I'd look at Subchapter B for exemptions to licensing laws in the state. Might be worth contacting the board to ensure there are no rules around the specific equipment you're producing.

Are you a design firm offering services, or are you a manufacturer of products? Or both? Exemptions typically apply to employees of companies doing work for internal use/consumption or for manufacturing. Texas has a particularly long list of exemptions, though, so you might find one that applies.

Thank You phamENG.

We part of engineering and operation service, we design, specify, and build pipeline metering skids which is installed on our product pipelines, and then handed it to operation team to maintain and operate.

Its exempt bc you're not offering services to the public.

That's seems correct, as these are not offered to public, and only on a industrial plants premises.

Is there a potential for the surrounding public to be affected if one of your products were to fail?

You really need to take a good look at the board rules.
There are utility-type exemptions- but be careful there, as some of those apply to the owner of the facility, but don't apply to consultants or contractors doing work for those owners.
There are manufacturing exemption, but if you're custom-engineering work for a particular site, I assume it wouldn't fall under that.
If the Department of Transportation or Railroad Commission or whoever are involved, make sure they don't have specific requirements on engineering licensing for work done on facilities under their oversight.

My experience/research is that if you work for the same company that is manufacturing the skids *most* (definitely not all) states would not require a sealed design. That is because you are selling an engineered product, not engineering services. If you are providing a design for the skids and another company will be building the skids *most* states would require that you are licensed in that state and require the design to be sealed.

I've never heard of the need to seal drawings for a process skid. Any construction permit would need something, I suppose, but good lord, sealed drawings for every skid you sold?