Cool solution for Singapore
The re-lining of a sewer pumping main set up a series of cooling challenges to keep materials workable, as Teh Peng Hooi and Katy Rademacher report.
The Sewer Main was assumed to be fully deteriorated and the Liner was designed according to ASTM-F1216-98. A Stand-alone-liner was required to fulfil the static (including negative pressure, which may exist in the pipe) and pressure technical requirements, as the existing pipe is assumed can no longer take the surcharge load above it.
This Stand-alone-liner consists of a felt layer, an endless woven sleeve and a PE-coating. The felt and the sleeve are impregnated with two component epoxy-resin. The hardened felt layer will provide resistance to the external load and the internal sleeve will provide the internal pressure resistance. Die PE-coating guarantees a perfectly smooth surface condition and provides exceptional chemical resistance.
The main problem encountered in Singapore for relining work using the Softliner System and reaction-resin is the high ambient temperature, which affects the resin hardening time upon mixing. To overcome this problem and to enable the use of the special Stand-alone-liner, additional preparation work and modifications of the equipment was carried out as follows:
- Cooling of the resin with a cooing-container prior to mixing
- Installation of air conditioning in the Phoenix Unit to pre-cool the reversion drum and also for the cooling of the impregnated liner during the transportation to site.
- Construction of an aftercooler (chiller) to cool the liner during inversion and to cool off after curing.
- Impregnation by means of a vacuum-pump to remove the trapped air in the liner to ensure complete success.
Due to high ambient temperature, the relining work of Pumping Mains in Singapore is carried out only during the night. Therefore, in the course of the morning of every relining day, cleaning and pre-CCTV-inspection were carried out. The mixing of the resin and the vacuum-impregnation of the Combi-Liner in the warehouse started in the late afternoon. After impregnation, the liner was transported and further cooled en route to the site.
The sections to be relined ranged from 100 - 120m for the DN500 Pumping Main and 80 - 180m for the DN350 Pumping Main. The relining work of each section took from midnight till the early morning. The pressure test at 9.5bar has successfully been carried out for the Pumping Main. The laboratory test (Tensile strength, flexural strength etc.) of lining samples was also carried out satisfactorily, conforming to ASTM-F1216-98 requirements.