular weight of organic acids increase their corrosivity decreases. Formic acid has the lowest molecular weight and is a strong acid. Type 304 can be used with formic acid though it will tend to discolor the solution. Acetic acid is probably the most commercially important of the organic acids and Type 316 is commonly used for storing and handling acetic acid.

Bases: Stainless steels Type 304 and 316 are unaffected by any of the weak bases such as ammonium hydroxide, even in high concentrations and at high temperatures. The same grades of stainless exposed to stronger bases such as sodium hydroxide at high concentrations and high temperatures will likely experience some etching and cracking.

Increasing chromium and nickel contents provide increasing resistance.

Organics: All grades resist damage from aldehydes and amines, though in the latter case Type 316 is preferable to 304; cellulose acetate will damage 304 unless the temperature is kept low. Fats and fatty acids only affect Type 304 at temperatures above 150 °C (302 °F), and Type 316 above 260 °C (500 °F), while Type 317 is unaffected at all temperatures. Type 316L is required for processing of urea.

Localized corrosion can occur in a number of ways, e.g. pitting corrosion, and crevice corrosion . Such localized attack is most common in the presence of chloride ions. Increasing chloride levels require more highly alloyed stainless steels.

Localized corrosion can be difficult to predict because it is dependent on many factors including:

  • Chloride ion concentration (However, even when the chloride solution concentration is known, it is still possible for chloride ions to concentrate, such as in crevices (e.g. under gaskets) or on surfaces in vapor spaces due to evaporation and condensation.)
  • Increasing temperature increases susceptibility
  • Increasing acidity increases susceptibility
  • Stagnant conditions increase susceptibility
  • The presence of oxidizing species, such as ferric and cupric ions

Pitting corrosion resistance: This is probably the most frequent form of corrosion. The corrosion resistance of stainless steels to pitting corrosion is often expressed by the PREN (Pitting Resistance Equivalent Number) obtained through the formula:

PREN = %Cr+3.3%Mo+16%N where the terms correspond to the contents by weight % of Chromium, Molybdenum and Nitrogen respectively in the steel.

The higher the PREN, the higher the pitting corrosion resistance . Increasing chromium, molybdenum and nitrogen contents provide increasing resistance to pitting corrosion

Crevice corrosion: While the PREN is a property of the stainless steel, crevice corrosion occurs when poor design has created confined areas (overlapping plates, washer-plate interfaces…) AND when the PREN is not high enough for the service conditions. Design and good fabrication techniques combined with correct alloy selection can prevent such corrosion.

Stress corrosion cracking (SCC) is a sudden cracking and failure of a component without deformation.

It may occur when three conditions are met:

  • The part is stressed (by an applied load or by a residual stress )
  • The environment is aggressive (high chloride level, temperature above 50 °C, presence of H2S)
  • The stainless steel is not sufficiently SCC resistant

The SCC mechanism results from the following sequence of events:

  • Pitting occurs
  • Cracks start from a pit initiation site
  • Cracks then propagate through the metal in a transgranular or intergranular mode.
  • Failure occurs

Whereas pitting leads in most cases to unsightly surfaces and in a worst case to perforation of the stainless sheet, failure by SCC can lead to very damaging consequences. It is therefore considered as a special form of corrosion.

As SCC requires several conditions to be met, it is relatively easy to avoid it:

  • reduce the stress level (The oil & gas specs provide requirements for max stress level in H2S containing environments)
  • assess the aggressiveness of the environment (high chloride content, temperature above 50 °C …)
  • select the right type of stainless steel: super austenitics such as grade 904L or super duplex (Ferritic stainless steels and duplex stainless steels are very resistant to SCC)

Galvanic corrosion (also called ‘dissimilar metal corrosion’) refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte. The most common electrolyte is water, ranging from fresh water to seawater. When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. Stainless steel, due to its superior corrosion resistance relative to most other metals, including steel and aluminum, becomes the cathode accelerating the corrosion of the anodic metal. An example is the corrosion of aluminum rivets fastening stainless steel sheets in contact with water. The relative surface areas of the anode and the cathode are important. In the above example, the surface of the rivets will be small compared to that of the stainless steel sheet. However if stainless steel fasteners are used to assemble aluminum sheets, galvanic corrosion will be much slower because the galvanic current density on the aluminum surface will be order of magnitude smaller. A similar, but frequent mistake, is to assemble stainless steel with carbon steel fasteners; whereas using stainless steel to fasten carbon steel plates is usually OK. Providing electrical insulation between the dissimilar metals, where possible, is effective at preventing this type of corrosion.

