Maximum Working Pressure of Restek Stainless Steel Tubing21 Oct 2013
One of the questions we get asked in tech service is for the recommended maximum working pressure of our Stainless Steel tubing. Since I’m not an engineer, I never really gave much of a thought to these numbers, because as a GC analyst, I was certain that nothing I used the tubing for came close to any maximum pressure. However, if you are not simply plumbing a gas chromatograph, knowing the maximum pressures may be important.
As I’m sure you all know, Restek is a manufacturer of chromatography columns and accessories; we are not a steel mill. Because we purchase our tubing from other manufacturers, we rely on the pressure numbers they provide to us. Recently I communicated with one of our suppliers, and I asked them about working pressures. They provided me details on how they perform their calculations. Only then did I realize that there are a variety of ways which one can determine the maximum working pressure of tubing. It appears three of the most common equations are Barlow’s formula, Lame’s formula, and Boardman’s formula. For those of you not familiar with these equations, there are two important pressure numbers associated with each formula:
- Burst Pressure – the average pressure at which tubing will fail.
- Working Pressure – a recommended maximum tubing pressure which the manufacturer deems as very unlikely to fail.
As I mentioned earlier, there are a variety of ways one can determine the maximum working pressure. First, not everyone may use the same minimum tensile strength number to determine the burst pressure. Even if they do, not everyone is likely to use the same safety factor number. However, in most cases for GC analysts, an exact maximum working pressure is usually not needed. As a result, I will provide our customers approximate maximum working pressures for our stainless steel tubing at room temperature*.
* The maximum working pressure will decrease if used above the temperatures shown in the table below. To determine the Maximum Working Pressure at a certain temperature, multiply the pressure above by the appropriate Temperature Derating Factor below.