Good Quality Glass-Lined Steel Biogas Tank: Gas-Tightness and Safety A good quality glass lined steel biogas tank holds both corrosive digestate and flammable biogas, so quality means gas-tightness as much as structural strength. The Glass-Fused-to-Steel (GFS) enamel fused at 820-930°C must be flawless, and every joint must seal. Engineered by Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel), these bolted digesters are built so the gas stays in and the hazard