High temperature corrosion (scaling): At elevated temperatures all metals react with hot gases. The most common high temperature gaseous mixture is air, and oxygen is the most reactive component of air. Carbon steel is limited to ~900 °F (480 °C) in air. Chromium in stainless steel reacts with oxygen to form a chromium oxide scale which reduces oxygen diffusion into the material. The minimum 10.5% chromium in stainless steels provides resistance to ~1,300 °F (700 °C), while 26% chromium provides resistance up to ~2,200 °F (1,200 °C). Type 304, the most common grade of stainless steel with 18% chromium is resistant to ~1,600 °F (870 °C). Other gases such as sulfur dioxide, hydrogen sulfide, carbon monoxide, chlorine, etc. also attack stainless steel. Resistance to other gases is dependent on the type of gas, the temperature and the alloying content of the stainless steel.

Oxidation resistance increases with Cr content, as well as Si and Al. Small additions of Cerium and Yttrium increase the adhesion of the oxide layer on the surface

Fe Cr Al ferritic stainless steels with Al up to 5% are used for electrical resistance alloys. In the form of wire or ribbons

Properties

Physical Properties of Stainless steels
Designations Density Modulus of
elasticity
Mean coeficient of
thermal expansion
[10−6·K−1]
Thermal
Conductivity
Specific
Heat
Electrical
resistivity
EN
[]
AISI/ASTM at 20 °C
[kg/dm3]
at 20 °C
[GPa]
20 °C
200 °C
20 °C
400 °C
at 20 °C
[W/(m·K)]
at 20 °C
[J/(kg·K)]
at 20 °C
[(Ω·mm2)/m]
Austenitic stainless steels
1.4301 304 7,9 200 16,5 17,5 15 500 0,73
1.4401 316 8,0 200 16,5 17,5 15 500 0,75
Duplex stainless steels
1.4462 2205 7,8 200 13,5 14,0 (g) 15 500 0,80
1.4362 2304 7,8 200 13,5 14,0 (n) 15 500 0,80
1.4501 7,8 200 13,5 (n.r.) 15 500 0,80
Ferritic stainless steels
1.4512 409 7,7 220 11,0 12,0 25 460 0,60
1.4016 430 7,7 220 10,0 10,5 25 460 0,60
Martensitic stainless steels
1.4021 420 7,7 215 11,0 12,0 30 460 0,60
1.4418 7,7 200 10,8 11,6 15 430 0,80
Precipitation hardening stainless steels
1.4542 630 7,8 200 10,8 11,6 16 500 0,71

Electricity and magnetism: Like steel, stainless steels are relatively poor conductors of electricity, with significantly lower electrical conductivity than copper.

Ferritic and martensitic stainless steels are magnetic.

Soft magnetic ferritic grades (i.e. low Hc) are used in electrovalves and in fuel injectors

Annealed austenitic stainless steels are non-magnetic. Work hardening can makecold-formed austenitic stainless steels slightly magnetic.

Galling, sometimes called cold welding, is a form of severe adhesive wear which can occur when two metal surfaces are in relative motion to each other and under heavy pressure. Austenitic stainless steel fasteners are particularly susceptible to thread galling, although it also occurs in other alloys that self-generate a protective oxide surface film, such as aluminum and titanium. Under high contact-force sliding this oxide can be deformed, broken and removed from parts of the component, exposing bare reactive metal. When the two surfaces are the same material, these exposed surfaces can easily fuse together. Separation of the two surfaces can result in surface tearing and even complete seizure of metal components or fasteners.

Galling can be mitigated by the use of dissimilar materials (bronze against stainless steel), or using different stainless steels (martensitic against austenitic). Additionally, threaded joints may be lubricated to provide a film between the two parts and prevent galling. Also, Nitronic 60, made by selective alloying with manganese, silicon and nitrogen, has demonstrated a reduced tendency to gall.

Grades: There are over 150 grades of stainless steel, of which 15 are most commonly used.

More from Wikipedia.

