Single Plastic Stent Vs. Fully Covered Self-Expanding Metal Stent on Benign Biliary Stricture Secondary to Chronic Pancreatitis

The goal of this clinical trial is to compare the efficacy and safety of a single plastic stent versus a fully covered self-expanded metal stent in relieving benign biliary stricture secondary to chronic pancreatitis. The main questions it aims to answer is: Whether the efficacy of a single plastic stent is non-inferior to that of a fully covered metal stent in patients with benign biliary stricture secondary to chronic pancreatitis？ Participants will be randomly assigned to receive either a single plastic stent (SPS) placement or fully covered self-expanded metal stent placement treatment for 6 months, and they will be followed up for 18 months.