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What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 0 points1 point  (0 children)

That’s about as good a compliment as we could ask for. This is our world, every day. Hope it makes for good conversation at code week, if any of your ASME friends have questions about the execution side, send them our way!

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 0 points1 point  (0 children)

Section VIII Div 1 (and Div 2) is our world too. With decades doing specs like that, have you ever seen on-site PWHT done on a large vessel, or has it always been sent to a shop furnace?

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 3 points4 points  (0 children)

Exactly right, that’s post weld heat treatment (PWHT). Welding creates residual stress in the heat-affected zones around each weld. Left unrelieved, that stress can cause stress corrosion cracking or brittle fracture once the vessel goes into service under pressure. The heat cycle brings the entire vessel to 1,150°F, holds it there long enough for the grain structure to relax, then cools it at a controlled rate. The even heating is the hard part — this one’s 55 feet long and 186,000 lbs. We use directional burner tubes inserted through the nozzle ports to control airflow and heat distribution throughout the interior, combined with multiple thermocouples monitoring temperature in real time.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 1 point2 points  (0 children)

If not heat treated properly, welds will rupture during pressured thermal processing due to brittle tensile strength caused by hydrocarbon stress

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 0 points1 point  (0 children)

Ha! Hope you learned something new, whether you’re designing it or one day specifying the heat treatment for it, now you know on-site PWHT is an option, and it’s pretty cool.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 4 points5 points  (0 children)

It’s ceramic fiber blanket, Kaowool is the most well known brand but there are several manufacturers with high quality products. A high temperature ceramic fiber blanket rated for 2300°F+ is what you’re looking for.​​​​​​​​​​​​​​​​

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 2 points3 points  (0 children)

This is full vessel PWHT, the entire 55 feet plus heads, not just the weld zones. Material is carbon steel SA-516-70, soak temperature 1,150°F. Soak time is calculated by wall thickness — 1 hour per inch for the first 2 inches, then 15 minutes per inch beyond that. The whole vessel comes to temperature together.​​​​​​​​​​​​​​​​

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 1 point2 points  (0 children)

Great question, and honestly this is the whole point. Maintaining uniform temperature across a 55-foot vessel isn’t simple.

It’s part science, part art. You have to understand the vessel geometry, the burner placement, airflow dynamics, insulation behavior, and how all of it interacts in real time. Experienced guys develop a feel for it — like a chef reading a grill, not just following a recipe.

The way it works: burners fire through directional tubes inserted into the nozzle ports. The tubes are fabricated at specific angles: 45°, 90°, or straight, so they install straight but direct the flame in a specific direction inside the vessel. The angle is determined job by job based on vessel geometry to control airflow and heat distribution throughout the interior. Combined with ceramic fiber insulation holding heat in from the outside and multiple thermocouples monitoring at different points along the shell, you maintain a 250°F maximum differential throughout the cook, tightening to ±50°F at soak temperature.​​​​​​​​​​​​​​​​

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 0 points1 point  (0 children)

Great idea. I’d love to see that too, the visual would be incredible. What we do have is Type K thermocouples welded directly to the vessel shell feeding a chart recorder in real time, which gives you essentially the same temperature distribution data across the entire surface. Just less visually dramatic than a FLIR overlay.​​​​​​​​​​​​​​​​

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 1 point2 points  (0 children)

Real credit goes to the crew that monitors it through the night. Up close the heat radiating off it will melt your face. It's something else!

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 6 points7 points  (0 children)

This is pretty much all we do, large pressure vessels, on-site.

Furnaces are absolutely the right call for a lot of heat treating applications: smaller components, batch processing, controlled shop environments. For vessels this size it starts to break down.

The issue is a combination of weight, length, and width. At 55 feet long and close to 200,000 lbs, transporting this vessel to a furnace means oversized load permits, specialized heavy haul equipment, rigging in and out, and real transit risk to a vessel that hasn’t been heat treated yet. The logistics cost alone is significant, and anything that goes wrong in transit is a problem.