Stainless Steel in the marine envionment is a complex issue due to the chromiums ability to produce chromium oxide in the presents of oxygen. This chromium oxide has the beneficial ability of being able to cover the stainless steel with a layer of durable chromium oxide that can prevent the iron molecules in the steel alloy from oxidizing into iron oxide (rust). Hence the steel is stainless with no rust staining. However, serious problems will rapidly develop if oxygen is not available to oxidize the chromium and produce the protective layer. Such is the case in bodies of water that lack oxygen saturation. These are often called “Dead Zones” as fish cannot survive there due to the lack of oxygen. But this can happen anywhere that the oxygen becomes depleted such as in hardware fasteners, isolated parts of machenery and other equipment. Common examples are:

PIX of Swimstep with Rust Staining from Fasteners.

Rust staining from fasteners. Bedding

PIX of Propeller Shaft & Cutlass bearing

Between propeller shaft and cutlass bearings.

PIX if Rigginng Joint

Inside rigging joints within fittings.

Index of Stainless Steel Galvanic values

Metal Index (Volts)
Most Noble (Most Cathodic)
Stainless steel 316 (passive) -0.05
Stainless Steel 304 (passive) -0.1
Stainless Steel 316 (active) -0.4
Stainless Steel 304 (active) -0.5
Least Noble (Most Anodic)

NOTES: Passive = Chromium oxide layer fully formed. Active = Lacks fully formed chromium oxide layer.

Two States: Active. Passive.

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Amalgams

An amalgam is an alloy of mercury with another metal, which may be a liquid, a soft paste or a solid, depending upon the proportion of mercury. These alloys are formed through metallic bonding, with the electrostatic attractive force of the conduction electrons working to bind all the positively charged metal ions together into a crystal lattice structure. Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten, and tantalum. Gold-mercury amalgam is used in the extraction of gold from ore and silver-mercury amalgams are important in dentistry, Dentistry has used alloys of mercury with metals such as silver, copper, indium, tin and zinc.

More from Wikipedia.

Dental amalgam is a liquid mercury and metal alloy mixture used in dentistry to fill cavities caused by tooth decay. Low-copper amalgam commonly consists of mercury (50%), silver (~22–32%), tin (~14%), copper (~8%) and other trace metals such as zinc (~2%). Dental amalgams were first documented in a Tang Dynasty medical text written by Su Gong (苏恭) in 659, and appeared in Germany in 1528. In the 1800s, amalgam became the dental restorative material of choice due to its low cost, ease of application, strength, and durability. Ever since its introduction in the Western world in the 1830s, amalgam has been the subject of recurrent controversies because of its mercury content. In July 2018 the EU prohibited amalgam for dental treatment of children under 15 years and of pregnant or breastfeeding women.

More from US FDA.

Galvanic corrosion occurs in an amalgam when electrolytic cells of anode and cathode set up in the presence of electrolytes. The multiphase structure of dental amalgam can contribute as an anode or cathode with saliva as electrolytes. Corrosion may significantly affect the structure and mechanical properties of set dental amalgam. In conventional amalgam, γ2 phase is the most reactive and readily forms an anode. It will break down releasing corrosion products and mercury. Some of the mercury will combine rapidly with unreacted alloy and some will be ingested. The rate of galvanic deterioration increases significantly when any highly noble metal such as gold is present, especially if the gold is in contact with the amalgam completing the electrical circuit. An example would be an amalgam filling immediately next to and in electrical contact with a gold filling or crown. In such cases, the amalgam filling(s) could be seriously affected in as little as a few months.

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Fatigue

In materials science, fatigue is the weakening of a material caused by repeatedly applied loads. It is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values that cause such damage may be much less than the strength of the material typically quoted as the ultimate tensile stress limit, or the yield stress limit.

Fatigue occurs when a material is subjected to repeated loading and unloading. If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators such as the surface, persistent slip bands (PSBs), interfaces of constituents in the case of composites, and grain interfaces in the case of metals. Eventually a crack will reach a critical size, the crack will propagate suddenly, and the structure will fracture. The shape of the structure will significantly affect the fatigue life; square holes or sharp corners will lead to elevated local stresses where fatigue cracks can initiate. Round holes and smooth transitions or fillets will increase the fatigue strength of the structure.

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More from Wikipedia.

