Ribbed neoprene for clamp

[fremgym]

Hi,

Does anyone here knows the function/ purpose of ribbed neoprene for offshore riser clamp? I've been searching for the difference between ribbed neoprene and flat neoprene with respect to its function. Just want to understand why some design specify flat neoprene and why some other design specify ribbed neoprene.

Thanks.

 

[BigInch]

Most likely the ribs are somebody's attempt to increase friction. I've always used flat. I think that flat has more surface area in contact with the pipe, so you might get more net, and more uniform friction using that, however more pressure might be developed under the rib, even if total net frictional force might be more, the same or less. I think flat neoprene and bolt tension develop enough friction to hold a pipe, provided the contact area is sufficient, without resorting to ribs. But you know how it goes today. Everyone wants some new and better gimmick to sell something. I guess I wouldn't have a problem using either, although some people might just have a preference for ribbed everything.

 

[fremgym]

Thanks BigInch for your thought.

In my case, it is a sliding clamp. A sliding clamp for offshore riser. But its neoprene is ribbed. I just don't understand why ribbed is provided. The outer diamter of riser (including LPE coating) has clearance about 5 mm with the inner diameter of the clamp (inner surface is ribbed neoprene). I was made to understand that the neoprene is provided as a coating. Riser is allowed to move axially upwards because it is subjected to vibration and expansion especially during transporting hydrocarbon.The sliding clamp is provided to restrict its movement laterally. neoprene is provided so that the movement of riser axially will not scratch the common coating. Hence, the reason of using neoprene to protect the inner layer of riser clamp.
But i still don't get why ribbed is provided for sliding clamp.

 

[SJones]

This report alludes to the use of ribbed neoprene "to accommodate potentially large lack of fit tolerances:"

http://www.hse.gov.uk/research/rrhtm/rr031.htm

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[fremgym]

Hi SJones,

Thanks for the reply.

 

[BigInch]

Interesting. Making an axially guided clamp. I've never done that.
What is,
Pipe diameter?
Coating thicknesses?
Clamp ID?
How thick is the neoprene, flat to top of rib?

 

[fremgym]

Hi BigInch,

Pipe(Riser) OD: 660 mm
Pipe(Riser) coating thickness: 3 mm LPE
So, TOTAL thickness of Pipe with LPE coating = 666 mm

Clamp ID: 726 mm
Neoprene thickness (top of rib)= 25 mm
Thus, effective clamp ID (considering 25 mm of top of ribbed neoprene)= 676 mm

So, there is 5 mm clearance in between Pipe OD and Clamp eff. ID.

You can refer to my attachment.

 

[BigInch]

Big difference in theory between this design and my methods. I have never seen anyone try to design sliding pipe clamps when running vertical pipe. Especially for such long distances up the side of a platform. The jacket braces will easily take the load of the pipe at each clamp. I've always designed all clamps as axially rigid that do not allow sliding. In my designs I have always used friction to hold the weight of the pipe at each clamp, so I do not want any clearance. In fact I want a tiny bit of negative clearance to ensure that full friction forces can be developed. I have always made the ID of clamps equal to the OD of Pipe plus Coatings.
Since the clamps do not form a complete circle, because there is always 100mm clearance between them where the clamp halfs come together for bolting, there is no need to try to hold such close tolerance of 5mm clearance. As the bolts are tightened, the flat neoprene will grip the pipe very well.

So you have all the weight of everything hanging on the one "hanger clamp" at elev 5629? What if that one corrodes, or something on a supply boat hits it. No other clamps to rely on, pipe falls into ocean. I've been diving on platforms years after they were constructed and have seen that construction contractors did not even close some clamps I had shown on my design. They ran the pipe through an open clamp, wrapped a "temporary" cable around it and never closed them, with no support provided to the pipe at all in any direction! I hope that close that one.

 

[BigInch]

Additional comments,

Considering the size of the pipeline, supposed tolerance is far too close both in ID of clamp and in the design dimensioning of the clamp's holding bracket.

I would been expecting to see a multidimensional clamp, that would enable sliding and 6 axis adjustments. A clamp in one axis, holding a clamp in another perpendicular axis. Such as one like this, or perhaps a similar variation of the same,

https://www.google.com/patents/US3557564

Furthermore, there does not appear to be any protection for the pipeline installation within the reigon possibly exposed to work and supply boat impacts. No fenders, or bumper guard of any kind is shown on the drawings. Nor does there appear to be any working platform installed in the vicinity of the ESD valve for testing and maintenance. Is someone supposed to hang on a rope from the celler deck while attempting to examine instrument tubings, or perform operational testing, or to simply lubricate the valve?

 

[LittleInch]

The drawing clearly says "J tube" in a couple of places so it's not a riser and should not be subject to any thermal movement or "vibration"

So why someone felt the need not to clamp it to the jacket I don't know.

The only reason for the ribbing as far as I can guess is that this makes it more "squishy" and hence any wave motion or other force can be absorbed into the bumps.

also during installation maybe someone thought it was less likely to "stick" if the tube was lowered from the top without damaging the coating of the J tube.

The continued integrity of the coating may have been considered as this allows water and air to pass around the j tube and drain out the other end without causing any areas where the pad might have stuck to the coating.

We're all guessing wildly, but my only real answer is that flat is for a proper clamp and ribbed is used for guides??

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

 

[BigInch]

It'll get plenty of vibration from waves alone.

What size is the actual pipeline?

 

[fremgym]

Hi,

Sorry for delay response.

To answer some questions:

a) "...something on a supply boat hits it..."
There is guard being provided to absorb impact from workboat/ supply boat.

b) "...What if that one corrodes..."
I believe they have periodic inspection to cater for that. It is above water and can be visually inspected. There is maintenance platform provided at that area and that elevation.

The drawings given are not full drawing because I do not own the drawings. I'm from fabricator side trying to understand the philosophy behind the design. I'm not sure if I can upload full drawing of the design here. I just uploaded part of the relevant drawings. And yes it's actually J-Tube drawing that I uploaded here. But actually, the detail is more or less same with risers.

To answer BigInch last question, the J-Tubes are meant for flexible pipeline. The flexible pipelines will be pull- in through J-tube.

Thanks all for your thought.

 

[BigInch]

OK. If you install the j to the jacket onshore, you probably won't need 6-axis clamps functionality.

 

[LittleInch]

I can only think that the jacket is limited in some way and cannot take the vertical and horizontal loads at the guide locations, but can take those loads at the top flange.

I think ribbed neoprene is just being used because someone thinks it will absorb the pipe movement easier?

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

 

[BigInch]

I doubt the jacket is a problem. I would however tend to put this on the jacket leg, not the jacket cross braces. Storm current, wave drag and intertial forces on a 24" can get problematic.

Actually I wouldn't care if it was ribbed or not. I'm pretty sure that both will supply adequate friction, or equally not supply adequate friction, depending on the actual loads.