Slope in steam lines

[morojlu]

Hi all,
The Slope in steam lines is different (exp 0.5%, 1%, 2% <---- as I see in some projects).
But Generally who should decide about the amount of slope (piping or process designer) and how the suffiecient slope is calculated? does any criteria exist to select the piping slope or related to experience?

Regards,

Mehdi

 

[dcasto]

I'm not a steam expert, the things I use to set the slope of any line that may have multi-phase flow are: outside temperature ranges, the ability to stop flow for long time periods, flow ranges (min, norm, max), pipe rack saging or bending, other elevation changes available, availability of future maintenance, and time available to study piping completely.

So steam piping in Alaska would be specified with more slope than in Kuwait. Steam purge lines that are off and on would have 3% or more. So experiance and thought about the total project will dictate.

 

[TBP]

Manufacturers with extensive backgrounds in steam systems & related products like Spirax Sarco, Armstrong, etc. have excellent references for this type of installation. Half an inch of slope in 10 feet is a pretty good rule. In some installations it can be necessary to go with a reverse slope, in which the condensate runs back to a drip leg under the steam flowing in the opposite direction (uphill).

I have never seen increased slope on steam lines in colder climates. The typical solution is to increase the insulation thickness. You might only need 1" of insulation in Kuwait, but may need 3" in northern Alberta. There is no other way but to run some calculations to determine what's both required and economical.

 

[rjstephens]

Hi Mehdi,

BS 806 requires a 1/100 slope with the flow for steam lines and a 1/40 against the flow for steam lines. Some of the clients require that more slope is used, but this generally causes other problems with weld fit-up and the use of pulled bends to accomodate the slopes, which is expensive.

Cheers

Rob

 

[RossABQ]

High pressure steam headers in constant use get the low end of slope, low pressure, cycling, saturated steam lines need the most. Driplegs should be full size up to 8"-dia. to be most effective but this is an area where contractors like to scrimp.

As noted by TBP, many programs for calculating condensate loading are out there; personally I like the TLV America methodology, which is in the free software download at this site:

http://www.tlv.com/en/index.html

 

[NozzleTwister]

I've worked on a lot of refinery steam sytems over the last 25 years and few if any had any slope requirements. They did have drip legs and traps at the low points and pockets.

NozzleTwister
Houston, Texas

 

[pennpiper]

My 45 years agree with NozzleTwister for a lot of refineries, chemical plants, petrochemical plants and even a few power plants.

 

[RossABQ]

Condensate removal is essential in any steam system. As long as you accomplish it, no problem. A positive slope primarily guarantees there is no negative slope, creating pockets or traps. HVAC steam systems tend toward overkill because they are unattended.

 

[0707]

“The subject of drainage from steam lines is covered in the European Standard EN 45510, Section 4.12.

EN 45510 states that, whenever possible, the main should be installed with a fall of not less than 1:100 (1 m fall for every 100 m run), in the direction of the steam flow. This slope will ensure that gravity, as well as the flow of steam, will assist in moving the condensate towards drain points where the condensate may be safely and effectively removed”


Go to

http://www.spiraxsarco.com/learn/modules/10_3_01.asp#link4

Cheers

Luis

 

[DSB123]

0707,
Spot on. Agree with your post entirely. I have been involved in many steam systems in the UK and practically every one of any length had slopes associated with them to ensure condensate drainage. I have seen the results of systems with inadequate drainage and it ain't pretty. You have rightly pointed to the spirax sarco site which gives recommended slopes for steam systems. Also in some cases because of the topography of the land slopes have been installed against the normal flow of the steam. In these cases the slops is increased to ensure that the condensate flows back to drain pots.