Consideration for -ve amb temp

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.