ID Misalignment

By pipewelder_1999 (****)

Date 02-12-2002 14:16

I think the velocity in boiler tubes is much less than in locations downstream. Similar to the relationship of air velocity inside a container compared to the velocity at the discharge of that same container.

I THINK being the key word.

Have a good day

Gerald Austin

By Niekie3 (***)

Date 02-12-2002 18:07

As you mentioned, there are a great number of variables involved in erosion failures. When it comes to misalignment and other "restrictions" in pipes, there are definite correlations with erosion failures. Just downstream from such artifacts you typically find an area of turbulance. Should you have any tendancy of the medium to erode, this will be much greater in these areas.

The question is therefore not "can it happen?", but rather "at what point will it start to become an issue?" As you stated, this is not a question that can be answered in isolation.

Hope this helps

Niekie Jooste

By dasimonds (**)

Date 02-13-2002 08:43

I see your point.
Do you know if there is a velocity for steam alone, that when exceeded, erosion will occur, given a suitable obstruction?
I'm not trying to put you on the spot.
I read that at velocities above 65-70ft/sec, removal of material from tube surfaces begins. But this statement concerned particulates. On the ID side the particulates are exfoliation of the steam-side scale, and on the OD it is high velocity fly ash.
I haven't read anything concerning steam alone, although I have seen it's effects.

Dale Simonds

By Niekie3 (***)

Date 02-15-2002 20:28

Sorry, but I can't give you information on the speeds etc. My experience has shown that if the steam contains condensate droplets travelling at high speed, it greatly increases the problem.

Regards
Niekie

By roybuck (*)

Date 02-14-2002 12:45

I spent a number of years in a facility that manufactured adhesives and abrasives, and the search for ways to improve the life of the piping that carried the abrasive materials is ongoing. My presupposition at first was that the abrasives would tend to "smooth" down the interior of the pipe, removing any "bumps" or high places. That is not what happens. I know it seems counter-intuitive, but the erosion takes place immediately downstream of the bump, and the bump is usually left in place, un-eroded. We had the best results with very little weld bead on the inside of the pipe. Misalignment was always deadly to these lines, I suppose because of the turbulence all around the joint.
My experience with erosion in steam piping is limited to 500 PSI and lower applications and was always in the condensate piping, usually at an elbow.
Roy

By jrcperu Date 02-16-2002 16:32

Well, pressure, rate of flow, particulate material, acid or alcaline formations, and then you are talking about problem.

Despite offset, any irregularitie in the internal surface of a pipe wil be detrimental for its integrity. The evaluation of this irregularities and the stress and job conditions, need to be made carefully.

I evalueted several pipes and pipelines failures, and I found that the cause of the failure was a combination of internal stress and eviromenntal conditions plus offset and surface irregularities, that incresse the stress and easy the enviromental attack. The pitty of this situation is that because a failure always involve several particularities, and offset is not a fancy one, inspectors and code makers look for CO2 or Hydrogen or other causes instead to verify in deep the surface irregularities. Check out API 1104 last edition (7.2 Alignment) and tell me if you are not surprise.

My advice is that misalignment must be as close as possible to zero or try to reduce the offset by machining or other applicable means; a good root pass is the best solution for offset up to 1/16 of inch.

Excuse me for my grammar I did not find the grammar correctior here,

My best regards

Jorge Ruiz Castro