How does one select the best piping plan? API 682 4^th Edition provides guidance in the form of flow charts.  Although these flowcharts (Sheets 7, 8 and 9 of Annex A) appear to be somewhat imposing at first glance, they are actually relatively straightforward and consistent.

Even without the benefit of the API flow charts, selection of the proper piping plan is relatively simple. For example, the most popular arrangement is a single seal and most single seals use Plan 11.  Most Arrangement 2 liquid systems use a basic Plan 52 and most Arrangement 3 liquid systems use a basic Plan 53A.  The outline below almost (but not exactly) summarizes Sheets 7, 8 and 9 of API 682 4^th Edition Annex A:

1. Arrangement 1 (single seal)
   1. Horizontal pumps – use Plan 11
   2. Vertical pumps – use Plan 13 or Plan 14
2. Arrangement 2 (“tandem” seal)
   1. Horizontal pumps – use Plan 11/52
   2. Vertical pumps – use Plan 13/52 or 14/52
   3. Dry containment seals – use Plan 71 or 72 instead of 52
3. Arrangement 3 (“double” seal)
   1. Wet systems – use Plan 53A (although some prefer 53B or 54)
   2. Dry systems – use Plan 74
4. Special considerations for piping plans
   1. Plan 23 is more efficient than Plan 21
   2. Plan 23 should not be used if process temperature is < 60 C (140)
   3. Plan 31 works best if the solid density is > 2x the liquid density
   4. Plan 32 can be expensive to operate
5. Process fluid considerations
   1. Hot water – use Plan 23
   2. Hot or flashing fluids – change to Plan 23 for inner seal
   3. Dirty fluids – change to Plan 31 or 32 for inner seal
   4. Crystallizing or coking fluids – add steam quench if Arrangement 1
6. Leakage monitoring
   1. Arrangement 1 (single seals) – use Plan 65 or Plan 66
   2. Arrangement 2 (tandem seals)
      1. Plan 52 includes monitoring
      2. Plan 71 or 72 needs Plan 75 or 76 for monitoring
   3. Arrangement 3 (double seals)
      1. Plan 53, 54 includes monitoring
      2. Plan 74 includes monitoring
7. Leakage management
   1. Arrangement 1 (single seals) – use Plan 65 or 66
   2. Arrangement 2 (tandem seals)
      1. Plan 52 includes management (if piped to disposal)
      2. Plan 71 or 72 needs Plan 75 or 76
   3. Arrangement 3 (double seals) does not include leakage management

API Sheets 7, 8 and 9 each include all three arrangements and are for

• Sheet 7 – non-hydrocarbons
• Sheet 8 – non-flashing hydrocarbons
• Sheet 9 – flashing hydrocarbons.

The following flow charts on SealFAQs are variations of the API Sheets but are grouped as follows:

• Non-hydrocarbon services
  • Chart 1 – Arrangement 1
  • Chart 2 – Arrangement 2 (tandem seals)
• Non-flashing hydrocarbon service
  • Chart 3 – Arrangement 1 (single seals)
  • Chart 4 – Arrangement 2 (tandem seals)
• Flashing hydrocarbon service
  • Chart 5 – Arrangement 1 (single seals)
  • Chart 6 – Arrangement 2 (tandem seals)
• All services
  • Chart 7 – Arrangement 3.

All of the above are really just guidelines and suggestions. Variations are not uncommon.  The user should consider the API 682 descriptions carefully before finalizing the piping plan.