NIPPING OF PRIMARY REFORMER TUBES

UreaKnowHow – where urea industry meets Forums Ammonia Mechanical & Maintenance NIPPING OF PRIMARY REFORMER TUBES

Viewing 8 posts - 1 through 8 (of 8 total)
  • Author
    Posts
  • #97970
    bilalhassan1919
    Participant
      • Participant

      Dear Friend;

      Nipping of furnace tube is activity which involves considerable risk of tube reputing or excessive bending if proper procedure is not followed. As per my experience, please consider the followings;
      1. Prepare a mock up to determine the nipping pressure to be applied and required preheat temperature of inlet hairpin and outlet pigtail.
      2. Nipping pressure and temperature depends upon the size, thickness and material of inlet hairpin and outlet pigtail.
      3. Temperature can be maintained either by the process feed gas mixture flowing through the tube and external heating by using ox-acetylene torch.
      4. Temperature used by us for inlet hairpin (Size 1.25″ Material A 312 TP 321H) was 400C and for outlet pigtail (Size 1″ and Material Micro alloy 35Ni 35CR) was 800C.
      5. Nipping pressure was 14000 psi for inlet hairpin and 17500 psi for outlet pigtail.
      6. Nipping of both inlet and outer tube to be performed at the same time. If it is not possible then start nipping of outlet pigtail first and before its completion nipping of inlet hairpin to be started.
      7. Stopper should be used between the nipping jaws to prevent over clamping of tubes and subsequent cracking.Length of these stoppers depends upon Clamping jaws thickness and Tube thickness.
      8. Bending of tubes is usual phenomenon after nipping of tubes. temperature of surrounding burners to be adjusted to minimize bending effect.
      Regards.
      BILAL HASSAN

      #97858
      Naresh Singh Karki
      Participant
        • Participant

        Dear friend

        Kindly clarify this term ….(A carbon plug developed (due to high heat flux compared to the low gas flux). specified by you in your post.

        Thanks and regards

        #97857
        Naresh Singh Karki
        Participant
          • Participant

          Dear G.schulz

          I would like to know the temperatures of nipped tube during runninng plant…. which further lead to bending. It would help us to controll burners near nipped tube to avoid bending of these tubes in future.

          thanks

          #97856
          Naresh Singh Karki
          Participant
            • Participant

            Dear friend
            my question is what procedure do u follow after removing insulation from pig tail and hair pin.

            You carry out nipping process completely once through before the pig tail tube cool down to 350 Deg. C. or you follow the procedure in steps, like checking explosive gas near clamps at every rise of 1000 psi in jack. Former procedure leads cooling of pigtail very fast and hence risk of rupture is enhanced.

            #97852
            Pablo Gaston Schulz
            Participant
              • Participant

              Dear Naresh,

              before replacing the whole tube bundle in 2010 we had 7 tube leaks, in all cases we proceeded in a way similar to the one described in the paper. We never had a rupture of the nipped portion. The only thing that you should be aware is that this procedure will allow you to operate some more weeks, but with time the tube bent so much that it almost touched the radiant wall. also in one of the tubes, during the turnaround when we where lifting it to take it out of the furnace, we observed a crack at the top part. Inside the tube, at the same hight a carbon plug developed (due to high heat flux compared to the low gas flux). If you were to nip pressing the tube so as to avoid all gas flux, then you risk rupturing it as happened to Yara. In fact we left on puropose as small gap so as to avoid this risk, but then the carbon plug can develop. It is ok if you do not try to operate a long period with a nipped tube. regards, G. Schulz

              #97850
              Naresh Singh Karki
              Participant
                • Participant

                DEAR FRIEND KINDLY FIND THIS ATTACHMENT


                Attachments:

                #97847
                norozi1972
                Participant
                  • Expert

                  Dear Friend
                  Please describe more detail about this procedure. This kind of trouble (leaky tube) is common for all company.
                  With best regard
                  Norozi

                  #92893
                  Naresh Singh Karki
                  Participant
                    • Participant

                    Dear all
                    I wish to know more about above said procedure i.e.NIPPING of primary reformer tubes. Recently we detect one leaky tube in our primary reformer and agree to follow this procedure. Nipping was successfully done. I wish to know how much effective is this procedure and if any one has followed this procedure ,kindly let me know.

                    Thanks and regards

                  Viewing 8 posts - 1 through 8 (of 8 total)
                  • You must be logged in to reply to this topic.
                  UreaKnowHow

                  UreaKnowHow.com is an independent group of nitrogen fertilizer specialists with an impressive number of years experience in designing, maintaining and operating nitrogen fertilizer plants.

                  Solution Providers offer their solutions to improve our member’s plants performance.