Pigtails in Hydrogen Reformer Plants

Equipment Used

D-HEAD MODEL 420

PIPEMASTER 516 POWER SUPPLY

 

Challenge

Hydrogen reformers are commonly used in chemical plants and refineries. Natural gas is fed through superheated catalyst tubes to produce pure hydrogen, which is then used in a crude oil upgrading processor or as a feedstock for chemical production. The vertical catalyst tubes are heated in a furnace 1400-200 degrees F (760 - 1100 degrees C). The inlet and outlet pipes (headers) are located outside the furnaces.

Because of the expansion of the catalyst tubes, which can grow several inches in length, they must be connected to the headers with expansion loops, commonly called "pigtails" due to their geometry. Pigtails are commonly fabricated of austenitic nickel-chromium-based superalloys such as Inconel™ alloy 625, due to improved ductility and ability to withstand cyclical stresses, maintain creep strength, and avoid embrittlement. The pigtails are commonly welded to "sockolets", requiring a fillet weld. Mechanized welding is ideal to minimize heat input. However, minimal straight lengths preclude the use of many orbital welding systems.

Solution

John W. Page Welding Consulting Ltd. a specialty contractor based in Alberta, Canada, uses D-Heads to make 3-pass fillet welds on the sockolets. The compact D-Head fits within the minimal axial straight length of the pigtails. Heat input is precisely controlled by the computerized Pipemaster system.

Prefabrication Of Furnace Tubing

Equipment Used

D-HEAD MODEL 420

PIPEMASTER 515 POWER SUPPLY

 

Challenge

Kubota Materials Canada Corporation manufacturers special heat resistant alloys which are centrifugally cast as tubes and fittings, in sizes ranging from 2.75 (70mm) to 14” (356mm) in diameter. These high carbon austenitic stainless alloys are used for fired heaters in the petrochemical industry, with typical service temperatures of 1400-2000 degrees (760 -1100 deg. C). Customers use these specialized materials for manufacturing plastics such as polyethylene from feedstocks. Frequently Kubota will be asked to fabricate tube lengths longer then the casting process allows, or to fabricate subassemblies such as U tubes and W tubes. The welds must all be made to meet B 31.3, sometimes with tight radial clearances between tubes.

Solution

Kubota uses multiple Magnatech systems to produce the x-ray quality GTAW welds their customers require. The compact radial clearance of the D-Heads allows multipass welds to be made in tight clearances which would make manual welding difficult.

Replacing Furnace Tubes in a Steam Cracker

Equipment Used

D-HEAD MODEL 420

PIPEMASTER 515 POWER SUPPLY

 

Challenge

The largest North American petrochemical facility must periodically shut down production trains for maintenance. One such operation is the replacement of steam cracking furnace tubes used in the production of ethylene.

The tubes used for furnace applications, such as steam crackers, have typical service temperatures ranging from 1400˚ to 2000˚ (760˚C - 1100˚C). To withstand these high service temperatures, a number of high-carbon austenitic stainless steel alloys are used, usually in the form of centrifugal cast tubes. Some common alloys for this application are HK-40 (0.4C-25Cr-20Ni) and HP-45 (0.4C-25Cr-35Ni). These alloys are specifically formulated for desirable properties, such as creep strength, but they pose significant welding problems.

Tube replacement requires large numbers of skilled and qualified welders for a short duration. A specific outage required 198 welds to be made on 3" (89mm), 1/2" (13mm) wall furnace tubes in a 30-day period. Past experience indicated that to do the task manually in the set time frame would require 32 welders. The problem was a shortage of welders in the area with the necessary skills. Another important factor was the time and cost associated with testing potential welders. Testing costs the company $500 per welder and in the past only one in four welders proved qualified. The application consisted of welding new tubes to new Y-fittings inside the confines of the furnace. The Y-fittings dictate a clearance between adjacent tubes of only 2-1/4" (57mm).

Solution

The company purchased the compact D-Head which only requires 2" (50mm) of radial clearance. Using multiple Pipemaster systems, the outage period was reduced by half. No defects were observed in the welds, and no costly cut-outs and rewelding.

I.D. Weld Overlay Buildup on Pressure Vessel Wall

Equipment Used

PIPELINER II WELD HEAD

MPS-4000 POWER SUPPLY

 

Challenge

Inspection of a large 50' (15m) diameter pressure vessel in a Canadian petrochemical facility revealed corrosion of 0.5" (13mm) beyond acceptable limits. Following excavation, the walls were mapped and the depth of weld overlay determined for each grid. Weld buildup had to meet ASME code standards and inspection criteria. Hundreds of kilograms of wire had to be deposited during the outage in a confined area as quickly as possible. A preheat requirement of 150˚C (300˚F) made for an extremely hot working environment for manual welders.

Solution

An FCAW weld procedure was qualified and Boilermakers trained in the use of the Pipeliner. Magnatech's Flx-Track was attached to the ID weld using magnets which allowed track installation and repositioning in minutes. The optional axial slide torch bracket combined with the long electronic steering stroke minimized track repositioning. By allowing the welder to remotely control the welding process away from the preheated surface, the job was done in record time.