Chain – Grades, Markings and Inspection

A chain does not weaken with a warning. It looks the same the day before it fails as it did the day it was made – unless someone actually inspects it.

Introduction

Chain is everywhere on deck. It secures the ship to the seabed. It lashes containers in the hold. It connects the hook to the load. It tensions cargo against the forces of the sea. And yet the working knowledge of chain among the average deck department rarely extends beyond ‘it’s there and it looks alright.’

The grading system exists because chain is manufactured to wildly different specifications depending on its intended use. Mixing up those grades – or failing to check – has put people in body bags. Grade markings, certificates, and traceability are not bureaucratic exercises. They are the only reliable way to know whether the chain in hand is fit for the job about to be asked of it.

Inspection of chain is the other half of the problem. A walk past a cable range or a glance at a lashing does not constitute inspection. It constitutes self-deception. Real inspection is slow, dirty, and methodical. It finds the things that kill.

Contents

• 1. Chain in Deck Service – Where It Lives and What It Does
• 2. The Grading System – Why Numbers Matter More Than Appearance
• 3. Grade 30 – The One That Must Never Lift
• 4. Link Markings and Certificate Traceability
• 5. Anchor Chain – Studded Links, Joining Shackles and Shot Markings
• 6. Inspection Criteria – What to Look For and Where
• 7. Anchor Cable Inspection – Not a Walk-Past
• 8. Closing Reality

1. Chain in Deck Service – Where It Lives and What It Does

On any ocean-going vessel, chain serves four broadly distinct functions, each with its own demands on material properties, certification requirements, and inspection regimes.

Anchor chain (cable). Studded link chain, typically Grade 2 or Grade 3 under IACS classification (U2/U3), sized and certificated to class requirements. Its job is to connect the anchor to the ship and, critically, to provide catenary – the weight of chain on the seabed that generates holding power. It lives in the chain locker, passes over the windlass gypsy, and spends most of its life in a dark, wet, unventilated space where corrosion works undisturbed.

Cargo lashing chain. Typically Grade 80, sometimes Grade 70, used in container lashing systems and in securing break-bulk or project cargo. Specified in the Cargo Securing Manual. Subject to the MSC.1/Circ.1353 regime and flag state requirements on regular inspection and proof-load testing.

Lifting chain (slings and assemblies). Grade 80 or Grade 100 as standard for modern lifting chain slings. Must comply with EN 818 series or equivalent. Certificated, marked, and subject to periodic thorough examination under national regulations (LOLER in the UK, or flag state equivalent).

General-purpose chain. Used for lashing stores, securing gangways, rigging safety barriers. Often of indeterminate origin, unknown grade, and dubious provenance. This is where problems quietly accumulate. A length of chain found in the bosun’s store and pressed into service as a makeshift sling has no certificate, no grade confirmation, and no business being anywhere near a suspended load.

If the grade is unknown, the chain is unfit for any critical purpose. Full stop.

2. The Grading System – Why Numbers Matter More Than Appearance

Chain grading defines the guaranteed minimum mechanical properties of the steel – principally its ultimate tensile strength and, by extension, its working load limit (WLL) for a given size. A 10 mm Grade 80 chain and a 10 mm Grade 30 chain look virtually identical to the naked eye. They are not remotely the same component.

The main grades encountered in maritime and industrial service:

Grade 30 (Proof Coil). Low-carbon steel. WLL roughly 25–30% of a Grade 80 chain of the same size. Intended for non-load-bearing applications: barriers, tow-chain guards, tie-downs where forces are low and predictable. Commonly found in hardware shops and general stores.

Grade 43 (High Test). Medium-carbon steel. Better strength-to-weight than Grade 30. Used in anchor chain for small craft and in some towing applications. Not rated for overhead lifting.

Grade 70 (Transport Chain). Heat-treated carbon steel. The standard for cargo lashing, load binders, and transport tie-down in road and maritime applications. Marked with the numeral 7 or 70 on the link. Not rated for overhead lifting under most standards, though it appears in older cargo securing inventories.

Grade 80. Alloy steel, quenched and tempered. The baseline standard for modern lifting chain slings and for high-specification cargo lashing. Marked with the numeral 8 or 80. Higher fatigue resistance than Grade 70. Rated for overhead lifting when properly certificated.

Grade 100. Higher-alloy steel. Approximately 25% stronger than Grade 80 at the same diameter, allowing lighter slings for the same WLL. Increasingly common in shore-side lifting but less frequently seen aboard ship.

Grade 120. The highest commercially available grade. Niche applications in high-performance lifting where weight savings are critical. Rarely encountered on deck.

