Impact Testing
Determination
ASME Section VIII,
Division 1
Impact Testing Determination
o Failure of materials and fabricated assemblies can occur In one of two ways:
Ductile or Brittle
o ASME impact testing rules determine ability to resist brittle failure. Characteristics Affecting Resistance To Brittle Failure
o Mechanical properties and chemical composition of: Base material , Weld material, Weldments
o Thickness
o Applied Stress
o Impact testing is required unless exempted by Code.
o Requirements for IT exemptions are described in Subsection C for a given class of material.
o Exemptions may appear either directly in Code paragraphs, or by paragraph reference to Code figures and notes.
ASME Code Rules
o When not exempted, impact testing shall be by the charpy V notch testing method & shall meet the requirements of UG-84 which may include testing of:
materials, including welding material, PQR material
UG - 84 Addresses:
(a) general
(b) test procedures (c) test specimens (d) IT of materials
(e) procedural requirements (f) IT of welds
(g) specimen location, orientation, testing temperature and acceptance values
(h) IT of PQR specimens
(i) Vessel (Production) IT test plates (j) rejection
o Rules for the performance of impact testing appear in UG-84. I.T. procedures and apparatus shall conform to 5A-370.
Calibration of IT. Equipment calibration shall be performed in accordance with ASTM E23.
Charpy V Notch Impact Testing Method
Principles of the Charpy V Notch Method
The height to which the pendulum rises in its swing after breaking the specimen is measured and used to determine the residual energy of the pendulum. The specimen is supported horizontally as a simple beam with the axis of the notch vertical. It is struck in the middle of the face opposite the notch.
SA-370, 21.1.1: A charpy impact machine is one in which a notched specimen is broken by a single blow of a freely swinging pendulum. The pendulum is released from a fixed height so that the energy of the blow is fixed and known.
Principles of the Charpy V Notch Method
Fig. UG-84 Simple Beam Impact Test Specimens (Charpy Type Test)
O = original width before break F = final width after break
NNotch Original cross section
o One "set" is composed of 3 specimens
o Specimens are tested at or below the MDMT of
the vessel.
o Testing determines
•
Ft/lb's
of
force
required
to
break
the
specimens,
• lateral expansion (mils), measured after
breaking,
• brittle or ductile fracture.
Section VIII, Div. 1
Flow Diagram for
o UG-20
(f) Impact testing per UG-84 is not mandatory for pressure vessel materials which satisfy all of the following.
(1) The material shall be limited to P-No. 1, Gr. No. 1 or 2, and the thickness, as defined in UCS-66(a) [see also General Note (1) in Fig. UCS-66.2], shall not exceed that given in (a) or (b) below:
(a) 1 / 2 in. (13 mm) for materials listed in Curve A of Fig. UCS-66;
(b) 1 in. (25 mm) for materials listed in Curve B, C, or D of Fig. UCS-66. (2) The completed vessel shall be hydrostatically tested per UG-99(b)
or (c) or 27-4.
(3) Design temperature is no warmer than 650°F (345°C) nor colder than −20°F (−29°C). Occasional operating temperatures colder than −20°F (−29°C) are acceptable when due to lower seasonal atmospheric temperature.
Thermal or mechanical shock loadings are not a controlling design requirement, cyclical loading is not a controlling design requirement.22
UCS-66 Materials
o (a) Figure UCS-66 shall be used to establish impact testing exemptions for steels listed in Part UCS.
o Unless otherwise exempted by the rules of this Division, impact testing is required for a combination of minimum design metal temperature (MDMT) and thickness which is below the curve assigned to the subject material.
o If a MDMT and thickness combination is on or above the curve, impact testing is not required by the rules of this Division, except as required by:
UCS-66Q), and UCS-67(a)(2)
o Pressure parts shall be evaluated as separate components (e.g., Shells, heads, nozzles, manways, reinforcing pads, flanges, tube sheets, flat cover plates, backing strips [remaining in place] and attachments essential to the structural integrity of the vessel when welded to the pressure containing component).
