Grade R4S Offshore Mooring Chain — Stud Link

Grade R4S Offshore Mooring Chain

Above R4 for heavier design loads. Manufacturers’ proprietary specifications for R4S may vary subject to design conditions and class acceptance (W22 §1.2.2).

Stud link offshore mooring chain to IACS UR W22, grade R4S, in diameters from 50 mm to 90 mm. Quoted on request.

Mechanical properties

Yield stress, minimum	700 N/mm²
Tensile strength, minimum	960 N/mm²
Elongation, minimum	12%
Reduction of area, minimum	50%

Loads, weight and pitch

Diameter	Proof load	Break load	Weight	5-link pitch
50 mm (1.97 in)	2,400 kN 245 t	3,040 kN 310 t	54.8 kg/m	1,100–1,128 mm
52 mm (2.05 in)	2,585 kN 264 t	3,275 kN 334 t	59.2 kg/m	1,144–1,173 mm
54 mm (2.13 in)	2,777 kN 283 t	3,517 kN 359 t	63.9 kg/m	1,188–1,218 mm
56 mm (2.20 in)	2,974 kN 303 t	3,768 kN 384 t	68.7 kg/m	1,232–1,263 mm
58 mm (2.28 in)	3,178 kN 324 t	4,025 kN 411 t	73.7 kg/m	1,276–1,308 mm
60 mm (2.36 in)	3,387 kN 345 t	4,290 kN 438 t	78.8 kg/m	1,320–1,353 mm
62 mm (2.44 in)	3,602 kN 367 t	4,562 kN 465 t	84.2 kg/m	1,364–1,398 mm
64 mm (2.52 in)	3,822 kN 390 t	4,841 kN 494 t	89.7 kg/m	1,408–1,443 mm
66 mm (2.60 in)	4,048 kN 413 t	5,127 kN 523 t	95.4 kg/m	1,452–1,488 mm
68 mm (2.68 in)	4,279 kN 436 t	5,420 kN 553 t	101.3 kg/m	1,496–1,533 mm
70 mm (2.76 in)	4,516 kN 461 t	5,720 kN 583 t	107.3 kg/m	1,540–1,579 mm
73 mm (2.87 in)	4,881 kN 498 t	6,182 kN 630 t	116.7 kg/m	1,606–1,646 mm
76 mm (2.99 in)	5,257 kN 536 t	6,658 kN 679 t	126.5 kg/m	1,672–1,714 mm
78 mm (3.07 in)	5,514 kN 562 t	6,984 kN 712 t	133.2 kg/m	1,716–1,759 mm
84 mm (3.31 in)	6,313 kN 644 t	7,997 kN 815 t	154.5 kg/m	1,848–1,894 mm
87 mm (3.43 in)	6,729 kN 686 t	8,523 kN 869 t	165.8 kg/m	1,914–1,962 mm
90 mm (3.54 in)	7,154 kN 730 t	9,062 kN 924 t	177.4 kg/m	1,980–2,030 mm

Proof and break loads calculated from the IACS UR W22 formulas. Tonnes are metric tonnes-force, given for comparison — the specification works in kN.

Any diameter, not just the ones listed

W22 does not publish a load table — it publishes formulas, so the figures above are calculated rather than looked up and we can quote a diameter that is not on the list. For R4S stud link, with d in millimetres and the result in kN:

Proof load	0.024 × d² × (44 − 0.08d)
Break load	0.0304 × d² × (44 − 0.08d)
Weight, stud link	0.0219 × d² kg/m
Five link pitch	22d minimum, 22.55d maximum

Studless chain is available in every grade. Its break loads are identical to stud link; the proof loads are lower above R3, and weight is calculated per design and submitted to class. Studless is normally deployed once, for permanent moorings with a predetermined design life (W22 §1.1.3).

Accessories — do not substitute anchor chain parts

W22 covers the mooring accessories as well as the chain: common stud and studless links, connecting common links, enlarged links, end links, detachable connecting links, end shackles, subsea connectors, swivels and swivel shackles. Kenter shackles are covered too, with their own machining requirement — the fillet radius must be at least 3 percent of nominal diameter (§3.1.3).

They are made to the R grade, and they are not interchangeable with anchor chain accessories. W22 §1.2.3 is explicit that each grade is approved individually and that approval for a higher grade does not constitute approval of a lower one, and §1.6.1 requires the forge or foundry supplying accessories to be separately approved by the Classification Society. A Grade 3 Kenter made for anchor chain is not an R4 mooring Kenter, whatever the diameter says.

Looking for ship's anchor chain rather than offshore mooring? That is Grade 1/2/3 to IACS UR A1 — see stud link anchor chain and the Kenter joining shackles that go with it.

ORQ — the name this used to have

ORQ, "Oil Rig Quality", is the older name for offshore mooring chain, from before IACS formalised the R grades. It still turns up constantly in enquiries, drawings and rig inventories, and it sits at the bottom of the modern range — broadly where R3 is now.

If your specification, your rig drawing or your old certificate says ORQ, we can quote it. See ORQ and oversize mooring chain.

Larger than 90 mm

The sizes listed match the diameters we carry across the rest of the range, so every chain size has a Kenter joining shackle to pair with it. Above 90 mm the chain is made to order — W22's own tolerance bands run to 222 mm and the formulas above hold the whole way, so we can quote any diameter exactly. Tell us what you need.

Certification

Supplied with Classification Society certification. Chain is manufactured in continuous lengths by flash butt welding and heat treated in a continuous furnace — batch heat treatment is not permitted (§3.2.1.1). Link shape and proportion conform to ISO 1704 or a specially approved design.

Tell us the grade, the diameter, the length and the society, and we will quote it delivered.