IMPROVED DWTT PERFORMANCE ON HEAVY GAUGE API PLATE AND COIL FROM 150 AND 180 MM THICKNESS SLAB AT NANJING IRON AND STEEL COMPANY, NANJING CHINA

摘要

Economical movement of energy through densely populated regions of China to support economic growth has resulted in typical natural gas transmission pipeline designs of API grade X70 that utilize wall thicknesses in a range between 17 and 32 mm and OD at 1016 mm. The DWTT requirement for many of the specifications is ≥ 85% shear average at - 10 °C to -15 °C in the plate or coil. Achievement of good fracture toughness, such as DWTT is heavily related to the total reduction from slab thickness to finish plate thickness. Ideally a total slab to finish plate thickness reduction in excess of 12:1 or at a minimum 10:1 is desirable to properly condition the austenite grains for good DWTT performance. Many of the Chinese steel producers, including Nanjing Iron and Steel Company (NISCO) have slab thicknesses less than 250 mm with several less than 200 mm, especially in wider widths to support the 1016 mm OD. This results in total slab to finish plate thickness reductions less than 10:1 and in some designs total reductions down to 7:1. This challenges the steel producer of plate or coil in achieving the required specification average DWTT percent shear on a consistent basis. For heavy gauge plate and coil in the widths required for the Chinese pipeline industry NISCO typically uses a 150 mm slab or a 180 mm slab. NISCO has to routinely use slab to finish plate or coil thickness total reductions less than 10:1. This paper will describe NISCO's successful development related to production of heavy gauge API X70/X80 grade plate and coil meeting the DWTT percent shear requirement in China utilizing slabs that result in total slab to finish plate/coil reductions of less than 10:1.