COLD CRACKING TESTS-REVISION
Th. Boellinghaus, E. Viyanit and P. Zimmer
I. PURPOSE AND RANGE OF APPLICATIONS
The purpose of this guideline is to describe the most usual test procedures for determining the hydrogen-assisted cold cracking susceptibility of steels and filler materials to hydrogen assisted cold cracking during welding. This description will provide a survey of the cold cracking test procedures and facilitate the selection of a test procedure as well as the evaluation of the results.
II. SURVEY OF THE DIFFERENT TEST PROCEDURES
Externally loaded tests:
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- Implant-Test (A,R)
- LTP-Test (A,R,S)
- TRC-Test (A,R,S)
Self-restraint tests:
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- Bead Bend Test (A,P,R,S)
- Tekken-Test (A,R)
- U-Groove Weld Cracking Test (A,R)
- Lehigh-Test (R)
- CTS(Controlled Thermal Severity)-Test (A,R,S)
- Cruciform-Test (A,R)
- WIC(Welding Institute of Canada)-Test (P,S)
- IRC(Instrumented Restraint Cracking)-Test (A,R,S)
- RGW-Test (A,R,S)
- GBOP(Gapped Bead-On-Plate)-Test (A,R)
- SCCT(Sample For Cold Crack Test) (A,P,R)
A=Acceptance test, P=Procedure test, R=Research and development, S=Simulation of component welds
III. EXPLANATORY NOTES
For evaluating the susceptibility of welds to hydrogen-assisted cold cracking susceptibility, a large number of test procedures is available. The specimens used in these tests may be externally loaded or self-restrained. With the self-restrained specimen, the mechanical loading of the specimen is imposed exclusively by residual stresses resulting from impeded strain and shrinkage and from microstructure transformations in the weld area. With the externally loaded specimen, upon which residual stresses do always act, too, the mechanical test load applied from outside is considered as the test loading.
Externally loaded specimens offer the advantage of a deliberate variation of the mechanical loading, self-restraint specimens have the advantage of a better component-likeness.
The strength properties of the filler material or of the weld metal, respectively, may affect the test result, even if the cold crack occurs in the HAZ.
The bead geometry which may take different shapes depending on the welding parameters, has – except for the Implant-Test – an influence on the cold cracking test result that is not to be ignored, on account of the different notch sharpness obtained.
All cold cracking test procedures mentioned above are ideal for research and development purposes as well as for ranking different steels regarding their cold cracking resistance. To do this, single-run welds are evaluated due to their higher cold cracking susceptibility. The transfer of results from cold cracking investigations to component welds is often an onerous task because of the many relevant boundary conditions that have to be considered. It is, however, possible to determine the required preheating temperature for a given hydrogen content of the filler material and heat input, or the most unfavourable case of the single-run welded root of a butt weld with free cooling or of a single-run fillet weld. The assessment of the influence of welding conditions at real components (e. g. holding of the preheating temperature, multiple runs, or others) on the required preheating temperature can only be accomplished with the help of additional experiments. The certainty of the findings from such experiments is, however, limited.
This guideline has been worked out by the experts in the IIW Subcommission II-A as an helpful overview for all confronted to cold cracking avoidance during practical welding and as an addition to the standardized cold cracking tests.
IV. DETAILED DESCRIPTION
IV.1 Implant-test
The Implant-Test allows the evaluation of the cold cracking susceptibility of a base material (HAZ) and the investigation of individual influencing variables. The result is a characteristic value, e. g. the critical Implant stress for a diffusible hydrogen content and for a respective hard microstructure.
A cylindrical notched specimen of the test material is inserted into an appropriate borehole of a C-Mn steel plate to be welded to it by one bead (see Fig. 1). After cooling down to the testing temperature (e.g. 150°C) a constant test load is imposed on the specimen. Fracture or incipient crack of the specimen is determined.
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Figure 1
Schematic illustration of the Implant-Test principle: a) View, b) Section.
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Objective of the test:
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Cold cracking susceptibility of base materials (BM).
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Main fields of application:
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Acceptance tests, research and development.
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Materials:
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Implant-specimen of high-strength unalloyed or low-alloyed steel (pipe, plate), in special cases made from weld metal.
