Pipe, API 5L X42 or X65 which one is better for H2S containing Service

[Iskandarzade]

Hi All,

We want planning for our client's sour service natural gas pipeline system. You know API 5L X42-X65 all satisfy the requirements of the NACE MR0175. But, I wonder if you can introduce me an any recommendation/document which compares X42 vs. X65. I want to know which one is much better for our application. We normally do our PWHT for thicknesses higher than 12.5mm for sour services; then, using X42 implies higher thickness and hence can bring the costly PWHT requirement.
On the other hand, X42 for a specific MAWP has a higher thickness and then it can be more resistive to corrosive environment.
There are many advantageous and disadvantageous for using both of them. But, some practice can be helpful, if their is any.

Best Regards
Mehdi Eskandarzade

 

[weldstan]

High hardness at the welds will be the principal issue with either. If you limit the maximum carbon equivalent of the X-42, it will more likely meet NACE hardness requirements in the welds.

Many years ago a major gas supplier specified X-42 for a similar application without specifying a max. CE. They were compelled to PWHT the welds to comply with hardness. The X-42 was equivalent to X-60 and had a CE to match.

 

[SJones]

....higher thickness and then it can be more resistive to corrosive environment

Taking the failure point as loss of corrosion allowance, time to failure will be mostly governed by the amount of corrosion allowance. The same corrosion allowance is likely to be applied to both grades of pipe once the pressure and stress calculations have been completed. Thus, the target would be to achieve a thickness that wouldn't need PWHT by your company's philosophy, and one which minimises costs of transport and other installation activities, whilst still maintaining weldability. Sour service X65 from major pipe mills is a reasonably straightforward weldability proposition these days but its cost per tonne will probably be higher.

It's a typical pipeline engineering/materials selection exercise that tends to go through a few iterations before landing on a choice.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.