Is hydrogen bake-out of small bore piping in wet H2S service necessary

[dcfrush]

My refinery has always done this in the past but I'm not sure it is necessary (small bore piping <2" and service with H2S >50 ppm in water phase). Would it be sufficient to maintain a preheat of ~200 degF, use E7018 low hydrogen electrodes, and follow up with a PT 48 hours after welding, assuming there was no history of cracking in the service or hydrogen blisters?

Thanks in advance,

- David

 

[blacksmith37]

If service conditions could have put H into the piping; baking that H out would be more important than baking after welding with E7018. The 200F for 48 hr prior to welding should be good.( I have assumed carbon steel that does not require PWHT). If you are on the US gulf coast; leave the pipe in the sun a couple days as a H "bake" out.

 

[dcfrush]

The preheat would only be for the welding, and the penetrant test (PT) would be done after waiting 48 hours after welding was complete to check for delayed hydrogen cracking. We would also check to make sure Brinnell hardness readings were <200.

I guess I should expand the question to include any thin-walled pipe (<= 1/2"). Thin walled piping in wet H2S service is usually relatively low pressure in these cases (< 200 psig) which is why I'm thinking we don't need to do bake-outs as often as we have in the past.

How does everyone else handle new-to-old piping in hydrogen service?

Thanks.