Design of Sampling Systems for Steam and Water

The proper design of a sampling system is critical in order to produce a sample which is representative of the conditions in the pipe. If the sampling system is not adequate, the pressure drop through the system could result in insufficient sample flow at the sample panel, or the deposition rate in the sample lines could be high, which could result in plugging of the sample line or a sample which is not representative of the conditions in the pipe.

Requirements for a Representative Steam Sampling Systems

With the increase of unit sizes, stresses, and heat fluxes, equipment aging, unit cycling, and the high cost of replacement power and steam, corrosion protection of the steam cycle components during operation and layup and the control of water and steam chemistry are of critical importance.

Objectives

• For steam Sampling, the isolation valves on the Jonas Nozzle and the sample tubing between the isolation valves and the primary sample cooler should have approximately the same bore as the Jonas Nozzle. This will maintain a constant flow velocity and minimize the amount of deposition between the Nozzle and primary cooler by eliminating dramatic pressure changes.

• The sample velocity in all tubing after the primary cooler should be in the turbulent flow range (Re > 4,000, 4 to 6 ft/sec for liquid water) so that the amount of deposition in the sample tubing is minimized. Also, the pressure drop throughout the entire sampling system must be low enough to ensure that there is enough pressure after the secondary sample cooler to provide adequate flow to the online instruments and grab sample tap.

• Sample tubing should be as short as possible, sloping downward along the entire length. For steam sampling, the tube section between the Sampling Nozzle and the primary sample cooler should be less than 20 ft long.

E2P Design of Sampling Systems

We will recommend any or all sampling system components, including the secondary sample cooler.

The Design Report includes sample tubing sizes and materials, valve sizes, and primary and secondary cooler materials and sizes. In addition, the pressure drop through each section of the sampling system and the overall pressure drop are calculated to ensure adequate sample flow. The entire system is designed based on industry recommended practices