{"id":1101,"date":"2026-01-10T22:33:39","date_gmt":"2026-01-10T22:33:39","guid":{"rendered":"https:\/\/hydrocarbon.sbs\/?p=1101"},"modified":"2026-03-24T23:23:28","modified_gmt":"2026-03-24T23:23:28","slug":"identification-marking-of-deadlegs","status":"publish","type":"post","link":"https:\/\/petrostreet.com\/main\/identification-marking-of-deadlegs\/","title":{"rendered":"Identification & Marking of Deadlegs"},"content":{"rendered":"\n

Hydrocarbon processing facilities encounter numerous credible damage mechanisms threatening the asset integrity however many of those damage mechanisms become even more detrimental when the flow is stagnant and the process parameters are the ones in the normal operating circuits. For Instance, in piping with hydrofluoric acid service, segments with stagnant flow are more prone to damages due to higher corrosion rate in comparison to segments where the flow is normal. Similar observations are also evident <\/del> as several damages to plant facilities with unexpectedly higher corrosion rates surfaced over the years after inspection of areas where the process flow is still. Deadlegs are all such areas where we do not have significant flow and such areas pose substantial threat to the integrity when compared to others.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Figure 1<\/strong>: Deadleg Example- Control valve bypass<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Figure 2:<\/strong> Deadleg Example – Piping with normally closed block valves<\/p>\n\n\n\n

Ideally speaking,  <\/del>during the design stage itself, identification of all potential unavoidable dead-legs, like a bypass to a control valve, should be done and efforts shall be in place to minimize or eliminate existence of deadlegs. However, in reality that does not happen, instead post construction of the plant we often have facilities under operation, where every other piping circuit contains one or multiple deadlegs. These deadlegs are either operational or related to the plant construction and are required to be identified and marked on drawings and tagged at site as well. Designers however are still responsible to eliminate any unnecessary deadlegs at the designing stage. This is not a difficult task to replace the piping length of piping instrument connections with forged fittings which would practically eliminate the deadlegs. Long weld-neck flanges (forged) can be used for drain and vent connections, which are potential deadlegs on equipment,<\/ins> in order to avoid any possible thinning of those forged components over the years with stagnant flow inside. Similarly it is also still practical to have forged fittings wherever a vent or a drain connection has to be provided on static equipment. Similarly dummy pipping legs can also be eliminated by providing structural supports wherever required. But at the same time, there are cases where this is practically not possible to eliminate a deadleg. Examples include bypass lines, pump and compressors recirculation lines, level bridles, relief valve inlet & outlet piping, sample points etc. Broad categories of deadlegs can be described as in Exhibit 1.<\/p>\n\n\n\n

Exhibit 1:<\/strong> Deadlegs Categories<\/p>\n\n\n\n

Blanked branches<\/strong><\/td>CV bypass line<\/strong><\/td>Drain<\/strong><\/td>Vent<\/strong><\/td>Equipment recirculation line<\/strong><\/td><\/tr>
Instrument connection<\/strong><\/td>Bleeders<\/td>Purge connection<\/td>Relief valve inlet<\/td>Pump recirculation line<\/td><\/tr>
Relief valve drain<\/strong><\/td>Relief valve outlet header<\/td>Bypass line<\/td>Normally closed block valves<\/td>Injection points<\/td><\/tr>
Level bridles<\/strong><\/td>Level transmitters<\/td>Lines with one end blanked<\/td>Corrosion probe<\/td>Sample points<\/td><\/tr>
Spare pump piping<\/strong><\/td>Spare filter piping<\/td>Flare outlet header<\/td>Emergency valve inlet<\/td>Comp. recirculation line<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

While identification of deadlegs, following criteria may be applied:<\/p>\n\n\n\n

    \n
  1. Pipe section connected to a flowing stream and not self-draining and is normally not flowing.<\/ins><\/li>\n\n\n\n
  2. Piping material has the potential for corrosion in service.<\/ins><\/li>\n\n\n\n
  3. Piping having length more than 3D or 1.22 m (4 ft) whichever is less where D represents pipe dia.<\/ins><\/li>\n<\/ol>\n\n\n\n

    Although within this criteria, the length of the piping segment with no-flow is the controlling parameter, the piping material however is also very important to consider while addressing and managing dead-legs. Generally, assets constructed from corrosion resistant materials are not marked with any deadlegs as potential for corrosion even in no-flow conditions is minimal. Similarly, some of the utility services which are not corrosive in nature and for those assets where some history records are available to support this should not be marked for deadlegs. Dry services can also be excluded as there is no potential to have active corrosion.<\/p>\n\n\n\n

    To start with the identification and marking of deadlegs, there must be a written guideline or a procedure available at hand which should be containing the minimum requirements based upon the agreement between Inspection, Maintenance & Operations teams. Inspection should be covering the requirements for identification of deadlegs based upon its basic definition, Operations should be endorsing the identification guidelines and Maintenance should be playing the support role to help Inspection carry out the tagging process and marking on the drawings. This guideline should also be defining the nomenclature which will then be used while marking the deadlegs on drawings and then at site. For example, a bypass line having stagnant flow could be identified as DLBYP. Similarly, a deadleg related to an instrument connection could be identified as DLIC. Additionally, piping systems & operating equipment with non-corrosive, non-flammable and non-toxic service may be exempted from the identification process and will not be required to be marked\/tagged with deadlegs. As a minimum two basic documents should have the markings of all the deadlegs at site, the P&ID and the piping isometrics. It should be carefully seen that the latest updated P&IDs and piping isometrics are being utilized for identifying and marking of deadlegs.<\/p>\n\n\n\n

