The Ma’ankou issue

1. According to GB/T20801.3, branch pipe connections include two forms: the direct welding of the branch pipe to the main pipe, and the connection between the branch pipe and the main pipe through connecting fittings. These connecting fittings include branch pipe supports, half-elbow joints, tees, etc. For branch connection fittings used in GC1 grade pipelines, integrally reinforced branch connection fittings or tees should be employed ； When socket or threaded branch fittings and half-fittings are used, the nominal diameter shall not exceed DN80. 2. When a branch pipe is welded directly to the saddle joint of the main pipe, pressure design shall be carried out, and reinforcement calculations shall be performed using reinforcement methods. If one of the following conditions is met, no reinforcement calculations are required, nor are any other reinforcement measures necessary: a) Threads directly welded to the main pipe, or socket-welded pipe fittings (GB/T 14626－1993, GB/T 14383－1993), and meeting all of the following requirements: 1) The nominal diameter of the branch pipe is not greater than DN50 ； 2) Db/Dh ≤ 1/4. b) Branch pipe seat welded directly to the main pipe (GB/T 19326－2003). c) Tees, crosses, or angled tees that have undergone verified pressure testing (GB/T 12459－2005, GB/T 13401－2005). d) Threaded or socket-welded tees, crosses, or elbow tees (GB/T 14626－1993, GB/T 14383－1993).