API Spec 15LT:1993 pdf download.Specification for PVC Lined Steel Tubular Goods
3.1 EXTRUSION PROCESS
Single Screw Extrusion一Favorable results of single screw extrusion with rigid PVC powder (dry blend) or PVC pellets rely on several basic but essential operations in the extrusion process. Promoting shear helps assure a competent level of work or energy in the compound which makes certain there is proper fusion, a homogeneous melt, and as8ures acceptable physical properties have been obtained, The shear is accomplished by running the extruder at high RPM and high compression (back pre8- Bure). In the single acrew process, generally PVC compounde can be handled for length/diameter (L/D) ratios of at least 24;1, and may differ in some operations. PVC extrudere typically use a vacuum vent for extraction of volatiles (air pockets or gas filled voids). Common working pressure at the vent section have a range of 15-22 inches Hg vacuum. PVC aingle screws incorporate a two-stage screw design; a mixing zone and a decompression zone at the vented area. The acrew al8o is designed with a hollow center for oil temperature control to assist in proper compound mix. Twin Screw Extrusion – – To achieve the best results in twin 8crew extruslon, low RPM along with low com- presaion are necessary, just the opposite of single screw. Thig in turn creates very low friction (shear) for a consid- erable lower running tomperature as well as a more con- sistent melt flow. In the twin screw process L/D ratio is generally not considered due t如o the flexibility of compounds used (less heat sensitive). Similar to the single acrew process, the twin screw process also uscs a vacuum vent for extraction of volatiles. Typical working pressure for the vent section is 15-22 inches Hg vacum. PVC twin screwa differ slightly in design between machines, but basically have a feeding z0ne, decompression zone (at the vent section) and a mixing Z0n0, The screws are each hollow centered for oll temperature control.
Unless previously waived in writing by the purchaser, each length to be lined shall be hydrostatic tested with test pressure and duration subject to agreement between purchaser and manufacturer. If no waiver or agreement is addressed between such parties, a minimum five sec- ond test duration shall be used. b. Steel tubular goods should be adjudged Buitable for lining by the manufacturer provided the following mini- mum requirementa have been met: 1. The maximum out-of-roundness should not exceed the manufacturer’s acceptable limita. 2. The steel tubular goods should have no deviation from straightness exceeding the manufacturer’s ac- ceptable limits, 3. Pin and coupling threads on threaded and coupled pipe should be visually inepected for pulled, galled, or otherwise damaged threads. Tubular goods with thread wear exceeding manufacturer’s acceptable limits should not be lined without reconditioning to meet these limits.
API Spec 15LT:1993 pdf download
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