Pipe Clamp Slippage on Cold Insulated Line 1

[uaepiping]

Dear Experts,
In one of our plants, the clamp supports displaced from the sleepers and fell down. The line data is like this:
Size = 10"
Design Temperature = -22 °C
Operating Temp = -8°C
Design Pressure = 27 Barg
Operating Pressure = 10 Barg
The line is connected to a 24" line which is connected to pump discharge.
Line Material = ASTM A333 Gr. 6
Insulation = Cold
Supports are on the cold insulation.
The problem as we could see is that gradually clamps slipped over the insulation and fell down ultimately.
This may have happened overtime with the movement of pipe due to start/stop of the pump (as it is not continuous running pump - a tanker filling pump) and line shrinkage. The sleeper top plate has a round bar welded on it and the shoes of the clamp support rest on it. The sign of slippage were clear during the site inspection. These supports are clamped over 1mm thick cladding steel plate.
.
Question to all of you:
How to hold the clamp on cladding so that it does not slip. We need to do it while the line is in operation; without removing insulation. So any solution for this problem?

 

[TD2K]

I would suggest a picture is going to help people understand what may be happening.

 

[europipe]

What type of insulation is used?
Can You provide firmer insul. at the location of the clamp?(i.e. azobe)

 

[uaepiping]

@TD2K, The photo of this is not possible due to company security policy.

@Europipe, The insulation type is PUF.
The supports are as the image below.

 

[LittleInch]

The available clamping force is very low. Hence your support needs to be double or more what you have now.

I don't see the bar you mention and the detail at the support foot looks odd– too short?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

It appears that the diameter of the clamp is too large, not allowing enough clamping force. Replace the clamp with a proper size clamp. See the picture:

Information is available on this site:

http://www.pipingtech.com/blog/tag/cold-shoes/

 

[uaepiping]

@Littleinch, the rod is welded on top of steel plate of sleepers. A few supports are on structure as shown below. Similar is location of rod for sleeper supports.
.

 

[LittleInch]

The rod is part of your problem. Assuming it starts in the centre of the support, as soon as it moves, the support becomes loaded differently one end from the other.

Normally this is negligible, but with such a weak material to clamp on, my guess is that the supports become tilted ever so slightly. Thus when the pipe tries to sllde back, there is more resistance and hence the clamp will tend to slowly jack itself along the pipe.

I would remove the rod and insert a Teflon pad to allow the clamp to slide on the support with less force / friction. You might need to re-do the stress analysis as the analysis will have assumed a certain level of friction / force at each support based on the current design (metal to metal)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Gator]

I'm going to presume that the first CAD "supports" drawing is an example of a drawing representing not what is installed (multiple "plates" of some sort between underside of pipe shoe and top of support and evidently no round bar/rod shown).

Why is there a round bar/rod attached to the top of the support, does anyone know?

Why is this called a "sleeper" in the OP first post? A sleeper is often a grade-floating concrete beam used to support pipes in a tank farm area (and, yes, they often have steel pipe embedded in them so that suppported piping does not sit on a concrete surface).

Piping Design Central

 

[bimr]

What thickness of metal are the metal clamps?

 

[uaepiping]

@thanks Littleinch for the useful advice. One question to you and bimr? How can we increase the clamping force. The supports used for this line are almost similar to what bimr has posted above. What difference will this make? The supports have 6 bolts to provide the clamping action; three on each side.
Also providing the Teflon pad shall not be easy. There are 7 other cold insulated pipes on the same structure/sleeper which do not have the slippage problem.

What I see is that whenever the pump is started, the surge in the line moves the pipe with a jerk and when the line intends to recover to its original position, the friction (and the effect as Littleinch pointed out) comes into action and some slippage occurs and over time, this totals to the fall of the line from support. I was seeking something to do on top of the steel cladding, which would provide a resistance to slippage of the clamp. But so far unable to find anything.

@Gator, please read my post at 10:55. The sketch shown is for structure as it is at a few points. All remaining are on sleepers "as you described".

 

[LittleInch]

I know this will sound a bit odd, but why don't you just weld on a few spikes of a depth about 1/4 to 1/3 of the PUF thickness?

PUF is essentially a closed cell system so water leakage is not significant even when the surface is held under water or the outer coating breached. The PUF is quite strong and will resist force well.

If that isn'rt what you want they why not wrap the steel with a thin material before clamping it? The metal on metal thing may be too slippery given you can't really clamp this too hard before essentially squashing the insulation.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[uaepiping]

@Littleinch again a thanks!
I am not sure if I get your statement about PUF correctly. Will these spikes be on the clamps on side towards the pipe? The problem will be removing the cladding and vapor barrier on PUF insulation would cause the moisture accumulation on the pipe (which is undesirable) as this line is in operation. Though we can think of it in next shutodown.

Regarding non slippery thin sheet between the metal to metal, I was thinking of putting 3mm neoprene rubber sheet between the two metals to give slippage a bit of resistance. PUF has sufficient compressive strength and normally bears to the clamping forces.

I have another problem of finding way to reinstate this line to original shape. The line shrinkage was on one side of the expansion loop where no limit stop was provided. This leg is 180m long. On expansion loop side, the line is now touching the adjacent pipe dure to shrinkage. Now how to pick the whole line and provide new shoes (Thinking of providing new clamp supports with longer shoe lengths).

 

[uaepiping]

Does any friend have value of coefficient of friction between neoprene rubber and steel?

 

[uaepiping]

The reason for rod welded on sleepers and structural support as per L.C Peng in his book "Pipe Stress Engineering":

In many cases, the pipe is supported with a cross rod or angle steel, making the contact a point contact. This type of point
contact is created to prevent crevice corrosion on the pipe surface.

 

[bimr]

A steel rod welded on sleepers and structural supports will not be very effective in stopping corrosion.

The "rod" should be made of a hard thermoplastic, not Teflon or steel.

http://stoprust.com/i-rod-pipe-supports/

uaepiping, from your comments, it appears that this piping was not properly anchored (in the midpoint of the pipe run) when installed.