Dear sir, As you said you want to convert the twin screw extruder to produce HDPE pipe of 50mm-100mm,As fas as I know,you have to change the mainframe,that is change into a single screw extruder 90/32 and change the mould is OK! Other things such as the spraying water tank and hualing engine you can still use that production line! If you have any other questions,don't hesitate to let me know! Best Regards, Sabrina(pls check our website and then contact me with my email address) Qingdao Fushun Plastic Machinery Co,.Ltd