By Alfredo Jones
Corrosion problems at pipe supports on onshore and offshore Oil and Gas facilities all over the world is one of the leading causes of piping failures. This paper discusses the various corrosion mechanisms that occur at pipe supports leading to these failures and a proven method of prevention to this problem.
Causes and innovative solutions for solving them
During routine inspections of onshore & offshore oil and gas production facilities all over the world, a recurring problem has been noted, namely corrosion on piping systems which often leads to a piping failure. Why are pipe support points prone to such localized corrosion and what can be done to prevent it?
The Corrosion Mechanism
•The problem starts at the pipe supports with the following:
•Crevice forming – This is the root of the problem.
•Water is trapped – The supports allow water to be held in contact with the pipe surface.
•The paint system fails – As the paint surface is in constant contact with water, it softens, exposing the bare steel of the pipe. This makes the pipe and support to be in direct contact with the trapped water.
•Corrosion is initiated – The small area of steel now exposed to the water starts to corrode and spreads. Soon the whole support area is bare steel.
•Crevice corrosion starts – At this point on, the galvanic crevice corrosion is driven by metal to metal contact.
•Pipe fails – Leading in some cases to some catastrophic consequences.
If we consider some of the more common types of pipe supports used in the oil & gas industry and we can see why the problems arise:
Pipe corrosion at saddle clamps
Saddle clamps are a potential corrosion hot spot. The saddle clamp often has a rubber liner designed to protect the coating on the pipe during installation. Sometimes this liner is required to provide electrical isolation between the pipe and clamp. In either case, the result is a tight crevice at the pipe surface. The crevice is so aggressive that any water falling onto the pipe in the area of the clamp may be sucked into this crevice by capillary action.
Once in there, it is difficult for the water to escape and thus the pipe surface stays wet. Pipe coatings, (paint) used on topside piping are designed to protect the pipe from atmospheric corrosion. They were never intended for immersion service. However, that is the service they find under these clamps.
The result is softening and failure of the paint and corrosion is able to proceed uninhibited. Saddle clamps offer other disadvantages: they provide for no inspectability under the clamp; are expensive, and are rarely removed during maintenance painting so that the coating is never repaired.
Corrosion at pipe supports
This is a very common method of supporting pipe runs. The pipes are usually stabilized with a U-bolt and it is not uncommon to see a neoprene pad installed under the pipe. The neoprene pad is designed to stop paint damage during installation and to reduce metal-to-metal contact. In truth, it aggravates the problem. Being soft, the material deforms under the weight of the pipe and forms a very aggressive crevice at the pipe surface. Paint failure then ensues by the same mechanisms as previously described. Again, Inspectability and access to maintain with painting is poor.
Half Saddles and Cradles
Pipe corrosion at half saddles and cradles
In many cases, these types of support could be substituted for multiple U-bolt type clamps and a lot of the problems would disappear. However, the point of contact at the beam or in the bottom of the cradle will always be a concern. The same problems of moisture retention, poor inspectability and maintainability apply to these support types.
How do we stop the problem of corrosion at pipe supports?
With a design that achieves the following goals:
• Eliminate the crevice and thus the ability to hold water in contact withthe pipe
• Be simple to install either on new or existing piping systems not requiring hot work
• Be inexpensive
• Provide inspectability and maintain-ability
• Eliminate metal-to-metal contact.
Deepwater corrosion inc, has developed a range of patented products that eliminate crevice corrosion at pipe supports, these include the Nu-Bolt which is a standard pipe U-Bolt modified with a variety of corrosion resistant treatments and the I-Rod and I-Clip which are half-round configuration rods made from a high-strength thermoplastic material. When introduced between the pipe and the support, it achieves all the ideal solutions.
The curved surface against the curved surface of the pipe minimizes contact area and water is shed from the pipe surface. The separation created also provides good access for separation and maintenance while eliminating metal-to-metal contact.
Easily installed either in continuous lengths across the top of pipe support beams or as an integral part of a U-bolt assembly to replace saddle clamps, the rods provide a cost-effective solution to the problem. Nu-Bolt, I-Rod and I-Clip have now been in service on hundreds of oil & gas facilities all over the world since 1987. Performance has matched or exceeded all expectations of the operators specifying them, with no reported failures.
Beware of inferior products
I-Rod Pipe Supports are specified by major operators because of their reliability and proven corrosion prevention capabilities. In 25 plus years, there has not been one reported failure of the I-Rod. The simple appearance of the Nu-Bolt assembly leads many companies to attempt to copy the trademarked design, but the I-Rod that is made of a half-round high-impact thermoplastic made is impossible to replace. No other known material possesses its heat-resistance and compressive strength, the key factors to its success.
The above images show how inferior products quickly fail, the thermoplastic rods put under the pipe, get crushed under the weight of the pipe, water is trapped and a crevice is formed, which leads to corrosion under the pipe supports. The genuine I-Clip, I-Rod and Nu-Bolts are only available from Alduco Energy in Nigeria and the Gulf of Guinea.
*The article was written by Alfredo Jones, Managing Director of Alduco Energy, an Asset Integrity Management Services company specializing in providing NDT, RBI, Cathodic Protection and Corrosion Control to the oil and gas sector in Nigeria and the Gulf of Guinea. For more information on Alduco Energy’s range of services you can visit www.Alduco.com or contact us at info@Alduco.com .