Pipe lining | technical article
together with an associated rise in operational tem- perature. Thus the limits of the service envelope of polyethylene are being reached, giving consideration to the use Solef. The key to any pipeline system is the way in which it
is connected or joined together – if it cannot be welded/ adhered to itself it cannot work within the system. A polymer liner in a steel pipeline presents a special diffi culty as there are two pipelines to be joined together and fusion welding of the steel is performed at temperatures above the melting point of the internal polymer liner. Consequently, alloy clad connectors such as the WeldLink system have been developed, enabling mechanical termination of the polymer liner a short distance away from the HAZ of the steel weld. Internal corrosion protection is maintained over the short section with CRA cladding. In the Swagelining design process, the sizing of the liner depends on the tolerances of the carbon steel host and knowledge of the steel welding technique used. The liner and host pipe are not mutually exclusive items, the liner is actually part of a composite pipeline system which consists of polymer pipe, steel pipe, polymer to polymer welds, steel to steel welds, polymer to steel connections and, where necessary, vents and fl anges to terminate the pipeline with a connection to other parts of the infrastructure. To confi rm the suitability of a polymer material for use as a liner in hydrocarbon environments, the fi rst step is to consider the required attributes: Suitability for reduction, reversion – elasticity, high YS/strain, ductility;
Butt welding compatibility with the process – ductil- ity of welds;
Collapse resistance at operating temperature – high modulus, low swell;
Mass variation 5
4.5 4
3.5 3
2.5 2
1.5 1
0.5 0
0 30 90 120 150 180 230 300 370 time (day)
Figure 2: The mass variation trends show that the H2S does not infl uence the swelling of Solef PVDF, the main variation of weight happens during
the fi rst month of exposure and the fi nal values are low (below 3%). Source: Solvay Specialty Polymers
Compatibility with hydrocarbon fl uids – chemical resistance;
Function with WeldLink or other connector – elastic- ity, ductility;
Availability/cost – high production capacity, competi- tive price;
And if venting is required – low swell, high modulus, permeation.
Although it is anticipated that all thermoplastics will work with the process to some extent, it is expected that some will be better than others. This, for example, will impact on the maximum single installation insertion lengths achievable. Solvay Specialty Polymers’ Solef PVDF demonstrates suitability for use with the Swage- lining technique. The industry view is that polymer liners collapse in hydrocarbon service, which is a constraint to progress. The collapse mechanism is envisaged to take place in two stages:
Solef PVDF Sweet Solf PVDF Sour
Below: liner
installation in 1.5km lengths for a 10 inch
water injection fl ow line
carried out in Norway
November 2012 | PIPELINE COATING 31
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