Monolithic Vessel Head Tube Joining Without Dissimilar Metal Welds

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Solution Overview

Problem

The manufacturing of reactor pressure vessel (RPV) heads involves complex and costly processes, including multi-stage forging, heat treatment, machining, and gas tungsten arc welding, which result in dissimilar metal welds (DMWs) that are difficult to produce and expensive to inspect, requiring frequent in-service inspections and potentially costly repairs.

Innovation Solution

A method of manufacturing a monolithic vessel head using a solid-state joining process to integrally join tubing and/or nozzles to a vessel head, eliminating the need for DMWs by forging, heat treating, boring, counterboring, and using friction hydropillar or induction heating methods to join the components in a single, monolithic structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If gas tungsten arc welding is used to attach tubes to the vessel head, then the tubes can be joined to the vessel head, but dissimilar metal welds are created that are complex and expensive to inspect

Engineering Contradiction:

Improveease of tube attachmentVSAvoidcomplexity of dissimilar metal weld

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent merges the tube and vessel head materials by using austenitic stainless steel tubes with low alloy steel vessel heads, creating a compatible material pair that eliminates the need for complex dissimilar metal welds. The tube material is selected to be compatible with the vessel head, allowing for simpler welding procedures and reduced inspection complexity.

Inventive Principle:

Principle #5Merging (Combining)

2Manufacturing precision

If conventional multi-stage manufacturing approach is used, then the vessel head can be produced with required tolerances, but production time extends over months

Engineering Contradiction:

Improvecomponent toleranceVSAvoidproduction time

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent applies preliminary action by pre-boring the vessel head to accept the tubes before welding, and by selecting tube materials that require minimal post-weld machining. This sequencing of operations and material selection reduces the number of iterative machining and welding passes required, thereby reducing overall production time while maintaining precision.

Inventive Principle:

Principle #10Preliminary action

3Strength

If J-prep weld design is used for tube attachment, then the weld can join the tube to the vessel head, but the weld is difficult to machine and weld due to confined spaces

Engineering Contradiction:

Improveweld strengthVSAvoidease of welding

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent inverts the conventional approach by using austenitic stainless steel tubes with low alloy steel vessel heads, rather than the traditional low alloy steel tubes with austenitic stainless steel vessel heads. This material inversion allows for simpler welding procedures and reduced inspection complexity, as the austenitic tube material is more weldable and compatible with the low alloy steel vessel head.

Inventive Principle:

Principle #13The other way round (Inversion)

4Strength

If dissimilar metal welds are used to join different materials, then the tube and vessel head can be joined, but expensive in-service inspections are required every 10 years

Engineering Contradiction:

Improvejoint strengthVSAvoidinspection complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent applies homogeneity by selecting tube and vessel head materials that are metallurgically compatible, creating a homogeneous joint structure that eliminates the need for complex dissimilar metal weld inspections. The austenitic stainless steel tube and low alloy steel vessel head form a compatible material pair that behaves more uniformly under service conditions, reducing inspection requirements.

Inventive Principle:

Principle #33Homogeneity

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach eliminates the complexity and expense of DMWs, reduces production time by 12-18 months, and saves millions of dollars per reactor head, while ensuring a single, monolithic component with no evidence of welds, enhancing manufacturing efficiency and reducing maintenance costs.

Implementation Method 1

inserting a tube into the at least penetration and using a solid-state joining process to join the tube to the vessel head

Methodology Applied

Scientific EffectFriction: Friction

Implementation Method 2

using friction hydropillar or induction heating methods to join the components

Methodology Applied

Scientific EffectFriction welding: Friction Welding

Implementation Method 3

using friction hydropillar or induction heating methods to join the components

Methodology Applied

Scientific EffectInduction heating: Induction Heating

Data Source

PatentUS20250128347A1Methodology to manufacture a monolithic vessel head with integral tube attachments via solid-state joining

Publication Date: 2025.04.24 ELECTRIC POWER RES INST INC

AI summary

A method of manufacturing a monolithic vessel head with integral tube attachments is disclosed. The method includes the steps of forging a vessel head; boring at least one penetration in the vessel head; and inserting a tube into the at least penetration and using a solid-state joining process to join the tube to the vessel head.