Inspection of headers in gas compressor station
Plant Integrity were asked by their Canadian contractor, AITEC, to assist in a novel Teletest inspection of headers in gas compressor stations in Montana and North Dakota in the USA.
The final client, the stations' owner, was Northern Borders Pipeline (NBPL). AITEC were sub-contractors to Mears Engineering LLC, NBPL's principal inspection company.
The challenges presented by these inspections were:-
- The presence of some twenty 12in branches
- The large diameters - 36, 37 and 42in
- The significant thickness - 44mm
As the photograph shows, the headers were supported on concrete blocks. The aim of the inspections was to detect possible atmospheric corrosion at the 6 o'clock position at the interface between the headers and the concrete supports.
Because of the thicknesses involved it was decided to inspect using torsional wave excitation. The Teletest collar was mounted at the quarter length positions of the headers, which were up to 60m (180 ft) long.
Despite the intervening branches, it was possible to 'see' to the dome ends. A small indication was seen at a range of about 42 feet corresponding to the position opposite the pressure take-off branch that can be seen in the photograph near the header end.
NBPL were completely satisfied by these inspections. The plan now is to use Teletest to inspect the headers on a regular three yearly basis.