Boiler Steam Supply Piping Basics November 18, ) Q: What kind of condensate traps should be used on vacuum condensate return systems?

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1 Boiler Steam Supply Piping Basics November 18, ) Q: What kind of condensate traps should be used on vacuum condensate return systems? A: What is often used in a vacuum system is a thermodynamic disc trap with sufficient (piping) head above the trap inlet to provide the required differential across it. Remember: 2.31 feet = 1 psig. 2) Q: What pressure do Inverted bucket traps not seal at? A: It s not a question of pressure, it s a question of maintaining a minimum amount of condensate at the bottom of the trap to seal the bottom of the (inverted) bucket to allow a seal so steam can be trapped. Operation of inverted bucket steam traps is affected by the differential pressure from the inlet to the outlet of the trap. The closing force is determined by the differential and orifice size while in order to open, the force created by the weight of the internal bucket must exceed the force created by the differential pressure across the orifice. 3) Q: With a constant load, customer wants to drop operational pressure, the velocity increases by a square factor? A: Velocity is directly related to mass flow and the internal size of the pipe through which the medium is flowing. If I double the flow, I double the velocity. However, when I doubled the velocity, my pressure drop was squared or increased 4 times. Now, when you drop the pressure, the volume of the steam in the line will increase, and with that, the pressure drop will increase too meaning not as much steam will be reaching the user. As an example, if my velocity is 120 ft/sec through a schedule 80, 2 line, and I reduce my pressure from 120 psig to 100 psig, my flow of steam goes from 2850#/HR to 2400#/HR. This is a 16% reduction in the amount of steam going to the user because of the pressure reduction. 4) Q: We are getting water hammer in the Cond. Return after the pumps. Can steam from leaking traps cause this? A: Yes it can, but it may not be the only cause. You may be experiencing thermal water hammer where discharges of condensate at different temperatures are entering the (common) condensate line, and the higher temperature ones are flashing, creating a void, and the surrounding condensate rushes to fill the void, causing the hammer. 5) Q: Heat exchanger introduce a major change in quality. Are there any special considerations where the HE is designed for major condensation? I am thinking of an HE that is designed to recover as much of the latent heat as possible, as in heat recovery from a steam source. A: All heat exchangers using steam as the heating medium will be designed to maximize heat transfer of the latent energy into the product to be heated. What is left now is hot condensate the temperature of which varies based on the pressure in the

2 system. The higher the pressure, the higher the condensate temperature. Some heat exchanges may have been designed to extract a portion of the sensible energy too, but normally this condensate is trapped out, and returned as hot as possible to the boiler feed system. 6) Q: Does Cleaver-Brooks offer Steam Trap Testing? If so, can they do it anywhere in the USA? A: Cleaver Brooks has a dedicated steam system assessment staff who work in conjunction with the local C-B representative within North America, and depending on availability of qualified personnel, will get involved with the actual trap audit and testing. 7) Q: How are the drips used in relationship to the traps? A: Reference slide numbers 32 & 33 in the presentation found on the C-B website, home page, archived webinars. You can also see and hear the replay of the entire webinar from the same location if that would be helpful 8) Q: Will the main be pitched to or from the boiler? A: The main in a long horizontal run, is normally pitched downward from the boiler connection at about ½ per 10 linear feet with properly sized drip pockets placed every 150 feet and no more than 300 feet along this expanse. This is to catch the gravity assisted condensate, delivering it to the trap for proper evacuation to the condensate return line. Q: At what point (inches of insulation) is it too much? A: Our recommendation would be to follow ASHRAE 90.1 for insulation thickness. The thickness in the table was derived from economic analysis to determine the best payback. Greater thickness will not hurt but at certain point there is a minimal return.