Reverse Bending Fatigue

Structures.

Electrical Wiring. Strands.

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Related Main Topic Pages with Links

2 – BOAT PRODUCTION.
2.6 – Boat Equipment (Vendors, Specs, Manuals, Reviews, Recalls,+).
2.6.4 – Galvanic Corrosion Protection.
2.6.5 – Hull Penetrations & Openings (Thru-Hulls, Scuttles, Skylights, Hatches,+).
2.6.6 – Deck Hardware & Equipment.
2.6.8 – Propulsion Machinery (Types, Configurations, Features, Control Systems,+).
2.6.8.1 – Engine Brands & Manufacturers (Petrol/Gasoline, Diesel, CNG, A~Z,+).
2.6.8.4 – Shafting (Propshafts, Couplings, Seals, Bearings, Struts, Keys, Nuts,+).
2.6.8.5 – Propellers (Screws, Water Jets, Paddle wheels,+).
2.6.9 – Electrical Systems (Direct Current, Alternating Current,+).
2.6.10 – Domestic Systems.
2.6.10.3 – Water Systems.

15 – BOAT REFITTING & REPAIR.
15.3 – Do-It-Yourself Refitting & Repair (Installation, Maint, Troubleshooting, Repair,+).
15.3.1 – DIY: Fundamentals.
15.3.1.2 – DIY: Rot, Corrosion, Fatigue,+.
15.3.1.3 – DIY: Troubleshooting, Failure Analysis,+.
15.3.2 – DIY: Vessel Structure.
15.3.2.1 – DIY: Hull & Deck.
15.3.2.2 – DIY: Steering & Thrusters (Mechanical, Hydraulic,+).
15.3.2.3 – DIY: Stabilizers & Trim Plates.
15.3.2.4 – DIY: Dewatering Devices.
15.3.2.5 – DIY: Galvanic Corrosion Protection.
15.3.2.6 – DIY: Hull Penetrations & Openings (Thru-Hulls, Scuttles, Skylights, Hatches,+).
15.3.2.7 – DIY: Deck Hardware & Equipment.
15.3.2.7.1 – DIY: Ground Tackle (Anchors, Rode, Windlass,+).
15.3.2.7.2 – DIY: Commercial Fishing Gear.
15.3.2.7.3 – DIY: Rigging.
15.3.2.7.4 – DIY: Sails.
15.3.3 – DIY: Propulsion Machinery (Control Systems,+).
15.3.3.1 – DIY: Engines (Fuels, Troubleshooting, Repair, Rebuilding vs Repowering,+).
15.3.3.1.1 – DIY: Engine Mechanical (Pistons, Rods, Crankshafts, Blocks, Heads, Valves,+).
15.3.3.1.2 – DIY: Engine Lubrication (Splash, Forced, Oil, Filtration, Additives, Oil Analysis,+).
15.3.3.1.3 – DIY: Engine Fuel (Petrol/Gasoline, Diesel, CNG,+).
15.3.3.1.4 – DIY: Engine Electrical (Starting, Charging, Instrumentation,+).
15.3.3.1.5 – DIY: Engine Cooling (Air, Raw Water, Fresh Water,+).
15.3.3.1.6 – DIY: Engine Exhaust (Dry, Wet,+).
15.3.3.1.7 – DIY: Engine Mounting (Hard, Soft,+).
15.3.3.2 – DIY: Engine-to-Marine Gear Interfaces (Adapters, Dampers, Jackshafts,+).
15.3.3.3 – DIY: Marine Gears (Inboards, Inboard-Outboards, Outboards, Sail Drives, Pods,+).
15.3.3.4 – DIY: Shafting (Shafts, Couplings, Joints, Thrust Bearings, Seals, Cutlass, Struts,+).
15.3.3.5 – DIY: Propellers (Screws, Water Jets, Paddle wheels,+).
15.3.4 – DIY: Electrical Systems.
15.3.4.1 – DIY: Direct Current.
15.3.4.2 – DIY: Alternating Current.
15.3.4.3 – DIY: DC to AC Inverters.
15.3.4.4 – DIY: Auxiliary Generators.
15.3.5 – DIY: Domestic Systems.
15.3.5.4 – DIY: Water Systems.
15.3.6 – DIY: Nav & Comm Systems (Charts, Compass, GPS, Radar, Lts, Flares, EPIRB, VHF,+).
15.3.9 – DIY: Tenders.