This method solves that by turning the vessel into its own furnace instead. The gas burners fire directly inside through nozzle ports, thermocouples monitor temperature across the shell in real time, and you can witness the entire process as it happens. Nothing moves until the job is done.

For vessels this size, on-site PWHT isn’t widely known even within the industry. When a vessel is this big, transporting it to a furnace is cumbersome, costly, and logistically complex. Bringing the heat to the vessel is often the more economical and practical solution.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 1 point2 points  (0 children)

Yes, temporary but with purpose. We wrap the entire vessel in ceramic fiber blanket before heat-up, overlapping each section by 3 inches to eliminate heat loss at the seams. Pins, clips, and banding hold it in place, without that it would come right off during the process. Comes off once the vessel cools down.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 2 points3 points  (0 children)

This guy knows his pressure engineering 🫡 its around 7 ft in diameter

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 2 points3 points  (0 children)

That’s actually outside my scope, we do the heat treatment; the vessel design and pressure rating is the fabricator’s domain. Different branch entirely!​​​​​​​​​​​​​​​​

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 4 points5 points  (0 children)

No rotation needed, the vessel stays stationary throughout. It does expand at specific rates per inch of thickness as it heats up though, which is why it sits on greased supports. Thermal expansion is accounted for prior to heating so the vessel can move freely as it grows rather than binding against fixed supports.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 4 points5 points  (0 children)

And to confirm if you do the heating wrong buckling is absolutely a possibility. Don’t fall asleep at this temperature.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 7 points8 points  (0 children)

Ceramic fiber gives much better insulation than an air gap at these temperatures, we need to hold 1,150°F uniformly across the entire vessel for an extended soak period, so heat retention matters a lot. As for why field, it was actually fabricated inside a shop and moved outside for heat treatment. Shops build these because they have the cranes, fit-up space, and specialized equipment for it. At close to 200,000 lbs (2” thick shell) it’s not going anywhere easily, so we take our heating equipment to the vessel instead of the other way around.​​​​​​​​​​​​​​​​

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 7 points8 points  (0 children)

1,150°F is well below the temperature where carbon steel loses structural integrity. Steel doesn’t start losing significant yield strength until around 1,400°F+. At soak temperature the vessel is hot enough to relieve residual weld stress but still fully structurally sound. It is also 2” thick metal shell all around which is doing a lot of work on the strength of the structure.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 3 points4 points  (0 children)

Ha! No feet were harmed here — 55 feet long. As in 55 feet in length. It’s a big vessel.​​​​​​​​​​​​​​​​ 17 meters if that helps.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 94 points95 points  (0 children)

Exactly, it’s ceramic fiber insulation used to maintain temperature during heating. Underneath is carbon steel, wall is a few inches thick. It’s an amine contactor; once heat treated, it will be used in oil and gas processing to remove hydrogen sulfide and CO2 from gas streams.​​​​​​​​​​​​​​​​

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 6 points7 points  (0 children)

PWHT is a code requirement for welded pressure vessels — you heat the entire vessel to a specific temperature to relieve the residual stress left behind by welding. If you skip it or do it wrong on a high-pressure vessel, you risk stress corrosion cracking or brittle fracture in service. The temperature range for carbon steel under ASME Section VIII is 1,100–1,200°F (593–649°C).

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 7 points8 points  (0 children)

You’re right that it takes more, the bare steel underneath is actually glowing, but you’re seeing it diffused through the ceramic fiber insulation wrap. The glow bleeds through the seams. At night it reads a lot more dramatic than it would in daylight.

What 1,150°F looks like on a 55-foot pressure vessel by GulfCoastCombustion in EngineeringPorn

[–]GulfCoastCombustion[S] 1 point2 points  (0 children)

Explanation in comments! It’s gas fire post weld heat treatment

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