The consistency of rocket engine and its parts is based on the several factors. A concurrent engineering approach topped with regular design reviews can be safeguard. The production of components directly influences their reliability. Manufacturing and material flaws can be avoided by tight process and quality control. The factors of quality control are stated as following:
- Material Quality- evaluation and test of raw materials is based on the nature of the part for the purpose they are made. Evaluation of materials includes testing for chemistry, uniformity, mechanical characteristics, fabrication and heat processing properties and other characteristics as required in the application.
- Traceability – in the time materials defect is evaluated, several components have been produced from the same type of material. if precise records have been maintained for various materials, it will be feasible to remove the damaged components. The significance of correct and complete records is evident.
- Process evaluation – It states to consider the components that are processed. It evaluates the functionality of operators, equipments and tools to determine the errors.
- Reclaim – The repair or replacement of faulty components is decided.
- End checking- this evaluation includes the complete checking of parts to guarantee that they meet the design requirements.
- Inspection of service functionality- this involves checking and studying the real functionality of components in the engines.
The precipitation hardened stainless steels offer excellent corrosion resistance with high strength at temperatures about 1100oF to 1300oF. Although many pH stainless steels are martensitic and are sensitive to stress corrosion cracking, hydrogen embrittlement and loss of hardness at cryogenic temperatures. Hastelloy A286 austenitic stainless steel has the entire characteristics of austenitic stainless steels combined with good strength. . It has been validated to be a suitable material for fasteners and is used for nozzle tubing. Poor weldability decreases the application range of alloy A286.
Nickel base alloys
Nickel base alloys consist of 65% of Space Shuttle Main Engine. These are widely used in the rocket engines for offering outstanding corrosion resistance, elevated temperature oxidation resistance and maintenance of significant characteristics for a long period at the different temperature ranges.
Nickel base alloys are mainly significant for supreme corrosion resistance including Nickel 200, Monel alloys, alloy 600, alloy 625 and electroformed nickel. Electroformed nickel is not attacked by galvanic corrosion when it is kept in contact with various other metals. Monel grades offer supreme corrosion resistance and possess significant magnetic characteristics at the cryogenic temperature and good resistance to ignition in oxygen. The Inconel grades consisting of Ni, Cr and Fe prevent oxidation attack at the high temperatures limits up to 1800oF.
The high strength nickel based superalloys keep large strength at the high temperatures. Inconel 718 high strength metal keeps its properties up to 1300oF, it offers good cryogenic ductility and welding properties. Suitably grained material is recommended for components that need to be electron beam welded.
The special application Nichrome alloys are significant for electrical resistance heating applications, Incoloy alloys for high temperature corrosion resistance and Invar for controlled thermal expansion purposes.
The whole nickel based superalloys are resistant to general corrosion and stress corrosion cracking however they are sensitive to hydrogen embrittlement at temperatures about -200oF. In order to prevent hydrogen embrittlement in the nickel based alloys they must be secured from plastic strains through as security barrier for example copper electroplating or weld accumulation with resistant materials.
Cobalt base nickel alloys
They offer outstanding elevated temperature strength and resistance to oxidation and are intact to hydrogen embritllement. They are resistant to corrosion and heat and offer high excellent cryogenic characteristics. They prevent stress corrosion cracking and can be welded through electron beam welding. These offer high strength and prevent corrosion resistance and are nonmagnetic in nature.
Iron base alloys
The controlled expansion iron base alloys have specific use in liquid propellent rocket engines for their good strength, small coefficient of thermal expansion and prevention of hydrogen embritllement.