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Test thicknesses:
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Specimen diameter 6 or 8 mm.
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Number of specimens:
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3 for each condition.
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Type of test:
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Testing of the HAZ in the Implant specimen.
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Loading:
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Constant optional test stress (e.g. base material yield strength).
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Test duration:
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≥ 16 hours.
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Tensioning:
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Multiaxial stresses as a result of a defined notch, defined imposed uniaxial tensile stress, transformational residual stresses.
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Crack location:
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HAZ.
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Crack identification:
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Visual examination, incipient crack examination by means of metallographic sections or opening by force after oxidizing annealing (250°C/3h). Point in time of cracking by evaluation of the stress history.
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Special influencing factors:
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Implant geometry, test load, defined preheating.
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Criterion for the cracking
susceptibility:
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Conditions (weld metal hydrogen content, preheating temperature,
heat input) on which no fractures or incipient cracks occur.
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References
[1] Guideline DVS 1001: Testing of the cold cracking behaviour during the Implant-Test (Oct. 1985). [In German]
[2] TGL 14914 Blatt 5 Ausgabe Juni 1988: Weldability testing – cold cracking resistance of the weld. [In German]
[3] Pohle, C.: Destructive materials testing in welding engineering. Fachbuchreihe Schweißtechnik, Vol. 103. DVS-Verlag, Düsseldorf 1990. [In German]
[4] Neumann, V.: A contribution to the investigation of the hydrogen-affected cold cracking susceptibility of relatively high-strength low-alloyed fine-grained structural steels using the Implant-Test. Forschungsbericht 79 der Bundesanstalt für Materialprüfung, Berlin. [In German]
[5] Florian, W.: Critical evaluation of the cold cracking research and latest investigation results using the Implant-Test. DVS-Berichte, Vol.146, pp. 39/45. DVS-Verlag, Düsseldorf 1992. [In German]
[6] IIW-Doc. IX-1240-82 (Rev.4): Cold cracking test methods using Implants.
[7] IIW-Doc. IX-1729-94: The investigation of Implant cold cracking test (Florian, W. et al).
[8] Davidson, J.A. et al: Assessing fracture toughness and cracking susceptibility of steel weldments – A review. Welding Research Council, 345 East 47th Street, New York.
[9] GOST 26388-84: Method of investigating the resistance against cold cracking during fusion welding. [In German]
[10] Mayer, B.; Nolde P.; Seyffarth, P.: Investigation of the cold cracking susceptibility of weldable high-strength structural steels. DVS-Berichte, Vol. 146, pp. 35/39. DVS-Verlag, Düsseldorf 1992. [In German]
[11] Ruge, J.: Welding engineering handbook, Vol.1: Materials. Springer-Verlag, Berlin 1991. [In German]
[12] Gnirß, G.: Hydrogen during welding, Part 1. Technische Überwachung 17 (1976), No.11, p. 367. [In German]
IV.2 Bead Bend Test
The bead bend test has been developed for evaluating HACC susceptibility of welded components. Different test conditions, e.g. interpass temperature, different layer sequence, etc. can considered as experimental variables influencing crack behaviour of components. In this approach, shrinkage of the testing welds during welding and subsequent cooling is hindered by anchored welds of test specimens with a massive bottom plate. A exposed time of 24 hours at room temperature after welding is required before machining a test specimen. After annealing at 250°C for 16 hours, the test specimen is bent in order to make visible micro cracks. The HACC susceptibility of the test specimen is assessed using visual observations on the polished test surface.
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Figure 2
Schematic illustration of the bead bend test.
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Objective of the test:
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Assessment of the HACC susceptibility of welded components and determination of the interpass temperature as a function of the wall thickness
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Main fields of application:
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Procedure test, R&D, acceptance test and simulation of component welds
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Materials:
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No restriction, welding consumables
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Test thicknesses:
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Plate thickness > 5 mm
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Number of specimens:
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At lest 1 specimen
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Type of test:
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V-butt joint, flat position
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Loading:
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Self-restrained specimen; load levels influenced by plate thickness, YS of parent metal, etc.
