Page 392 - Pipelines and Risers

360 Chuifer 19

A test program was undertaken to determine the properties of the pipe steel and the weldment.
The pipe wall strength was determined using round bar tensile specimens because the strain-
hardening behavior of the bainitic material leads to a large Bauschinger effect. The proof
stress values measured on flat rectangular specimens taken from the pipe do not correlate well
with the actual proof stress value of the pipe wall. The specified minimum values of yield and
tensile strengths were exceeded in the tests.

The impact energy values measured on the base material exceeded 95 J, thereby exceeding the
minimum value for crack arrest recommended by the European Pipe Research Group (EPRG).
The ductile-brittle transition temperatures measured on the drop-weight tear test (DWTT)
specimens were well below the specified test temperature of 0°C. The impact energy values of
the longitudinal weld metal measured at O'C, the commonly specified test temperature in
Germany, varied between 100 and 200 J. The average values of the impact energy for the base
material and weld metal were 190 J and 158 J respectively (Chaudhari et al. (1995)).

The strength of the seam weld was checked by means of flattened transverse weld specimens
with the weld reinforcement removed by machining. For all specimens, failure occurred in the
base metal, outside the weld region.

The field welding for GRS 550 TM required the development of a new concept in order to
achieve the mechanical-technological properties for the welding metal and welding joint. For
this project, it proved necessary to implement a combined manual welding technology using
cellulose-coated electrodes for root and hot pass welding and lime-coated (basic) electrodes
for filler passes and cap pass welding.

The pipe sections were hydraulically tested to German guidelines in lengths up to 100 m and
corresponding to 6,000 m3 of water. At the lowest point of the pressure test section,
considering the rugged terrain, the pipes were tested up to 108% of the SMYS. (Using the
equivalent stress criteria in BS 8010, a Von Mises equivalent of 93.5% of yield is obtained
and thus below yield stress). Dry pigging of thc pressure test sections was performed with a
pig equipped with an aluminium calibration disk with a diameter of 98% of pipe ID.

iii) NOVA Pipeline Projects

Pipe supplied to the two Canadian projects were to CSA 2245.1, typical compositions are
again given in Table 19.5. The first Canadian project was a short (126 welds) cross over
section of the 42-inch diameter pipeline at the Express East Compressor Station in Alberta,
Canada, completed in 1990. A Japanese steel mill supplied the pipe.

The second Canadian project was 53.8 km of 48-inch diameter pipeline for the Mitzihwin
project in Alberta, Canada, completed in 1994. A Canadian steel company supplied the pipe.

iv) Conclusions