Grade R4 Offshore Mooring Chain — Stud Link

Grade R4 Offshore Mooring Chain

The workhorse of deep-water mooring. Higher tensile strength and better fatigue resistance, for long-term offshore deployments on floating production units.

Stud link offshore mooring chain to IACS UR W22, grade R4, in diameters from 50 mm to 90 mm. Quoted on request.

Mechanical properties

Yield stress, minimum	580 N/mm²
Tensile strength, minimum	860 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)	2,160 kN 220 t	2,740 kN 279 t	54.8 kg/m	1,100–1,128 mm
52 mm (2.05 in)	2,327 kN 237 t	2,952 kN 301 t	59.2 kg/m	1,144–1,173 mm
54 mm (2.13 in)	2,499 kN 255 t	3,170 kN 323 t	63.9 kg/m	1,188–1,218 mm
56 mm (2.20 in)	2,677 kN 273 t	3,396 kN 346 t	68.7 kg/m	1,232–1,263 mm
58 mm (2.28 in)	2,860 kN 292 t	3,628 kN 370 t	73.7 kg/m	1,276–1,308 mm
60 mm (2.36 in)	3,048 kN 311 t	3,867 kN 394 t	78.8 kg/m	1,320–1,353 mm
62 mm (2.44 in)	3,242 kN 331 t	4,112 kN 419 t	84.2 kg/m	1,364–1,398 mm
64 mm (2.52 in)	3,440 kN 351 t	4,364 kN 445 t	89.7 kg/m	1,408–1,443 mm
66 mm (2.60 in)	3,643 kN 372 t	4,621 kN 471 t	95.4 kg/m	1,452–1,488 mm
68 mm (2.68 in)	3,851 kN 393 t	4,885 kN 498 t	101.3 kg/m	1,496–1,533 mm
70 mm (2.76 in)	4,064 kN 414 t	5,156 kN 526 t	107.3 kg/m	1,540–1,579 mm
73 mm (2.87 in)	4,392 kN 448 t	5,572 kN 568 t	116.7 kg/m	1,606–1,646 mm
76 mm (2.99 in)	4,731 kN 482 t	6,001 kN 612 t	126.5 kg/m	1,672–1,714 mm
78 mm (3.07 in)	4,962 kN 506 t	6,295 kN 642 t	133.2 kg/m	1,716–1,759 mm
84 mm (3.31 in)	5,682 kN 579 t	7,208 kN 735 t	154.5 kg/m	1,848–1,894 mm
87 mm (3.43 in)	6,056 kN 618 t	7,682 kN 783 t	165.8 kg/m	1,914–1,962 mm
90 mm (3.54 in)	6,439 kN 657 t	8,167 kN 833 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 R4 stud link, with d in millimetres and the result in kN:

Proof load	0.0216 × d² × (44 − 0.08d)
Break load	0.0274 × 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.