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Test duration:
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40 hours: welding time + 24 hours on a massive backing plate + extracting of the test specimen + 16 hours annealing + bending
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Tensioning:
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Residual stresses as a result of shrinkage restraint and transformational residual stresses
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Crack location:
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Weld metal
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Crack identification:
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Visual examination of the polished test surface
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Special influencing factors:
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Plate thickness, homogeneous preheating of the specimen
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Criterion for the cracking susceptibility:
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Quantity, length and location of cracks at the polished test surface
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Reference
[1] Perteneder, E; Königshofer, H.: Capabilities and limitation of cellulosic electrodes - a producers perspective. First international conference on weld metal hydrogen cracking, 1999, Wollongong, Australia
[2] M.Fiedler, H.Königshofer and G.Posch: Investigation of HASCC Susceptibility with the (Bead/Joint) Bend Test
IV.3 LTP-Test
The LTP-Test has been developed for examining the HACC susceptibility of steel welds. This test is one of externally loaded tests. The HACC susceptibility of the welds can be evaluated by immediately applied tensile load to the welded component after welding, or by application of tensile load to the welded component at several days after welding.
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Figure 3
Schematic illustration of the LTP-Test.
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Objective of the test:
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Investigation of HACC susceptibility of welds
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Main fields of application:
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Acceptance tests, research and development and simulation of component welds
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Materials:
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No restriction
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Test thicknesses:
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Requirement of test specimen to avoid any mechanical deformation during testing
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Number of specimens:
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> 1 specimen
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Type of test:
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T-joint welding
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Loading:
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External application of constant tensile load
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Test duration:
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Dependence on the test conditions
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Tensioning:
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Generation of local load depending on levels of constant global load
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Crack location:
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HAZ
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Crack identification:
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Visual examination with metallographical observations
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Special influencing factors:
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Plate thickness, global load levels and starting time for application of global load
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Criterion for the cracking susceptibility:
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Time to failure of the welded components
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References
A. Million: “Stand der Kenntnisse über die Kaltrißbildung und die Beurteilung der Kaltrißanfälligkeit”, DVS Bericht Band 64, pp. 9 –22. [in german]
IV.4 TRC-Test
The TRC-Test (Tensile Restraint Cracking Test) has been developed based on an externally loaded concept. This can be employed for investigating the susceptibility of component welds to cold cracking. A specific level of constant global load is applied to welded component for evaluation of cold cracking behaviour.
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Figure 4: course of the tensions with the TRC-Test in the comparison to the IRC-Test.
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Figure 5: Schematic illustration of the TRC-Specimen type BAM.
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Figure 6: Schematic illustration of the TRC-Specimen type TU Braunschweig.
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Objective of the test:
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Investigation of HACC susceptibility of welds
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Main fields of application:
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Acceptance tests, research and development and simulation of component welds
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Materials:
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No restriction
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Test thicknesses:
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Dependence on the type of test methods
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Number of specimens:
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Requirement of the sufficient number of specimens to confirm test results
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Type of test:
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Butt joint welding
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Loading:
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External application of constant tensile load
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Test duration:
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Dependence on global load conditions
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Tensioning:
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Generation of local load depending on levels of constant global load
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Crack location:
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HAZ and weld metal
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Crack identification:
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Visual examination with metallographical observations
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Special influencing factors:
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Welding condition
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Criterion for the cracking susceptibility:
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Time to failure of specimen
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References
A. Million: “Stand der Kenntnisse über die Kaltrißbildung und die Beurteilung der Kaltrißanfälligkeit”, DVS Bericht Band 64, pp. 9 –22. [in german]
IV.5 Tekken-Test
The Tekken-Test is used to examine a single-run butt weld (root weld) with the aim of determining the preheating temperature required for these test conditions. The test is applied by steel fabricators to assess the cold cracking susceptibility of their steels and may also be applied by processing companies to evaluate the required welding conditions. For producing real welds, e. g. multi-run welds, or for maintaining the interpass temperature it yields, in case, too conservative values. As test weld, a single-run bead is welded into a specially prepared single-V butt joint (see Fig. 7), of which the root gap is kept constant by previously produced anchor welds. The crack surface formed under given welding conditions is determined.
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Figure 7
Schematic illustration of the TEKKEN-Test principle: a) View, b) Test weld and anchor weld preparation.
