How to Detect Leaks in Plate Heat Exchangers with Tracer Gas

Introduction

Heat exchangers are vital components across various industries, facilitating heat transfer between gases, liquids, or a combination thereof. Accurate integrity testing by manufacturers is crucial for ensuring the reliability, safety, and performance of these heat exchangers, thereby preventing costly repairs.

Applications

From power generation to manufacturing, healthcare, and data centers, heat exchangers enhance efficiency, safety, and energy savings in thermal processes. They range from small units for domestic applications to large industrial units used in power plants, chemical plants, and oil refineries. The size and volume vary significantly based on the type, application, and heat transfer requirements. This document focuses on leak detection in plate heat exchangers using INFICON tracer gas leak detectors.

Traditional Methods

A common method for leak detection is the pressure drop test. This involves filling the heat exchanger with air, pressurizing it, and monitoring pressure changes over time. This method is sensitive to temperature variations and has limited sensitivity, only indicating a system leak without pinpointing its exact location. Visual leak identification can be attempted by applying a soapy solution after pressurization; bubble formation indicates a leak. While simple and economical, this technique is best suited for checking flanges, joints, and seals, and is not effective for very small leaks. Submersion tests, where a pressurized heat exchanger is immersed in water, also reveal leaks through bubble formation, but excessive bubbling can hinder precise leak identification. Water bath testing requires visual access to all component surfaces, including those not easily visible to the operator. These techniques are unsuitable for large components or in-service exchangers, as they necessitate system shutdown and subsequent drying.

INFICON Solution: Tracer Gas Leak Detection

A non-destructive and more sensitive method is tracer gas leak detection, employing gases like helium or a 5% hydrogen in nitrogen mixture (formation gas). Depending on the heat exchanger's size, flow rate, and sealing requirements, either accumulation or vacuum testing can be used.

Tracer gas leak detection is an effective method for plate heat exchangers where small leaks are difficult to detect with conventional methods. The process typically uses helium or a mixture of nitrogen and hydrogen as the tracer gas.

1. Evacuate liquids and gases from the heat exchanger for accurate tracer gas filling and precise results.
2. Pressurize the heat exchanger with tracer gas at the operating pressure.
3. Detect leaks by measuring the tracer gas in the chamber and using a sniffer probe to locate leaks.

Accumulation Test with Leak Localization

For small to medium-sized heat exchangers with low to medium production volumes, the accumulation test with tracer gas offers an economical solution for verifying water or oil leaks. The component is evacuated and pressurized with hydrogen, then placed in a chamber with air circulated by a fan. Escaped hydrogen accumulates in the chamber, and its concentration indicates the leak size. The INFICON solution includes the Sentrac hydrogen leak detector, equipped with a dual-probe connection, and the AP29ECO sampling probe. Managed by the Sentrac detector, the AP29ECO waits for a predetermined accumulation time before sampling air from the chamber for analysis. The probe features an automatic purge function, activated before and after sampling, and whenever the concentration exceeds a threshold, allowing for rapid elimination of gross leaks within seconds. If the hydrogen concentration exceeds the set tolerance limit, the Sentrac detector triggers an alarm. Simultaneously, a manual sniffer probe, connected to the detector, is used to precisely locate leaks immediately after the test, while the component is still pressurized.

Accumulation Test with Maximum Sensitivity

For very fast leak tests, when extremely small leaks are anticipated, or in all circumstances where a leak detector for both helium and formation gas is preferred, the LDS3000 AQ leak detector is the ideal choice. This unit operates with both gases and detects leaks down to 10⁻⁵ mbar·l/s. The component is filled with tracer gas and placed in the accumulation chamber, where escaped gas concentrates over time. The LDS3000 AQ measures the rate of tracer gas increase within the chamber; a rapid rise indicates a significant leak.

Vacuum Test

For large-sized heat exchangers, those with medium to high production volumes, or components tested for refrigerant leaks, helium leak testing in a vacuum chamber is preferred. In this method, the heat exchanger is first evacuated and filled with helium, then placed in a chamber where pumps create a vacuum. If a leak is present, the LDS3000 helium leak detector identifies escaping atoms and activates an alarm signal.

Advantages of Tracer Gas Leak Detection

• Improved Leak Test Quality: Detects even the smallest leaks.
• Easy Leak Localization: Pinpoints the exact leak location.
• Fast Leak Detection: Results are obtained quickly, minimizing downtime.
• Clean and Non-Destructive Method: No need to disassemble or dry the component.
• Temperature and Humidity Independent: Reliable results with high repeatability.

Comparison of Testing Methods