Slope for steam line 4

[PAN]

My senior comments that I should make slope for steam line. I checked previous design in the existing plant and found that no slope. There are only steam trap and low point drain (from drip leg). Is this a good design practice to make slope? In my opinion, it is not standardized to weld the inclined pipe shoes for setting the line at the same elevation. Please comment.

 

[jproj]

In my experience, steam lines have a negative (down-hill) slope such that if steam in the line condenses to liquid, the liquid will drain in the direction of the flow to a point where it (liquid) can be removed.

jproj

 

[TBP]

Steam lines MUST have slope, as no matter how effective the insulation is, some heat will always be lost, and a portion of the steam will condense. This water must be effectively removed. The preferred method is forward slope, in which the steam and condensate flow in the same direction. Recommended forward slope is 1" in 20 feet. You can also have reverse slope, but some care needs to be given to more frequent drip-leg/trap arrangements, and steam velocity, as the steam and condensate are running in opposite directions, in the same line.

Spirax Sarco's literature has some good info. The more basic book is "Steam Utilization", and the one I carry around with me is "Hook-Ups".

If you want some graphic reports of what can happen with improperly drained steam lines, check out

http://www.kirsner.org

. There are several published reports on accidents due to water hammer with large steam systems. These usually happen at low pressures, on start-up.

 

Slope in steam line is must to remove the condensate. .If slope is not provided there may be chance water hamering

 

[TD2K]

I'm going to go against the general theme here and say that sloping of steam lines is not typical in my experience.

I also talked to a couple of other engineers who have worked in many plants and they do not recall that this is a typical installation/construction detail in their experience either. I talked to one of our senior piping designers who said he has seen it in a couple of plants as a customer requirement but the majority he has worked in do not require steam lines to be sloped to low points. It could be that they weren't aware of it yet all were aware of ensuring flare lines are properly sloped yet no one recalls steam lines being sloped as a routine design practice.

Condensate removal from steam lines in my experience is addressed by installation of drip legs at various locations, either where the steam header rises up or at every xx ft down main headers where xx is set usually by a company's engineering specifications.

 

[TBP]

I've been "up close & personal" for a couple of very interesting (read "terrifying&quot water hammer events. I didn't much care for the experiences, so I do what I can to get condensate out of steam lines as quickly & effectively as possible. There's just nothing like being the guy actually holding on to the valve handwheel, or standing very close to him to really focus your interest in this matter. Especially if you're down a manhole, or all squashed into some little space between equipment and piping with no quick & easy way out.

Do the plant operators and maintenance people a favour by helping condensate drain from steam lines by sloping them to the drip legs. Really.

 

[UtilityLouie]

I would have to agree with TD2K. I have specified sloped steam piping, only to be laughed at by construction management and contractors. When you hear an old timer pipe fitter say that he has never, in his 20 years of installing pipe, installed a sloped steam line. You wonder what is really going on out there. I have gone back and made pipers slope lines that are on roller type clevis hangers, but with welded shoe type bottom support, this can't be done too easily.

The truth is that sloping steam piping is the correct way to do things. However, in actual application this may not happen. The best way to make sure that you don't have a water hammer event is to drip trap your mains. I have read a rule of thumb for drips is one every 200' for piping sloping in the direction of flow and 100' for piping sloping against flow. A drip at a riser will take the place of one of these drips. I put a trap every 100' just to cover myself.

This is a case of engineers knowing the correct way something should be done and the field doesn't believe that it is important. Cover yourself. It might cost a little more, but unless you get a contractor you can work with, you need to make sure your design is a good one.

 

[TD2K]

I think the point here is to ensure you get the condensate out of the steam piping. Sloping the line to the drip traps isn't the answer if the trap fails. I wonder how many water hammer incidents occured because bypasses or drains on the piping weren't checked or left open during startup to ensure that you were removing all the condensate from the piping.

TBP suggested a slope of 1" in 20 feet. The main piperack along the back side of our crude and FCCU cracking unit is close to 3000 feet. I can attest that one end isn't over 12' higher than the other end.

 

[jproj]

PAN:

I have seen a recommended slope from as little as 0.25" in 100' to (listed here) 1" in 20'. Given that your senior (as well as nearly everyone here) is telling you to slope the steam line, I would recommend that you listen. They have the experience. If you want to know how much to slope the line, ask your senior. If you disagree, confront your senior with your concerns! Let your senior share their knowledge and enlighten you (there's no substitute for communication!).

jproj

 

[svanels]

Well I want to point at some facts in the industry:

1) The steam system in it's totality is overlooked as an area which needs proper attention and preventive maintenance.

2) Steam leaks are in most cases repaired when production targets are in danger

3) Plants are loosing 30% or more of their steam production in leaks if they do not have a pro-active maintenance program which focusses op steam trap inspection and repairing.