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Objective of the test:
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Cold cracking susceptibility of butt welds (HAZ-WM combination).
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Main fields of application:
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Acceptance tests, research and development.
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Materials:
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High-strength unalloyed or low-alloyed steel (plate) and respective appropriate filler material.
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Test thicknesses:
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t ≥ 10 mm.
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Number of specimens:
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1 to 3 for each condition. The required preheating temperature (Tpreh) must be proved by at least 3 specimens without incipient crack
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Type of test:
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Butt weld (root run), testing of the weld (HAZ-WM)
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Loading:
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Self-restrained specimen, load level dependent on plate thickness
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Test duration:
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≥ 16 h
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Tensioning:
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Stresses as a result of shrinkage restraint and transformational residual stresses. The root face of the single V butt joint is partially penetrated in order to achieve a corresponding notch effect
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Crack location:
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HAZ and/or WM
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Crack identification:
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Visual examination, incipient crack examination by means of metallographic sections or opening by force after oxidizing annealing (250°C/3h).
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Special influencing factors:
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Plate thickness, joint preparation, homogeneous preheating
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Criterion for the cracking susceptibility:
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Crack free conditions (weld metal hydrogen content, preheating temperature, heat input), crack coefficient: ratio of total crack surface to weld cross-sectional area
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References
[1] Uwer, D.; Höhne, H.: Characterization of the cold cracking behavior of steels during welding. Schweißen und Schneiden 43 (1991), No.4, pp. 195/99. [In German]
[2] Uwer, D.; Höhne, H: Determination of appropriate minimum preheating temperatures providing for cold cracking resistance during steel welding. Schweißen und Schneiden 43 (1991), No.5, pp. 282/86. [In German]
[3] TGL 14914 Blatt 5 Ausgabe Juni 1988: Weldability testing – cold cracking resistance of the weld. [In German]
[4] IIS/IIW-93-62 (ex-doc IX-290-61): Information on cracking tests.(Granjon, H.)
[5] Pohle, C.: Destructive materials testing in welding engineering. Fachbuchreihe Schweißtechnik, Vol. 103. DVS-Verlag, Düsseldorf 1990. [In German]
[6] Davidson, J.A. et al: Assessing fracture toughness and cracking susceptibility of steel weldments – A review. Welding Research Council, 345 East 47th Street, New York.
[7] GOST 26388-84: Method of investigating the resistance against cold cracking during fusion welding. [In German]
[8] Mayer, B.; Nolde P.; Seyffarth, P.: Investigation of the cold cracking susceptibility of weldable high-strength structural steels. DVS-Berichte, Vol. 146, pp. 35/39. DVS-Verlag, Düsseldorf 1992. [In German]
[9] Ruge, J.: Welding engineering handbook, Vol.1: Materials. Springer-Verlag, Berlin 1991. [In German]
[10] Gnirß, G.: Hydrogen during welding, Part 1. Technische Überwachung 17 (1976), No.11, p. 367. [In German]
[11] Satoh, K. et al: Japanese studies on structural restraint severity in relation to weld cracking. Welding in the World 15 (1977), No. 7/8, pp.155 ff.
IV.6 U-Groove Weld Cracking Test
The U-groove weld cracking test is a Japanese Industrial Standard test for detecting the cold cracking generated in the welds of the carbon steel and the low alloy steel by shielded metal arc welding, gas shielded arc welding and self-shielded arc welding.
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Figure 8
Schematic illustration of the U-groove weld cracking test.
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Objective of the test:
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Cold cracking susceptibility of butt welds (HAZ-WM combination).
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Main fields of application:
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Research and partial acceptance test.
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Materials:
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Carbon and low alloy steels and appropriate filler materials.
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Test thicknesses:
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One-side U-groove: t<25 mm, both sides U-groove: t>25mm.
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Number of specimens:
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n/a
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Type of test:
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Butt weld (root run), testing of the weld (HAZ-WM).
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Loading:
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Self-restraint.
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Test duration:
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≥ 48 hours.
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Tensioning:
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Residual stresses as a result of shrinkage restraint and transformational residual stresses.
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Crack location:
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WM.
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Crack identification:
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Visual examination, incipient crack examination by metallographic sections or by opening by tension or root bending.
