Flow Elements

ASME PTC 6 - 2004 Flow Sections

The Test Code for Steam Turbines was one of a group of ten codes forming the 1915 edition of the ASME Performance Test Codes. Various revisions have been undertaken to incorporate industry changes including improvements in primary technology and the development of high accuracy instrumentation.

The Test Code provides procedures for the accurate testing of steam turbines. It is recommended for use in conducting acceptance tests of steam turbines and any other situation in which performance levels must be determined with minimum uncertainty. The intent of the code is that accurate instrumentation and best possible measurement techniques be used to determine the performance.

The accurate determination of primary flow to the turbine is necessary to compute turbine heat rate or steam rate. The Code recommends measurement of water flow in the feedwater cycle. Extreme care must be taken to obtain a high order of accuracy in primary water flow measurement.

Excellent results in the measurement of feedwater have been obtained using a low-beta-ratio throat tap nozzle. The use of this primary element is therefore the recommended method. The Code includes stringent requirements for the primary flow device. Triad Measurement & Equipment, Inc. (Triad) has extensive experience in the design and manufacture of these devices and can provide your company the help it needs. Triad has completed hundreds of successful projects that include primary elements manufactured in accordance with the Code.

The basic design of a PTC 6 flow section includes a throat tap nozzle with a beta ratio between 0.25 and 0.50. The flow section must be calibrated and shall have an upstream pipe section a minimum of 20 diameters long. The Code also requires the use of a flow straightener installed at least 16 pipe diameters upstream of the primary element.
 
Because of the high degree of accuracy necessary, the Code provides stringent requirements in the manufacture of the flow section. Great care must be taken in the manufacture and inspection of the throat tap nozzles, particularly in the geometry of the nozzle and downstream pressure taps, otherwise, difficulties meeting the calibration criteria may occur.

If you have an application requiring a PTC 6 flow section, Triad Measurement & Equipment, Inc. can assist in all phases of the project. If you have any technical questions or would like additional information please use the Contact Us tab of the
website for a listing of the individuals on our team.