Part II. On the Mac Kay River Pipeline, the foam cutback was specified as 175 mm nominal, which did not provide enough space for standard induction coils or catalytic

On the Mac Kay River Pipeline, the foam cutback was specified as 175 mm nominal, which did not provide enough space for standard induction coils or catalytic heaters. As such, the following procedure was used for field-coating application:

- Preheating the girth weld with propane torches.

- Preheating the girth weld with propane torches due to rapid cooling of the steel.

- Brush blasting the girth weld to remove contaminants and flash rusting caused by reheating.

- Brushing off girth weld.

- Applying the liquid epoxy.

- This procedure was less than ideal, considering that abrasive blasting coating operation were nevermore than one joint apart.

Achieving reasonable liquid-epoxy cure times required that temperature of the steel to be high but not so high as to damage the coating or initiate release of harmful vapors.

Pipe adjacent the girth weld acted as massive heat sinks, cooling the girth weld area and leading to extended epoxy cure times. In order to improve die process, entire welded sections of pipe were preheated by blowing hot air in one end. Injection of foam into the molds proved relatively trouble free.

Once the liquid epoxy had cured and was holiday free, steel molds were mounted over the girth weld. Since the isocyanine in the foam reacts with water, the girth welds were wiped dry before the foam injections. The polyurethane foam was injected into the mold, the amount being controlled by either timing or counting the number of pumps strokes. The steel molds were treated with a silicone-based release agent. The amount of release agent used was minimized because any residue would adversely affect adhesion of the shrink sleeve to the PE overlap and to the polyurethane foam.

Before heat shrink-sleeve application, after the foam insulation had cooled? The mold was removed and the insulation inspected for defects before heat shrink-sleeve installation. The PE overlap was abraded to improve sleeve adhesion and to remove all traces of foam adhering to the PE.

The PE overlap area was preheated to the minimum preheat temperature recommended by the sleeve manufacturer. Heating of the polyurethane foam was minimized to avoid damage and to reduce off gassing.

Adequate and even preheating of the PE overlap area was critical to ensure that die hot-melt adhesive used on the sleeve was activated. The sleeve was installed with a minimum overlap of 75 mm.

Sufficient rolling during the sleeve application was required to ensure all entrapped gases were removed.

Drill sections of more than 500 m long were required for crossing major waterways and several roads. Edge protectors were applied to the leading edge of all shrink sleeves to lover the risk of sleeve damage.

In addition, the diameter of the drill bore was oversized to reduce the possibility of damage. All directional drills were successful as the coating on the lead joints pulled beyond the exit was in good condition and resistance-to-ground measurements taken at each crossing revealed high resistance.

Valves and fabricated bends were coated in the shop, with the liquid epoxy approved for girth welds, through plural-component spray application. Aboveground portions of the valves were painted with an epoxy phonetic paint.

These items were coated in the field with polyurethane foam with a sequential injection molding process and subsequently coated with a spray-applied pleurae coating.

Repairs to the outer jacket and the heat-shrink sleeves depended upon the size of the defect. For all sizes of defects, the PE outer jacket was abraded before application of the repair material.

Repairs smaller than 50 mm x 50 mm were affected with PE repair patches, Ensuring a minimum overlap of 75 mm. Heat-shrink sleeves were used to repair any larger defects.

Before lowering of the pipe in the ditch, the outer jacket was carefully inspected for damage and repaired as required.

Questions:

1 What was used for field-coating application?

2 Why were welded sections of pipe preheated by blowing hot air in one end?

3 On the Mackay River pipeline, the foam cutback didn’t provide enough space for standard induction coils, did it?

4 Were the girth welds wiped dry before the foam injections?

5 Was the diameter of the drill bore or pipe oversized? Why?

17.1 What is this article about?