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Special influencing factors:
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Plate thickness, joint preparation, homogeneous preheating of the specimen.
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Criterion for the cracking susceptibility:
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Surface crack ratio: ratio of total length of the test bead to the added length of the surface cracks, root crack ratio: ratio of total length of the test bead to added length of the root cracks,
respective section crack ratio: ratio of the minimum thickness of the test bead to the added height of the root cracks.
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Reference
[1] JIS Z 3157: Method of U-groove weld cracking test, 1993
IV.7 Lehigh Restraint Test
The Lehigh Restraint Test is used to create quantitative data on solidification or hydrogen cracking susceptibility of deposited welds. This testing method is used to evaluate the crack susceptibility of welds based on the basic principle of the degree of restraint which is required to produce a weld metal crack.
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Figure 9
Lehigh Restraint Test specimen.
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Objective of the test:
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Investigation of the crack susceptibility of plate materials.
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Main fields of application:
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Research and development.
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Materials:
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Steels in plate form.
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Test thicknesses:
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< 20 mm.
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Number of specimens:
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Requirement of large amounts of the test specimens for obtaining reliable crack susceptibility index.
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Type of test:
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Butt weld with the U-groove edge preparation.
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Loading:
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Self-restraint controlled by sawing slots along the sides and ends of plate.
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Test duration:
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> 24 hours.
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Tensioning:
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Residual stresses as a result of transformational residual stresses and shrinkage restraint. The restraint levels are inversely proportional to the length of slots. Thus, the cracking index decreases by decreasing the restrain by longer slots.
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Crack location:
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Weld metal during cooling to RT.
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Crack identification:
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Uses of visual examination on the surface of welds. The absence of cracks should be verified by NDT-tests and by using conventional metallographic examinations.
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Special influencing factors:
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Chemical compositions of filler materials and base metal, preheating, heat input and weld-bead geometries.
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Criterion for the cracking susceptibility:
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Various levels of restraint caused by sawing cut slots are usually assessed to gether with existing crack length in order to explain the cracking susceptibility of testing materials.
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Reference
[1] AWS B4.0M: 2000: Standard Methods for Mechanical Testing of Welds, Approved by American National Standards Institute, July 25, 2000.
IV.8 CTS-Test
The CTS-Test is used to examine single-run fillet welds. By comparison with the Tekken-Test, the CTS-Test yields lower required preheating temperatures.
Two test welds (fillet welds) are welded to two plates joined by anchor welds (see Fig. 10). The conditions (WM hydrogen content, preheating temperature, heat input), under which cracking just does not yet occur, are established.
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Figure 10
Schematic illustration of the modified CTS-Test principle: a) Front view, b) Top view, c) Side view.
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Objective of the test:
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Cold cracking susceptibility of fillet welds (HAZ-WM combination).
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Main fields of application:
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Acceptance test, simulation of component welds.
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Materials:
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High-strength unalloyed or low-alloyed steel (plate) and respective appropriate filler material.
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Test thicknesses:
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6.3 mm ≤ t ≤ 5.4 mm.
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Number of specimens:
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1 to 3 for each condition. Tpreh must be proved by at least 2 specimens without incipient crack.
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Type of test:
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Single-run fillet weld, testing of the weld (HAZ-WM).
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Loading:
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Self-restrained specimen, load level dependent on plate thickness.
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Test duration:
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≥ 16 h.
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Tensioning:
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Stresses as a result of shrinkage restraint and residual stresses.
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Crack location:
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HAZ and/or WM.
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Crack identification:
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Visual examination, crack examination by 4 metallographic sections.
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Special influencing factors:
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Plate thickness, homogeneous preheating of the specimen, welding sequence, base material properties in Z-direction.
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Criterion for the cracking susceptibility:
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At least 3 of the test weld transverse sections must be crack free, the critical heat dissipation in the CTS-specimen is compared to that of components (Thermal Severity Number).
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References
[1] Uwer, D.; Höhne, H: Determination of appropriate minimum preheating temperatures providing for cold cracking resistance during steel welding. Schweißen und Schneiden 43 (1991), No.5, pp. 282/86. [In German]
[2] IIS/IIW-93-62 (ex-doc IX-290-61): Information on cracking tests.(Granjon, H.)
