Use of flanges in buried raw water pipeline

[JFCmech]

Hi
Does anyone have any experience in the use of flanged joints in a buried steel raw water pipeline? Is it a good idea? Has anyone done it? If so, what problems were found?

We are looking at 8km of 600NB pipe, with some above ground and some buried. The pipe has an internal epoxy coating, which would be easier to apply in 12m lengths, and quicker to install, as prefabrication is possible. This is a fast track project, hense the time concern. Cathodic protection and Denso wrap on outside. I'm not overly comfortable with the idea, due to maintenance concerns. Any thoughts?

 

[ione]

Forget flanged joints when dealing with buried pipes, this configuration is specified for aboveground service. Soil movements could produce critical bending loads on these connections, and this could be a concern due to the rigidity of the joint. For under ground pipeline butt welded connections are undoubtedly preferable.

 

[JFCmech]

Thanks, do you have any examples where flanges were used and this happened?

 

[BigInch]

I know of many examples where flanges were used both underground and offshore-undermud and nothing happened, but use welds... if you have a choice. If you don't have a choice, don't worry about it. Provide enough flexibility and you shouldn't have problems. But do put a protection clamp band around the flanges with a grease fitting and release valve and fill that space up. IMO corrosion is more of an enemy than stress misalignment.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

I bury flanges any time the client's spec's allow it (often they don't). Many of these burried flanges have been in the ground for decades, when we dig them up, the studs are always in bad shape and have to be scarfed off (even with grease applied prior to burial or those plastic grease-filled boots that have been around since the mid 90's, nothing works), but I've never found that to be a big deal.

On the other hand, a flange every 12 m will be the most expensive line ever laid. You didn't say what the design pressure of the line is, but I'll assume it is too high to use HDPE. It would be less expensive to weld the line and then pull a poly liner through it. They make those poly liners pretty long so you would only have a flange every couple of km or so (six flanges and a poly liner will be a small fraction of the cost of 700 flanges).

David

 

[ione]

JFCmech,

You can consider BigInch as one of the most authoritative members of Eng-tips and his advises are always valuable. Anyway, if I am not mistaken, you are still in a pre-project phase, and have to design a brand new pipeline. If so I wouldn’t go for flanged connections.

http://books.google.it/books?

id=Ja28hvTxVpwC&pg=PA390&lpg=PA390&dq=water+and+wastewater+flange+buried&s
ource=bl&ots=wy0ios2tgW&sig=cRxVIYGftjGZjRLw1EptRTNOMpU&hl=it&ei=rPViS5S2C
s2gsQab2cnGAw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CA0Q6AEwAA#v=one
page&q=water%20and%20wastewater%20flange%20buried&f=true

 

[BigInch]

ione, I do agree with you. There's no doubt that I do not prefer flanges above or below ground, but sometimes "you just gotta do what you gotta do."

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rconner]

Flanged joints have been a proven means of joining piping elements for hundreds of years; however, they are obviously also quite rigid and for the modern world also quite labor-intensive (if assembled rigorously!)and labor reliant. In addition, just the simplistic term “flanged joints” in and of itself does not necessarily/suitably define all elements conducive or arguably necessary for good long-term performance. There are all manner of past and present flange designs, fabrication/insulation procedures, bolting materials/types, and also gasketing material and types etc. that might be applied in the field. I think it is safe to say all conceivable permutations of all these things are confusing, not necessarily equal, and maybe particularly so for buried service (that might involve more uncertainties in support etc., than e.g. exposed pipes on surveyed pier supports or hangers with solid foundations).


AWWA Manual M11, Steel Pipe – A Guide for Design and Installation, includes the guidance,

“The requirements of installation and operation of a pipeline may dictate the use of more than one type of field joint. The type of internal lining and pipe diameter will also determine factors in joint selection. Bell-and-spigot gasket joints cost the least on an installed-cost basis. Flanges are commonly used to join steel pipe to valves, meters, and other flanged accessories. Thermal stresses may be a consideration…” Under the headings of “Valve Connections” and “ Flanged Connections” in this same manual, there are also some caveats for provision of flexible joints nearby, e.g. with the latter used at branch outlets, “”Outlet nozzles should be as short as possible to reduce the leverage of any bending force applied to the outlet. In general, every outlet should have a valve firmly attached to the mainline and a flexible connection to the pipe downstream from this valve.”

 

[MJCronin]

There are other types of mechanical joints available other than flanges that are suitable for buried piping.

Have you considered any of these ?

http://www.victaulic.com/content/default.htm

-MJC

 

[rneill]

I think the main concern with buried flanges has mostly to do with the difficulty of providing adequate corrosion protection (e.g., coatings) the awkward shape. Unfortunately, most of the alternatives to flanges for mechanical connectors (such as the Victaulic) will also result in an awkward assembly that will be similarly difficult to coat.

