Line pipe, seamless

The process for manufacturing seamless line pipe is shown schematically in Figure 5.8. In this process, a heated metal cylinder is pierced and then formed into the proper diameter and wall thickness. Seamless pipe is available through 26 in. (660 mm) diameter, but it is normally used only up to 16 in. (405 mmi diameter. Although seamless line pipe is the most expensive (15 to 25% above ERW), it is the most reiitable Even so, failures do occur. Hydrostatic test records reveal that about one failure occurs every 500 mu (800 km) of test. Some mills produce seamless pipe that has a significantly higher failure rate thus, it is important to ensure adequate quality control. 

Examples of SOHIC failure in spiral-welded line pipe are common forms of failures. Failures were also encountered in electric-resistant welded pipes because of HIC. Failures of seamless line pipes have also been reported (30). HIC-related damage and failures of 20 line pipes in H2S and CO2 atmospheres have been reported (19). Despite the availability of adequately HIC-resistant line pipe since the late 1970s, failures are still occurring in pipelines constructed since then. 

Certain seamless extruded thermoplastics (e.g., CPVC) can be suitable when properly supported but are limited in size. In all but the smaller plants, they are not available in the diameters required for chlorine headers. In the past, rubber-lined piping was used, but its service life was limited and it required more Hanged connections than butt-connected piping. The standard choice for chlorine headers today is still FRP. 

A Russian ammonia pipeline of nearly 2400 km extends from Togliatti on the Volga River to the Port of Odessa on the Black Sea, and a 2200-km, 250-mm dia branch line extends from Godovka in the Ukraine to Panioutino. The pipeline is constmcted of electric-resistance welded steel pipe with 7.9-mm thick walls but uses seamless pipe with 12.7-mm thick walls for river crossings. The pipeline is primed and taped with two layers of polyethylene tape and suppHed with a cathodic protection system for the entire pipeline. Mainline operating pressure is 8.15 MPa (1182 psi) and branch-line operating pressure is 9.7 MPa (1406 psi) (11). 

Example 9-1. Specify the correct pipe size and material for a high-pressure water line operating at 250 F and handling 20,(KM) lb of water per hour at 1,500 psia. Seamless piping of ASTM Serial Designation A106 is required by state code. 

Particular attention must be given to transfer pipework where seam-welded pipe runs are used. In such cases, experience from the American power industry steam reheat line catastrophic failures should be borne in mind. The critical factors identified are weld geometry, weld metal and flux compositions and pipe ovality. Generally, older CRU units utilise seamless pipe in this service but some instances are known, particularly in larger capacity units, where seam-welded pipe is in service. Where necessary, this factor can be taken into account in the assessment procedure described below. Seam welds are subject to the full pressure hoop stress, as well as to many of the system loads. Failure of such a weld is likely to lead to a full-scale rupture, rather than a leak. Accordingly, they must be treated as critical items for assessment, and replacement, rather than repair, should be considered the ultimate outcome. 

For 96 - 98% acids, seamless mild steel pipe may be used, but mild steel tube with non-metallic lining, polypropylene or PTFE is preferred. Ben should have a minimum radius of 5 pipe diameters. For continuous duty the velocity should not exceed 0.6 m/s in mild steel pipes. 

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