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|Maximum allowable drag pressures?
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|Author:||Ebaffoni21 [ October 29th, 2014, 12:46 pm ]|
|Post subject:||Maximum allowable drag pressures?|
We use fusion machines from the 2LC up to the 412. From a compliance standpoint how much actual weight/pressure can there be when pipe is being fused?
|Author:||Joshua [ October 29th, 2014, 4:33 pm ]|
|Post subject:||Re: Maximum allowable drag pressures?|
I am not sure exactly what you mean by "a compliance standpoint" There are several possible perspectives. The question of maximum drag comes up from time to time and it can turn into a complicated answer. Here is an attempt to keep it simple.
Assuming the pipe is properly supported on level ground and assuming there are not extra forces to consider (i.e. the pipe is not in a bend causing it to push or pull away from the fusion machine)
From an ASTM F2620 Fusion Standard standpoint, drag pressure is defined but acceptable range is not defined.
From a pipe manufacturer standpoint, there is a maximum tensile load that can be put on the pipe. A fusion machine will generally not come near this force but a bore rig can.
From our standpoint, it is generally advisable to keep the drag pressure as low as possible. Drag pressure is often a result of the machine being put in a bind by misaligned pipe or is caused by a force other than overcoming the friction of the pipe on the rollers and the ground. These are often not acceptable situations. However, when doing tie-ins and fusing longer fused pipe strings together, there may be significant drag. The fusion machine has a maximum pressure and force capability. Figure it by putting the carriage in fusion mode and dialing the pressure all the way up. Remember that number. (That number minus drag pressure for the empty carriage, times the TEPA listed on the cylinder is the force the machine could apply.)
Measure drag like this: http://www.mcelroy.com/fusion/animations/drag.htm and remember that number.
Calculate your fusion pressure using 0 as the drag value.
Theoretical Fusion Pressure plus Drag Pressure must be less than the pressure capability in Fusion mode.
Remember that maxing the machines out is seldom the best course of action. Fuse pipe strings together before they get so long that there is a high drag pressure. It is always advisable to ensure your pipe is supported and aligned properly to be sure you are not putting your machine in a 'tweak'.
Hope this helps.
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