Is Chinese chain safe for anchoring your yacht?

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Yachting Monthly’s expert metallurgist Vyv Cox tests various
samples of 8mm anchor chain – grade 30 and 40 – from Europe and the Far East

Composition of carbon steels for chain
manufacture

 

The
strength of the finished chain is determined by the composition and treatment
of the steel used for its manufacture. Marine chain with the lowest strength is
Grade 30, made from low carbon steel such as DIN 10301 (EU) SAE 1008 (US). For
Grade 40 the carbon and manganese contents are increased, giving about a 25% increase
in strength, but without heat treatment. This steel is typically DIN 1.1133
(EU) SAE 1022 (US). These grades may be galvanized without concerns over
strength reduction.

 

Grade
70 chain is manufactured from the same steel as Grade 40 but it is heat treated
to increase strength by a further 20%. There is a risk that re-galvanising this
grade could induce hydrogen embrittlement, which would weaken it. Any owner
contemplating re-galvanising this grade is advised to seek expert advice before
going ahead.

 

The
major benefit in going to higher grades is that the weight of chain being
carried can be reduced for no reduction in strength.

 

Properties of chain steels

 

 

Grade
30

 

 

Grade
40/43

 

 

Grade
70

 

Composition

 

 

 

 

 

 

 
Iron

 

 

Balance

 

 

Balance

 

 

Balance

 

Carbon

 

 

0.08

 

 

0.17
– 0.23

 

 

0.17
– 0.23

 
Manganese

 

 

0.6
max

 

 

0.7
– 1.4

 

 

0.7
– 1.4

 
Phosphorus

 

 

0.035
max

 

 

0.05
max

 

 

0.05
max

 
Copper

 

 

0.2
min

 

 

 

 

 
Sulphur

 

 

0.04

 

 

0.05
max

 

 

0.05
max

 

Quench/temper

 

 

 

 

 

 

875/600
C

 

Tensile
strength

 

 

302 – 357 Mpa

 

(19.5 – 23.1 ton/in2)

 

 

550
Mpa

 

(35.6
ton/in2)

 

 

550
– 700 Mpa

 

(35.6
– 45.3 ton/in2)

 

Chain dimensions and calibration

 

Chain
dimensions, and therefore the gypsies that will accept them, vary considerably
according to whether they are made to imperial or metric standards and even
between manufacturers. European made chain is to DIN766 and/or ISO4565 and most
European gypsies will accept it. There is a strange anomaly that has caught out
many owners. The dimensions of the two standards are identical for all chain
sizes except 10 mm, in which the link length is 2 mm different. The gypsy should be
marked in some way to identify to which standard it conforms.

 

Suppliers
normally proof test chain to between 40% and 50% of the rated MBL, whereas the
quoted Safe Working Load (SWL) is only 25% of the MBL.

 

Note
that many other standards exist for short link non-marine chain, for example
EN818-3, whose dimensions are different. Chain to this standard will not fit
any gypsies.

 

American
chain is made mainly to ISO G30 and G43 standards but these have longer links
that will not fit European gypsies. Note that the dimensions of these two
grades are not the same. G43 (Grade 40) is more widely used for anchor rodes in
USA.

European
dimensions (all millimetres except where shown))

 

Grade 30

 

Wire
size

 

 

A

 

 

B

 

 

C

 

 

SWL,
kN (tons)

 

 

MBL,
kN

 

(tons)

 

 

 

6

 

 

6

 

 

18.5

 

 

8

 

 

4
(0.4)

 

 

16
(1.6)

 

 

DIN
677 and ISO4565

 

7

 

 

 

 

 

 

 

 

 

 

24.4
(2.44)

 

 

DIN
677 and ISO4565

 

8

 

 

8

 

 

24

 

 

12

 

 

7.5
(0.75)

 

 

30
(3.0)

 

 

DIN
677 and ISO4565

 

10

 

 

10

 

 

28

 

 

14

 

 

12.5
(1.25)

 

 

50
(5.0)

 

 

DIN
677

 

10

 

 

10

 

 

30

 

 

14

 

 

12.5
(1.25)

 

 

50
(5.0)

 

 

ISO4565

 

12

 

 

12

 

 

36

 

 

18

 

 

17.5
(1.75)

 

 

70
(7.0)

 

 

DIN
677 and ISO4565

 

Grade 40

 

Wire
size

 

 

A

 

 

B

 

 

C

 

 

SWL,
kN (tons)

 

 

MBL,
kN (tons)

 

 

 

6

 

 

6

 

 

18.5

 

 

9

 

 

6.75
(.675)

 

 

27
(2.7)

 

 

DIN
677 and ISO4565

 

7

 

 

 

 

 

 

 

 

7.75
(.775)

 

 

31
(3.1)

 

 

DIN
677 and ISO4565

 

8

 

 

8

 

 

24

 

 

10.5

 

 

10
(1.0)

 

 

40
(4.0)

 

 

DIN
677 and ISO4565

 

10

 

 

10

 

 

28

 

 

14

 

 

12.5
(1.25)

 

 

50
(5.0)

 

 

DIN
677

 

10

 

 

10

 

 

30

 

 

12

 

 

15.5
(1.55)

 

 

62
(6.2)

 

 

ISO4565

 

12

 

 

12

 

 

36

 

 

15

 

 

22.5
(2.25)

 

 

90
(9.0)

 

 

DIN
677 and ISO4565

 

Grade 70

 

Wire
size

 

 

A

 

 

B

 

 

C

 

 

SWL,
kN (tons)

 

 

MBL,
kN (tons)

 

 

 

8

 

 

8

 

 

24

 

 

 

 

14
(1.4)

 

 

70
(7.0)

 

 

DIN
677 and ISO4565

 

10

 

 

10

 

 

28

 

 

 

 

22
(2.2)

 

 

110
(11.0)

 

 

DIN677

 

10

 

 

10

 

 

30

 

 

 

 

22
(2.2)

 

 

110
(11.0)

 

 

ISO4565

 

12

 

 

12

 

 

36

 

 

 

 

31.6
(3.16)

 

 

158
(15.8)

 

 

DIN
677 and ISO4565

 

What do the abbreviations
mean?

 

SWL
is the Safe Working Load. This value is a quarter of the MBL = Minimum Breaking
Load as specified for the chain, giving a factor of safety of 4.

 

UTS
= Ultimate Tensile strength of the chain, the figure measured in our tests.
This should always exceed the MBL.

 

How is chain made?

 

The
process commences with a coil of wire of the appropriate diameter. The first
step is to straighten the wire, performed by pushing it through a series of
straighteners, rather like sheaves, in a machine known as a ‘former’. Precise
lengths that will form one link of the chain are sheared. Each link is formed
to shape in a die and then rotated so that the next length can be inserted
through it. This is formed to shape in the same way and then rotated back for
the next link to be formed.

 

The
un-welded chain passes through the welder, where the gap in each link is
pressed closed and is simultaneously subjected to a high current that welds the
ends together. A trimmer shaves excess metal from each link while it is still
hot.

 

The
finished chain passes through a calibrator, where lengths of 20 – 30 links are
pulled to a fixed length, which both calibrates and proof tests it.