Zhoushan Dock — DN800 Large-Bore Pipe Project
Client /A ship-repair yard in Zhoushan
Location /Zhoushan (survey & installation), Shenzhen (manufacture)
Date /2025
A Zhoushan ship-repair yard · DN800 large-bore seawater-pipe replacement
Project Background
A large vessel under repair at a Zhoushan ship-repair yard needed three seawater main lines replaced — DN800 bore, about 25 m total, with 10 flanges, 6 elbows and 3 DN600 reducing branches. By the yard's traditional method, pipe this large and complex would have to be removed whole and copied section by section in an onshore workshop as a template — slow, labour-intensive, and the removal itself risks some damage to the hull structure.
Challenges & Requirements
The core difficulty: the old pipe could not be removed to serve as a copying template. On one hand, Chinese customs tightly controls landing used pipe from foreign vessels; on the other, neither owner nor yard wanted the extra time and hull-damage risk of removal. The yard had never before made pipe this large and geometrically complex from a purely digital survey, and doubted whether the dimensions could be right first time.
Core need: zero old-pipe removal, zero on-site trimming, 100% digitally prefabricated installation
The Irwin Solution
While the vessel was berthed in Zhoushan, the Irwin team boarded and scanned the three in-service DN800 lines directly with Automet, building an as-built digital twin. The workshop laid out and cut the spools to the digital model, using the Automet FAB system to verify dimensions at the tack-weld stage — keeping overall dimensions, including gasket and coating allowances, within PFI-ES3 tolerance of the digital twin. After welding, Automet verification was repeated to confirm no weld distortion before PE lining and external coating.
Process
Results
All three large-bore spools fitted first time, with no on-site trimming or rework
The yard's first pipe replacement with zero on-site hot work — all fabrication done in the workshop
Completely avoided hull-structure damage and customs-compliance risk
Installation time cut to a third of the traditional method, greatly reducing dock occupancy
✅ 100% first-time installation — all three large-bore spools fitted first time, with no on-site trimming or rework.
✅ Zero on-site hot work — the yard's first pipe replacement needing no on-site welding or cutting.
✅ No old-pipe removal — avoiding hull damage and customs-compliance risk.
✅ Installation time cut 67% — greatly reducing dock-occupancy cost.
Client Value
For the Zhoushan ship-repair yard, the project meant more than a successful pipe replacement — it was a shift in working philosophy. The yard experienced for the first time the efficiency and quality assurance of the "digital twin + centralised prefabrication" model, overturning the old belief that complex large-bore pipe must be copied from the removed original. The yard has since actively recommended Irwin's prefabricated approach on several later repair projects.