Pressure Vessel Heat Treating & PWHT FAQ

Fabricators, plant managers, and procurement leads ask us these questions regularly. If you don’t see your question here, call James directly at 832-797-3428 or reach the office at 713-425-3773.

What is post weld heat treatment (PWHT)?

Post weld heat treatment is the controlled heating and cooling of a pressure vessel after welding is complete. The process relieves residual stresses that form in the heat affected zone during welding. For carbon steel vessels, the vessel is brought up to a soak temperature between 1,100°F and 1,200°F, held for a calculated period based on wall thickness, and then cooled at a controlled rate. The result is a vessel with improved mechanical properties, reduced risk of stress corrosion cracking, and a complete documentation trail proving the process met code. For a full technical walkthrough, see The Fabricator’s Complete Guide to Pressure Vessel PWHT.

When is PWHT required on a pressure vessel?

PWHT requirements are governed by ASME Section VIII Division 1, specifically UCS-56. The code triggers PWHT based on material type, wall thickness, and intended service conditions. Vessels built for lethal service, high-temperature service, or certain corrosive environments carry additional PWHT requirements. Beyond the code minimum, many oil & gas and petrochemical end clients specify requirements that are more stringent than ASME mandates. Gulf Coast Combustion builds every execution plan to meet or exceed both the governing code and any customer-specific requirements.

What is direct gas fire combustion PWHT?

Direct gas fire combustion is a method of performing PWHT where high-velocity gas burners are fired directly into the vessel through its own nozzles and manways. The vessel is wrapped in ceramic fiber insulation, effectively turning it into its own furnace. This method delivers more BTU energy per dollar of operating cost than electrical resistance at scale, making it the most cost-effective approach for large, heavy-wall pressure vessels. Gulf Coast Combustion specializes in this method and performs more on-site pressure vessel PWHT per year using direct gas fire than any other mobile heat treating company in the U.S.

What is the difference between direct gas fire and electrical resistance heat treating?

Direct gas fire combustion fires high-velocity gas burners directly into the vessel interior, heating the vessel uniformly from the inside out. Electrical resistance uses flexible ceramic pads strapped to the exterior surface to heat specific weld zones. Both methods have their place. For large vessel full-body PWHT, direct gas fire is the standard because it can heat the entire vessel uniformly and economically at scale. Electrical resistance is commonly used for localized PWHT of pipe spools, nozzle welds, flange faces, and vessel repair welds where only a specific area needs treatment. Gulf Coast Combustion offers both.

How long does on-site pressure vessel PWHT take?

Most on-site jobs run 36 to 72 hours from setup to strip out. That includes insulation wrap, thermocouple attachment, the controlled heat-up cycle, soak period, controlled cool-down, and equipment removal. Wall thickness is the biggest variable: thicker walls require slower heat-up and cool-down rates, and longer soak times. GCC develops a custom execution plan for each vessel before arriving on site, so you’ll know the expected timeline before the crew shows up. For more detail, see How Long Does On-Site Pressure Vessel PWHT Take?

What soak temperature and hold time does GCC use?

For carbon steel pressure vessels under ASME Section VIII Division 1, GCC’s standard soak parameters are 1,150°F ±50°F (with the code range being 1,100°F minimum to 1,200°F maximum). Hold time is calculated per wall thickness: 1 hour per inch for the first 2 inches, plus 15 minutes for each additional inch beyond 2 inches. A 1-inch wall gets a minimum 1-hour soak. A 3-inch wall gets a minimum 2 hours and 15 minutes. Customer specifications that exceed ASME minimums are accommodated on every job.

What documentation do I receive after a PWHT job?

Every Gulf Coast Combustion job ships with a full documentation package: a Heat Treatment Record (HTR) signed by both GCC and the client representative, a strip chart recorder trace showing every thermocouple channel throughout the entire cycle, a NIST traceable recorder calibration certificate, and the pre-approved execution plan specific to that vessel. This documentation becomes part of the vessel’s permanent record and is built to hold up under any code audit or client review.

Can GCC develop a custom execution plan for my vessel?

Yes, and we do it on every job. Before GCC arrives on site, a custom execution plan is developed for each specific vessel. The plan documents the vessel ID, governing code, soak temperature, hold time, thermocouple count and placement, burner assignment, heat-up and cool-down rates, and all relevant technical specifications. The execution plan is submitted to the client for approval before work begins. GCC management and quality control must approve all heat cycles and setups before any PWHT starts.

Can you heat treat very large or heavy-wall pressure vessels?

Yes. On-site direct gas fire combustion has no furnace-size limitation, which is one of the main reasons fabricators choose it for large vessels. GCC has heat treated vessels over 120 feet long and up to 600,000 pounds. Our gas train consoles deliver up to 10 million BTU, and we calculate burner count and placement based on vessel weight and geometry to ensure uniform heating across the entire vessel. For large vessels that can’t be transported to a shop furnace, on-site PWHT is often the only practical option.

Where does Gulf Coast Combustion operate?

GCC is based in Spring, TX (North Houston) and mobilizes anywhere in the United States. Our primary service markets include Houston, Beaumont/Port Arthur, Corpus Christi, Midland/Odessa, Dallas, Baton Rouge, Oklahoma, and Wyoming. See our full list of service areas.

What certifications do your technicians hold?

GCC maintains a formal four-level technician certification program written by owner James Benefield and in continuous use since 2015. All new technicians start at Level 1 regardless of prior experience and must accumulate a minimum of 1,000 hours before advancing. Level 4 (Project Manager / Lead Technician) requires a minimum of 5 consecutive years in the heat treating industry. Every GCC technician at Level 2 and above has the authority to stop work for any unsafe condition or any situation where the job scope does not match what was specified.

How quickly can you respond to an urgent job?

GCC typically requests 48 hours’ notice to schedule labor, equipment, and materials. That said, we understand that timelines shift in this industry, and we’ll work to accommodate shorter notice when we can. If you have an urgent job, call James directly at 832-797-3428 and we’ll give you a straight answer on what’s possible.

How do I get a quote?

Call, text, or email James Benefield directly. To speed the process along, send available drawings so we can see the vessel dimensions, wall thickness, and any customer-specified PWHT requirements. For most standard jobs, we can turn around a verbal estimate the same day. Larger or more complex projects may need slightly more time to price accurately, but you’ll hear back fast. Job walks at your facility are also available and are actually our preferred method for quoting. Contact us here or call 713-425-3773.

Is there anything my company can provide to reduce cost?

Yes. Clients who have a natural gas line or propane supply on site can save significantly by providing their own fuel instead of having GCC arrange propane delivery. For localized PWHT jobs that require electric power, clients with at least 480V available on site can save the cost of bringing a generator. GCC will always work with you to find the most cost-effective approach for your specific job.

Does GCC offer services beyond pressure vessel PWHT?

Yes. In addition to on-site pressure vessel PWHT, Gulf Coast Combustion provides refractory dry outs, localized PWHT for pipe spools, nozzle welds, and vessel repairs, in-house furnace heat treating (up to 25,000 lbs, 30′ x 10′ x 10′), coating and paint cures, hydrogen bake-outs, welding pre-heats, and heat treating consulting. See our full services page for the complete list.