If as I believe the original question was one of being able to join precoated pipe spools of approximately 12 m length, there are even better solutions out there that will actually allow you to buttweld the precoated spools without causing damage to the internal coating.

Check out the Tuboscope Thru-Kote system and their U.B. insert fittings and sleeve system. Both systems allow for butt welded joints while still providing for the integrity of the internal coating. Externally, you can easily coat the joints for external corrosion protection.

http://www.nov.com/Tubular_and_Corrosion_Control/Tubular_Coating/Internal_Coatings/Line_Pipe.aspx

 

[JFCmech]

Wow - thanks for all the info and advice. I will check out the internal sleeve/liner idea, as the reason for flanging was partly to ensure a good internal coating. Our client may consider other options. The line is 25bar, so HDPE is not an option. I would love to not flange, but project timeline pressure may dictate its use. Cheers

 

[StephenA]

Ductile iron spigot and socket pipes would be much faster to lay than flanged pipes

Stephen Argles
Land & Marine

http://www.landandmarine.com

 

[brimmer]

On a personal note, I avoid using underground flanges like the plague (due to the number of leaks from external corrosion), sometimes I do have to use the odd one. I'll comment on Denso wrap coating as the other members have provided excellent comments in other areas. As per rniell, flanges are difficult to coat, my experience with the Denso is that it does not resist soil stresses and gets moved around by the soil, often leaving no coating on the flange itself over time. If your soil is clay, Denso will not hold up over time, dry sand, you might be okay. The wrap will become very brittle over time as well. The one thing I have noticed is that it seems to disbond so completely that it does not shield CP...

 

[cvg]

if corrosion is a big concern, then you should be considering methods of corrosion protection such as bonding, test stations, cathodic protection or imprest current. External epoxy or mortar coating should be the bare minimum and not expected to protect completely against aggressive soils. The fact that you do or do not have flanges will have little consequence on overall corrosion protection methods.

 

[JFCmech]

Thanks- We are about to get soil resistivity tests for the pipeline route. The soil seems to be mostly sand, rock and gravel. We have an added challenge of overhead powerlines crossing and running parallel to the pipeline route, so cathodic protection is most likely going to be needed. Apart from Denso, BigInch mentioned a grease filled protection band. Are there any brand names for these bands so that I can try and source them locally?

 

[BigInch]

Throw the rocks and gravel bigger than 3/4 inch diameter away.

http://www.m-p.com/flange protector belts.htm

http://www.drakespec.com/flangeprotector.html

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[brimmer]

If you have overhead powerlines paralleling the ROW, be aware that AC current can be induced onto your pipeline (either steady state or during a ground fault). Standards indicate the maximum steady state voltage acceptable is 15 VAC, otherwise you may be endangering operators. Where your pipe comes above ground you may need grounding to disipate current to protect workers, and you may need underground AC mitigation depending on any steady state AC levels induced on the line. You can also have the potential for AC induced corrosion on the underground section. Also, make sure the external pipe coating you use has a high enoug dielectric strength so as not to be damaged during a fault condition. Don't know what kind of current the powerlines have, but you should probably do some AC modeling to give you an idea. It is useful to do these studies before the line is built as any mitigation required can be installed at the same time, if after, it gets much more expensive. CP will not stop AC induced corrosion (if you have any) as you might have implied above? (but please do put CP on the line as before to protect against regular soil side corrosion), the AC will have little affect on your CP system.
As far as external coating for flanges, you are limited, they are all similar. I have been using Tapecoat H50 or H35 for a little added strength and mechanical resistance, I believe Denso makes a Densyl tape which is very similar you can use for added strangth over top, resists soil stresses better than just denso grease and wrap.

 

[zdas04]

brimmer,
Have you ever seen overhead power lines induce a current on a pipe? I've heard of it forever, but with the regulator's resistance to new surface disturbance, I've run pipe in high-line right of way many times and have never seen a charge accumulation on the pipe (and I've looked). I've also never seen increased external corrosion on lines that do not have cathodic protection.

I'm thinking it is an Urban Legend unless someone has seen and measured it themselves.

David

 

[brimmer]

Yes, I have seen it first hand (experienced a leak on an HVP pipeline!), and also caught corrosion in areas close by the leak before they leaked on the same pipeline (this is why I mentioned it, though in this case he is only installing a water line). The thing is you need coating disbondment for actual AC corrosion, even though you have AC induced on the line. You can measure AC potentials using a normal Cu/CuSO4 half cell and multimeter setting on AC, we see it in most locations where our lines parallel power ROW, usually voltages stay low enough not to be such a concern, but in many instances they are high enough we require mitigation (for safety and to stop any corrosion). We have measured AC voltages as high as 60. The longer your pipeline paralles the same ROW, the worse it is. CP will have little effect on stopping it, the areas of concern is where AC current leaves your pipeline at a coating defect.

 

[zdas04]

That is interesting.

David