16 – PUBLICATIONS & MEDIA + Lending Library (w/Reviews).
16.1 – Authors.
16.2 – Books.
16.3 – Magazines.
16.4 – Product Documentation (SpecSheets, Installation Drawings, Manuals, Parts Books,+).
16.5 – Videos (Movies).
16.6 – Websites (w/Links).



Visit our FEATURED ARTICLES Home Page
to see examples of our website's comprehensive contents!

Thanks to our amazing contributors for the steady flow of articles, and to our dedicated all-volunteer staff who sort, polish and format them, everyday we get a little bit closer to our goal of
Everything About Boats. If you would like to submit an article,
see Submitting Articles.

— TOP 20 MOST POPULAR ARTICLES —

Ford Industrial Power Products Diesel Engines
Ford 2715E
Lehman Mfg. Co.
Detroit Diesel 8.2
Universal Atomic 4
Chrysler & Force Outboards
Eska
Perkins
ZF Friedrichshafen AG
Allison Transmission
American Marine Ltd (Grand Banks)
Boat Inspection
Types of Marine Surveys
Marine Surveyors by Regions
Boat Builders By MIC
Beta Marine
Waterwitch
DIY Boat Owner Magazine
ABYC
USCG NVIC 07-95 Guidance on Inspection, Repair and Maintenance of Wooden Hulls


What our nonprofit Anchors Aweigh Academy and its EverythingAboutBoats.org website have accomplished so far.

  • Published over 300 website main topic webpages, many with full articles on the topic. See our Website Contents in the Right Sidebar for the listing of the main topic pages.
  • Published over 9,000 marine vendor webpages, all with their contact information, most with a description of their products and services, many with product documentation, specifications and independent reviews. (Includes: Boat designers, boat building tools, material and equipment manufacturers and suppliers, boat builders and dealers, yacht brokers, marine surveyors, boat insurers, boat transporters, skippers and crews, boatyards and marinas, yacht clubs, boat rentals and yacht charters, boating, seamanship and maritime schools, marine law attorneys and expert witnesses, boat refitters and repairers, book authors and publishers, and video producers)
  • Acquired over 120,000 pages of product documentation including Catalogs, Brochures, SpecSheets, Pictures, Serial Number Guides, Installation Manuals, OpManuals, Parts Schematics, Parts Bulletins, Shop Manuals, Wiring Diagrams, Service Bulletins, and Recalls. And have made all viewable to academy members through the EAB website.
  • Acquired over 1,200 books and magazine back issues in our academy library and so far have made over 700 viewable to academy members through the EAB website.
  • Published over 500 DIY How-To articles about boat design, construction, inspection, operation, maintenance, troubleshooting and repair. We are working hard to do more.

We are currently formatting and polishing the Anchors Aweigh Academy online and hands-on courses. The Marine Surveying course has proven to be excellent for both the beginner and the seasoned surveyor, and especially helpful to the Do-It-Yourselfer.


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Comments for Public Viewing

Anyone may submit comments for public viewing via email to:
Comments@EverythingAboutBoats.org
(Put this webpage's title in the subject line)

FROM Donald: "This is an awesome website. I found the information that I needed right away from one of the over 10,000 free articles that you provide as a public service. I'm surprised that so much if this site is free. But I still signed up so I could access the thousands of expanded pages, interesting articles, and dozens of valuable programs! The member's library of books, magazines and videos that I can view online is really terrific! I understand that you and your staff are all unpaid volunteers. Please keep up the good work. And I commend you for your plans to add another 10,000 free informative articles over the next year. I'm thrilled to support you in this endeavor with my small membership donation. Thanks again for all your hard work."

FROM Huey: "I agree with my Uncle, I too have found the articles to be very enlightening. They say that it will take about 50,000 articles to cover the full scope that they have envisioned for the website. They have over 10,000 articles so far and that's doing pretty well, but it could take several years to get the rest. I also noticed that many of the Main Topic Pages and some of the article pages are still in the rough draft stage. I guess that they will fill in as they can get volunteers to work on them. But what I can't figure out is why anyone would spend the time writing informative in depth articles just to give away free to this website for publication? What's in it for them?"

