**COMMENTS ON NUMI DECAY PIPE REVEIW**

Robert Sanders

7/12/01

**(1) Decay Pipe Out-Of-Roundness**

> There appears to be concern that the wet cement, when it is poured,
> will distort the decay pipe into an oblong cross section at the ends.
> It could then become difficult to weld the end caps onto the decay
> pipe. There was also mention made that the contract with Healy may
> need to be changed to prevent or deal with this potential problem. In
> light of this, it is appropriate to look at the implications of the
> out-of-roundness specifications in section UG-80 of the ASME Boiler
> and Pressure Vessel Code.
>
> UG80 must be followed in order to use UG28 of the ASME code.
> Therefore, since the contractor determined the external pressure
> rating of the decay pipe using the equations from UG-28; the decay
> pipe must satisfy the roundness requirements of UG 80. If, after the
> decay pipe is installed and after the concrete is poured, the decay
> pipe does not satisfy the roundness requirements of UG 80 there are
> implications for both Fermilab and the contractor.
>
> For Fermilab, the ES&H manual chapter 5033 requires the decay pipe, as
> a vacuum vessel, be built to the ASME code. This is a safety standard,
> not a contract specification that can be changed at will. A damaged
> out-of-round decay pipe that does not satisfy UG80 is a serious and
> difficult safety concern that would have to be addressed through the
> formal safety review process of the vacuum vessel engineering note.
>
> For the contractor, if the Decay pipe after the concrete is poured
> does not satisfy UG-80 then it does not satisfy 3.1-A of the contract
> specification. Specification 3.1-A requires the decay pipe to be
> fabricated in accordance with the ASME Boiler and Pressure Vessel
> Code. The contractor is therefore obligated to repair or replace any
> damaged decay pipe. The contractor must be made to understand that the
> present contract requires that the entire decay pipe satisfy UG80.

**(2) Damage of Copper Pipe Due to Falling Concrete**

> The contractor is required by the contract to install the copper
> cooling pipes in accordance with ANSI standards. The applicable
> standard here is the ANSI B31.3 piping code. If, while pouring
> concrete, the contractor damages, bends and twists the copper cooling
> pipe then the contractor must either demonstrate that the pressure
> rating of the damaged pipe is adequate in accordance with the ANSI
> B31.3 piping code or else replace the damaged pipe. Permanent bending
> of the copper pipe causes work hardening and plastic deformation which
> will affect the pressure rating of the pipe. By emphasizing this to
> the contractor, Fermilab also minimizes the chance of the copper pipes
> being twisted about to touch the decay pipe and causing galvanized
> corrosion.

**(3) Concrete Pouring**

> In light of comments #1 and #2 above, it is mandatory that the wet
> concrete be poured in such a way that the decay pipe and copper
> cooling pipes do not suffer permanent deformation or damage.

**(4) Plastic sleeves on Copper Pipe**

> The copper cooling pipes pass through the ring stiffeners placed every
> 210" along the length of the decay pipe. Plastic sleeves should be
> inserted into the holes in the stiffeners through which the copper
> pipes must pass. One end of the sleeve should have a lip to prevent it
> falling through. Perhaps the sleeves could be glued in place. Ideally
> the sleeves would have a snug fit around the copper pipe to help
> restrain its deflection.

**(5) Deflection of Copper Pipe**

> To prevent the copper pipe from deflecting and touching the decay
> pipe, consider keeping the copper cooling pipes under tension when
> pouring concrete. This will greatly minimize the lateral pipe
> deflection while being agitated by the swirling motion of the wet
> cement. Copper pipe of this type are sometimes pulled through holes in
> the ground much like pulling wires through conduit. It effect, you
> would be pulling the copper pipes into the straight paths you want
> through the wet cement.
>
> One could also consider using circular disks of plastic with annular
> holes that slide over the copper pipes. These spacers, placed at
> discrete intervals, would keep the copper pipes from touching the
> decay pipe. The axial position of the plastic spacers could be
> maintained with clamps (or tie-wraps???) around the copper pipes.
>
> The possibility of using commercial processes to coat the copper pipe
> with dielectric coating could be considered. See item #9 below.

