technical paper | Lifetime testing
Table 2: MFI measurements on exposed and unexposed PP samples Sample
Unexposed fi eld joint Exposed fi eld joint Unexposed foam Exposed foam
MFR (g/10 min) 0.559 0.560 0.713 0.759
Table 3: OIT measurements on exposed and unexposed PP samples Sample
Unexposed fi eld joint Exposed fi eld joint Unexposed foam Exposed foam
of the Thermotite system and the coating was per- formed in KWH’s plant in Vasa, Finland, in 1992. The application process, although no longer used, was as follows: Step 1: Cleaning and blasting of steel; Heating of steel and application of FBE and powder adhesive. Step 2: Application of adhesive, foam and outer shield by cross head extrusion to cold pipe; Induction heating to fuse the materials applied in Step 1 to the materials applied in Step 2. The fi eld joint process was an early version of the
IMPP process. One facet of this process is that the use of the induction coil to fuse material resulted in a region within the insulation layer, close to the FBE / adhesive, where the foam density is higher than the core of the foam layer. The Tordis line pipe insulation system was built up
as follows: FBE (300 micron); Adhesive (700 micron); PP foam (density 700 ±40 kg/m3
, 45 mm) BA202E; Solid PP
shield (4 mm) Borcoat EA165E. The Tordis injection moulded polypropylene fi eld joint was built up as follows: FBE (300 micron); Adhesive (700 micron); Solid PP (56 mm) Borcoat EA165E.
OIT /min. 49 54 20 17
Samples and analysis As the Tordis project was a milestone for subsea polypropylene foam (PPF) technology, several samples were retained as demonstration pieces. These have been kept in offi ce conditions and thus not exposed to compressive loads, thermal loads or environmental stresses. These have been used in the current paper as refl ecting the initial state of the produced insulated pipe (t=0).
The end of life sample was retrieved as part of a
corrosion study and 2m of the retrieved section included a section of the injection moulded polypropylene (IMPP) fi eld joint. Operational data supplied by Statoil indicates that the
sample had been operated close to the design tempera- ture for a signifi cant part of the fi eld life (Figure 1). In order to determine the extent of change in the
materials it is important to address aspects of change in the material at the molecular level. The following techniques were used: Gel Permeation Chromatography - providing information on change in average molecular weight and molecular weight distribution. Melt Flow Index measurements - providing a single point viscosity measurement indicative of changes in molecular weight. In order to determine change in mechanical
properties the following techniques were used: Three-point fl exural testing. Uni-axial tensile testing. Oxygen induction time measurements were also
performed to determine the level of residual anti-oxi- dant in the samples and thermal conductivity was measured on the exposed foam samples and compared to the design curve for the material to confi rm whether the 20 year design assumptions were met. Where possible, tests were performed on both
exposed and unexposed samples. However, due to the shape and quantity of the unexposed samples this was not possible in all cases.
Figure 1: Operation data - temperature after subsea choke 22 PIPELINE COATING | May 2013
GPC test results Gel Permeation Chromatography (GPC) analysis was carried out according to ISO 16014-1, 2 and 4, 140˚C,
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