o UCS-66(a) continued... Each Component shall be evaluated for impact test requirements based on its individual material:
Classification Thickness
MDMT
UCS-66 Materials
Governing Thickness UCS-66(a)(1)
o The following thickness limitations apply when using Fig. UCS-66. Excluding castings, the governing thickness (tg)of a welded part is as follows:
o(a)(l)(a) For butt joints (except those in flat heads and tubesheets), the nominal thickness of the thickest welded joint [see Fig. UCS-66.3, sketch (a)],
o(a)(l)(b) For corner, fillet or lap welded joints, including attachments, the thinner of the two parts joined,
O(a)(l)(c) For flat heads or tubesheets, the larger of (b) above or the component thickness divided by four,
O(a)(l)(d) for welded assemblies comprised of more than two components (e.g., nozzle-to-shell joint with reinforcing pad), t and MDMT of the individual welded joints of the assembly shall be determined, and the warmest of the MOMTs shall be used as the MDMT of the welded assembly, [see Figure UCS-66.3, sketch (b)]
Governing Thickness UCS-66(a)(1)
o If the governing thickness at any welded joint exceeds 4 inches and the MDMT is colder than 120°F (49° C), impact tested material shall be used.
o (4) The governing thickness of a nonwelded dished head [Fig. 1-6 sketch (c)] \s the greater of the flat flange thickness divided by 4 or the minimum thickness of the dished portion.
o (5) If the Governing thickness of a nonwelded part exceeds 6 inches (152 mm) and the minimum design temperature is colder than 120°F (49°C), impact tested material shall be used.
Governing Thickness UCS-66(a)(1)
o (2) The governing thickness of a casting shall be its largest nominal thickness.
o (3) The governing thickness of flat nonwelded parts, such as bolted flanges, tubesheets, and flat heads, is the flat component thickness divided by four.
o (b) When the coincident ratio defined in Fig. UCS-66.1 is less than one, Figure UCS-66.1 provides a basis for the use of components made of Part UCS materials to have a colder MDMT than that derived from UC5-66(a) without impact testing.
UCS-66(b), Reduction In MDMT Without
Impact Testing
o (b)(l)(a) For such components, and for a MDMT of -55°F (-48°C) and warmer, the MDMT without impact testing determined in (a) above for the given material and thickness may be reduced as determined by Fig, UCS-66.2.
o If the resulting temperature is colder than the required MDMT, impact testing of the material is not required.
o (b)(l)(b) Fig. UCS-66.1 may also be used for components not stressed in general primary membrane tensile stress (defined in Appendix 3).
o (b)(l)(c) In lieu of using (b)(l)(b), the MDMT determined in UCS-66(a) or (c) may be reduced for a flange attached by welding, by the same reduction as determined in (b)(l)(b) for the neck or shell to which the flange is attached.
UCS-66(b), Reduction In MDMT Without
Impact Testing
o (b)(2) For minimum design temperatures colder than -55°F (-48°C), impact testing is required for all materials, except as allowed in (b)(3) and in UCS-68(c).
o (b)(3) When the MDMT is colder than -55°F (-48°C) and no colder than -155°F (-104°C), and the coincident ratio (Fig. UCS 66.1) is < 0.35, impact testing is not required.
o If postweld heat treating is performed when it Is not otherwise a requirement of this Division, a 30°F (17°C) reduction in the impact testing exemption temperature may be given to the minimum permissible temperature from Fig. UC5-66 for P-No. 1 materials. The resulting exemption temperature may be colder than -55°F (-48°C).
UCS-68(c) Exemption when PWHT is Performed
o No impact testing is required for the following flanges when used at MDMTs no colder than -20°F (-29°C):
(1) ASME B16.5, ferritic steel (2) ASME B16.47, ferrltic steel
(3) split loose flanges using SA-216 GR WCB
o Unless specifically exempted in Fig. UCS-66, materials having a specified minimum yield strength greater than 65KSI (448MPa) must be impact tested.
