Using large-diameter flanges for pressure testing may lead to leakage.

The technical department of Shanghai Seojang analyzed that the leakage phenomenon may occur during the pressure test of large-diameter flanges used in Shanghai Seojang rubber expansion joints. According to the requirements, our rubber joints require special butterfly valve flanges with the same inner diameter as the rubber joint. This is to prevent leakage!

On September 10th, 2015, technicians from Shanghai Songjiang Group Co., Ltd. conducted a site visit at a construction site in Suzhou and observed a DN400 rubber expansion joint with a ruptured sealing surface. Upon measurement with a tape measure, it was found that the internal diameter of the ruptured sealing surface was 430mm (attached are photos of the actual product). Additionally, at the pump room site, technicians found a blind plate used for on-site pressure testing, welded with a large-diameter flange inside, with a measured internal diameter of 430mm (attached are photos of the actual product). This diameter coincided precisely with the internal diameter evidence of the ruptured DN400 rubber joint. Therefore, our technicians preliminarily determined that the leakage issue observed on-site with the DN400 rubber joint occurred due to the use of a large-diameter flange during temporary pressure testing, causing the sealing surface of the rubber joint to rupture when pressurized to 16kg.

Upon further inspection of other pipelines, it was observed that pipelines without rubber joints were welded with butterfly valve special flanges, indicating no issues. However, once rubber joints are installed, it is difficult to ascertain whether butterfly valve special flanges were used, as the internal diameter of the flanges cannot be measured post-installation. To ensure similar leakage issues do not occur with rubber joints in the future, our factory recommends using butterfly valve special flanges for installation. If other flanges were used, we advise replacing them with butterfly valve special flanges before conducting further acceptance pressure tests to mitigate losses.

This analysis is provided by the after-sales department of Songjiang. For further inquiries, please contact us at +86 13032112360.