What to Look For When Buying Used or Custom-Engineered Gas Processing Equipment

When purchasing used or custom-engineered gas processing equipment, particularly high-pressure JT skids, evaluating specific mechanical and thermodynamic factors beyond just throughput is crucial for long-term profitability and operational safety. Key considerations include verifying MAWP and design pressure ratings, ensuring appropriate metallurgy for low-temperature operation, implementing effective hydrate management, and assessing process adaptability for changing gas compositions. Buyers must weigh the CAPEX savings and faster deployment of used JT skid equipment against the precise design alignment and complete documentation provided by custom-engineered units.

When purchasing used or custom-engineered gas processing equipment—especially high-pressure units like a JT skid—buyers often focus primarily on baseline throughput. However, long-term profitability and operational safety depend on evaluating specific mechanical and thermodynamic factors before signing a purchase order.

Critical Considerations for JT Skids & High-Pressure Systems

Whether sourcing pre-owned units or designing built-to-spec modular equipment, run through this inspection checklist:

  • MAWP and Design Pressure Ratings: High-pressure wellhead applications often require 1440 psig JT skid equipment to handle harsh pressure drops without upstream choke throttling. Verify that ASME section VIII code stamps, vessel wall thicknesses, and flange ratings (ANSI 600 vs. ANSI 900) match your maximum anticipated shut-in tubing pressure (SITP).

  • Joule-Thomson Expansion Valve & Cold-Box Metallurgy: The thermodynamic temperature drop across the expansion valve can easily push system temperatures below freezing (down to −20∘F or lower). Ensure the downstream cold separator, piping, and valving are built with low-temperature carbon steel (e.g., LTCS / A333 Grade 6) rather than standard carbon steel to prevent brittle fracture.

  • Methanol/Glycol Injection & Hydrate Management: Rapid cooling across JT skids instantly creates ideal conditions for methane hydrates. Inspect the liquid desiccant or methanol injection quills, pumps, and distribution manifolds to confirm they are sized correctly for your inlet gas water content.

  • Separation & Liquid Dump Capacity: High liquid-to-gas ratios (LGR) require adequate retention time in the cold separator. Verify the internal mist eliminators (vane packs or mesh pads) are intact and that automatic liquid dump valves are rated for cryogenic, erosive multi-phase service.

  • Process Adaptability for Changing Gas Compositions: For custom-engineered JT skids, request process simulations (HYSYS/ProMax) across multiple composition profiles. A skid engineered solely for initial rich wellhead gas may lose dew-point control or liquid recovery efficiency as the reservoir depletes and gas composition leans out over time.

Key Trade-offs: Used vs. Custom-Engineered Equipment

  • Lead Time and Deployment: Used JT skid equipment offers near-immediate availability (typically 1 to 3 weeks for transport and site prep), whereas custom-engineered units generally require 12 to 24+ weeks for engineering, procurement, and fabrication.

  • Capital Expenditure vs. Fit: Sourcing used equipment can cut initial CAPEX by 30% to 50%. However, custom units guarantee design alignment with your exact flow rates, pressure drops, and NGL yields, eliminating the need for costly field modifications later.

  • Inspection and Certification: Pre-owned skids require thorough non-destructive testing (NDT), ultrasonic thickness gauging, and fresh hydrotesting to verify structural integrity. Custom builds come with complete factory acceptance testing (FAT) and full manufacturer documentation from day one.