**(6) Future Larger Vacuums Pumps**

> Fermilab should not do anything to prohibit the installation of bigger
> vacuum pumps in the future if the need for them ever arises. What is
> done is done, but just don't back yourself into corner in case vacuum
> problems develop.

**(7) Additional Ports**

> The decay pipe should have a drain at the bottom and a vent at the
> top. They could be welded off, but my strong personal preference is to
> run the pipes to an accessible location and install high quality
> valves such as Whitey ball valves that are vacuum tight and lock them
> shut. The drain valve could be used to drain water or vacuum pump oil
> from the decay pipe. The drain and vent valves together could be used
> to purge the decay pipe with nitrogen gas to dry it, if the need ever
> arose.
>
> Additional vacuum instrumentation ports (i.e. ¼" SS tubing runs)
> should be installed at the decay pipe top and bottom as well. Do not
> add instrumentation, but if vacuum problems arose additional
> instrumentation could be added to these ports to aid with the
> diagnostics. I would terminate these taps with high quality valves
> such as Nupro 4BKs and lock the valves closed. These ports may never
> be needed but this is a cheap thing to do. Minimizing the number of
> instrumentation ports is not a good practice especially on a on a ½
> mile long vacuum vessel.

**(6) Safety What-If questions**

> What would happen if the entire decay pipe filled with water? Also
> what would happen if the entire decay tunnel filled with water but not
> the decay pipe?

**(7) Fatal leak Size in Decay Pipe**

> The vacuum pump will have a speed of 400 cfm pumping down to 1 Torr.
> How big of a hole would it take in the decay pipe to overcome this
> vacuum pump? The leak rate would be 400/760 = 0.526 scfm air. If I
> assume the hole in the decay pipe is a sharp edged orifice (flow
> coefficient of 0.62) with choked sonic flow of air with an upstream
> pressure of 14.3 psia (Fermilab typical ambient air pressure) and
> apply equations from the AGCO series 80 catalogue; I find a hole size
> of .06" diameter in the decay pipe could cause such a leak. My
> calculations should be checked.
>
> That's about a 1/16" diameter hole - a pretty big hole - in the decay
> pipe that would overwhelm the vacuum pump. My gut feeling is that
> leaks much-much smaller than that would be found by the leak detection
> test specified in the contract section 3.7D for the decay pipe welds.
>
> I feel that NUMI is on the right track by closely monitoring how the
> leak testing is done. If the tests are done properly, it appears there
> should be little problem achieving the desired vacuum in the decay
> pipe. Knock on wood.

**(8) Leak Testing Advice**

> If expert advice is needed on the solution film leak teak testing
> decay pipe, there are independent non destructive testing (NDT) labs
> and companies in the Chicago area. Argonne National Lab , many years
> ago, had a very good non-destructive testing group and for all I know,
> it may still be good.
>
> If you really don't trust the contractor, an outside NDT group could
> be brought in to do some spot checks on the leak testing

**(9) Decay Pipe Paint Job**

> Underground pipelines are common. The companies than put in
> underground natural gas and oil pipe lines certainly expect their
> pipelines to last much longer than 10 years. By applying the same
> technology used for these underground pipelines, it should be possible
> to get the decay pipe to last 10 years.
>
> Since there is concern about corrosion on the decay pipe, Fermilab
> should look at proven techniques used to prevent corrosion on
> underground pipes. I recommend reviewing the adequacy of contract
> specification 2.1 D for painting the decay pipe. Perhaps (and perhaps
> not) an additional coating should be applied to the decay pipe or the
> copper cooling tubes to prevent corrosion. For example if a dielectric
> coating is needed, there is a company BendTec (
> http://www.bendtec.com/coatline.html ) which among other things can
> paint and apply dielectric coatings to large underground pipes to
> prevent corrosion.