Fiberglass Cable Tray vs Steel: Which Is Better for Offshore Platforms?

A fiberglass cable tray is a pultruded glass-reinforced polymer (GRP/FRP) cable support system, and on offshore platforms it is specified instead of galvanized or stainless steel when chloride corrosion, topside weight and maintenance access decide the material call.

For most open-deck, riser and module cable routes, the honest answer is fiberglass. GRP trays do not rust, weigh roughly a quarter of an equivalent steel tray, and hold their mechanical properties for 20–25 years in a marine atmosphere. Steel keeps the job in high-temperature process areas, jet-fire-rated zones, and anywhere heavy short-span loading or immediate local repair outweighs corrosion risk.

The short version:

• Weather deck, riser and module routes → fiberglass.
• Fire-rated escape routes, hot process areas (>120 °C), jet-fire zones → steel, or a GRP system with tested fire-rated enclosure.
• Mixed environment on one platform → hybrid route plan, material selected zone by zone.

Key Takeaways

• Fiberglass is the default material for ISO 12944 C5-M marine atmospheres; steel needs galvanizing plus recurring recoating, or a higher alloy grade.
• Pultruded GRP runs near 1,800 kg/m³ against roughly 7,850 kg/m³ for carbon steel — a three-to-four-fold weight saving per metre of route.
• Steel stays non-combustible above 400 °C; standard fire-retardant GRP handles continuous service around 120 °C.
• Over a 20-year field life, lifecycle cost usually flips the decision that purchase price alone would not.
• Every choice still has to be checked against the IEC 61537 load class and the platform's earthing design.

Why Offshore Decks Punish Steel Cable Trays

A platform is a corrosion test rig with people living on it. Salt-laden air, 80–100% relative humidity, deluge washdown, sour gas traces and UV radiation attack metal supports from every direction at once.

• Atmosphere: ISO 12944-2 puts offshore and coastal installations in category C5-M, "very high corrosivity, marine."
• Salt spray: Hot-dip galvanized steel at 85 µm typically shows first red rust between 720 and 1,000 hours in an ASTM B117 neutral salt spray test.
• Stainless is not a free pass: 316L resists pitting in chlorides up to a point, but crevice corrosion accelerates above roughly 60 °C in concentrated brine.
• Access: Every maintenance hour offshore is expensive. A tray that needs recoating every few years is a schedule problem, not just a materials problem.
• Weight: Structural steel topside costs real money per kilogram. Cutting support steel also cuts deck load and, on floating units, ballast demand.

Fiberglass vs Steel Cable Tray: Side-by-Side Comparison

Factor	Pultruded GRP/FRP	Hot-dip galvanized steel	Stainless steel 316L
Density	~1,800 kg/m³	~7,850 kg/m³	~8,000 kg/m³
Tray mass per metre (300 mm ladder)	roughly 1.5–3 kg/m	roughly 4–7 kg/m	roughly 4–7 kg/m
Corrosion in C5-M	Not attacked by chloride	5–10 years to first red rust at 85 µm zinc	Pitting and crevice risk in warm brine
Expected service life offshore	20–25 years	7–12 years with recoating	15–25 years, grade dependent
Fire behaviour	ASTM E84 Class A; LOI ≥ 28% (ASTM D2863)	Non-combustible	Non-combustible
Max continuous temperature	~120 °C (vinyl ester resin)	400 °C+	500 °C+
Electrical continuity	Requires separate bonding conductor	Inherent	Inherent
Purchase price	~1.5–2.5× galvanized	Baseline	~3–5× galvanized
Maintenance routine	Washdown and visual inspection	Recoat every 3–5 years	Passivation and inspection

The table makes the trade-off visible: you pay more per metre and accept a lower temperature ceiling, and in return you delete the corrosion maintenance cycle.

