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The local AHJ has asked if any part of the system piping will be routed below ground and has requested details on required corrosion protection system, trenching, and backfill. They cite the following sections of NFPA2: 7.1.15.3.2 Contact with Earth. 7.1.15.3.2.1 Gas piping in contact with earth or other material that could corrode the piping shall be protected against corrosion in an approved manner. "55:7.1.17.2" 7.1.15.3.2.2 When cathodic protection is provided, it shall be in accordance with 7.1.18. "55:7.1.17.2.1" 7.1.15.3.3 Underground piping shall be installed on at least 6 in. (150 mm) of well-compacted bedding material. "30:27.6.5.1" 7.1.15.3.4 In areas subject to vehicle traffic, the pipe trench shall be deep enough to permit a cover of at least 18 in. (450 mm) of well-compacted backfill material and pavement. "30:27.6.5.2" 7.1.15.3.5 In paved areas where a minimum 2 in. (50 mm) of asphalt is used, backfill between the pipe and the asphalt shall be permitted to be reduced to 8 in. (200 mm) minimum. "30:27.6.5.3" The instrument, air and hydrogen lines are stainless steel and will be installed in a PVC sleeve. In the Panel’s experience, is this adequate cathodic protection for the lines?

The Panel considers two approaches to be acceptable. 

  1. Stainless steel (corrosion resistant) lines embedded in concrete. This keeps the piping out of direct contact with the earth and provides a degree of physical protection from activities such as digging. 
  2. Lines enclosed within a PVC sleeve. The PVC sleeve would usually be directly buried but could also be…
Category: Piping
Keywords: Piping, Underground, Corrosion, Physical Protection
Can compression fittings for 304 or 316 SS tubing that use compressive forces to swage the fitting on onto tubing be used? The fitting is made for up to three pieces. One concern is the potential for hydrogen embrittlement in the area around the joint compression as the pipe is under large stresses when the joint is made. There is a video on how this works at the link below, starting at ~ 2 min 20 secs. (437) The Lokring High Performance Connector System - YouTube

The HSP is not familiar with this particular fitting or its potential application in H2 service but can offer engineering judgment. Many similar compression-type swaged fittings are used in H2 service. These fittings must be used within the manufacturer recommendations for pressure, temperature, and fluid service. Deformation is also introduced into stainless steel tubing in other ways, such…

Category: Piping
Keywords: Piping, Fitting, Lokring Technology, Material Selection
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This material was prepared as an account of work sponsored by an agency of the United States Government.
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