Detachable Tubesheet Plate for Urea Reactor Welding

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Solution Overview

Problem

In urea condensation and synthesis reactors, the tube-to-tubesheet joint is challenging due to the need for high-pressure resistance and corrosion resistance, making welding difficult and maintenance hard, especially with thick tubesheets and the risk of crevice corrosion.

Innovation Solution

A reactor design with a tubesheet divided into a high corrosion-resistant metal plate for contact with the reaction fluid and a low corrosion-resistant metal plate for pressure resistance, allowing for easier welding and maintenance, using inner bore welding for attaching heat exchange tubes to the high corrosion-resistant plate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single tubesheet plate is used for both corrosion resistance and pressure resistance, then corrosion resistance is improved, but welding difficulty and maintenance complexity increase due to thick plates and crevice corrosion risks

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidwelding difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The tubesheet is divided into two separate plate members: a first plate member (corrosion-resistant layer) made of high corrosion-resistant metal and a second plate member (pressure-resistant layer) made of low corrosion-resistant metal. This segmentation allows each layer to be optimized for its specific function while simplifying the welding process by providing access to the weld zone from the pressure-resistant side.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The corrosion-resistant function is extracted as a separate thin plate member (first plate member) that can be easily attached to the pressure-resistant plate member. This thin corrosion-resistant layer can be welded using inner bore welding techniques without the accessibility problems associated with thick single-layer tubesheets.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If inner bore welding is used through thick tubesheets, then corrosion resistance is maintained, but maintenance and repair accessibility deteriorates

Engineering Contradiction:

Improvejoint reliabilityVSAvoidmaintenance accessibility

Core Design Contradiction:

ReliabilityVSEase of repair

Solution Approach 1:

Instead of welding from the corrosion-resistant side through thick plates (conventional approach), the invention inverts the approach by welding from the pressure-resistant side. The first plate member is made thin and detachably attached to the second plate member, allowing welding torch access from the rear side for easy maintenance and repair.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If a thin corrosion-resistant plate is used, then welding accessibility is improved, but pressure resistance deteriorates

Engineering Contradiction:

Improvewelding accessibilityVSAvoidpressure resistance

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

Different regions of the tubesheet structure are assigned different material properties: the first plate member (corrosion-resistant layer) is made thin with high corrosion resistance but low pressure resistance, while the second plate member (pressure-resistant layer) is made thicker with high pressure resistance but lower corrosion resistance. Each layer's thickness and material are locally optimized for its specific function.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The tubesheet is constructed as a composite structure with two different metal plate members: a high corrosion-resistant metal (e.g., high-chromium austenite steel, titanium, or 316L austenite steel) and a low corrosion-resistant metal (carbon steel or low-alloy steel). This composite structure combines the advantages of both materials to achieve both corrosion resistance and pressure resistance.

Inventive Principle:

Principle #40Composite materials

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 design facilitates reliable and easy welding of heat exchange tubes and maintenance, reducing the risk of leaks and corrosion-related issues, while minimizing the complexity of accessing and repairing welds within the thick tubesheet.

Implementation Method 1

The reaction heat of ammonium carbamate formation (ammonium carbamate is an intermediate product) is removed by cooling by way of the tube bundle

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

condensing and recycling the gas mixture to the urea synthesis zone

Methodology Applied

Scientific EffectCondensation: Condensation

Data Source

PatentUS7763215B2Reactor having detachably fixed tubesheet plate member

Publication Date: 2010.07.27 TOYO ENG CORP

AI summary

A reactor including a reactor vessel and heat exchange tubes provided in the reactor vessel. The reactor vessel includes a tubesheet and is configured to receive a reaction fluid. The tubesheet has a first plate member configured to contact the reaction fluid and a second plate member configured to not contact the reaction fluid. Heat exchange tubes are provided in the reactor vessel and fixed to the first plate member. The heat exchange tubes are configured to receive a heat exchange medium. At least a portion of the first plate member configured to contact the reaction fluid is made of a metal that has a high corrosion-resistance against the reaction liquid, and the second plate member is made of a metal that has a low corrosion-resistance against the reaction liquid. The second plate member is detachably fixed to a remainder of the reactor vessel.