FROM Dewey: "Well Huey, to me It looks like most of the articles on this website are written by very informed people, like boating instructors, boat designers, boat builders, riggers, electricians, fitters, marine repair technicians and marine surveyors. Writing such articles helps establish them as knowledgeable professionals. After all, this website was originally created by a school for marine technicians and marine surveyors. The website is growing in content every day. They even had to move to a bigger, more powerful server on October 15, 2018 because the website's traffic has been growing exponentially."

FROM Louie: "I agree with everyone above. This site is quickly becoming the ultimate reference resource about every aspect of boats and ships for everyone from the beginning recreational boater to the seasoned professional mariner. I use the topic pages on the right sidebar to browse around the website. It's like a Junior Woodchucks' Guidebook for Boaters. Their Members' Library of over 300 popular and obscure books and over 200 magazine back issues that can be viewed online is fabulous. The Academy's magazine is especially informative. On top of that, there is the "Ask-An-Expert program for members where you can get an expert's answer to any of your boat questions. And a whole years membership is only $25. What a deal! I really love being part of this "Everything About Boats" community and help provide thousands of helpful articles free to the public. I think that I'll sit down right now and write an article about my experiences boating with my uncle."

FROM Scrooge: "You rave about this website like it was the best thing since sliced bread. Well, I think it stinks. Sure, it has a lot of good information for boaters, and they're adding more every day, but it will probably never be finished. Furthermore, I don't even own a boat. And I wouldn't have a boat even if someone gave me one. Boats are a waste of money and time and energy and money! They're just a hole in the water you pour money into. If you gave me a boat, I'd sell it quicker then you could say Baggywrinkle. Then I'd lock up the cash with all my other money so I could keep my eye on it and count it every day. Bah humbug."

FROM Daisy: "I'm just so glad that Donald got the boat so we and the boys could enjoy boating — together. And of course all of the girls, April, May, and June, love to be on the water too, especially when that is where the boys are. Oh poor Scrooge, boating is more fun then you could possibly imagine."

FROM Editor: "For those of you that have stayed with us this far, Thanks. You inspire us to keep working on this labor of love. We know that we have a lot more to do. Ultimately, we hope that we can help you enjoy the wonder filled world of boating as much as we do. We are all waiting to see what you have to say about this webpage article. And we assure you, your corrections, updates, additions and suggestions are welcomed. Let's work together on this.

FROM Oliver: This site is a rip off. From ‘Page under Construction” to Don Casey reprints it is hardly comprehensive or authoritative. I want my money back.
Oliver Moore
Retired Publishing Director Yachting; Editor MotorBoating.

FROM Editor: Dear Oliver, From your comments, I have to believe that you don’t really understand what we are trying to do through this website. I invite you to take a closer look at the sign-up page and at some of the over 10,000 free articles that we have published for everyone to view as a public service. This page will be an example of such an article for everyone to freely view when its finished. We are hoping that someone will step up soon and finish it, as we depend on knowledgeable people like you to contribute comprehensive and authoritative articles so that we can fulfill our vision of making boating safer and more fun for everyone. I look forward to your future comments.
P.S. As a non-profit research and educational organization we do not accept advertisements from for-profit businesses. We depend entirely on donations from generous contributers that want to support our goals by covering our overhead. We are thankful to have experienced phenomenal growth as word has spread, mostly by word-of-mouth and Google, and to have still been able to make ends meet has been incredible. Ultimately, we aspire to be the “Wikipedia” for boaters. And don’t say that we can’t do it, because we are doing it!

FROM Frank: I just checked the subscription prices on the MotorBoating website. us$93.99 for one year. us$174.49 for two years. us$86.99 for one year (Rolling). us$73.99 for one year (iPad + iPhone). And the magazine is chuck full of advertisements. They must be really raking in the dough. And he calls this site a rip off?

FROM Dan: The real Oliver S. Moore III has been publisher and editor of boating magazines for years and is too wise and informed to have said what this impostor said. Just shake it off and press on. You have a terrific vision for this website.

FROM Editor: Someone has stepped up and is working to finish this page. It is starting to fill in nicely. Check back and watch their progress. We appreciate them so much. Thank you. Keep up the good work. You can help by commenting and making suggestions on their content, layout, etc. Follow instructions for commenting above or below. Thanks.

FROM Name: Text.


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