GB2267137A

GB2267137A - Piggy-back pipework

Info

Publication number: GB2267137A
Application number: GB9210612A
Authority: GB
Inventors: Andrew C R Tyrer; Robert Gibson
Original assignee: C R P Marine Ltd; CRP Marine Ltd
Current assignee: C R P Marine Ltd; CRP Subsea Ltd
Priority date: 1992-05-19
Filing date: 1992-05-19
Publication date: 1993-11-24
Anticipated expiration: 2012-05-19
Also published as: GB9210612D0; GB2267137B

Abstract

A piggy-back clamp assembly, comprises a saddle (10) adapted to be mounted on the pipeline of larger diameter and defining a channel (22) for receiving the pipeline of smaller diameter. A strap (12) extends around the pipeline of larger diameter. A tensioning means (14) for the strap comprises a single bolt (26) and a pair of toggles (28, 30). A saddle cover (16) is mounted on the saddle (10) so that the pipeline of smaller diameter is embraced between the saddle and the saddle cover, the saddle cover (16) being fixed to the saddle independently of the belt tensioning means (14). More than one (Fig. 4 not shown) pipeline of smaller diameter may be mounted. <IMAGE>

Description

DESCRIPTION CLAMP ASSEMBLY FOR MOUNTING PIPELINES TOGETHER TOGETHER IN PARELEL RE #TI ONSHI P The present invention is concerned with clamp assemblies for use in mounting one or more pipelines to another in parallel relationship (so-called piggyback clamp).

In a typical practical situation, one or more smaller diameter pipes is, or are, to be disposed in close parallel relationship with a larger pipe. For example, in the case of gas pipelines, it is often required to mount a smaller pipeline, carrying a fluid such as methanol (for use in hydrate formation reduction and corrosion reduction), onto a larger, gas-carrying pipeline. Various clamping assemblies have been proposed hitherto for this purpose.

It is an object of the present invention to provide an improved clamp assembly of this type.

In accordance with the present invention, there is provided a clamp assembly for use in mounting a pipeline of smaller diameter on a pipeline of larger diameter in parallel relationship therewith, the clamp assembly comprising a saddle adapted to be mounted on the pipeline of larger diameter and defining a channel for receiving the pipeline of smaller diameter a strap for extending around the pipeline of larger diameter, a tensioning means for the strap which is received within a slot in the saddle, and a saddle cover mountable on the saddle so that the pipeline of smaller diameter is embraced between the saddle and the saddle cover, the saddle cover being fixed to the saddle independently of the belt tensioning means.

Preferably, the belt tensioning means comprises a single bolt and a pair of toggles attached respectively to the two ends of the strap, one of the toggles receiving the bolt shank with clearance and the other being in screw-threaded engagement with the bolt.

Preferably, the saddle cover is fixed to the saddle by means of one or more bolts which engage in respective nuts embedded in the saddle material.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which Figs. 1 to 3 are a sectional elevation, side elevation and plan view, respectively, of a first embodiment of a clamping assembly in accordance with the present invention; and Figs. 4 to 6 are a sectional elevation, side elevation and plan view, respectively, of a second embodiment of a clamping assembly in accordance with the present invention.

Referring first to Figs. 1 to 3, the first embodiment comprises a saddle 10, strap 12, tensioning means 14, saddle cover 16 and cover fastenings 18.

The saddle 10 rests directly on a gas line (not shown) and acts as a spacer between it and the piggyback line. Its upper surface 20 is provided with longitudinal half-cylinder recesses 22 into which the smaller diameter line can be positioned.

The saddle has a central transverse slot 24 into which the two ends of the clamp strap 12 are introduced. The single strap 12 runs around the circumference of the gas line but lies within the recess provided conventionally in the concrete coating of the gas line.

The two looped ends of this strap 12 are held together by the tensioning assembly 14. Its purpose is to generate a tension in the circumferential strap, thus holding the saddle firmly in place. The tensioning assembly 14 comprises three components; a central bolt 26 and two transverse toggles 28,30.

The bolt 26 passes through the toggle 30 with clearance but is screw-threadedly received in the other toggle 28. The bolt 26 has a head 32 by which it can be rotated to cause the two ends of the strap 12 to be drawn together.

Once the smaller line has been positioned on top of the saddle in the recess 22, the saddle cover 16 is fitted over it. Positive location of the cover 16 is assisted by the provision of two dowels 34. To prevent the smaller diameter line lifting out of the saddle, the cover is fastened in place using two bolts 36 which are received by captive nuts 38 moulded into the saddle. Positioned adjacent the nuts 38 and also moulded into the saddle are two annular plates 40.

Moulded into the saddle cover 16 are two further annular plates 42 for engagement by the heads 44 of the fixing bolts 36.

The embodiment of Figs. 4-6 is essentially the same in principle but enables two smaller lines to be fitted in a spaced parallel arrangement to a larger main line. Parts serving similar functions in Figs.

4-6 are given the same reference numerals as in Figs.

It is now widely available and in used extensively in the off shore industry, particularly for fasteners in a severe service environment.

The material exhibits the following beneficial properties: a) Outstanding long term corrosion resistance in a subsea environment.

b) A relatively high yield stress (490 N/inm2) when compared to other corrosion resistant metals.

c) Good resistance to stress corrosion cracking.

This is of particular importance when fasteners are buried.

d) Completely compatible with polyurethane elastomer.

The saddle covers 16 are preferably moulded from an identical material to that used for the saddles themselves. The polyurethane elastomer material is in direct contact with the external surface of both the methanol line and the umbilical. This contact does not cause any undue damage to either the methanol line or the umbilical.

The service environment for the cover fastening 18 is, of course, similar to that of the strap tensioning system. However, in this case each component is subject to a lower axial load. For this reason it is sufficient to use fasteners in accordance with ASTM A276 S31254.

The preferred material used is commonly known as 6Mo due to the presence of 6% Molybdenum in its chemical make-up. Although closely related to the 300 series stainless steels (e.g. 316), 6Mo exhibits a much superior corrosion resistance and has a significantly higher yield stress (300 N/mm2).

With regard to the installation procedure, since both the clamps of Figs. 1-3 and 4-6 are similar, then a single installation procedure is available, as follows: (1) Position the saddle centrally on the gas pipe within the 300mum wide groove provided.

(2) Fit the tensioning system toggles into each end of the strap.

(3) Fit the plain toggle (i.e. plain bore) into its locating slot in the saddle.

(4) Pass the strap under the gas pipe and position the threaded toggle in front of the saddle slot.

(5) Pass the tensioning bolt through the plain toggle and engage in the threaded toggle.

Claims

1. A clamp assembly for use in mounting a pipeline of smaller diameter on a pipeline of larger diameter in parallel relationship therewith, the clamp assembly comprising a saddle adapted to be mounted on the pipeline of larger diameter and defining a channel for receiving the pipeline of smaller diameter, a strap for extending around the pipeline of larger diameter, a tensioning means for the strap which is received within a slot in the saddle, and a saddle cover mountable on the saddle so that the pipeline of smaller diameter is embraced between the saddle and the saddle cover, the saddle cover being fixed to the saddle independently of the belt tensioning means.

2. A clamp assembly as claimed in claim 1, wherein the belt tensioning means comprises a single bolt and a pair of toggles attached respectively to the two ends of the strap, one of the toggles receiving the bolt shank with clearance and the other being in screw-threaded engagement with the bolt.

3. A clap assembly as claimed in claim 1 or 2, wherein the saddle cover is fixed to the saddle by means of one or more bolts which engage in respective nuts embedded in the saddle material.

4. A clamp assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying