U-bend specimens

Corrosion of metals and alloys stress corrosion testing. Part 2 Bent-beam specimens Corrosion of metals and alloys. Part 3 U-bend specimens... 

G30, Standard Practice for making and using U-bend Specimens for Stress-Corrosion Testing, ASTM, West Conshohoken, PA, 1997. 

Fig. 15. Corrosion test probes, (a) Electrical resistance (b) linear polarization (c) zero resistance (d) weight loss coupon (e) U-bend specimen (f) tensile specimen and (g) large radius bend specimen.

FIGURE 4.20 C22-U-bend specimen coupon tested in the gaseous HI gaseous decomposition environment. 

U-bend shapes are shown in Fig. 9.3 [15]. They consist of a bar or sheet plastically deformed over a mandrel by a 180° bend. The ends of the specimen are constrained by a bolt. The U-bend specimens are used to evaluate the resistance of alloys under various corrosive solutions. However, it is very difficult to reproduce the stress conditions for the new specimen because the stress distribution within the specimen is not known. Fabrication of U-bend specimens is given in the ASTM G 30-97 standard method [15]. 

A laboratory programme on ESC was formulated to back up the site work. This ensured that data was available on the effect of likely organics to be encountered and possibly to define the life of HDPE under gross spillage conditions. HDPE samples (Bell telephone test, U-bend specimens. 

Figure 11.8 shows other test configurations that are often employed. Stressed U-bend specimens (Figure 11.8(a)) are subjected to a constant plastic deformation. Their use is therefore limited to ductile materials. Because of extensive plastic deformation, fracture occurs in a short time. Qualitative results can thus be obtained rapidly, e-ring specimens shown in Figures 11.8(b) and (c) are machined from metal... 

Figure 11.8 Specimens used for the testing of stress corrosion cracking (a) U-bend specimens (b) and (c) C-ring specimens (d) uniaxal-tension-test specimen.

Determining susceptibility of a materitJ to stress corrosion cracking or hydrogen embrittlement in a soil environment has been studied using buried U-bend specimens [S]. 

FIG. 6—Typical U-bend specimen dimensions (examples only not for specification) [32]. 

S] Corrosion of Metals and AUoys—Stress Corrosion Testing— Part 3 Preparation and Use of U Bend Specimens, ISO 7539-3, 1989. 

The specimens may then be tested by methods outlined in ASTM G 36, ASTM G 41, ASTM G 44, or ASTM G 50. A constant strain condition is maintained in the U-bend geometry specified in ASTM G 30 varying the bend radius controls the strain level. ASTM G 39 describes the bent beam SGG test specimen, which is similar in concept to the U-bend specimen, but is subject only to elastic strain. Axial loaded SGG test specimens are covered in ASTM G 49 and can be tested under constant strain, constant load, or varying strain rates. All of the SGG specimen preparation procedures for sheet and strip reqiiire careful sampling, due to the anisotropy introduced by rofllng specification of rolling direction on each specimen is mandatory. 

Heat and/or mechanical deformation may lead to loss of corrosion resistance. Welding may cause severe problems for certain materials for example, sensitization of the base metal in the heat-affected-zone, or molybdenum segregation of weld metal. Welded specimens are often tested to study potential problems. Specimens may be deformed to study the effect of residual stresses fi-om forming or welding. U-bend specimens are often exposed. If sp>ace is restricted, a Brinell hardness indentation can be used on a flat specimen to create a region of high residual stress. 

Figure 29 Lifetimes of U-bend specimens made from Alloy 600 (0.01% C) up to stress corrosion...

Zirconium U-bend specimens were tested in boiling, concentrated NaOH at TWC. During the test period, the concentration changed from 50% to about 85%, and temperature increased from 150 to 300°C. The PTFE washers and tubes used to make the U bends dissolved. However, the zirconium U bends remained ductile and did not show any cracks after 20 days. It should be noted that stainless steel is susceptible to SCC in alkaline solutions, including NaOH solutions. 

U-bend and double U-bend specimens LP turbines, piping, feedwater heaters, condensers, boilers Detects general corrosion, pitting, and SCC double U-bends simulate crevice and galvanic effects... 

U-bend specimens were annealed with a yield strength of703 MPa (102 ksi) and a tensile strength of 772 MPa (112 ksi). Source A.J. Sedriks, P.W. Slattery, and E.N. Pugh, Stress Corrosion Cracking of Alpha Titanium in Nonaqueous Environments, Proceedings of ... 

U-bend specimen. 30 day exposure U-bend specimen. tOO-day exposure Ubend specimen, 504 hr. exposure NCNo Cracks CCracked —Not tested Localized attack... 

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