Preventing Leaks with Anaerobic Thread Sealants
Leaks are serious business. The costs from leaks go far beyond the value of the estimated one billion liters of fluids and gasses lost. This article explores the theory and recent practice of preventing leaks for pipe thread fittings. Anaerobic thread sealants can prevent leaks by serving as a protective umbrella over the many potential causes of leakage. These metal adhesives offer significant benefits over other sealing methods.
The cost of leaks: more than money alone
Leaks are serious business. Governments legislate against them, technical societies create standards to avoid them, anufacturers expend great efforts to prevent them, and maintenance departments work continuously to staunch them. Industry wastes an estimated one billion liters of industrial fluids through leaks every year. Leakage exists in all systems to some degree. Apart from the value of lost fluids and gasses, there are the unknown but frequently high costs of cleaning the spillage, firefighting, personal safety and wastewater treatment to remove harmful liquids. There are also the expenses of maintenance, rework on new equipment, or worse, correction of leaks that develop after new owners take possession of equipment. Experts estimate leakage costs industry more than $200,000 per day.
More than money is at stake. Leaks affect toxicity in the environment, emissions, safety, contamination, fire and personnel. They may also affect the manufacturer’s image.
How leaks develop
Most leaks are located at pipe joints. Threaded joints in piping systems are unavoidable. Pipe system designers seek to reduce the number of joints wherever possible, but without demountable joints, each repair would require the removal of massive pipe links. Unfortunately, these essential joints often are assigned improper pipe support and sealing methods, leading to leaks.
In an ideal pipefitting, the connection of threads forms an impenetrable barrier against liquids or gasses. In reality, complete metal-to-metal contact is not achieved and the spaces left become leak paths. Commonly, leak paths are spiral-shaped because they follow the clearance between the crest and the root of pipe threads.
The most unavoidable cause of leaks is human error. Tapered hydraulic pipe threads are imprecise and it is not possible to install them with a specific torque. The assembler tightens the fittings manually. Too much torque can crack or distort fittings, while too little results in improper alignment of thread flanks. Each time routine maintenance requires disassembly and reassembly of the same joint, the risk of damage from improper assembly multiplies.
Assuming joints have been assembled correctly and no leak paths have been created, conditions from everyday operation can quickly lead to leaks. Excessive pressure in hydraulic lines will enlarge microscopic leak paths; vibration and shock can loosen joints and different temperatures in the two components of a pipe joint (thermal cycling) can cause misalignment or cracking.
Design options to prevent leaks
Several widely accepted system design and assembly approaches can help reduce leakage:
• Avoid use of separable connections when practical;
• Choose swaging and shrinking over threaded joints if possible;
• Design piping systems with fittings in mind;
• Use flared tubing when possible.
But sealing a port remains necessary and it is here that engineers frequently have to decide between the tapered pipe thread fitting and the SAE straight thread with Oring seal. In a perfect world, straight thread pipes would be available for every situation because they allow the most metal-to-metal contact. However, straight thread fittings must be precision cut for each use, making them cost – and time – prohibitive in most cases.
Tapered pipe threads are imprecise. They are not cut to precise dimensions, nor can they be installed with specific torque. During the course of use and repair, threads become damaged and more vulnerable to leakage. However because they are the least expensive, tapered pipe threads are the most common. This means leaks are bound to occur from a number of causes.
Threadsealing with anaerobic sealants
Engineers have several options to seal pipe threads, among which anaerobic thread sealant is the most effective method.
In 1953, Loctite developed anaerobic metal adhesives technology. Anaerobic adhesives are single component liquid resins that harden to a tough solid state when activated by a combination of contact with metal in the absence of air. The resulting cured material is a thermoset plastic that does not melt when heated and resists most solvents. Once cured, anaerobic sealants lock fittings, preventing loosening from vibration.
Anaerobic sealants offer a number of benefits over other methods of threadsealing:
• Lubricity: Containing PTFE filler, the material eliminates galling or other component assembly problems. These products prevent over-torque when creating a seal.
• Due to high wicking ability, the material fills threads so well that nicks, scratches and dents do not permit leakage and leak paths do not develop.
• Due to the longer curing time of the liquid thread sealant, it is possible to adjust the fittings during assembly without compromising the quality of the resulting seal.
• Anaerobic sealants lock fittings, preventing loosening through vibration.
• Fittings sealed with anaerobic thread sealant can be re-used and retreated with the same adhesive without danger of leakage.
• All characteristics of anaerobic thread sealants are predictable so they can be selected for a specified cure time, shear strength, viscosity, chemical resistance, and gap-filling ability.
• Anaerobic sealants can withstand chemical attack from hydraulic fluids, solvents, fuels, lubricants, gases, and synthetics.
• Because they cure to form structural solids, anaerobic sealants are able to resist pressures beyond burst ratings of pipes.
• Each anaerobic thread sealant is different, but many can resist temperatures as low as -65°F (-53OC) and as high as 300° F (149℃） .
• Unlike the tape sealant, PTFE-based sealant does not contaminate lines and valves.
Anaerobic thread sealants are so effective that they are often used with straight threads, which enter or plug pressure vessels. They lock freestanding fittings such as gauges effectively and make tapered fittings as effective as O-rings at a fraction of the cost. Liquid thread sealants can also improve the 98% effectiveness of yielding metal joints to almost 100%. In addition, they are effective even when only a light torque is used on tapered threads.
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Author(s):
• Girard S. Haviland –Henkel Loctite Application Engineer, North America
• Robert A. Valitsky – Henkel Loctite Technical Manager
• Dale Barsness - Henkel Loctite Application Engineer, North America
• CS Woo – Henkel Loctite Customer Services Manager, Asia Pacific
Company Information
Loctite® is the world’s leading brand of engineering adhesives and sealants. Since the original invention of anaerobic adhesives in 1953, the Loctite® brand stands for innovative technologies, superior performance, cost savings, and strong partnership with its customers. Today, Loctite® is the flagship brand of Henkel adhesive technologies and offers over 5,000 unique products through a wide distribution network covering 125 countries. Industrial users across the globe trust Loctite® products to improve reliability of their assemblies and reduce overall costs.
For more than 130 years, Henkel has been a leader with brands and technologies that make people's lives easier, better and more beautiful. Henkel operates in three business areas – Home Care, Personal Care, and Adhesive Technologies – and is ranked among the Fortune Global 500 companies. In fiscal 2008, Henkel generated sales of €14,131 million and adjusted operating profit of €1,460 million. With more than 55,000 employees in more than 125 countries, people trust in brands and technologies from Henkel. Henkel – A Brand Like A Friend.
Information for editors: http://www.iLoctite.com/press