The existing 304 and 316 stainless-steel tubing and fittings at the Launch Complex 39 launch pads are susceptible to pitting corrosion. This pitting corrosion can cause cracking and rupture of both high-pressure gas and fluid systems. The failures can be life-threatening to launch pad personnel in the immediate vicinity. Outages in the systems where the failure occurs can affect the safety of Shuttle launches. Improved corrosion-resistant tubing systems will greatly enhance both personnel and Shuttle safety concerns. These new-generation materials will require less maintenance over their lifetime and significantly reduce costs associated with these systems.

A range of materials was selected for testing to include stainless steels (austenitic, low-carbon, Mo-alloy, superaustenitic, duplex, and superferritic), Ni-Cr-Mo alloy, Ni-Mo-Cr-Fe-W alloy, and austenitic Ni-base superalloy. Four separate conditions that could be experienced at the launch facilities are being tested: normal seacoast unsheltered, normal seacoast sheltered, acid environment unsheltered, and acid environment sheltered. Two of the four racks are sprayed once every 2 weeks with an acid slurry to simulate Solid Rocket Booster (SRB) deposits accelerating corrosion rates. One of the acid-rinsed racks, as well as a nonrinsed rack, has a protective roof (cover) to simulate partial shelter. Each test article contains a series of 90-degree bends, 37-degree tube flairs, and an orbital weld.

Tubing failures occurred in the 300-series control tubing assemblies after only 10 months under acid rinse conditions. The majority of the remaining high-alloyed steels showed little or no corrosion damage. All failures were identified as pitting corrosion failures. Other tubing test articles are subject to inspection of specific areas such as clamp points, wire loop contact points that retain identification tags, and orbital weld sites.

Areas inspected are compared to those of the 300-series tubing brought in because of tube failure. These areas are of concern because of the increased corrosion potential caused by crevice corrosion and in heat-affected zones of welded areas.

Benefits of this project include the following:

• Corrosion-resistant tubing in launch pad applications would greatly reduce the probability of future pitting corrosion failures.
• Improved safety, increased reliability, reduced downtime, and lower maintenance costs would result from using the more corrosion-resistant alloys.

Key accomplishments:

• Analyzed first-year failures.
• Compared the different alloys at critical corrosion sites such as clamp points and wire loop contact points that retain identification tags.
• Performed orbital welds.

Key milestones:

• Determined performance/cost benefits to recommend new material for Launch Complex 39 applications.
• Presented paper at the NACE 2002 Conference.
• Completed progress report.

Contacts: L.G. MacDowell (Louis.MacDowell-1@ksc.nasa.gov), YA-C2-T, (321) 867-4550; and Dr. L.M. Calle, YA-C2-T, (321) 867-3278
Participating Organization: Dynacs Inc. (J.J. Curran and T.R. Hodge)