Dryseol Pipe Threads
Dryseal pipe threads differ from the USA (American) pipe thread, as their purpose is to seal pressuretight joints without the necessity of using sealing compounds. To accomplish this some modification of thread form, greater accuracy in manufacture, and more analytical gaging are required. The roots of both the external and internal threads are truncated slightly more than the crests, Le. roots have wider flats than crests, so that metal-to-metal contact occurs at the crests and roots coincident with or prior to flank contact, see Fig. 1. Thus as the threads are assembled by wrenching, the roots of the threads crush the sharper crests of the mating threads. This sealing action at both the major and minor diameters tends to prevent spiral leakage and makes the joints pressuretight without the necessity of using sealing compounds, provided that the mating threads are in accordance with standard specifications and tolerances and are not damaged by galling in assembly. These ends are accomplished by the use of properly designed threading tools. Also, it is necessary that both external and internal threads have full thread height for the entire effective length of the thread makeup. That is, the diameters of the hole before tapping and of the external thread blank correspond to the maximum material limits.
However, where not functionally objectionable, the use of a compatible lubricant or sealant may be used to minimize the possibility of galling. This is desirable in assembling Dryseal pipe threads in refrigeration and other systems to effect a pressuretight seal.1
1The refrigeration industry has generally accepted the use of a sealant to obtain an absolute pressuretight joint, when assembling taper pipe threads made according to USAS B2.1 or USAS B2.2.