Tech Briefs

Shipbuilders Design Pipeline Dredging Barge With FEA Software

Finite element analysis software aids in the design of an undersea natural gas liquids pipeline.

A South American pipeline project that traverses the Amazon jungle and the Andes Mountains to the Pacific coast originates in the Camisea fields of eastern Peru, which are among the world’s largest natural gas (NG) reserves, holding approximately 11 trillion cubic feet of NG and 600 million barrels of associated natural gas liquids (NGL). To access these reserves, a $500-million (USD) project was led by Pluspetrol Peru Corporation S.A. (Pluspetrol) that included construction of two pipelines — one for NG (714 km) and the other for NGL (540 km). As construction of the pipelines neared completion, work focused on endpoints such as the fractionation plant where NGL would be processed into commercial products including propane, butane, and condensates.

ImageServicios Industriales de la Marina (SIMA Peru S.A.), a state-owned corporation and shipyard serving the Peruvian Navy, was commissioned by Pluspetrol to build a steel barge that could carry a 180-ton excavator and related equipment for digging a sub-sea piping canal in Pisco Bay. The company used finite element analysis (FEA) software from ALGOR, Inc. to verify the barge and meet a challenging design and fabrication schedule.

Using the software, SIMA designed a safe barge requiring less steel than had been originally quoted and approved by the customer. SIMA was able to deliver a fabrication drawing of the barge’s spud legs to its shop less than one month after obtaining the FEA software. All fabrication drawings were delivered in less than two months, and the manufactured barge was delivered to the customer within four months. The canal was dug, the piping installed, and the plant is now transporting NGL products through the sub-sea piping to a loading platform for export on ships.

The barge, named Leyla, was designed and manufactured at the SIMA shipyard in Callao, Peru, and was designed as a steel platform with three spud legs of hydraulic operation (with independent drive and lift), similar to an offshore oil rig. A spud is a sharppointed vertical post that can be forced by power through a socket or bearing to anchor a barge or platform into the ocean floor. The three spuds of the Leyla barge, which were 20 meters in length, provided a self-elevating and stable work platform. The barge carried a 180-ton Hitachi EX 1800-II excavator, which lifted soil from the sea bottom at a maximum depth of 16 meters and deposited it onto other barges for transport.

The primary engineering challenge in designing the barge was to ensure it would withstand the high-load operating conditions expected while in continuous service. The service loads of the excavator, as well as ocean wave surge, wind, and weights — including ballast and deck equipment — were considered. In addition to the excavator’s 180-ton weight, its service loads were calculated at 30 to 66 tons, depending on the sea height. The ballast weight was 210 tons and the deck equipment was 60 tons. The effects of a maximum wind speed of 28 knots and maximum wave height of 0.7 meter also were considered. While all of the highload zones were important, the spud legs were of particular concern since they are very large and tall structures and had to work 24 hours a day under high loads. The load on the three spud legs was 340 tons.