Hello,
In the Piping system we use dummy and base supports at a lot of places.
Till now I have seen/used both Pipes and Steel members as these supports.
I want to know that what is a general practice to use a pipe or Steel.
As profile cutting is easier on pipe dummies, still why we go for steel shapes.

Thank You
Siddharth Jain

The vast majority of the incidents where a Dummy Support or a Base Support is required pipe Pipe extension method is the preferred.

In my many years in the design office, the pipe fabrication shop and the field, I found this to be true.

The only place where I used or saw Steel Shapes used was in Hydrogen service where you wanted to avoid the possibility of trace Hydrogen build-up that could result in an explosion.

I'm seeing more and more steel shapes rather than pipe for dummy legs and base supports. Our standards here are all steel shapes. Ever see a L5"X5" on a 3" elbow for a dummyleg. It just looks very weird.....but thats our standard for the Exxon Mobil refinery I work in. I miss pipe dummylegs.

Thank You JOP and HC

So the real question comes from the answer of HC.
If it looks wierd (having ST3.5 or L5X5 on 2" or 3" Pipes/Elbows).
why our standards are going toward this?
do these provide good strength?
Probably not for small Sizes as we have problems of failure of Dummy Joint(welding point of pipe and steel) during the Dummy Check with Autopipe. Which prevents the use of long dummies.(Our stress group resticted us for dummy length of 1.5' till pipe sizes 4").

Thank You
Siddharth Jain

Sidjain,
You wrote:
"(Our stress group restricted us for dummy length of 1.5' till pipe sizes 4")."

I think we should all question the logic behind some of the "Restrictions" that are placed on us by "Stress Engineers"

Example:
I am currently looking at a "Piping Span Chart" for Seamless Carbon Steel A53 Gr. B pipe.
It recommends no more than 23'-0" span with a deflection of 1" for 2" Sch 80 pipe..

Lets consider three lines.
We have pipe supports spaced at 20' 0'' apart.
Line #1 - 2" sch 80 straight pipe that spans from pipe support to pipe support with no change in direction or branches. No problem.

Line #2 - 2" sch 80 straight pipe line that spans from pipe support to pipe support with two branches near the mid point . No problem.

Line #3 - 2" Sch 80 pipe line must leave the pipe rack 5'-0" short of the next pipe support we are restricted from using a dummy support longer than 1'-6". Why can't I use a 2" dummy to complete the span?

Thanks JOP for your inputs.
Yes it is right that we do not have any problem in Case1 and Case2.
Now for Case3-----
A) Do you want to Increase the HDR pipe till next Pipe support (i.e. 5' Away) and want to weld a cap with it?
But in this case it will become a dead leg for liquid and liquid will get accumulate there which is not acceptable.
B) If you want to use dummy support (i.e. Pipe dummies) our project standard refuses for it.

Now I want to make clear that with steel shapes everything works good except the welding between pipe and steel.
This welding gets fail for longer dummies, because of the higher moments generated.

One more thing our support standard allows us to use dummies of Length 4'0" till 4" Pipe size; But not the stress guys.

Thank You
Siddharth Jain

I'm surprised by your 1'6" restriction on your dummy legs. Thats really, really short. I'm looking at our steel shapes DL standards and Fluor pipe DL standards and they both allow for 6 feet max to the support and 12" after the support. That can even be extended once structural has done their calcs if need be. I'm actually a tiny bit surprised by stress limiting you below your standards which should have already been calculated by structural as strong enough. Why have standards then.

Some background:
I spent more than 45 years in Process Plant (Refineries, Chemical, Power, etc) Piping Engineering and Design.
My experience ranged from entry level to Piping Department Manager and included some related assignments into Materials Management, Field Engineering, pipe fabrication shop Engineering Manager and Software Development.

During my years I worked with people in all of the sub-groups of piping as a project Piping Lead and as the department manager. As department manager I was responsible for their hiring, training, assignment and performance.. The vast majority of the people in each piping sub-group were well educated, well trained, well experienced and possessed good common sense. There were also people who because of some unknown reason could not or would not perform at the same level as the majority.

The average EPC (Engineering/Procurement/Construction) company piping department is large and complex.
There will be:
70% +/- Piping Designers
10% +/- Piping Material Engineers
7% +/- Piping Material Control
6% +/- Pipe Stress Engineers
7% +/- Department Manager & Staff

I worked with a lot of Pipe Stress Engineers (PSE) and I have worked with some of the best. The large percentage (90% to 95%) of all the PSE that I came in contact with (on the job or as Manager) were very good to great. The balance were not worth having on the staff.

The reason the good Pipe Stress Engineer is good and the bad Pipe Stress Engineer is bad are related.

The good ones got to know the designers and worked with them.
The good ones could read drawings.
The good ones took the time to understand the design.
The good ones knew how to suggest alternates that might solve the problem.
The good ones would teach the designers how to avoid stress problems.
The good ones knew and understood that all the stress analysis in the world does not make a bad design good.
The good ones knew how to be a team player.

As the Project Piping Lead I say that a Pipe Stress Engineer who says that a 4" Dummy support must not exceed 1'-6" is NOT a good Stress Engineer and I would demand a second opinion and ask that he or she be removed from the project.

As the department manager I would remove the PSE from any project work until a program of retraining is successfully completed.

Damn Jop, I'd like to borrow your hammer and throw it down a few times. Maybe I wouldn't hate this business so much.

Thank You JOP and HC.
I am Agree with what you said.
But I have seen the Situation here. the Stress Guys are new in PSE (similar as Piping Design Engineers). More or Less having the same experience as of mine(~2.25yrs).
Currently they are very much reliable on Softwares. It will take some time for them to reach at the levels you mentioned as they grow as more experienced.
So probably I should not go in the direction of hiring and firing.
We should now stop this discussion here.

Thank You everybody who replied read this topic.
Thank You
Siddharth Jain