Heat exchanger repair and maintenance requires a keen eye and a good understanding of a wide range of potential problems. In this blog we shall outline some of the common causes of poor performance of heat exchangers and provides some ways for solving them.
Heat exchanger fouling
Heat exchanger fouling is a serious problem not just for maintenance engineers but also the global economy. Some estimates suggest that heat exchanger fouling costs an estimated 0.25% of the GNP of industrialised countries due to over-design, additional fuel consumption and maintenance, loss of production, etc
A build-up of deposits on the tube bundle can significantly reduce heat exchanger performance. As such, regular maintenance to remove build-up in beneficial in the long-run.
There are two main methods of removing fouling from heat exchanger tubes:
Mechanical repair of fouling in heat exchanger tubes
These techniques require the heat exchanger to be taken offline and dismantled in order to conduct the cleaning. The most common methods employed are steam-blasting using high-pressure steam lines or hydro-blasting, using high-pressure water jets, to remove the surface build-up.
Neither of these techniques tend to be 100% successful at removing fouling deposits and surfaces may remain rough even after treatment. It is also labour intensive, with a lot of time spent dismantling machines which keeps the heat exchanger offline for considerable amounts of time.
Chemical cleaning of fouling in heat exchanger tubes
These techniques present a range of benefits over mechanical repair in that they are relatively quick, less labour intensive and can reach parts of the machine that mechanical cleaning would struggle with.
Chemical cleaning solutions normally mean the heat exchanger can be repaired insitu without the need for costly dismantling. This speeds up the overall process and allows the heat exchanger to get back online quicker reducing downtime and associated costs.
The basic process for chemical cleaning follows a five step procedure:
- Alkaline clean: Removes organic material build up such as oil and fats leaving the inorganic surfaces exposed and ready for treatment.
- Rinse: Following each step there is a rinse using high flow water flushes which removes loose debris and remaining chemical residue.
- Acid cleaning: The inorganic material is now treated with an appropriate acid blend designed to soften or disvolve the fouling material.
- Rinse: The process of rinsing occurs once more to remove any debris, sludge or residual acid from the heat exchanger following the acid cleaning process.
- Passivation: This is required to add a protective coating to the base metal that is now exposed and vulnerable to oxidation should it continue to be exposed to the atmosphere.
Heat exchanger repair of corroded of fouled division plates
Division plates or tube plates often suffer the same fate as tube bundles within heat exchanger. They suffer from fouling or corrosion which can cause leakage and inefficient performance. As these are often sealing faces, a good surface finish is important in order to comply with industry standards.
Insitu machining of heat exchanger flanges
Flange facing machines are common tools amongst on-site service engineers but few people realise that flange facing machines by Mirage can be adapted to repair corroded heat exchanger flanges and division plates also.
Here's a video of Mirage's heat exchanger mounting kit and flange facing machine demonstration:
The benefits are significant in that, like with the chemical repair mentioned about, the heat exchanger can remain insitu throughout the repair work. Even with the demanding tolerances required, Mirage flange facing machines and heat exchanger mounting kits can deliver workshop quality tolerances on-site.
Work is carried our in a costly, timely manner so as to avoid expensive dismantling and logistics associated with off-site repair.