What is a coned and threaded connection?
High pressure coned and threaded connections are used to contain high-pressure liquids and gasses in research and production applications. These reliable connections are made quickly and provide reliable containment for pressures as high as 150,000 psi (10,342 bar) and temperatures as high as 1,200F (650C). The coned and threaded connection design varies by the pressure it is designed to contain, but generally consists of a piece of high-pressure thick-walled tubing, a collar, and a gland. The term "coned-and-threaded" refers to the machining operation used to prepare the high-pressure tubing so that it will seal in the connection. Cone shape is machined on the ends of the tubing and then a left-hand thread is applied to the outside of the tube. The collar is threaded onto the tube and the gland is used to push on the collar to make the seal.
How do I make a coned and threaded connection?
There are three common methods for coning and threading tubing - using a lathe, using manual coning and threading tools, or using a coning and threading machine. A good machinist can easily cone and thread the tube. The only challenging part is picking up the required left-hand thread at the proper location. Manual coning and threading tools work very well for low volume and smaller line sizes 9/16" maximum. A coning and threading machine is recommended for higher volume and larger tube sizes greater than 9.
Why is there a hole in the side of my high-pressure fitting (and why is it leaking)?
Coned and threaded connections are designed to seal effectively at pressures from 20,000 psi to over 150,000 psi. Autoclave Engineers' valves and fittings include a weep hole in the side of the block. It is intended to alert the operator to a leak and vent any pressure that could otherwise eject the tube and gland. It is a safety feature built into each high-pressure fitting from Autoclave Engineers.
Where should I apply lubrication to my high pressure coned and threaded fittings?
Coned and threaded fittings should be lubricated during assembly. The gland threads and the face of the gland in contact with the collar should be lubricated. The threads of the collar should be lubricated as well. If a process compatible lubricant is available, also lubricate the tip of the tubing cone. This helps the line contact area slide during assembly and prevents gulling.
How does a coned and threaded fitting seal?
Coned and threaded fittings are unique in how they seal. Other types of tube connections use threads to seal (NPT) or they use a compression ferrule design to grab the tube (Swagelok, Parker A-line, etc..) For the extremely high pressure, these methods are not sufficient to guarantee safety. A coned and threaded connection uses a metal-to-metal line contact seal created by inserting a tube with a 59o cone angle into a connection with a 60-degree cone angle. The two cones coming together form a line contact seal.
Where should I put the collar when making up a coned and threaded connection?
When threading the collar on to the tube of a coned and threaded connection, leave 1-1/2 to 2 threads exposed on the gland side. This assumes that the tube has the proper thread length for the size of the connection. If the collar is not threaded onto the tube far enough, the gland will not push the tube far enough into the connectin to seal. If the collar is placed too far onto the tube, not enough of the gland threads will be engaged to contain the pressure.
How much torque do I need for my high-pressure Autoclave coned and threaded connections?
Coned and threaded connections are designed to seal with very low torque values relative to the operating pressure. Glands should be torqued to the values shown in the chart ranging from 20 ft-lbs to 200 ft-lbs.
How much torque should be applied to seal a 15,000 psi Autoclave Engineers Speedbite connection?
Low-pressure Speedbite connections do not require a specific torque. Instead, they should be tightened until the sleeve begins to grip the tube. From that point, the gland should be turned another 1 to 1-1/4 turn to finish setting the sleeve.
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