3 9) Q: How to reduce water hammering in single pipe steam? A: Reducing (differential) water hammer is a matter of controlling velocities in the steam distribution piping as well as properly pocketing and trapping the condensate as it forms in the piping system along with assuring the steam entering the piping system is not moisture laden. Visit our website and review a past webinar entitled Capturing Liquid Gold Condensate. Believe you ll find some helpful hints. 10) Q: Can you provide a list of acceptable steam piping distribution materials? A: I would highly recommend you visit either Armstrong International or Spirax Sarco websites for very useful information concerning this question. Below are typical piping material for high pressure steam piping. 2" and Smaller above grade in buildings: ASTM A53, type F, standard weight (schedule 40) black steel pipe with ASTM A126/ANSI B16.4, Class 250 cast iron threaded fittings. 2 and Smaller in heating plants and below grade distribution systems: ASTM A106, Grade B, standard weight (schedule 40) black steel pipe ASTM A105 grade II/ANSI B16.11, threaded or welded (for inaccessible piping) forged steel fittings. 2-1/2" and Larger above grade in buildings: ASTM A53, type E or S, standard weight (schedule 40) black steel pipe with ASTM A234 grade WPB/ANSI B16.9 standard weight, seamless, carbon steel weld fittings. 2 1/2 and Larger in heating plants and below grade distribution systems: ASTM A106, Grade B, standard weight (schedule 40) black steel pipe with ASTM A234 grade WPB/ANSI B16.9 standard weight, seamless, carbon steel weld fittings. On steam piping serving turbines, the piping and fittings shall be pickled, cleaned and capped before shipment to the site. 11) Q: How is the trap sized? A: The trap is sized first by knowing the amount of steam which will be used for that particular application. This steam, when the latent energy is used in the process, returns to condensate, pound for pound. Then you need to know the inlet pressure to the trap and the discharge pressure the trap will experience when discharging condensate. The difference between these (inlet/outlet) pressures is the differential. Then a safety factor is added to accommodate for cold starts and other variables. 12) Q: Rating traps by energy loss (least steam bypassed)? A: The amount of energy loss through the trap is not dependent on the trap classification or type within the classification. It is dependent on the traps application and the way it was sized and the safety factor applied.

4 13) Q: I am curious as to when to use each type of steam trap or the correct application they require to be used for? A: Visit the presentation now posted on the C-B website under Archived webinars, and the pros and cons for each trap is shown toward the end of the program. 14) Q: We use Amine here and we have one of the directors very sensitive to the smell, and says she can tell when we are putting out day tank that feeds the d.a. tank, is there an alternative chemical or process that could be used in place of the chemical? A: I would suggest you contact your chemical supplier or one of the larger chemical companies such as Nalco, and ask their opinion of what can be done if anything. 15) Q: Is the pressure relief valve selection part of the steam supply system? A: If you are referring to the pressure relief valve on the boiler, no, it is not part of the steam supply system. It is there to protect the boiler in the event an over-pressure situation occurs with it, and it is always provided by the boiler manufacturer. There are instances; however, where certain pieces of equipment or processes within the steam supply system need protection to prevent over pressurization. In these cases, a relief valve would need to be specified and selected. 16) Q: Formulation for steam loops in underground or hung piping - quick methods for determination? A: If you are referring to the piping expansion loop, these need to be closely calculated by an experienced engineer to minimize space and cost while providing ample flexing and deflection for the piping system. The 2012 ASHRAE HVAC Systems and Equipment Handbook (Chapter 46) has tables and calculations for determining the size of commonly used U and L bends for pipe expansion. 17) Q: What is the rule of thumb for lifting condensate based on its steam pressure? How high can we lift condensate say on a 50 psig steam system? A: For every 2.31 feet of vertical piping you have one pound of pressure. So with 50 pounds of pressure behind the condensate, you can lift it about 21 feet. 18) Q: Could the panel discuss slope of the piping on the supply side? A: See question/answer #8. 19) Q: Is it true that a significant steam pressure drop is required across a control valve to achieve proper control? A: A minimum pressure drop is definitely required to prevent hunting of the valve mechanism at varying loads.

5 20) Q: Installed a new feed pump (stack type) and sounds like there is cavitation going on even though DA tank seems to be operating fine. Any thoughts on what might be causing this? A: Sounds like you have a vertical multi-stage centrifugal pump which is not getting the minimum NPSH it needs to avoid cavitation. First, check the strainer on the suction side of the pump to see if it is fouled. If so, clean it. Next, slightly throttle the valve on the discharge side of the pump to see if this stops the cavitating sound. If it does, it means the pump is running to the right of its curve, lacking the TDH it needs to stay within its proper pumping range. This often happens when the operating pressure of the boiler was arbitrarily reduced from its original operating point when the pump was initially selected.