Corrosion Performance: Where Steel Loses Ground

ISO 12944-5 treats an 85 µm zinc coating as a medium-durability system, which means first maintenance in roughly five to seven years in C5-M conditions. A duplex system — galvanizing plus a suitable topcoat selected under a standard such as NORSOK M-501 — stretches that to 20 years, but it is a coating system with an inspection regime attached, not a material property.

GRP works differently. The resin matrix is chemically inert to chlorides, so there is no sacrificial layer to consume. Two details matter in practice:

• Resin choice: Isophthalic polyester covers general marine exposure. Vinyl ester is the specification where acid splash, solvent or produced-water contact is possible.
• Surface protection: A synthetic surface veil or polyester surfacing mat keeps glass fibres away from the surface, which blocks wicking and UV degradation.

For verification, buyers should ask for mechanical and hardness testing rather than a datasheet claim: tensile strength to ASTM D638 (typical pultruded GRP values fall in the 200–400 MPa range along the fibre axis), flexural properties to ASTM D790, and Barcol hardness to ASTM D2583 as a cure check on delivered panels.

Weight and Structural Load on Topside Structures

Cutting mass is not a side benefit offshore — it propagates. Lighter trays mean wider support spacing, fewer brackets welded to primary steel, less hot work, and lower deck loading.

• A pultruded GRP profile has a density near 1,800 kg/m³ versus 7,850 kg/m³ for carbon steel, so a GRP tray typically weighs 25–35% of its steel equivalent.
• The trade-off sits in stiffness, not strength. Pultruded GRP shows a flexural modulus in the 15–20 GPa range against about 200 GPa for steel, so deflection usually governs the span table rather than stress.
• That is why GRP ladder tray is commonly specified with shorter spans for heavy power cable fills and longer spans for instrument cable bundles. Always build the route from the manufacturer's load-versus-deflection curve, with the project's deflection limit (often L/200) applied.

Fire Performance and Regulatory Acceptance

This is where steel advocates push back hardest, and they are not wrong to. Steel cannot burn. GRP can, unless the resin system is formulated not to sustain combustion.

• Fire-retardant GRP grades are tested to ASTM E84 and reach Class A ratings, meaning a flame spread index of 25 or below.
• Limiting oxygen index testing to ASTM D2863 commonly returns values of 28% or higher for offshore-grade formulations, above the ~21% oxygen in air.
• IEC 61537 is the governing standard for cable tray systems and covers classification, load testing and material performance; project specifications often layer owner and classification-society requirements (DNV, ABS, Lloyd's Register) on top.
• In fire-rated boundaries and escape routes, the deciding element is usually the enclosure or the fire-rated system as a whole, not the tray material. The cable itself often carries more combustible load than the tray beneath it.

Specify fire performance as a tested system result, not as a resin description.

Earthing, Bonding and EMI: The Hidden Specification Item

GRP is an electrical insulator, and that changes the design, not the viability.

• A separate earth continuity conductor — typically tinned copper sized by the project, often 6 mm² and upward — must run the full route and be bonded at every joint and at both ends.
• Lightning protection design follows IEC 62305 principles, and hazardous-area installations under IEC 60079 require documented bonding continuity as part of the inspection regime.
• Steel trays give continuity for free, but a steel tray is not automatically a compliant earthing conductor either — the same bonding discipline applies.

Budget for the conductor and the bonding hardware when you compare costs, because it is a real line item on a GRP route.

Service Life, Maintenance and Lifecycle Cost

Purchase price is the number everyone quotes and the wrong one to decide on. On a 20-year field life, three cost lines separate the materials:

• Capital: GRP trays typically land at 1.5–2.5× the price of a galvanized steel tray of the same width. Stainless can run 3–5×.
• Recurring maintenance: Galvanized steel in C5-M needs recoating on a roughly 3–5 year cycle, with offshore access and scaffolding costs often exceeding the coating material itself.
• Replacement: A galvanized route may be replaced once or twice in a 20-year life. A correctly specified GRP route is normally inspected, not replaced.

