Creep and Stress Rupture

Above temperatures of 900°F, the austenitic stainless steel and other high alloy materials demonstrate inereas-ingly superior creep and stress-rupture properties over the chromium-molybdenum steels. For furnace hangers, tube supports, and other hardware exposed to firebox temperatures, cast alloys of 25 Cr-20 Ni and 25 Cr-12 Ni are frequently used. These materials are also generally needed because of their resistanee to oxidation and other high temperature corrodents. 

Furnace tubes, piping, and exchanger tubing with metal temperatures above 800°F now tend to be an austenitic stainless steel, e.g., Type 304, 321, and 347, although the chromium-molybdenum steels are still used extensively. The stainless steels are favored beeause not only are their creep and stress-rupture properties superior at temperatures over 900°F, but more importantly because of their vastly superior resistance to high-temperature sulfide corrosion and oxidation. Where corrosion is not a significant factor, e.g., steam generation, the low alloys, and in some applications, carbon steel may be used. 

In computing ordinary short-term characteristics of plastics, the standard stress analysis formulas may be used. For predicting creep and stress-rupture behavior, the method will vary according to circumstances. In viscoelastic materials, relaxation data can be used in Eqs. 2-16 to 2-20 to predict creep deformations. In other cases the rate theory may be used. 

The basis for establishing the maximum allowable stress values in the ASME BPV Code is given in ASME BPV Code Sec. II Part D, Mandatory Appendix 1. At temperatures where creep and stress rupture strength do not govern the selection of stresses, the maximum allowable stress is the lowest of... 

At temperatures where creep and stress rupture strength govern, the maximum allowable stress is the lowest of... 

Yun, H.M., J.C. Goldsby, and J.A. DiCarlo. 1994. Tensile creep and stress-rupture behavior of polymer derived SiC fibers. Pp. 17-28 in Advances in Ceramic-Matrix Composites 11. Vol. 46 in Ceramic Transactions, J.P. Singh and N.P. Bansal (eds.). Westerville, Ohio ... 

J.A. DiCarlo and H-M. Yun, Creep and Stress Rupture Behavior of Advanced SiC Fibers, Proceedings of ICCM-10, vol. y/(Cambridge, England Woodhead Publishing Limited, 1995), 315-322. 

Marline, E.A., Long term tensile creep and stress rupture evaluation of uni-directional fibre glass reinforced composites. Paper 94, SPI 48th Annual Conference, Cincinnati, USA, 1993,... 

The ASME Code establishes allowable stresses at temperatures where creep and stress rupture govern based on the following ... 

In the ASME Code, Section II, Part D, Table 2A, the allowable tensile stress values for the materials that are governed where creep and stress rupture govern are indicated by italics. However this is not the sole criteria... 

It should be noted that creep- and stress-rupture-test data are obtained pnder atmospheric exposure additions in laboratories and under uniaxial loading. The stress condition existing in a vessel part under field service conditions Usually comprises stresses in three directions, a fact which complicates the application of the experimental data. In addition, the vessel material may be exposed to a corrosive atmosphere and be subject to scaling, hydrogen embritlle-menl, intergranular corrosion, and strain hardening. 

Voorhees, Sliepcevich, and Freeman (204) have presented a procedure for calculating the time of rupture from creep and stress-rupture data normally available to a designer. Prior to the work of Voorhees the design of thick-walled vessels at high pressures and elevated temperatures was usually based upon the maximum principal stress and an allowable stress determined from creep and stress-rupture test data. This is the current method recommended by the ASME code (11) for vessels operating at pressures up to 3000 psi. 

Figure 3-31. Typical creep and stress-rupture curves.

Manson, S. S., and Haferd, A. M. A Linear Time-Temperature Relation for Creep and Stress Rupture Data. NACA, TN 2890, 1953. 

Source A. Blalherwick and A. Ceis, FaHgue, Creep, and Stress-Rupture Properties ofn-13V-11Cr-0AITitanium Alloy B-120VCA). AFML-TR-66-293,1966... 

Mechanical Properties of Arapree Part 4 Creep and Stress-rupture, Report 25-87-31, TU Delft, 1991... 

Boyer, H. E. (Editor), Atlas of Creep and Stress-Rupture Curves, ASM International, Materials Park, OH, 1988. 

Creep and Stress Rupture 4.3.1 High-Temperature Failure... 

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