The numbers are not arbitrary marketing tiers. They correspond to specific minimum breaking forces per unit of cross-section. A Grade 80 chain has a minimum breaking force roughly 2.5 to 3 times that of a Grade 30 chain of identical diameter. Visually, they are brothers. Structurally, one is a working component and the other is decoration.

3. Grade 30 – The One That Must Never Lift

This point deserves its own section because the error persists.

Grade 30 chain is cheap, widely available, and looks exactly like proper lifting chain if the markings have worn off or were never checked. It has no place in any lifting operation, any cargo-securing application where significant dynamic forces are expected, or any situation where a failure under load could cause injury.

Its elongation characteristics are wrong. Its fatigue life under cyclic loading is poor. Its response to shock loading is unpredictable. It does not have the alloy content or heat treatment to absorb energy before fracture.

A length of Grade 30 in a lifting sling is not an undersized component. It is a death trap with a hook on it.

The problem is compounded by the fact that unmarked or poorly marked chain defaults, in practice, to ‘whatever the last person assumed it was.’ On a vessel where stores arrive from multiple suppliers across multiple ports, the chain in the bosun’s store may include Grade 30 mixed in with Grade 80. Without checking every link for markings, there is no way to tell.

Any chain of unknown grade found aboard should be marked as such, segregated, and excluded from lifting or critical lashing duty. If it cannot be positively identified, it goes over the side of the classification. Not into the sling locker.

4. Link Markings and Certificate Traceability

Properly manufactured chain carries markings on the link body – typically raised or stamped characters identifying the manufacturer, the grade, and often the nominal size. For Grade 80, look for the numeral 8 or 80. For Grade 70, the numeral 7 or 70. Manufacturer codes vary but are registered and traceable.

These markings appear at regular intervals along the chain – typically every 20 or 25 links, though this varies by manufacturer and standard. On a long length of chain, there should be multiple marked links visible. If there are none, the provenance of that chain is already in question.

Certificates tie a specific batch or length of chain to its test results: proof load, breaking load, material composition, heat treatment batch. For lifting chain, the certificate must accompany the chain through its working life and be available for inspection. For cargo lashing chain, the Cargo Securing Manual should reference the equipment specifications, and individual items should be traceable to their test certificates.

Anchor cable is certificated by the classification society at manufacture and at periodic survey. Each length (shot) carries a certificate tying it to its proof-load test. When shots are replaced, renewed certificates must follow.

A certificate in the office means nothing if the chain on deck has no markings to connect it to that certificate.

The traceability chain – from marked link to test certificate to equipment register – is the only thing that separates a rated, verified component from a random length of steel. When that traceability is broken, the chain reverts to unknown grade, and unknown grade is unfit for purpose.

5. Anchor Chain – Studded Links, Joining Shackles and Shot Markings

Anchor cable is a world of its own. The studded link design – a crossbar welded or cast within each link – serves two purposes: it prevents the chain from kinking under its own weight in the locker, and it increases the chain’s resistance to deformation under load by bracing the link internally. A studded link that has lost its stud is a compromised link. The stud is structural, not cosmetic.

Standard cable is manufactured in shots – typically 27.5 metres (15 fathoms) per shot, though this varies by flag state tradition and class requirement. Shots are connected by joining shackles (sometimes called Kenter shackles), which are larger than the individual links, have a distinctive shape, and are designed to pass over the windlass gypsy. The joining shackle is a known weak point – not because it is poorly made, but because it is the point of connection between two separately manufactured lengths, the point where wear concentrates during windlass operation, and the point most exposed to bending stress.

Shot markings follow a standard scheme to allow the bridge and fo’c’sle to identify how much cable is deployed. The convention uses a combination of turns of wire, painted links, and shackle markings to indicate the shot number. One shot out: one turn of wire on the first stud from the joining shackle, the link painted white. Two shots: two turns of wire on the second stud, link painted white. And so on, with colours alternating (white, red, white, red – or similar, depending on the operator’s standing orders). At the halfway point and near the bitter end, additional distinctive markings warn of the approaching limit.

The bridge relies on these markings for anchoring decisions. If the paint has washed off, the wire has corroded away, and the joining shackles have been ground smooth by the gypsy, the mate is guessing how much cable is out. That is not anchoring. That is hope.

Shot markings must be renewed as part of every cable inspection. If they cannot be read from the fo’c’sle in operational conditions, they do not exist.

6. Inspection Criteria – What to Look For and Where

Chain inspection – whether for lifting slings, lashing components, or anchor cable – follows the same fundamental logic: examine each link for evidence that its load-bearing cross-section has been reduced, its geometry has been altered, or its material integrity has been compromised. The specifics:

Wear at link ends. The contact point between adjacent links is where metal grinds against metal under every load cycle. This produces a flattened or grooved surface at the crown (the bearing surface at each end of the link). Wear here directly reduces the cross-sectional area at the most highly stressed point. Measurement with calipers against the nominal diameter is the only reliable assessment. A 10% reduction in diameter at the crown is the typical condemning limit for lifting chain; anchor cable limits are set by class rules and are usually tighter.

