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Material Selection and Evaluation Considerations for Low Temperature Operation ASME Section VIII, Division 1 Procedures

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Publication Date: 2012-May-04

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Ethylene Producers Safety Meeting - Kellogg's Comments

MATERIAL SELECTIONAND EVALUATION CONSIDERATIONS

For Low Temperature Operation

ASME SECTION VIII, DIVISION 1PROCEDURES

1. ESTABLISHINGTHE DESIGN TEMPERATURE Establishinga Minimum Design Metal Temperature (MDMT):

UG-20(b) - Considerations for selecting an MDMT

The lowest operating temperature coincident with full design or operating pressure.

0 Operational upsets - autorefrigeration, the coincident reduction of temperature and pressure.

Atmospheric conditions - low atmospherictemperature coincident with normal or

0 design pressure.

UG-2O(f) - Successfulexperience

The Code provides exemptions from the required impact testing requirements per UG-84if all of the following qualifications are met. This is the successful experience basis that was included in the Code rules prior to implementationof the new toughness requirements added to Part UCS in 1987.

Thickness Limits:

(l)(a)- 1/2*for any structural grade plate (A283 and A36), and structuralshapes when used as presstl're parts. Pressure part use of these materials is also limited by UCS-6 to 518".


(l)(b)- 1"for all other materials and product forms.

Other Qualifications:

(2) - The vessel must be hydrotested. Hydrotestingis a warm prestress proof test. The overload (1.5 x design pressure minimum) blunts built-in stress raisers and residual stresses (notch blunting) by causing local yielding, thereby improving notch ductility and toughness.

(3) - Design temperature (normal operatingldesign temperature coincident with full operating pressure) is not lower than -2OOF.

This is the minimum temperature limit for exemption from impact testing priorto introduction of the new toughness rules in 1987.

(4) - Shock loadings (thermal and mechanical)are not controlling. A guideline for determining if a thermal change is a shock loading is when the difference betweenthe temperature of the fluid being introduced into the vessel and the metal temperatureof the pressure part in contact with the fluid is morethan 40OF.

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Ethylene Producers Safety Meeting - Kellogg's Comments


(5)

 - Cyclic loading (fatigue type loading) is not a controlling design requirement. Implicit in this limitationis that cyclic loading conditions will not cause an existing crack to grow.

2. OLDER VESSELS - FIG.UCS-66CURVE SELECTION
API Recommended Practice 920, Prevention of Brittle Fracture of PressureVessels, gives guidelines for Figure UCS-66curve selection in Appendix 6. For the common plate steels used in pressurevessels during the 1950's and 19603, the recommended curves are:

Curve A: SA 201 and SA 212 if not producedto fine grain practice. Also included should be any structural grade steel, or any plate steel produced to a specification that does not have a carbon limit. In addition, all other product forms such as forgings and pipe produced to obsolete specifications should be assignedto CurveA. As will be illustrated in the GoverningThickness di...