Drip Legs in Steam Lines

Drip legs are to be provided at all low points. The quantity of the condensate likely to collect at the point is to be calculated depending on the associated pipe length and other parameters.

Yeah that is a useful information for all of us, but my question is what r the calculation behind calculating the distance between two driplegs. For example: suppose there is a 150 m horizontal run and there are 3D loops on both sides. as we know after some distance the condensate will start forming and later on it may cause the water hammering effect. what r the calculations behind this thing i.e. distance after which the subtantial amount of condensate starts forming which will lead to the surge formation.

Before every expansion loop elbow you must provide a drain point. Otherwise there will be pitting of elbows due to the condensates. Considering the normal span of the expansion loops, it is not necessary to make the detail calc for the condensates.

I think it was really good explanation. But Mr. Mech Can we go in a little more depth?

1. could you please put some light on both the tables. I mean if you could take an example where you calculate the Warm Up load and Running loads for a particular case??

2. How to proceed futher in calculating the Distance between driplegs after determing the two loads mentioned above?. ( i understand as u mentioned it is difficult to come at some specific figure).

I want to know about the warm up load and the running load ? How these loads are going to make an impact on my sysetem? I feel warm up l oad will come into play only during start up case of system.

Hi guys,

Sorry I can't explain anymore right now - it is 3:00 am and I am going to bed.

Please download and review the following two documents on the righthand side of the page: Design of Fluid Systems: Utilization and Hook-ups

http://www.spiraxsarco.com/us/training/

If you have would like more details, after review those handbooks, feel free to reply and I will get to them in the morning.

And yes, anoopbindal - you are correct, the "warm-up" load does only come into play during start-up (both initial start-up and any start-up after the line/system has been out of service for any length of time {multiple hours or days})

I do not believe there are any calculations........one has to look at the system drip legs can be installed not only length but also determined how many impingement areas there are, such as valves and such. And if your in doubt, .........ask someone there that may know for assistance (if there is such a person), its hard for us to tell you......we are not there or even know the system.

phoenix911

Xmech has provided very in-depth answers and resources in which to calculate the amount of condensate forming in the pipe as it is being distributed through the line.

I do want to make a couple of comments/clarifications:

• Steam pipe should be pitched 1/2" per 10 ft
• Trapping distances should be between every 100 to 200 ft. Running 300 ft without a steam trap does not provide adequate protection against waterhammer due to if one of the traps fails, condensate could travel 600 ft before reaching an operational trap, which will be a HUGE waterhammer issue.
• If the condensate needs to flow counter current to the steam (due to pitching the pipe in the opposite direction of flow) then the steam pipe should be oversized (usually by 1 pipe diameter) and trap intervals should increase to every 50 ft
• All drip traps should be sized for start-up load. Note that unless your pipe is in excess of 6", a typical 3/4" steam trap has sufficient capacity for the application.
• In addition to adequately spaced drip traps, the drip pocket MUST be designed correctly, or the condensate will not have an opportunity to fall out of the pipe & into the trap. The drip trap should located at LEAST 18" below the header pipe. The diameter of the drip pocket should be equal to the steam main up to 6". After which it can be 1/2 the diameter of the steam distribution pipe, but not less then 6" in diameter.

Please keep in mind, as was illustrated in Xmech's post, if you distribute 100 psig through a 6" pipe, the warm-up load is 67 lb/hr, which is 8.02 GPH. That is approximately 1 CUBIC FOOT of water per Hour per 100 ft! The amount formed can be even greater right at the boiler header due to carry over (boiler water gets sucked out of the boiler and into the steam header - YES, it happens all the time, and is the #1 reason for hammering in the steam header).

With that said, drip legs and their associated pipe should be considered SAFETY devices in a steam system, and as such should be:

1. Installed every 100-200 ft
2. Installed at every natural low point in the system
3. Any change of direction in the pipe (especially vertically up)
4. At the end of all steam lines
5. Off of process equipment
6. Upstream of every isolation valve
7. Upstream of any modulating/on-off control valve

You can go to the following link to calculate your start-up load (and if you click on the question mark it will provide more in-depth information):

http://www.spiraxsarco.com/us/resources/calculators/pipes/start-up-and-running-losses.asp

For more information on proper hook-up & lot's of supporting mathematics:

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-distribution/steam-mains-and-drainage.asp

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/equations/equations.asp#head44

At the end of the day, use the chart for start-up & running loads provided by Xmech as they are accurate (as long as your ambient temperatures are not below 0 deg F -you will need to apply the correction factor for 0 deg F shown on the table, but it works).

Alternatively, you can go to the following web site and download the free software that the US Department of Energy uses, and it will calculate the BTU loss in various pipe diameters & modify that loss based on insulation type & thickness.

http://www.pipeinsulation.org/

As a final side note/parting comment: HP, MP & LP are relative terms depending on the industry in which the steam is being used and the individual facility. Power Plants HP, MP & LP are typically 4,000 PSIG, 1,000 PSIG, 300 PSIG, 100 PSIG. Hospitals 100 PSIG, 80 PSIG, 50 PSIG, 10 PSIG. So as you can see there is a HUGE disparity...

between 75 -90 meters and maximum 150 meter.

This is old, and it ruffles some members feathers for whatever reason…

It depends on where the steam is being deleivered too.

As mentioned in previous posts, drip leg are position at low points.

If its where you require a dry steam such as culinary steam any type of impingement points at atleast imtermedary.