Heater Treater (Emulsion Treater) Firetubes

[dtn6770]

Upstream oil and gas producers frequently utilize pieces of equipment known as heater treaters (API 12L emulsion treaters) which are vessels that contain liquids produced from wellheads. Heat is introduced to the liquids through the use of a natural gas or hydrocarbon liquid burner that is mounted inside of a flanged firetube assembly that projectes into the vessel. The firetube assembly typically consists of a flat, round or obround pressure retaining cover (one of the vessels main bolted closures) that is penetrated by a U-tube which houses the burner and directs combustion gases to a vertical, atmospheric exhaust stack external to the vessel.

Relative to the BPVC Section VIII Division 1, fabricators and their Authorized Inspectors have routinely exempted firetubes from complying with the Code and have done so with a minimal amount of disclosure to the end users. A relatively recent ASME Interpretation, BPV VIII-1-18-01, affirms that firetube assemblies are within the Code’s scope in the context that they are considered combination units having a differential pressure on the common elements exceeding 15 psi. The interpretation further clarifies the applicability of special service “DF” consideration and marking.

All of that stated, discussion on anyone’s experience and / or approach to this topic would be greatly appreciated. My supervision is curious as to how others navigate these waters.

Gratitude!

 

[bpv66]

FYI... The interpretation you referenced was recently rescinded by the Code Committee and a team made up of manufacturer's and AIAs are working on a Heater-Treater Appendix that will address construction requirements.

 

[dtn6770]

You are correct. There was a special meeting in Dallas on May 7th where the issue was discussed. The push-back ASME got after publishing the interpretation didn't come from any owner-operators of the equipment. ASME Committee correspondence states that, “ASME received several letters from [3] manufacturers of fired heater treater pressure vessels concerning the impact Interpretation BPV VIII-1-18-01 would have on their business.” That’s an interesting spin on a safety Code. To be clear this is a safety issue, less so about the literal tubular / pipe portion of the assembly which is easily evaluated using Code methods. The more safety relevant component is the bolt-on, pressure retaining, cover that’s penetrated by the tubes and the corresponding flange that’s welded to the pressure vessel’s firetube ‘nozzle.’ Those parts are inconvenient in that they can’t necessarily be addressed by a manufacturer’s pressure vessel design software of choice which means having to do some engineering [U-2(g)] or start proof testing [UG-101] designs.

There’s the manufacturers’ claim that heater treater owner-operators don’t want Code firetube assemblies. I would challenge that as being an overly broad statement that assumes all owner-operators are aware of the situation. Any owner-operation with an EHS department and an understating of the potential consequences of knowingly, therefore willfully, using un-rated pressure equipment components would likely sign up for a Code design. Those types of owner-operators may be satisfied by a non-Code fireture assembly that’s certified by the manufacture as being suitable for the corresponding heater treater’s MAWP base on that manufacture’s own design basis and acceptance criteria.

Another argument, made by just manufacturers, against Code firetube assemblies is that they’re disposable items and owner-operators don’t want to be burdened with all that would be involved with a legitimate replacement part. I can see that; an organization whose moral compass doesn’t compel them to have rated firetube assemblies probably isn’t going to jack with API 510 or NBIC NB23. That same organization probably doesn’t require the heater treaters to be a Code vessel in jurisdictions that don’t require it.

The final argument that I’ll debate, for now, that came up is the claim that the manufacturers that are aware of and attempt to honor the interpretation will be at a business disadvantage to manufactures that are unaware of the interpretation. Shouldn’t the Authorized Inspection Agencies level the playing field through the AIs’ interaction with their customers, all manufacturers? [Rhetorical] I’d like to believe that the AIAs and AIs are disciplined enough to monitor for interpretation and give their customers a heads up.
So…it’s an owner-operator safety issue relating to a safety Code that appears to be largely influenced by manufacturers and AIAs that have a financial stake in the game and an incentive to keep life simple. As stated by an AI speaking to a manufacturer, “Until they [ASME] come up with hard fast rules we are recommending that they [firetube assemblies] be treated as you are now doing.”

I struggle with understanding what rescinding the interpretation means, in practice. ASME isn’t changing their mind or pretending the inquiry wasn’t ever made, so I guess it comes down to ASME allowing all partied involved, except for the unaware owner-operator, to continue to feel okay and justified in maintaining the status quo until what…the 2021 Edition of the Code which becomes mandatory in 2022.

But hey, at least my ASME membership qualifies me for specially priced life insurance.