Re: [PipingDesign] Sloped headers

From: <John>
Date: Tue Jan 15 2008 - 07:47:00 EST

In very high temperature piping trunnions, staunch ions, or "Circular Hollow welded attachments" to the header that then go downwards to a plate have an advantage over shoes or saddles that are extremely long (greater than 12").

The longer the welded attachment the greater the chance for differential thermal strains to build up. Don't forget that the attachment loses heat drastically after it leaves the insulation, so while where its attached to the pipe it may be at 1100F at the bottom of the saddle or shoe it may only be @ 300 - 400 F. This differential may cause extremely high strains to form at the weld line. There are strategies to negate this such as skip welding etc..

However the trunnion or welded pipe can have as long a baseplate on it as required with little differential strain becoming a problem. Excessively tall trunnions should be avoided because they will create an overturning moment when the base plate is asked to slide. And finally don't forget to grease the sliding surfaces.

Best Regards,
John C. Luf
Cleveland Ohio U.S.A when I'm not in Austria

Member B31.3, Piping Engineer - Stress Analysis, Pipe Supports, Component Design, and Surge Analysis... according to my daughters master of unimportant trivia

http://suntzuquote.blogspot.com/

             Hi Mandar,

Thank you. I appreciate your explanation. I have always worked to three

definitions to your one: "Trunnions", as I previously described. "Dummy

legs" (horizontal piece of pipe welded onto an elbow), and "Base Ell

Supports", such as those used at a control valve station and as you say

a vertical piece of pipe welded "downwards". It is interesting and

important to recognize that, while we all do the same work, we differ in

our vernacular.

I agree that a base support, or vertical trunnion would work for

convenient elevation change, however this approach mandates that a plate

be incorporated into the design on the piperack TOS that is of adequate

size to accommodate the thermal growth. While I personally have not seen

base supports used in a rack, I'm still inclined to agree with Ravi's

checker. Not because it's unconventional to me but because shoes meet

the requirement without adding a plate.

Plus, using Ravi's 120m distance and a conservative slope of 1:500. The

first base support is going to have to be 315mm high and work down to

75mm to give the fabricator some meat to work with. A shoe has a

horizontal length to vertical height ratio of 3:1 (300mm long x 100mm

high). Assuming a NPS 6 base support this ratio is 0.53:1 at the highest

support down to 2.24:1 at the lowest. Regardless of the NPS pipe size

for the base support, it'll never be as favourable a ratio as a shoe,

and I predict a higher likelihood of binding with the base support

design over the shoe design.

It's an opinion, and we all learn from sharing.

One last thing. I have never heard of a client opposing base ells or

dummy legs on elbow. What is the reason for this?

Best wishes, and thanks for the fast response,

Richard B.

Calgary, Canada

  -----Original Message-----

From: PipingDesign@ yahoogroups. com [mailto:PipingDesign@ yahoogroups. com]

On Behalf Of mapte@technip. com

Sent: January 14, 2008 11:19 PM

To: PipingDesign@ yahoogroups. com

Subject: RE: [PipingDesign] Sloped headers

Richard,

A trunion can be defined as a dummy pipe welded to a pipe for supporting

purpose (i.e. without puncturing the main pipe).

This trunion can be on verticle pipe (One that you have explained) or it

can be on a horizontal pipe (Downwards)

The trunion on horizontal pipe (Downwards) supports the pipe from below.

Additional supporting arrangement can be added to the trunion like

guides,

anchor, adjustable supports etc...

Advantage of using trunion on sloping horizontal pipe is that the

trunion

length can be varied as per the slope, but the supporting beam elevation

(On which the trunion rests) can be same.

If the line size is too big a finite element analysis may be necessary

to

determine if the trunion can take the load (Normally the support

standards

are prepared taking this in to consideration)

Trunions are very commonly used to support the control valve stations.

Trunions can be either welded to the pipe or to the elbow (Although some

clients do not prefer trunion on elbow)

Have a nice day.

-Mandar.

Motivation will almost always beat mere talent.

Richard Beale

<r_beale@shaw. <mailto:r_beale% 40shaw.ca> ca>

Sent by: To

PipingDesign@ yaho PipingDesign@ <mailto:PipingDesig n%40yahoogroups. com>

yahoogroups. com

ogroups.com cc

Subject

15-01-2008 09:15 RE: [PipingDesign] Sloped headers

Please respond to

PipingDesign@ yaho

ogroups.com

Hi Mandar,

I just read your post on this subject. By now you've seen my post. I am

still puzzled as to how trunnions would apply in a sloped line, whereas

you're seeing something I don't. Can you help me in this? If my

definition of a trunnion matches yours, how does this apply to a slopped

line? If my definition of a trunnion differs, then in what respects,

and specifically in regard to the use in a sloped line.

Many thanks,

Richard B.

Calgary, Canada

-----Original Message-----

From: PipingDesign@ <mailto:PipingDesig n%40yahoogroups. com>

yahoogroups. com [mailto:PipingDesig n@

<mailto:PipingDesig n%40yahoogroups. com> yahoogroups. com]

On Behalf Of mapte@technip. <mailto:mapte% 40technip. com> com

Sent: January 14, 2008 9:51 PM

To: PipingDesign@ <mailto:PipingDesig n%40yahoogroups. com>

yahoogroups. com

Subject: Re: [PipingDesign] Sloped headers

Ravi,

There is nothing fundamentaly wrong in using trunions for sloped lines.

Some companies use trunions of a certain maximum length (e.g. 400mm). If

your trunion lengths are within the support standard allowable lengths,

it's OK.

If the line runs on shoes/saddles, the supporting structure elevation

has

to change after every few supports.

However some clients (Operators) do not prefer pipe sections in supports

due to difficulties in monitoring their corrosion.

Check if this is applicable to your project.

Have a nice day.

-Mandar.

Motivation will almost always beat mere talent.

ravi patel

<ravi_9211@yahoo.

com> To

Sent by: PipingDesign@ <mailto:PipingDesig n%40yahoogroups. com>

yahoogroups. com

PipingDesign@ yaho cc

ogroups.com

Subject

[PipingDesign] Sloped headers

14-01-2008 20:47

Please respond to

PipingDesign@ yaho

ogroups.com

In the current project of a petrochemical plant, one of the senior

designers had run a sloped header 120 m long on trunions of varying

height.

he had issued the drawing 2 months ago.

Now we have a senior checker in company, who was going through the model

review.

he wants it to revise the header and run it on shoes/saddle.

I just wanted to know whether anything was wrong with using trunions.

Is it fundamentally wrong to run sloped headers on trunions??

Thanks

Ravi

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Received on Tue Jan 15 07:47:00 2008

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