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NSTX Centerstack Upgrade Project Meeting

P. Titus March 23 2011

American Welding Society Stainless Steel Edition

AISC Table 1.17.5 Minimum weld sizes recommended for joined plate sizes. Appears in ASME, and AWS for Carbon Steel - But it doesn’t appear in AWS-SST

Rib is ½ inch thick and top plates are 5/8

The nature of inquiries directed to the American Welding Society and the Structural Welding Committee has indicated that there are some requirements in the code that are either difficult to understand or not sufficiently specific, and others that appear to be overly conservative. It should be recognized that the fundamental premise of the code is to provide general stipulations applicable to any situation and to leave sufficient latitude for the exercise of engineering judgment. Another point to be recognized is that the code represents the collective experience of the committee and while some provisions may seem overly conservative, they have been based on sound engineering practice. The committee, therefore, believes that a commentary is the most suitable means to provide clarification as well as proper interpretation of many of the code requirements.

1.1 ScopeThis code covers welding requirements applicable tostainless steel structures and weldments subject to designstress. It shall be used in conjunction with any complementarycode or specification for the design or constructionof stainless steel structures and weldments. Whenthis code is stipulated in contract documents, conformancewith all provisions of the code shall be required,except for those provisions that the Engineer (see 1.4.1)or contract documents specifically modify or exempt.This code is not intended to be used for pressure vesselsor pressure piping.

2.1.4 Weld Size and Length. Contract design drawingsshall specify the effective weld length and, for PJPgroove welds, the required weld size “(E).” For filletwelds and skewed T-joints, the following shall be providedon the contract documents.

2.3.2.2 Fillet Welds and Welds in Skewed T-Joints.Stress on the effective area of fillet welds and of welds inskewed joints shall be considered as shear stress, regardlessof the direction of application.

2.3.2.3 Intermittent Fillet Welds. Intermittent filletwelds may be used to carry calculated static stress.

2.14.3.3 Intermittent groove welds are prohibited.2.14.3.4 Intermittent fillet welds are prohibited.

2.3.2.7 Allowable Stresses Established by Testing.Mechanical properties of joints and allowable stressesmay be established by testing. These tests shall be agreed between Engineer and Contractor (see Notes in Table 2.1b and Annex I, Clause I2.2).

2.3.3 Fatigue Provisions. Fatigue stress provisions forstructures subject to cyclic loading shall be determined by the Engineer and be included in the contract specification. Contractual fatigue provisions shall be established by the Engineer based on:(1) Applicable research data.(2) The environmental conditions such as fluids, temperaturesand atmospheres to which the structure will besubjected.(3) Conditions specific to thin-walled structures, typical for stainless steels, such as load-induced distortion and local stress concentration. Hot spot stress approach may be considered to accommodate these conditions.(4) Consideration of the stress intensification effects of the weld details.(5) Fatigue performance of the applicable type and grade of stainless steels.

Structural Welding Code—Stainless Steel

1.4.1 Engineer’s Responsibilities. The Engineer shallbe responsible for the development of the contract documentsthat govern products or structural assemblies producedunder this code. The Engineer may add to, deletefrom, or otherwise modify, the requirements of this codeto meet the particular requirements of a specific structure.If alternate requirements are proposed by other partiessuch as the Contractor, the Engineer may approve

them based on provided documentation. Alternaterequirements shall be based upon evaluation of suitabilityfor service using past experience, experimental evidenceor engineering analysis considering material type,service load effects, and environmental factors. Allrequirements that modify this code shall be incorporatedinto contract documents. The Engineer shall determinethe suitability of all joint details to be used in a weldedassembly.

Conclusion:

1/8 inch fillets on plate thicker than ¼ inch are not acceptable structural welds

Intermittent welds are unacceptable for cyclic service

Unless:

There is an appropriate qualification program consistent with section 1.4.1, 2.3.3, 2.3.2.7