Min ambient temp considerations
- 1. 0 • Carbon steels and low alloy steels exhibit a drastic change in their room temperature ductility at sub-zero service temperatures. • There is a sudden, phenomenal drop in their notch-toughness properties below the "transition" range of temperature. • Above transition temperature range, impact specimens fracture in a "ductile" manner, absorbing relatively large amounts of energy • At lower temperatures, i.e. below the transition temperature range, the impact test specimens are found to fracture in a brittle (cleavage) manner, absorbing less energy. • A material would be invulnerable to a sudden drop in notch-toughness at the lowest specified service (or design) temperature, if it is proved by conducting Charpy V-notch Impact tests on representative test samples, at reference (the lowest service) temperature. • The purpose of an impact test is to determine the ability of the material to absorb energy during a collision. This energy may be used to determine the toughness, impact strength, fracture resistance, impact resistance or fracture resistance of the material • As per ASME, impact energy is 16 J and as per CE, it is 27J • Grain refined carbon steel forgings and wrought materials (thoroughly worked and normalized) generally exhibit good notch toughness. WHY IMPACT TEST
- 2. 1 Following clauses to make exemption assessment for ASME impact test requirement: UG-20(f) →→→UCS-66(a) →→→ UCS-66(b) →→→UCS-68(c) UG-20(f) requirements: Impact testing is not mandatory for pressure vessel material that satisfy all of the following: 1. The material shall be limited to P-No 1 Gr no 1 or 2 (CS material->Refer ASME IID) AND the thickness shall not exceed 13 mm (for material listed in curve A of Fig UCS-66) and 25 mm (for material listed in Curve B, C or D of Fig UCS-66) 2. The completed vessel shall be hydrostatically or pneumatically tested. 3. Design temperature is no warmer than 650 ̊F (345 ̊C) nor colder than -20 ̊F (-29 ̊C). Occasional operating temperature colder than -29 ̊C are acceptable when due to lower seasonal atm temperature 4. The thermal or mechanical shock loadings are not controlling the design requirement 5. Cyclic loading is not a controlling design requirement If you are exempted from UG-20(f) clause, you do not need proceed further But if you are not exempted by UG-20 (f), you have to proceed to UCS-66(a), but again if you are exempted, there is no need for more assessment ASME CODE SECTION VIII DIV 1 EXEMPTION RULES
- 3. 2 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-66(a) IMPACT TEST EXEMPTION CURVE Curve A: All CS & low AS plates, structural shapes, bars not listed in B,C,D. SA216 WCB/WCC & 217 WC6 if normalized and tempered Curve B: 217 WC9 if normalized and tempered ; SA516 Gr 70 if not normalized, SA 285 Gr A & B; SA216 WCB/WCC for thk <50mm, fined grained, water quenched & tempered; All mtl of curve A if fine grained & normalised Curve C: SA182 F21 & F22 if normalized & Tempered; SA302Gr C&D; SA387 Gr22 if normalized & tempered; SA533 Gr B, C & E Curve D: SA 516 if normalized or quenched and tempered
- 4. 3 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-66(a) EXAMPLE For example: MOC : Normalized SA 516 Gr.70 Thickness : 0.75 inch MOC listed in : Curve D Impact test required : No. Since normalized SA 516 Gr.70 is listed in curve D and as per UG-20(f), up to 1 inch thickness is exempted for materials listed in curve D. Of course, you will be carry out hydro-static test and ensure that the mentioned loadings are not a design controlling factor in your considered pressure vessel. MOC : Normalized SA 516 Gr.70 Thickness : 1.125 inch MOC listed in : Curve D Impact test required : Yes. Since thickness of material (Normalized SA 516 Gr.70 ) listed in curve D is 1.125 inch instead of 1 inch and hence will not be exempted by UG-20(f) and UCS-66(a) to be referred to for further evaluation Now based on clause UCS-66(a), MDMT and thickness will play the deciding role. MDMT (assumed) : -20 degree F Refer Fig. UCS-66 and locate a point corresponding to MDMT (-20 degree F) & thickness of 1.125 inch If the point falls above the curve D (because MOC is listed in curve D) you are exempted. Otherwise you are not. For the current example, the point is above the curve D so you are exempted from impact testing. For (Normalized SA 516 Gr.70, Curve D, 1.125 inch thickness), the minimum permissible temperature without impact test is -26 degree F.
- 5. 4 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-66(a) IMPORTANT NOTES
- 6. 5 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-66(a) IMPORTANT NOTES
- 7. 6 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-66(a) for nuts and bolts
- 8. 7 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-66(b)) EXAMPLE MOC : Normalized SA 516 Gr.70 Thickness : 1.125 inch MOC listed in : Curve D MDMT (assumed) : -26 degree F Impact test required : No. If MDMT changes from -26 degree F to -27 degree F, then impact test has to be carried out as per UCS- 66(a), and UCS-66(b) will have to referred to for further evaluation for exemption. Refer to Fig UCS-66.1 and calculate the formula: Ratio= tr E / (tn –c) tr : Required design thickness for all applicable loading. Assume it is 0.95 inch. E : Joint efficiency (assume for this vessel it is 1) This means your vessel is RT2 tn : nominal thinness, which in the example from above it is 1.125 inches C : corrosion allowance (assume it is 0.125 inches) Ratio = 0.95x1/(1.125 – 0.125) Ratio= 0.95 See Fig UCS-66(b): Corresponding to Ratio =0.95 (Y axis), you will be able to reach a value of 8 in the horizontal axes. This 8, is your 8 degree F bonus from table UCS-66, Means: The min permissible temperature without impact testing : -26 degree F (Fig UCS-66(a) Reduction in the temperature as per UCS-66 (b) : 8 degree F Hence allowable temperature for impact test exemption : -26 - (8) = -34 degree F Given MDMT : -27 degree F You are exempted from impact testing with this clause.
- 9. 8 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-66(b) )
- 10. 9 ASME CODE SECTION VIII DIV 1 EXEMPTION RULES (UCS-68(c)) Let's assume that MDMT : -45 degree F and see how UCS-68 ( c) can be used for impact test exemption MOC : Normalized SA 516 Gr.70 Thickness : 1.125 inch MOC listed in : Curve D MDMT (assumed) : -45 degree F Impact test required : Yes. Since as per UCS-66(b), min permissible temperature is -34 deg F How UCS-68(c) might be helpful for impact test exemption? As per UCS-68(c ), if post weld heat treatment is not a code requirement and MOC P-No is 1 and post weld heat treatment has been carried out, 30 degree F bonus will be granted to reduce the minimum permissible temperature in table UCS-66. So when post weld heat treatment is code requirement? It is code requirement when: Service : lethal Thickness for P-No. 1 : > 1.5 inch For our example: Service : not lethal P-No. : 1 Thickness : 1.125 and it is less than 1.5 inch therefore, post weld heat treatment is not code requirement. It means if post heat treatment is carried out ,30 degree F bonus will be granted by this clause. Hence min permissible temperature : -34-30=-64 degree F Whereas MDMT : -45 degree F Hence MOC with -45 Deg.F MDMT is exempted from impact testing.