DESERT PROJECT SHOWS HOW BIG, HOT LINE IS REHABILITATED

The successful field rehabilitation of a section of a 48-in. oil pipeline, the largest diameter job vet, has advanced the prospects for routine use of this in situ technique. The trial project on 4,960 m (nearly 3 miles) of the Saudi Arabian Oil Co. (Saudi Aramco) QJ-3 oil pipeline was completed in April by Al-Qahtani Pipe Coating Terminal of Dammam, Saudi Arabia. The 48-in. OD pipeline is a Grade B, spiral weld seam pipe with 0.375-in. wall thickness. It was originally coated with single wrap

June 21, 1993

3 min read

The successful field rehabilitation of a section of a 48-in. oil pipeline, the largest diameter job vet, has advanced the prospects for routine use of this in situ technique.

The trial project on 4,960 m (nearly 3 miles) of the Saudi Arabian Oil Co. (Saudi Aramco) QJ-3 oil pipeline was completed in April by Al-Qahtani Pipe Coating Terminal of Dammam, Saudi Arabia.

The 48-in. OD pipeline is a Grade B, spiral weld seam pipe with 0.375-in. wall thickness. It was originally coated with single wrap tape. Some pipe areas were coated with double wrap tape.

Figs. 1-12 present a pictorial history of the project prepared by J.A. Durham, general manager of Al-Qahtani's field construction division. The basic steps were:

Pipe excavation, Fig. 1
Manual removal of outer layer, Fig. 4
Hydroblasting, Fig. 6
Sand preblasting, Fig. 7
Grit blasting, Fig. 8
Spray coating, Figs. 9 and 10.

Table 1 lists the pipeline rehabilitation equipment spread developed by Al-Qahtani. It is the industry's first self-propelled spread of this type, Durham says. Eleven tracked equipment units were used.

The surface condition achieved was Sa 2 1/2 (near white metal). The coating was applied to an average of 31 mils thickness with a 3.8 mil anchor profile, exceeding Saudi Aramco's specification of respectively 24 mils and 1.5 mils.

HIGHLIGHTS

This is also the largest diameter rehabilitation project to be line spray-coated with Protegol UT 32-10R coal tar/polyurethane coating material, Durham says.

The rotating spray head, line-travel coating unit was modified for field use by Al-Qahtani to apply the coal tar/ polyurethane coating with minimal runs, drips, or sags on hot pipe exteriors-up to 160 F. in this case-prevalent in the Middle East. The unit was also able to coat in one coating pass full encirclement weld repair sleeves with external reinforcement weld strips.

In all, 204,724 sq ft of pipe surface was coated.

The project was hampered by the wettest rainy period in recorded history for this region of Saudi Arabia, making it difficult to obtain larger sieve size quantities of dry sand sufficient for preblasting.

Also, numerous pipe sections had to be reblasted after exposure to rain. These weather conditions dictated that the preblast (sand) crew, grit blast crew, and line-travel coating crew plus seven of the prime contractor's sideboom tractors had to work on the same pipe section at the same time. At the end of the project when weather conditions improved, the coating production exceeded 300 linear m/day for 4 days in a row.

There were 30 coating days during the period Feb. 27 through April 17. The job required three separate mobilization moves.

To eliminate the shortage of preblast sand experienced on this job, Al-Qahtani will now stockpile dry abrasive materials for use during the rainy season.

SECOND JOB

This was not the first job of this type in the region.

In October 1992, Al-Qahtani completed the rehabilitation of a 15.89 km (9.5 mile), 24-in. natural gas line for Saudi Aramco. On this job, the maximum line coating exceeded 3,281 linear ft, or 1 km, on the best production day.