The roundness of the reducing elbow should not exceed 1% of the corresponding outer diameter of the ends, with allowable deviation of ±3mm. The material for the reducing elbow is in compliance with SY/T5037, GB/T9711, GB/T8163, ASTM A106/A53 GRB, API 5L, APT5CT, ASTM A105, ASTM A234, ASTM A106, DIN German standards, and customer-specified standards. Reducing elbows (reductions) are pipe fittings used at pipe transition sections for changing pipe diameters. Common forming processes include necking down, expanding, or a combination of both, and stamping forming may also be used for certain specifications.