Question: you say you design pipes for oil and gas, what materials does that include? and why are they the best for the job?

Neil Taylor answered on 7 Mar 2015:

Hi tia!

This is a really cool question – especially since materials are a special area of interest for me!

Let me first say that a full answer to your question would take many pages (people have written books on the subject!), so I won’t be able to cover everything… But I’ll give my best shot at explaining things briefly!

Pipelines are generally made from high strength steel. Steel is mostly made of iron, mixed with a little carbon. Steel is strong, relatively cheap, easy to make into the shape that you want (in our case a pipeline!), and it is easy to join bits of it together (by welding).

There are other substances (elements) that can be added to steel to make a mix of metals (an “alloy”) to suit a particular purpose. Typically, an element called Manganese is added to the steel to enhance its properties (e.g. make it stronger). This creates “Carbon Manganese” steel, which is commonly used for pipelines.

Other elements that can be added include Vanadium, Titanium, and Chromium. Higher levels of Chromium help prevent rusting (corrosion). These steels are called “Corrosion Resistant Alloys” or CRAs. Steels with 22% or more chromium are called “Duplex” steels, and steels with 25% or more chromium and called “Super Duplex” steels. These steels are more expensive, so sometimes a thin layer is secured to the inside of a cheaper “Carbon Manganese” pipe. This helps protect against rusting, but is cheaper than making the whole pipe out of it!

The type of steel that is “best” for the job depends on the situation. It depends on the pressure/temperature of the oil/gas (e.g. how thick you would need to make the pipe with that material to avoid the pipe bursting), how much rusting you are expecting, and the cost – among a lot of other factors! You need to carry out calculations for all the different options that you are considering before you come to a choice – which may take a little time, but it is also fun finding out what is best!

Other materials that may be added as layers around pipelines include plastics (such as Polypropylene) and concrete. The plastic acts as insulation to keep the oil and gas warm (if the cold seawater cools the pipe down too much then a waxy substance can form and block the pipe!). Concrete is sometimes added to make the pipe heavier and make it more stable.

Hope this helps!