[3] Pohle, C.: Destructive materials testing in welding engineering. Fachbuchreihe Schweißtechnik, Vol. 103. DVS-Verlag, Düsseldorf 1990. [In German]
[4] Davidson, J.A. et al: Assessing fracture toughness and cracking susceptibility of steel weldments – A review. Welding Research Council, 345 East 47th Street, New York.
[5] Ruge, J.: Welding engineering handbook, Vol.1: Materials. Springer-Verlag, Berlin 1991. [In German]
[6] Gnirß, G.: Hydrogen during welding, Part 1. Technische Überwachung 17 (1976), No.11, p. 367. [In German]
[7] Cottrell, C.L.M.: Controlled thermal severity cracking test, Welding Journal, Vol.32 (1953), No.6, pp. 257s.
[8] Pedder, D.J. et al: CTS testing procedures: the present position, The Welding Institute Research, Bulletin, Sept. 1975.
[9] British Standard (BS) 7363: Controlled thermal severity (CTS) test and bead-on-plate (BOP) test for welds, 1990
[10] AWS B4.0M: 2000: Standard Methods for Mechanical Testing of Welds, Approved by American National Standards Institute, July 25, 2000.
IV.9 Cruciform-Test
The Cruciform-Test corresponds to some extent to the CTS-Test. Whereas during the CTS-Test it is not possible for angular contraction to occur due to the specimen geometry and to the anchor welds, the test weld is stressed by this kind of distortion during the Cruciform-Test.
The cruciform specimen has to be prepared as indicated in Fig. 11 in the welding sequence. The fillet welds have to be performed as stringer beads in flat position. Welding direction and working temperature must be the same for each weld. The conditions, e.g. WM hydrogen content, preheating temperature, heat input, under which cracking just does not yet occur, are established.
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Figure 11
Schematic illustration of the Cruciform-Test principle: a) Front view, b) Side view, c) Specimen dimensions.
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Objective of the test:
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Cold cracking susceptibility of fillet welds (HAZ-WM combination).
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Main fields of application:
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Acceptance test, research and development.
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Materials:
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High-strength unalloyed or low-alloyed steel (plate) and respective appropriate filler material.
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Test thicknesses:
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t ≥ 10 mm.
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Number of specimens:
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1 to 3 for each condition. Tpreh must be proved by at least 2 crack free specimens.
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Type of test:
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Single-run fillet weld, testing of the weld (HAZ-WM).
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Loading:
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Self-restrained specimen, load level dependent on plate thickness
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Test duration:
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≥ 20 hours.
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Tensioning:
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Residual stresses as a result of shrinkage restraint and transformational residual stresses. The stress rises with increasing number of welds. Angular shrinkage is of primary importance.
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Crack location:
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HAZ and/or WM.
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Crack identification:
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Visual examination, crack examination by metallographic sections.
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Special influencing factors:
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Plate thickness, homogeneous preheating of the specimen, welding sequence, base material properties in Z-direction.
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Criterion for the cracking susceptibility:
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Crack free conditions (weld metal hydrogen content, preheating
temperature, heat input).
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References
[1] TGL 14914 Blatt 5 Ausgabe Juni 1988: Weldability testing – cold cracking resistance of the weld. [In German]
[2] IIS/IIW-93-62 (ex-doc IX-290-61): Information on cracking tests.(Granjon, H.).
[3] Davidson, J.A. et al: Assessing fracture toughness and cracking susceptibility of steel weldments – A review. Welding Research Council, 345 East 47th Street, New York.
[4] GOST 26388-84: Method of investigating the resistance against cold cracking during fusion welding. [In German]
[5] Poteat, L. E. et al: The cross weld for testing the cracking susceptibility of plates, Welding Journal. J. 39 (1980), No. 2, pp. 70s.
[6] Satoh, K. et al: Japanese studies on structural restraint severity in relation to weld cracking. Welding in the World 15 (1977), No. 7/8, pp.155 ff.
[7] AWS B4.0M: 2000: Standard Methods for Mechanical Testing of Welds, Approved by American National Standards Institute, July 25, 2000.
IV.10 WIC-Test
The WIC-Test is a test specially intended for downhill welding. It simulates the conditions of field pipe welding.
