Lightning Strike Damage: Delamination Under the Receptor

Author: RAS Thermal Co., Ltd. · Updated 2026-10-07

TL;DR Threshold: 6 mm delamination limit per Table G.1, applied to the whole attachment zone. Payloads: PAUT, eddy current and thermography available on the field crawler. Environment: IP67 and NEMA 4X sealed, rated to minus 20 °C, tracked at 300 mm/s. Basis: the post-strike scan uses the same volumetric methods as the factory cell.

A lightning attachment leaves a charred mark at a receptor, and the laminate underneath proves worse than the surface suggests. A lightning attachment dumps current into the blade structure at a point, so the visible mark is the entry and the damage is the separation it drove through the laminate. The surface can look contained while the plies beneath are separated over a wider area. That mismatch is why the in-service scan is run over the whole attachment zone rather than at the mark, and why a field crawler capable of the same volumetric methods as the factory cell matters after a storm.

Common root causes

Root cause	What you see	Where it bites
Attachment at a receptor or tip	a charred mark with separation spreading beneath it	receptor zones, tip and down conductor path
Current path through the laminate	delamination along the conduction route rather than at the mark	structure adjacent to the down conductor
Thermal damage at the strike point	resin degradation and ply separation around the entry	attachment zone
Hidden separation over a wider area	the surface mark understates the extend of the damage	shell laminate around the receptor

What the numbers allow

The zone is scanned to the same 6 mm volumetric floor as the primary structure, because lightning damage is delamination and delamination is what Table G.1 bounds at 6 mm. The field crawler carries PAUT, eddy current and thermography payloads on one platform and returns the data at 300 mm/s on the curve, sealed to IP67 and NEMA 4X for a marine site and rated to minus 20 °C. So the post-strike scan uses the same methods as the factory gate, which is what lets the two results be compared. A 6 mm separation is held to the same Table G.1 limit after a strike as before it, per the primary-structure clause, so a second threshold would be an invention rather than a standard.

Threshold: 6 mm delamination limit per Table G.1, applied to the whole attachment zone
Payloads: PAUT, eddy current and thermography available on the field crawler
Environment: IP67 and NEMA 4X sealed, rated to minus 20 °C, tracked at 300 mm/s
Basis: the post-strike scan uses the same volumetric methods as the factory cell

How to confirm it

Work down this list in order. The first check that changes the result has found the cause.

Scan the whole attachment zone. Extend the scan well beyond the visible mark, because the surface entry understates how far the separation runs through the laminate.
Apply the 6 mm floor. Judge the separation against the same Table G.1 limit used for the primary structure, so the post-strike disposition rests on the same basis as the as-built inspection.
Bring the right payload. Use PAUT for the planar separation and thermography for any coating or near-surface change, since the in-service platform carries several payloads on one interface.
Confirm the environment rating. Check the crawler is sealed to IP67 and NEMA 4X and rated to minus 20 °C before a marine deployment, because a post-strike scan often happens in poor conditions.
Log against the serial. Record the damage extent against the blade serial so the repair scope and any later comparison have a common origin.

Prevention

Maintain the lightning protection system and verify the down conductor path on schedule, then scan the attachment zone properly after any strike rather than judging from the mark. Lightning damage is delamination underneath, and the scan is the only thing that bounds it before a repair is scoped.

The numbers below are drawn from the equipment records and field campaigns this site already publishes, not from a generic catalogue.

Frequently Asked Questions

Does the visible lightning mark show the full damage?

No. The mark is the attachment point, and the separation it drives runs through the laminate around it. That is why the post-strike inspection is run over the whole zone rather than at the mark, and judged against the 6 mm delamination limit.

What methods suit post-strike blade inspection?

PAUT for the planar separation, with eddy current and thermography available on the same field platform. The in-service crawler carries those payloads on one interface, so the post-strike scan uses the same volumetric basis as the factory cell.

Can lightning damage be inspected offshore?

Yes. The field crawler is sealed to IP67 and NEMA 4X for salt-fog service and rated to minus 20 °C, so it can run the scan on a marine site where the conditions after a storm are rarely kind.

How big a separation is acceptable after a strike?

The same Table G.1 limit that governs the primary structure, 6 mm. The strike changes where the defect is, not the threshold it is judged against.

Bottom line: Lightning leaves a mark at the attachment and drives the damage through the laminate around it, so the scan runs over the whole zone and not the mark. Apply the 6 mm Table G.1 floor, use the field platform's volumetric payloads, and bound the separation against the blade serial before the repair is scoped.