Lapped Joint Flange Characteristics and Applicable Scenarios
Publication Date:
Jul 30,2026
Author:
Dacheng Jiaye
Lapped joint flange assemblies consist of two independent parts: loose flange plate and pipe lap stub end. Different from integral welding flanges
Lapped joint flange assemblies consist of two independent parts: loose flange plate and pipe lap stub end. Different from integral welding flanges, the flange plate does not connect directly with pipelines. The stub end is welded on pipe ends, and the loose flange plate can rotate freely around the stub end. This unique structural design brings obvious advantages in pipeline construction and later maintenance. The rotatable flange plate can adjust bolt hole directions freely during assembly. When pipelines are prefabricated and installed on site, workers do not need to precisely control rotation angles of pipe ends. It greatly reduces construction difficulty, especially for long-distance prefabricated pipeline modules and space-limited installation locations. Another advantage lies in cost optimization for high-alloy and stainless steel pipelines. The lap stub end contacts transported media, so it needs anti-corrosion metal materials. The loose flange plate only bears fastening force and does not contact internal medium. Manufacturers can adopt low-cost carbon steel to produce loose flanges while using stainless steel for stub ends. This material collocation effectively cuts overall engineering costs compared with full stainless steel integral flanges. In maintenance processes, if flange sealing surfaces are damaged, only loose flange plates need replacement, without cutting and re-welding pipelines. The maintenance workload is significantly lower than welded flanges. However, lapped joint flanges also have inherent limitations. The contact between loose flange and stub end forms a contact surface without rigid fixed connection. Under ultra-high pressure and severe pipeline vibration conditions, relative displacement may appear between two components, affecting sealing stability. Hence lapped joint flanges are not recommended for ultra-high pressure pipelines and pipelines with strong continuous vibration. The sealing surface is set on the stub end instead of the loose flange plate. Operators should focus on protecting stub end sealing surfaces during transportation and installation. Any scratch on stub end surfaces will cause sealing failure. Common application scenarios include stainless steel process pipelines, urban heating pipelines, ship pipeline systems and equipment auxiliary pipelines with frequent assembly demands. In overseas engineering projects requiring large amounts of stainless steel pipelines, lapped joint flange solutions are widely adopted to control investment budgets. Standard specifications define dimension matching requirements between stub ends and loose flanges. Buyers must ensure both components follow the same production standard to avoid assembly mismatch.
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