    To start off the process, it is imperative to look into a P&ID and identify the deadlegs such as normally closed valves, instrument connections, spare pumps, control valves (having bypasses), lines with closed ends. Drain, vent, purge connections can then also be easily found. Once these deadlegs are identified on P&ID, it is generally a good practice to validate the length of the potential deadlegs as per SL#C of the aforementioned criteria. A master list of deadlegs can then be prepared against each piping tag in the plant where any deadleg is present. A sample master list is show in Exhibit 2.<\/p>\n\n\n\n

    Table 2:<\/strong> Sample Master List of Deadlegs<\/p>\n\n\n\n

    Sl. No.<\/strong><\/strong><\/td>P&ID<\/strong><\/strong><\/td>Piping tag<\/strong><\/strong><\/td>No. of identified deadlegs<\/strong><\/strong><\/td>DLBYP<\/strong><\/strong><\/td>DLIC<\/strong><\/strong><\/td>DLPG<\/strong><\/strong><\/td>DLDRN<\/strong><\/strong><\/td>DLLNC<\/strong><\/strong><\/td><\/tr>
    1.<\/strong><\/td>UY332<\/td>SH56843<\/td>6<\/td>1<\/td>1<\/td>1<\/td>1<\/td>2<\/td><\/tr>
    2.<\/strong><\/td>UY333<\/td>PF56653<\/td>1<\/td>1<\/td>0<\/td>0<\/td>0<\/td>0<\/td><\/tr>
    3.<\/strong><\/td>UY345<\/td>PF56772<\/td>3<\/td>0<\/td>2<\/td>1<\/td>0<\/td>0<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Once all the deadlegs have been identified and marked on P&IDs and piping isometrics, the complete set of documents then should then be shared with Process & Operations team in order to verify the marking done and provide their comments. It has to be understood that Operations being the asset owner has even better understanding on the lines with no significant flow. During their review, they may even point out those marked up portions which actually have flow but the P&IDs are erroneously marked with a normally closed valve instead. Such validations not only improves the overall confidence of the deadleg database but also aids in identifying requisites for necessary amendments in the plant drawings through appropriate MOC process.<\/p>\n\n\n\n

    After Operations review, it is to be ensured that all the piping portions which have been now finally declared as deadlegs should also be marked with Condition Monitoring Locations (CMLs) in order to ensure that Inspection of these portions are not omitted while Inspection of the asset. As a general rule, each deadleg should have minimum of one CML. Deadlegs having longer lengths should consist of more CMLs depending on the piping run and its plane (vertical, horizontal or angular). Bends, reducers & Tees should all be considered as CMLs. While marking for CMLs, it is recommended to perform field visits for each P&ID along with the piping isometrics. These visits would also ensure that any routing deviations from the drawings would be captured, highlighted and an appropriate MOC action would be taken along with discussion with Operations, if required. A deadleg marked as per dimensions mentioned on the isometric drawing may not be a deadleg when the actual dimensions are verified at field. In addition, there can be some additional deadlegs like a pressure guage or any other instrument connection or a drain point that are not appearing in drawings. Though the latest drawings should be considered during all this exercise, variations are still expected and mismatch between the site and drawings is common and hence field verification should not be missed out.<\/p>\n\n\n\n

    Deadlegs marked-up P&IDs, Isometrics & Master List should then be handed over to site responsible RBI Engineer so that all the tags having deadlegs would then be flagged in Inspection Management\/RBI System governing the site. Generally, assets that consist deadlegs are required to be inspected more frequently as the damage factor of the RBI analysis is significantly impacted while the RBI analysis which shortens the RBI frequency. From here on, actual work of deadlegs\u2019 inspection starts. Each piping tag which is getting due for any Non-Destructive Testing (NDT) to measure pressure wall thickness must mandatorily have the deadlegs identified, marked and validated at site and must be inspected along with inspection of the asset. It is to be noted that data gathered for each deadleg should be managed separately from the piping tag itself. This is the minimum inspection requirement mentioned in API 570 para 6.6.1\u2019 \u201cDeadlegs with CMLs should be tracked in a separate piping circuit from the mainline piping.\u201d<\/p>\n\n\n\n

    NDTs which are helpful to inspect deadlegs include Profile Radiography for smaller dia vents & drains and Ultrasonic Thickness (UT) or Radiography Testing (RT) for larger dia runs.<\/p>\n\n\n\n

    While identifying & marking deadlegs, it should be noted that all the equipment having any deadlegs should also be taken in consideration and marked properly so that those portions should also get inspected. In case there have been some forged high thickness components used like long weld neck flanges, such components can be exempted. However, when normal piping is used for vents, drains, purge connections and other such components with insignificant flow, it is recommended to identify, mark and inspect them.<\/p>\n\n\n\n

    In summary, management of deadlegs which include identification, marking, validation and inspection of deadlegs should be done through controlled procedures at operating facilities. Unexpected leaks through process lines often occurs due to insignificant or no-flow conditions which eventually leads to higher corrosion rate when compared to rest of the piping components facing normal flow. That is the core reason of tracking deadlegs separately from the mainline piping.<\/p>\n\n\n\n

    <\/p>\n","protected":false},"excerpt":{"rendered":"

    Hydrocarbon processing facilities encounter numerous credible damage mechanisms threatening the asset integrity however many of those damage mechanisms become even […]<\/p>\n","protected":false},"author":1,"featured_media":2183,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_uag_custom_page_level_css":"","_ppp_document_settings_meta":"{\"product_ids\":[{\"label\":\"Identification & Marking of Deadlegs - 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