Aviation fuel piping 1

[HVAC68]

Hopefully, I am in the right forum to ask this question.

We are installing a 18" (450mm) dia pipe underground (to be buried under the apron of an airport) for carrying aviation fuel pipe. This involves 100% radiography and X-ray testing, etc.

There are some contractors who are able to do a good job. However, for a person from a different background, I would like to understand the methodology of installation.

I did some "google" search, but didn't very satisfactory results. Can anybody point to a website which will provide me the information - I have the material specs, but am looking for the installation methodlogy.

Thanks a lot.

HVAC68

 

[Creeker]

Can you clarify a little bit what information you are looking for?

To start, is it a new airport, or do you have to deal with removal and replacement of the existing apron and tie into an existing system? Do you have to build a valve chamber / vault?

Our contractors typically shop-weld 40' spools into 80' sections before field welding on-site. Excavation and field welding would start around the same time. Depending on the layout, the contractor would lift 200' to 300' sections into the trench at a time, followed by back-fill.

When we are tying into an existing system, the last section of pipe to go in the ground would be the tie-in section. The critical part of the tie-in is the drain-down, where you remove fuel from the existing line. This requires co-ordination with the fuel system operator and the airport for two reasons:

1. it will affect the ability to fuel aircraft between isolation valves.
2. more importantly, this is the most risky part of construction for causing a spill or worse, an accident.

If we're in a hurry to do a tie-in, we'll use a Plidco coupling (

http://www.plidco.com)

join the new pipe to the existing, otherwise a final field weld and x-ray.

Once the system is refilled, check for leaks all around and vent air out of the system.

Where are you / the work located? Do you have a contractor already?

Hopefully this is the sort of thing you are looking for.

 

[HVAC68]

Thanks for the immediate response. A star for you.

1. Yes, it's a new airport.
2. We have to build valve chambers.
3. There's time to do the job - However, I will check out the details regarding the Plidco coupling.

I am interested in finding out the work methodology for lifting the 200' to 300' sections into the trench at a time.

The data you have furnished is very much I am looking for. If there's a website that you can point to, which will give some detailed work methodology and some pictorial representations, it would be great.

Thanks again.

HVAC68

 

[Creeker]

Sorry, I don't know of any websites.

I also realise that I forgot to mention hydro testing and holiday / jeep testing. These are both done before the pipe goes in the ground.

I've seen both cranes and backhoes used to lift the pipe into the ground. Our contractor prefers to use the hoes, since he already has them around and you don't have to worry about height restrictions at the airport.

For a 200' to 300' section, there would probably be 3 hoes. The pipe would be assembled parallel with the trench, maybe 15' or 20' from the edge, so the pipe just has to be walked forward. The foreman would be directing, and they take it very slow. It definitely requires some co-ordination.

We prefer to use field welds over Plidco's, if at all possible, since the Plidco's can't be x-rayed.

 

[HVAC68]

Thanks again. This has given me some insight into the process and helped me whilst discussing with a potential contractor.

Best regards

HVAC68

 

[JohnBreen]

Hi HVAC68,

There is a very good piping forum here in the Mechanical Engineering section. I think I may have seen some discussion in the past on the type of system that you are describing. Eng-tips also has a Caesar II (software) forum where many piping engineers hang out. There is also the

http://www.coade.com

discussion forum for the Caesar II software (follow the "support" hyperscript).

Your design issues are "buried piping" (and how to perform structural analysis of it) and likely, the analysis of thin wall stainless steel piping. When you "Googled" you should have found some "hits" having to do with the several failures of such piping systems. These systems are typically thin wall (schedule 10S) stainless steel piping. Many of them have longitudinal seam welds (the pipe is made of plate that has been formed into a cylinder and welded. These systems MUST have "pulsation dampeners" (aka "pressure surge bottles") because at the delivery end they have VERY QUICK closing valves in case the fueler drops the hose while fueling. When the valve slams shut, there may be a significant pressure spike in the system. When the piping is manufactured, the "rounding" process together with the automatic seam welding DOES NOT leave the pipe with a circular cross section. Exaggerating a little, the resulting cross section is "heart shaped". When there is a pressure spike, the pipe section wants to "go round" (i.e., become circular in response to the higher pressure). Then when the "spike" diminishes the pipe cross section "goes back" to its manufactured shape. The problem is that after several (many) of these pressure transients the pipe may experience a fatigue failure in the area adjacent to the weld. The "pulsation dampeners" mitigate the pressure spike problem to some degree. Obviously, the consequences of a pipe failure under the concrete are grave.

Preparing the pipe trenches to "bed" the pipe is very important. The thin wall pipe must be protected from local denting so the material that is in contact with the pipe must be chosen with consideration of this. Of course, chlorides attack the pipe material and so the "bedding" material must also address this issue. Settlement can be an issue. There will be several "valve pits" (steel reinforced concrete vaults) located around the fuel system network and these may settle at a different rate than the piping. So, there has to be some "settling" gaps where the pipe enters and leaves the valve pit.

Regards, and good luck, John.

 

[JohnBreen]

..........having said all of that, take a look at this web site:

http://www.pipingdesign.com/

 

[HVAC68]

Thanks. I am not looking for the design aspects of the piping system, but on the construction methods.

As regards corrosion, we will be coating the pipes both internally and externally as well as do cathodic protection.

Our design engineers have taken care of the stress analysis and surge analysis and arrived at the minimum acceptable thickness of pipe.

HVAC68