Stretch (elongation). Chain under repeated heavy loading will elongate. Measure the internal length of individual links and compare against nominal. An elongation of 5% over the original manufactured dimension is a common condemning criterion. Stretched chain has been plastically deformed – the steel has yielded and will not return to its original dimension. Its residual strength is unknown.

Distortion. Twisted, bent or deformed links indicate overloading or shock loading. A bent link concentrates stress at the deformation point and no longer distributes load symmetrically. It is condemned, not straightened. Straightening a deformed link changes its metallurgy at the bend point and introduces residual stresses that cannot be inspected visually.

A straightened link is weaker than the bent one it replaced. There is no such thing as field repair of a deformed chain link.

Cracking. Cracks in chain links are rare in properly heat-treated material but devastating when present. They occur at the weld (flash-butt weld on link closure), at stress concentration points where corrosion pitting has initiated a fatigue crack, or at the stud weld in anchor cable. Detection requires close visual inspection in good light and, for critical applications, MPI or dye penetrant testing. A crack of any size in a chain link is an absolute rejection criterion.

Corrosion and pitting. General surface corrosion reduces cross-section uniformly and is assessed by diameter measurement. Pitting corrosion is more insidious – it creates localised stress concentrations that act as crack initiators under cyclic loading. Deep pits on the inner bearing surfaces of links are particularly dangerous because they are hidden during casual inspection and sit at the point of maximum contact stress. Anchor cable that has spent years in a poorly ventilated chain locker with standing water will show pitting that a fresh coat of paint does an excellent job of hiding.

Stud condition (anchor cable). Every stud must be checked for looseness, weld cracking, and displacement. A loose stud rattling inside the link has already failed in its structural role. A missing stud leaves the link prone to collapse under compressive loading on the gypsy.

7. Anchor Cable Inspection – Not a Walk-Past

There is a version of anchor chain inspection that satisfies nobody except the person who wants to tick a box. It involves walking the length of the cable on deck while it is ranged, noting the overall condition as ‘satisfactory,’ and retreating to the office to complete the paperwork. This is not inspection. It is theatre.

Proper anchor cable inspection means ranging the full length on deck or on the wharf, cleaning it sufficiently to see the steel surface, and examining it link by link. Not every link will get calipers on it – that is a class survey requirement at defined intervals – but every link must be looked at closely enough to identify cracks, weld defects, missing or loose studs, and advanced pitting.

Joining shackles receive particular attention. The taper pin, lead pellet, and securing arrangement must be intact. A joining shackle that has worked loose or lost its locking arrangement will come apart at exactly the moment it is loaded hardest – when the cable is running and the brake is applied.

The bitter end securing must be inspected and, critically, must be designed to fail before the chain locker structure does. The bitter end is not there to hold the ship. It is there to provide a last warning that all cable has been deployed. If it is so heavily built that it will tear out the chain locker bulkhead before it parts, the design intent has been defeated.

The windlass and gypsy are part of the inspection. Worn gypsy pockets that no longer grip the link properly will chew the chain. A slipping gypsy puts dynamic shock loads through individual links that far exceed steady-state design loads.

Inspection frequency depends on operational profile. A vessel anchoring regularly in deep water, coral bottoms, or high-current anchorages will degrade its cable faster than one that anchors twice a year in sheltered mud. The class five-yearly survey is a minimum, not a ceiling. Good operators range and inspect annually, and after any heavy anchoring evolution.

The cable that parted at anchor was last inspected on paper. On paper, it was fine.

8. Closing Reality

Chain does not stretch a warning before it fails. It does not creak, groan, or telegraph its distress the way a wire rope might strand by strand. It holds, and then it does not hold. The energy release is instantaneous and total.

The grading system, the marking regime, the certification trail, and the inspection criteria exist to intercept that failure before it happens. None of them work passively. A Grade 30 chain with no markings left will not announce its inadequacy. A corroded anchor link with 15% section loss will not feel different passing through the spurling pipe. A joining shackle with a missing taper pin will hold until it does not.

Every chain on deck exists in one of two states: verified, or unknown. There is no middle ground. The verified chain has markings that match a certificate, an inspection history that records its condition against condemning criteria, and a clear allocation to a duty within its rated capacity. Everything else is unknown, and unknown chain is not a resource. It is a liability.

Inspection is the price of confidence. It is slow, it is dirty, and it is boring – until the day it finds the crack, the stretch, the pitting that would have killed someone next week. That is the day it earns everything it ever cost.