4) In a small petrochemical or chemical plant with medium pressure steam and steam tracing on product lines you can encounter easily more then 500 steam traps. Are they regularly checked and inspected? The answer is no.

5)Companies are throwing money into their boilers and are not even aware of it.

6)These facts show that people do not know what they are dealing with. The construction guy in general do not know the sh.. he leaves behind when there is no slope. I will try to get a number from the books, but I would point to a very interesting article called"Steam Trap Performance Assessment" from The US Department of Energy

http://www.pnl.gov/fta/15_steamtrap/15_steamtrap.htm

Regards Steven van Els
SAvanEls@cq-link.sr

 

[TBP]

svanels - you are right on. I've seen companies actually purchase & install an additional boiler, only to discover that it made absolutely no difference at all. The problem wasn't steam production related, it was totally a steam distribution issue. For a fraction of what that boiler cost, they got some of the more severe sloping/traping/sizing issues addressed. Presto - things work a LOT better, and...they don't even fire the additional boiler. They don't need it.

And don't even get me started on piping code issues. It is nothing short of amazing that there aren't more fatal accidents.

 

[br549]

The answer to this question is always room for debate!

1. Good pratice says slope and trap to the excess, if you have ever seen An 8" elbow separate because of water hammer start-up you will understand.

2. Because you specifed slope dosen't mean your contractor installed it that way.

3. Provide for easy warm-up on start-up is also a key. Large bore piping with quick opening valves lead to trouble. Provide a small by-pass to allow steam to heat up the piping befor full flow.

 

[svanels]

I have seen a recommended slope of 0.5%, if this unacceptable devide the line in several parts with collection points at every 30 to 50m. In general, steam headers have expansion loops, where the loop is on a higher elevation, this is the apropriate place to put collection points. On a piperack of 3000 ft, the crude line should be straight, but steam headers should have expansion loops on different elevations. Steven van Els
SAvanEls@cq-link.sr

 

[PAN]

svanels,
Your latest reply reminds me to ask another question about expansion loop. I always find the expansion loop of steam line in horizontal. However, you said steam headers should have expansion loop on different elevations. Please comment.

 

[svanels]

The expansion loop or U is in a horizontal plane, but at a higher elevation than the straight header. The direction of the header would be:

north --> up --> east --> north --> west --> down -->north
Steven van Els
SAvanEls@cq-link.sr

 

[svanels]

TBP wrote "There's just nothing like being the guy actually holding on to the valve handwheel"
I have found some very very interesting articles on this topic at

http://www.kirsner.org/pages/articlesAlt.html

in PDF format.
These articles are about accidents with steam, condensate removal, and the mechanisms involved.

If you read the following articles: Condensation Induced Waterhammer, and What Caused the Steam Accident that Killed Jack Smith? , you will understand why steam lines must have a slope among other things. Steven van Els
SAvanEls@cq-link.sr

 

steam piping should be designed for complete condensate removal. how? by providing drip legs on all low points and dead ends and by installing steam traps at low points and drip legs of the steam header.

damage due to the water hammer - sure if condensate is present and startup procedure is not done right. slope is not the answer. this is easy to find out. climb a cage ladder and check out the main steam header on the pipe rack. what do you observed? its very crooked most especially near the limit stop and the loops. no point checking out the slope there. check out the pipe shoe and notice that a lot are lifted. again no point checking out the slope.

 

I'd like to hear about any specific water hammer experiences in steam systems you have had--especially if you can tell me what the circumstances were that led up to the hammer (like a manhole flooded or a blocked trap). You can contact me thru my website at

http://www.kirsner.org.

In answer to the slope question, standard engineering specs call for 1/4" slope in 10' for steam flow in direction of pipe pitch. Traps are recommended to be from 300 (newer) to 500'(older) apart in mains if there are no other rises in the line. Traps on mains have safety factors of around 20 in pipe that is perfectly insulated. Assuming pipe is only 80% insulated (as SARCO does in their tables) smallest traps are still way oversized for load so no need to put traps closer than 300'.

 

[AJN]

I have just joined Eng Tips - very interesting

Good design dictates that principal distribution mains incorporate a slope of no less than 1:240 (or thereabouts)in the direction of flow.

Clearly this must be complimented with adequately sized drain stubs and trap sets if effective condensate removal is to be achieved.

 

[benriemens]

I've been very close to a 30" steam line at startup where the designers told us that no slope and drains where needed.
First time we started introducing steam in this line.......
Once but never again I would like to see this happening.
This 30" line started to have a life of it's own, moving 1 - 2 meters at each hammer blow!!

So please don't tell that there isn't a need for sloping and traps!

Ben