Maritime

This paper describes those strategies to minimize the risks associated with the seawater injection process and to reach production targets. Also, an expert system developed for seawater injection plants is introduced.

Structural, ballistic, and mobility requirements have led to the selection of aluminum alloy 2519 as the primary structural material for the Advanced Amphibious Assault Vehicle (AAAV).  Two-year seawater alternate immersion exposures of welded AI 2519 panels with and without protective coatings were conducted to simulate the expected AAAV service environment.

 A novel evaluation technique, based on an artificial pit electrode, has been developed for inhibitor studies. The first example is of three generic inhibitors, against localised corrosion. The second is of three industrial inhibitors against existing localised corrosion on a north sea production platform

The nut and bolt thread protector system is a patented, ultraviolet stabilized polyethylene thread protector, which seals nut and bolt threads in pressurized grease to effectively prevent corrosion and provide protection against physical damage.

Much progress has been made in testing of offshore paint systems in the past 10 years. But more work is needed to understand what is happening and give us the confidence to correlate the laboratory accelerated test to the field service life of offshore coating systems. The new NACE Standards are a move in the right direction.

Since 1982, there has been a move to Thermal Sprayed Aluminum (TSA) coating in the “splash zone” of offshore structures.  Our experience indicates that an experience applicator, good surface preparation and quality of wire combined to achieve required thickness and apply the sealer to seal the entire surface.

A test programme was conducted to study corrosion behaviour of - 1. carbon and low alloy steels, 2. austenitic, martensitic and duplex stainless steels and 3. nickel-based Alloy 718 - in low oxygen content (20 & 200 ppb) seawater.

Laboratory testing to qualify several materials for high strength fastener applications for two projects has shown that, in the presence of cathodic protection, nickel alloys 718 and 725 offer the best resistance to hydrogen embrittlement and are available in the strength/size required for high pressure and moderate temperature applications for sub-sea applications.

Twelve-year laboratory tests of rebar reinforced concrete beams partially submerged in artificial seawater have confirmed that steel corrosion may occur a few months after immersion and may continue for many years.

In seawater, higher strength nickel-copper alloys are used as alternatives to copper alloys. These  can be susceptible to chloride stress corrosion cracking and hydrogen embrittlement in conditions where cathodic protection is utilized.  Copper-Nickel-Tin alloys (CuNiSn) show low corrosion rates in the free and coupled conditions.  Resistance to hydrogen embrittlement is demonstrated.

This study seeks to generate corrosion data with a view to determining weak sections of the flow lines/wellhead structural facilities and installations. The offshore corrosion survey is also aimed at ascertaining the effectiveness of the CP system and integrity of the Crude Oil/Gas networks.