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How to choose ship anchor chain to meet your needs
How to choose ship anchor chain to meet your needs
Grade:
The Grade denotes strength rather than any physical measurements of a link. The higher the grade letter M (20Mn2) versus L (Q235) and G4 (20Mn2) versus G3 (Q235) the stronger the chains. Note: alphabetical delineation of chain is the more contemporary method of classification.
Tensile Force or Breaking Load (BL):
This is the load at which the chain will fail. This is measured by representative testing. It is quite possible the chain will exceed the number of Kilonewtons (kN) stated.Material: HDG or AISI 316?
This refers to whether the chain is hot dipped galvanized (HDG) or made from marine grade stainless steel (AISI 316). HDG is the most common form of chain for anchoring using a gypsy or windlass. Stainless steel is prohibitively expensive yet looks beautiful when matched with a stainless anchor. The downside of stainless chain is it becomes brittle over time, when immersed in salt water. It is essential to periodically wash your chain locker and chain in fresh water. The more frequent the better.Load:
This is the load that the manufacturer recommends you never exceed. This is to allow for wear and tear over the years you'll be using it. WLL is usually 20 to 25% of the chains maximum tensile force or Breaking Load (BL). WLL is measured in Kilograms force (kgf).Yield Strength (BL):
This is the stress at which a material begins to deform plastically. It is quite possible the chain will exceed the number of Kilonewtons (kN) stated.Steel Grade:
Short link galvanized chain is usually available in standard grade steel (Q235) or high quality (20Mn2). 20Mn2 is by far superior.
Q235 is low tensile chain. 20Mn2 is medium/high tensile chain.
Q235 has a tensile force (see definition below) of 0.370kN whilst 20Mn2 steel has a tensile force of 0.785kN.
Q235 has a yield strength (see definition below) of 0.235kN whilst 20Mn2 steel has a yield strength of 0.590kN.
Chain Welding:
Short link chain welding can either be semi automatic or automatic. Automatic welding is far smoother and consistent without weld deformation or bumps.
Galvanizing (non-stainless chain):
Galvanizing protects the base metal by becoming a sacrificial anode. This means that the zinc will actually “sacrifice” itself to oxidation before the base metal is attacked by oxidation. Hot dip galvanized chain follows the process whereby the bare steel chain is washed in a bath of an acid and caustic solution. The cleaned chain is then dipped into a bath of hot zinc. The steel and zinc react together at 450 Celcius to form a protective anti-corrosive layer. The chain is then centrifuged to give an even coating.
Zinc Coating Thickness:
Coating thickness – Corrosion protection offered by hot dip galvanizing is linear, meaning that if a 1 mil coating thickness lasted 1 year, then 3 mils (100 u) will last 3 years under the same conditions.
In Australia the acceptable galvanising thickness is:
- 75 microns (u) or 3 mils for marine grade anchor chain (periodic use)
- > or = 100 microns (u) or 4 mils for marine grade mooring chain
1 mils (thousandths of inch) = 25.4 u (microns)
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