UCS-66(f), Impact Testing Based On Yield
Strength
UCS-66(g), Material Specification Impact Testing
o Materials produced and impact tested in accordance with the requirements of the specifications listed in Fig. UG-84, General Note (c), are exempted from impact testing by the rules of this Division at MDMTs of not more than 5°F (3°C) colder than the temperatures required by the specifications.
o No impact testing is required for metal backing strips which remain in place made of materials:
assigned to Curve A of Fig. UCS-66;
with thicknesses not exceeding 1/4 inch (6.3 mm); and the MDMT is -20°F (-29°C) and warmer.
UCS-66(h), Exemptions for Metal Backing
Strips
UCS-66(i), Part UCS Impact Tested Materials
o Fig. UCS-66.1 provides a basis for the use of impact tested material at MDMTs colder than the IT. temperatures, provided the coincident ratio (Fig. UCS-66.1) \s less than one and the MDMT \s not colder than -155°F (-104°C).
(1) For such components, the MDMT shall not be colder than the impact test temp, less the allowable temp, reduction as determined from Fig. UCS-66.2.
o When the base metal Is exempted from impact testing by UCS-66(g)(material specification required IT.), Or by Fig. UCS-66 Curves C or D, -20°F (-29°C) is the coldest MDMT to be assigned for welded components that do not meet the requirements of UCS-67(a)(2) [SFA material classed by IT. at a temperature not warmer than the MDMT].
UCS-67, Impact Testing Of Welding Procedures
o Except as exempted in UG-20(f), the Welding Procedure Qualification shall include impact tests of the welds and heat affected zones (HAZ) made in accordance with UG-84 when required by the following provisions:
o The MDMT used below shall be that stamped on the nameplate or the exemption temperature of the welded component before applying the temperature reduction permitted by: UCS-66(b) [ reduction in MDMT based on material thickness ratio] UCS-68(c). [non-mandatory PWHT]
o UCS-67(a) Welds made with filler metal shall be impact tested in accordance with UG-84 when any of the following apply:
(a)(l) when either base metal is required to be impact tested by the rules of this Division,
(a)(2) when joining base metals exempt from impact testing by UCS66(g) or Fig. UCS66 Curve C or D and the MDMT is colder than -20°F (-29°c) but not colder than -55°F (-48°C), unless the welding consumables which have been classified by impact tests at a temperature not warmer than the MDMT by the applicable SFA spec. are used; or
(a)(3) when joining base metals exempt from impact testing by UCS-66(g) [materials produced and impact tested LAW the material specification] when the MDMT is colder than -55°F (-48°C).
o UCS-67(b) Welds in UCS Materials made without the use of filler metal shall be impact tested when the thickness of the weld exceeds
1/2 inch (13mm) for all MDMTs; or
when the thickness of the weld exceeds 5/16 inch (8mm) and the MDMT is colder than 50°F (10°C).
o This requirement does not apply to welds made as part of the material specification.
UCS-67, Impact Testing Of Welding Procedures
o UCS-67(c) Weld heat affected zones produced with or without the addition of filler metal shall be impact tested whenever any of the following conditions apply:
(c)(l) when the base metal is required to be impact tested,
(c)(2) when the welds have any individual pass exceeding 1/2 inch (13mm) and the MDMT is colder than 70°F (21°C): or
(c)(3) when joining base metals exempted by UCS-66(g) when the MDMT \s colder than -55°F (-48°C)
o UCS-67(d) Vessel (production) impact tests made in accordance with UG-84(i) may be waived for any of the following:
(d)(l) weld metals joining steels exempted from impact testing by UC5-66 for MDMTs of -20°F (-29°C) and warmer: or
UCS-67, Impact Testing Of Welding Procedures
(d)(2) weld metals defined in (a)(2) above; or
(d)(3) heat affected zones (HAZ) in steels exempted from impact testing by UCS-66, except when (c)(3) above applies.