On an indicative 20-year cost index where a galvanized steel route is set at 100, a GRP route commonly lands between 60 and 90 once recoating, access, and one partial replacement are included. The gap widens in the splash zone and in areas with chemical spill risk.

Where Steel Still Wins

Fiberglass is not a universal answer, and pretending otherwise damages your credibility with the structural engineer.

• High temperature: Above roughly 120 °C continuous, standard GRP resins lose mechanical performance. Steel does not care.
• Jet fire and hydrocarbon fire scenarios: Steel remains the conservative choice unless a tested fire-protected GRP system is specifically approved for the zone.
• Heavy short-span loading: Very dense power cable fills or high-impact locations from dropped objects favour steel.
• Field modification: Steel can be cut, welded and re-galvanized or coated on site by a competent crew. GRP is machined and re-sealed, and joints rely on correct bolting and sealing practice.
• Static dissipation: Where a conductive path is a hard requirement, steel needs no additional engineering.

Specifying a GRP Cable Tray for Offshore Duty

Work through this sequence before releasing an inquiry, and the material debate usually resolves itself:

• Assign an ISO 12944-2 corrosivity category to each cable route, zone by zone.
• Select the load class per IEC 61537 (or NEMA VE 1 for US-spec projects) using total cable weight plus a safety factor.
• Set the deflection limit — L/200 is common — and take spans from the manufacturer's test data.
• Fix the resin: isophthalic polyester for general marine, vinyl ester for chemical exposure, fire-retardant grade with LOI ≥ 28% where required.
• Confirm UV stabilisation and a surface veil on all exposed faces.
• Detail the earth continuity conductor, bonding jumpers and support spacing.
• Require test certificates: ASTM D638 tensile, ASTM D790 flexural, ASTM D2583 Barcol hardness, ASTM E84 fire data.

Where the material sits next to process equipment, the same reasoning applies across the whole package. A route plan that already uses GRP for cable support often makes sense paired with a GRP/FRP Storage Tank for brine, inhibited acid or produced water on the same deck, since both face identical chloride exposure and both benefit from one corrosion strategy rather than two.

The logic extends to the shore base, too. A Fiberglass Underground Storage Tank buried at the supply yard or used for below-deck drainage duties faces wet, saline soil that eats coated steel in a decade, and it carries the same resin chemistry as the tray above it. Manufacturers such as Hebei Yongchang Composite Material Technology Co., Ltd., working from a 50,000 m² facility in Hengshui, Hebei with six fully automatic microcomputer-controlled filament winding lines, produce pipe, fittings, flanges, cable tray and tanks from a common GRP family — which simplifies spares and inspection paperwork offshore.

Footprint matters topside as well, where every square metre competes for space. A GRP/FRP Vertical Storage Tank occupies a small deck patch while holding dosing chemicals or wash water, and it can be specified in the same vinyl ester chemistry as the cable tray, so one material approval covers several items in the same hazardous area.

FAQ

Is fiberglass cable tray fire rated for offshore use?

Fire-retardant GRP grades tested to ASTM E84 achieve Class A ratings and limiting oxygen index values of 28% or higher. Whether that satisfies the zone depends on the project: escape routes and fire-rated boundaries usually require a tested fire-rated system, which may mean steel or a protected GRP assembly.

How much lighter is GRP than steel?

Pultruded GRP density is around 1,800 kg/m³ against roughly 7,850 kg/m³ for carbon steel. In practical tray terms, a 300 mm ladder tray drops from about 4–7 kg/m to about 1.5–3 kg/m, which reduces support steel and installation crane time.

Do fiberglass trays need an earth continuity conductor?

Yes. GRP is non-conductive, so a separate tinned copper conductor must run the route with bonding at every joint and at both ends. Size it to the project's fault-current and IEC 61537 requirements.

**How long does GRP cable tray last on