Two test plates are anchored on a firm bottom plate by fillet welding (see in Fig.12) and are welded together over the width in the vertical downhill position, with defined joint preparation and welding parameters and application of carbon electrode. The crack condition (crack depth) is determined.
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Figure 12
Schematic illustration of the WIC-Test principle: a) Specimen configuration, b) Joint preparation.
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Objective of the test:
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Cold cracking susceptibility of pipes during field welding (pipeline construction) (HAZ-WM combination).
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Main fields of application:
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Procedure test, simulation of circumferential pipe welds.
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Materials:
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High-strength unalloyed and low-alloyed pipe steels and appropriate vertical position down electrodes (carbon type).
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Test thicknesses:
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Plate thickness.
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Number of specimens:
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3 specimens.
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Type of test:
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Single-run butt weld (made by vertical position down welding), testing of the weld (HAZ-WM)
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Loading:
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Self-restrained specimen, load level dependent on plate thickness.
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Test duration:
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≥ 24 hours.
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Tensioning:
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Residual stresses as a result of shrinkage restraint and transformational residual stresses.
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Crack location:
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HAZ and/or WM.
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Crack identification:
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Visual examination, incipient crack examination by means of metallographic sections.
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Special influencing factors:
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Plate thickness, homogeneous preheating of the specimen, definitely prespecified, relatively rigid restraint, vertical position down weld.
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Criterion for the cracking susceptibility:
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Conditions (weld metal hydrogen content, preheating temperature, heat input) on which no incipient cracks occur: if sum of crack heights <5% at s < 7.3 mm <3% at s ≥ 7.3 mm.
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References
[1] Davidson, J.A. et al: Assessing fracture toughness and cracking susceptibility of steel weldments – A review. Welding Research Council, 345 East 47th Street, New York.
[2] North, T.H. et al: Weldability of high strength line pipe steels. Welding Journal Research Suppl. 1982.
IV.11 IRC-Test
The IRC-Test is a comparatively elaborate test which can be used to simulate component welds under high shrinkage restraint. In this procedure, the real shrinkage restraint of a structure is at first determined and then reproduced in the test by respective selection of the testing facility and of the specimen dimensions. The cracking susceptibility of component welds is determined by recording the reaction stresses and moments during the test.
The IRC-specimen, in the form of two plates, is firmly fixed and welded in the test set up (see Fig.13a). During welding and subsequent cooling, the shrinkage reaction force and the two shrinkage reaction moments are online measured and recorded in order to determine the reaction stress distribution (see Fig. 13b).
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Figure 13
Schematic illustration of the IRC-Test principle with exemplary dimensions:
a) View for butt weld and fillet weld, b) Top view, c) IRC-Test diagram for a specific intensity of restraint RFy [kN/(mm⋅mm)].
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Objective of the test:
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Cold cracking susceptibility of butt and fillet welds (HAZ-WM) for restraint intensities previously determined on constructions.
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Main fields of application:
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Research and partial acceptance test, simulation of component welds.
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Materials:
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Steel plates and tubes and appropriate filler material.
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Test thicknesses:
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t ≥ 10 mm.
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Number of specimens:
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1 to 3 for each condition. The required preheating temperature (Tpreh) must be proved by at least 3 crack free specimens.
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Type of test:
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Single-run or multi-run butt or fillet weld, testing of the HAZ and WM.
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Loading:
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Self-restrained specimen, load level dependent on plate thickness and on the length between clamps.
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Test duration:
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≥ 20 hours.
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Tensioning:
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Residual stresses as a result of shrinkage restraint and transformational residual stresses, weld geometry (e.g. root notch).
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Crack location:
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HAZ and/or WM.
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Crack identification:
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Visual examination, crack examination by metallographic sections or by opening by force after oxidizing annealing, time of cracking by evaluation of the recorded reaction stress condition.
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Special influencing factors:
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Plate thickness, type of preheating, variable residual stresses by optional restraint conditions and component-oriented preheating.
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Criterion for the cracking susceptibility:
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Crack free conditions (weld metal hydrogen content, preheating temperature, heat input) Crack coefficient: ratio of total crack surface to weld cross-sectional area.
