ORQ and Oversize Mooring Chain
Our listed mooring chain runs to 90 mm, which is where the rest of our range tops out so every chain size has a joining shackle to pair with it. Plenty of enquiries fall outside that — and they are the ones worth talking about rather than looking up.
ORQ — "Oil Rig Quality"
ORQ is the older name for offshore mooring chain, from before IACS formalised the R grades in UR W22. It has not been a current designation for a long time, but it has never gone away: it is still written on rig inventories, on old certificates, on drawings that have been reissued a dozen times, and in purchase specifications that were copied from the last job.
In the modern range ORQ sits at the bottom, broadly where R3 is now. If your paperwork says ORQ, that is usually what you are being asked to match.
We can quote it. Send us the specification, the certificate or a photograph of the drawing and we will tell you what the modern equivalent is before you commit to anything.
Larger than 90 mm
Offshore mooring chain is made far larger than our listed range. W22's own dimensional tolerances run to 222 mm, and the load formulas hold the whole way, so a diameter not on our list is a quoting question rather than a technical one.
Because the loads are calculated rather than looked up, we can give you exact proof and break figures for any diameter, in any grade, before the enquiry goes anywhere. Proof and break in kN, with d in millimetres:
| Grade | Proof load | Break load |
|---|---|---|
| R3 | 0.0148 × d² × (44 − 0.08d) | 0.0223 × d² × (44 − 0.08d) |
| R3S | 0.0180 × d² × (44 − 0.08d) | 0.0249 × d² × (44 − 0.08d) |
| R4 | 0.0216 × d² × (44 − 0.08d) | 0.0274 × d² × (44 − 0.08d) |
| R4S | 0.0240 × d² × (44 − 0.08d) | 0.0304 × d² × (44 − 0.08d) |
| R5 | 0.0251 × d² × (44 − 0.08d) | 0.0320 × d² × (44 − 0.08d) |
Stud link. Weight 0.0219 × d² kg/m. Five link pitch 22d to 22.55d. Studless share the break formulas; proof loads are lower above R3.
Is R5 the top?
In IACS UR W22 Rev.6, which is the revision we work from, yes — §1.2.1 names five grades and stops at R5. Above R4 the specifications are already partly proprietary: W22 §1.2.2 allows manufacturers' own specifications for R4S and R5 subject to design conditions and class acceptance.
R6 exists commercially, developed for deep-water and floating wind, and appears in newer standards work outside the W22 revision we hold. It is not something to assume on a drawing — if a specification calls for R6, tell us and we will confirm what a mill can actually certify against before quoting.
Custom and one-off
Things we would rather quote than list:
- Non-standard diameters, in any grade.
- Studless chain, which is normally made per design for a permanent mooring with a predetermined life.
- Matched accessories — connecting links, enlarged links, end links, end shackles, swivels, subsea connectors and Kenter shackles, made to the same R grade from a class-approved forge.
- Replacement lengths for an existing mooring, where the new chain has to match what is already in the water.
- Chafe chain for single point mooring arrangements.
One caution worth repeating
Mooring chain grades and anchor chain grades do not overlap. Anchor chain cable is Grade 1, 2 or 3; offshore mooring chain is R3 to R5. W22 §1.2.3 says 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 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. If you are replacing a connector in a mooring, check which it is before ordering — see anchor chain if that is actually what you need.
Tell us what you have
There is no price list for this and there is no useful one to write — it moves with the steel market, the grade, the mill's schedule and the freight. What makes a quote fast and right is detail. Send us whatever you have:
- Grade and diameter, or the old specification if that is all you have.
- Length, and whether it is a full mooring or a replacement length.
- Stud link or studless.
- Which Classification Society certificate you need.
- Destination port, and when you need it.
- Photographs of the existing chain, the certificate or the drawing — genuinely useful, especially on an old ORQ specification.
Contact us — telephone 514-694-9830 or sales@dibbleeindustries.com. We are in Montreal, Canada and we ship worldwide.