;with cte as (
  select t.*, row_number() over(order by start desc) ord from (
    values
      (3, 3815.755, 3844.558477),
      (3, 6599.593, 6607.176916),
      (3, 8526.033, 8527.847989),
      (3, 16865.97, 16868.7632),
      (3, 25544.64, 25550.58006)
  ) t(pipeline, start, [end])
)
select pipeline, lag([end], 1, 0) over(order by start), start from cte
union all
select pipeline, [end], 70000 from cte where ord=1

;with cte as (
  select t.* from (
    values
      (3, 3815.755, 3844.558477),
      (3, 6599.593, 6607.176916),
      (3, 8526.033, 8527.847989),
      (3, 16865.97, 16868.7632),
      (3, 25544.64, 25550.58006)
  ) t(pipeline, start, [end])
  union all
  select 3, 70000, -1
)
select pipeline, lag([end], 1, 0) over(order by start), start from cte

;with cte as (
  select t.* from (
    values
      (3, 3815.755, 3844.558477),
      (3, 6599.593, 6607.176916),
      (3, 8526.033, 8527.847989),
      (3, 16865.97, 16868.7632),
      (3, 25544.64, 25550.58006)
  ) t(pipeline, start, [end])
  union all
  select 3, 70000, -1
), cte2 as (
  select *, row_number() over(order by start) ord
  from cte
)
select e1.pipeline, isnull(e2.[end],0), e1.start
from cte2 e1
left join cte2 e2 on e2.ord=e1.ord-1

;with cte as (
  select t.* from (
    values
      (3, 3815.755, 3844.558477),
      (3, 6599.593, 6607.176916),
      (3, 8526.033, 8527.847989),
      (3, 16865.97, 16868.7632),
      (3, 25544.64, 25550.58006)
  ) t(pipeline, start, [end])
  union all
  select 3, 70000, -1
), cte2 as (
  select *, row_number() over(order by start) ord
  from cte
), cte3 as (
  select pipeline, start, [end], convert(numeric(11,6),0) [from], start [to], ord from cte2 where ord=1
  union all
  select e1.pipeline, e1.start, e1.[end], convert(numeric(11,6),e2.[end]), e1.start, e1.ord
  from cte2 e1
  join cte3 e2 on e2.ord=e1.ord-1
)
select pipeline, [from], [to] from cte3 option(maxrecursion 0)

;with PIPELINE as
(
          select ROW_NUMBER() over(order by V1 asc, V2 asc)NN,       V1,       V2 from TT
union all select                                            0,     null,        0
union all select                                   COUNT(*)+1,    70000,    NULL  from TT )

select t1.NN, t1.V2, t2.V1
from PIPELINE T1
join PIPELINE T2 on T2.NN = T1.NN+1
where
      t1.V2 != t2.V1 -- Если отрезки идут сразу
order by t1.NN asc

ROW_NUMBER()

-- таблица труб
declare @pipe table (pipeline int, [from] numeric(20,8), [to] numeric(20,8));

insert @pipe values (1, 12345.678, 56789.012);
insert @pipe values (3, 0, 70000);

-- таблица отрезков
declare @t table (pipeline int, [from] numeric(20,8), [to] numeric(20,8));

insert @t values (3, 3815.755, 3844.558477);
insert @t values (3, 6599.593, 6607.176916);
insert @t values (3, 8526.033, 8527.847989);
insert @t values (3, 16865.97, 16868.7632);
insert @t values (3, 25544.64, 25550.58006);

insert @t values (1, 13000.64, 18000.58006);
insert @t values (1, 19000.55, 20000.68009);

if object_id('tempdb..#tmp') is not null drop table #tmp;

select identity(int,1,1) as id, pipeline, [from], [to]
into #tmp
from
(
  select pipeline, [from], [to]
  from @t
  union all
  select pipeline, [from], [from]
  from @pipe
  union all
  select pipeline, [to], [to]
  from @pipe
) t
order by t.pipeline, t.[from];

alter table #tmp add primary key (id);

select t1.pipeline, t1.[to] as [from], t2.[from] as [to]
from #tmp t1
     inner join #tmp t2 on t2.id = t1.id + 1 and t2.pipeline = t1.pipeline
where t1.[to] <> t2.[from];