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References
[1] Hoffmeister, H.; Ruyter, E.; Braathen, O. et al: Cracking risk assessment of highly restrained offshore steel joints of the SNORRE TLP structure by onsite restraint measurement and IRC-testing. Proc. of the 10th Conf. on Offshore Mechanics and Arctic Engineering (OMEA), Stavanger 1991, Vol. III, pp. 495 ff.
[2] Ruge, J.: Welding engineering handbook, Vol.1: Materials. Springer-Verlag, Berlin 1991. [In German]
[3] Satoh, K. et al: Japanese studies on structural restraint severity in relation to weld cracking. Welding in the World 15 (1977), No. 7/8, pp.155 ff.
[4] Hoffmeister, H.: Concept and procedure description of the IRC-Test for assessing hydrogen assisted weld cracking, Steel Research (AEW), Vol. 57(1986), No.7, pp. 344 ff.
IV.12 RGW-Test
The RGW-Test is also used to simulate component welds. The component stresses are simulated by selecting the specimen length and thickness.
The clamping and the pairs of specimen elements have to be prepared according to Fig. 14 and fixed by means of the clamp bolts. The test weld has to be performed as a single-run stringer bead. The conditions, e.g. WM hydrogen content, preheating temperature and heat input, under which cracking just does not yet occur, are established.
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Figure 14
Schematic illustration of the RGW-19-KR-Test principle: a) Normal section, b) Top view.
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Objective of the test:
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Cold cracking susceptibility of butt and fillet welds
(HAZ-WM combination).
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Main fields of application:
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Research and partial acceptance test, simulation of component welds.
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Materials:
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High-strength unalloyed or low-alloyed steel (plate) and appropriate filler material.
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Test thicknesses:
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t ≥ 10 mm.
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Number of specimens:
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1 to 3 for each condition. The required preheating temperature (Tpreh) must be proved by at least 3 specimens without incipient crack.
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Type of test:
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Single-run or multi-run butt or fillet weld, testing of the HAZ and WM.
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Loading:
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Self-restrained specimen, load level dependent on plate thickness and on the length between clamps.
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Test duration:
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≥ 16 hours.
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Tensioning:
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Residual stresses as a result of shrinkage restraint and transformational residual stresses, weld geometry (e.g. root notch).
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Crack location:
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HAZ and/or WM.
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Crack identification:
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Visual examination, incipient crack examination by means of metallographic sections or opening by force after oxidizing annealing.
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Special influencing factors:
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Plate thickness, type of preheating, variable residual stresses by three different lengths between clamps and inhomogeneous or homogeneous preheating.
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Criterion for the cracking susceptibility:
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Crack free conditions (weld metal hydrogen content, preheating temperature, heat input), Crack coefficient: ratio of total crack surface to weld cross-sectional area.
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References
[1] TGL 14914 Blatt 5 Ausgabe Juni 1988: Weldability testing – cold cracking resistance of the weld. [In German]
[2] GOST 26388-84: Method of investigating the resistance against cold cracking during fusion welding. [In German]
[3] Mayer, B.; Nolde P.; Seyffarth, P.: Investigation of the cold cracking susceptibility of weldable high-strength structural steels. DVS-Berichte, Vol. 146, pp. 35/39. DVS-Verlag, Düsseldorf 1992. [In German]
IV.13 Gapped Bead-On-Plate Test
The Gapped Bead-On-Plate Test is a simple test for evaluating the relative sensitivity to hydrogen cracking of weld metal. Although critical preheat is determined in the test, it is not intended to directly predict preheat requirements for practical welding procedures. The test is designed to promote transverse cracks through the weld metal.
A short, single pass weld bead is deposited over a gap formed when two blocks, one having a shallow recess machined in it, are clamped together.
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Figure 15
Schematic illustration of the Gapped Bead-On-Plate Test: a) Top view, b) Side view.
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Objective of the test:
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Relative susceptibility to hydrogen cracking of weld metals.
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Main fields of application:
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Research and partial acceptance test.
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Materials:
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Structural steel (blocks) and appropriate filler material.
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Test thicknesses:
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Block thickness 50 mm.
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Number of specimens:
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n/a
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Type of test:
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Single-run butt weld, testing of the weld.
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Loading:
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Self-restraint
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Test duration: < |