Dual-Fuel Piping Fabrication
Dual-fuel propulsion puts a gas line through the length of a ship. Class rules respond to that by treating the piping itself as a safety system — double-walled where it passes through accommodation and machinery spaces, ventilated, monitored and fully traceable.
Meritus sources gas fuel piping and associated skids from Chinese fabricators who have done the work before, and verifies the weld and material records that the IGF Code makes non-negotiable.
Scope we cover
High- and low-pressure gas fuel piping; double-walled gas piping with annular ventilation; gas valve unit (GVU) skids and enclosures; fuel supply and return spools; nitrogen purge and inerting lines; ventilation ducting for gas-safe arrangements; supports, penetrations and bulkhead arrangements for gas lines.
IGF Code requirements
The code drives material selection, wall thickness, joint type, NDT extent and the arrangement of every penetration. We confirm the fabrication scope against the approved drawings rather than the enquiry documents, since the two diverge more often than anyone expects, and keep the as-built records aligned with what class approved.
Weld and material traceability
Radiographic and ultrasonic coverage on gas piping is specified, not sampled. We verify NDT extent against the class requirement, check welder qualifications against the procedures in use, and cross-check pipe and fitting heat numbers to mill certificates. Every order runs through the same quality chain: shop pre-qualification, material traceability against mill certificates, in-process and final inspection, and a documentation pack released before shipment.
Failure modes we inspect for
NDT extent applied as a sampling percentage when the code specifies full coverage. Welders qualified for a different procedure than the one in use. Bulkhead penetrations fabricated to a generic detail rather than the approved arrangement. And as-built records that describe the enquiry design rather than the approved one — which surfaces at class review, when the vessel is nearly complete.
How an order runs
Enquiry and specification review; shop shortlisting against the actual scope rather than a general vendor list; quotation with the inspection plan priced in, not added later; kick-off with agreed hold and witness points; in-process inspection at those points; final inspection, document pack release and shipment; arrival support if anything is queried. On gas piping we reconcile the fabrication scope against the class-approved drawing set before production and again before release.
Frequently asked questions
What makes dual-fuel gas piping different from process piping?
Class treats it as a safety system. Double-walled construction through accommodation and machinery spaces, annular ventilation, gas detection, specified NDT coverage and full traceability are requirements rather than options.
What is a GVU?
The gas valve unit — the skid that controls, filters and isolates gas fuel immediately upstream of the engine, and one of the most tightly specified items in the fuel system.
How much NDT is required?
The extent is set by the code and class rather than by sampling convention. Meritus verifies coverage against that requirement rather than accepting the shop's customary rate.
Can this be sourced alongside the FGSS?
Yes — gas piping and the fuel gas supply system are commonly scoped together, which removes the interface risk between the two.