Check out the figures achieved on this 100' + vessel:
120 – length of vessel in feet
11.5 – width of vessel in feet
195,765 – weight of vessel in lbs.
4 - # of gas trains used
24,000,000 – minimum BTU’s used in equipment
280 – labor hours needed to complete in less than four days
6,000 - sq. feet of fiberglass insulation used
PWHT on any vessel takes specialized knowledge, preparation and execution to complete. But what about those big vessels over 100’ in length? They take strategic measures and planning to complete accurately and quickly.
Some tips for fabricators to prepare for heat treating 100’ + vessels:
1. Vessel growth. As a rule of thumb, vessels can grow by up to 1” per 10’ of length during the heat cycle. The longer vessels need more space in their supports to accommodate this growth.
2. Plenty of exhaust. With up to four gas trains (or more), hot air must have enough exhaust to escape so it doesn't lead to back pressure.
3. Industrial power supply. Many shops will opt to let us to use their industrial power source for equipment during heating. Each gas train requires 480V (3) phase with 30 amps start up.
On-site servicing of these vessels is the most desired way to achieve PWHT in most circumstances because of the sheer volume of vessel to be transported. The less these vessels must get on the roads, the better, resulting in less chance of damage through transportation. On-site PWHT can save thousands of dollars in heavily permitted transportation costs.
Interested in post weld heat treatment on a 100' vessel? Give us a call! (713) 425-3773.
Measuring and recording the time and temperature of the heat cycle is one of the most important aspects of heat treatment. Heat treating cycles must be accurate so that the product being manufactured can fully withstand the high pressure, high temperatures and/or various materials that the product endures once it’s in use. The recording of the heat cycle is proof that heat treatment occurred at the time and temperature that conforms to the engineered specifications. Recording the time and temperature is accomplished through the use of thermocouple wire and a strip chart recorder that are interconnected to the heat treating console.
What is Thermocouple wire?
Thermocouple wire is a “sensor” composed of dissimilar metals used for measuring temperature of an object. It has the ability to convert heat energy into electrical energy in predictable amounts. The information is sent to a temperature control device (heat treating console) that regulates power to the heating source and documents the temperature on the recorder. Thermocouple Wire (aka: T/C) is insulated with a brown jacket and can withstand high temperature applications. GCC uses ANSI Type ‘K’ T/C wire because it provides the widest operating temperature range. Base metals of Type ‘K’ are Chromel (90% nickel and 10% chromium) Alumel (95% nickel, 2% manganese, 2% aluminium and 1% silicon.)
How are T/C's attached?
Most T/C’s are attached by means of a Low Capacitator Discharge Unit. A thermocouple attachment unit (TAU) by capacitor discharge action will affix fine thermocouple wires directly to the workpiece so that the surface of the material becomes the thermocouple junction and as a result, gives an immediate penetrative temperature. In other words, the T/C is “welded” onto the workpiece via TAU and will read the true temperature.
The number of thermocouples required for heat treatment vary widely between materials and engineering code standards. Gulf Coast Combustion's extensive knowledge of ASME code (among others) and alloy specifications form the groundwork to constructing a highly customized heat treating procedure for our clients.
What is a recorder?
A recorder is a heat treating instrument that uses a strip chart to record time vs. temperature. A strip chart is a continuous piece of paper that records (via printer) temperature and time for as long as a particular procedure requires. The strip chart is coupled with a chart sticker identifying all measured thermocouples and their placement and given to clients at the end of the job. A digitally recorded strip chart is a newer technology available to clients, and will be discussed in detail in a future post.
Where each thermocouple is placed measures 1 point, or zone, on the recorder. Recorders come in multiple zones – 6, 12 and 24 pt. On a 24 pt. recorder you can measure twice the amount of thermocouples as a 12 pt and 4x as much as a 6 pt. One recorder is usually sufficient to complete most jobs. More than one recorder might be used when there are two different heat treating projects at one jobsite or there is a workpiece large enough to require more than the 24 allotted zones.
Recorders are used on every job and must be calibrated to remain accurate. Calibration is "the setting or correcting of a measuring device, usually by adjusting it to match or conform to a dependably known and constant measure." GCC’s recorders read very high temperatures in real time, without delay, to accuracies of +/- 3°F. Over time there is a tendency for results and precision to deviate when measuring parameters like temperature. To be confident in the results being measured, there is an ongoing need to service and maintain the calibration of equipment throughout its lifetime for reliable and constant measurements.
GCC’s recorders are annually calibrated (at a minimum) by third party vendors and a calibration certificate is provided with every recording.
An accurate temperature recording is the key to flawless heat treatment. Thermocouples and recorders are used in conjunction to conform to the specifications of each and every workpiece to maintain industrial standards and safety. Click here for our Services Offered or get in touch with Gulf Coast Combustion today to discuss your heat treating needs.