Hi everyone,

Is it required to provide thrust block on bends for welded Carbon steel Pipe?(Underground Piping - Medium - Water )

Thanks in Advance.

Regards,
Balu

1. Required by what regulatory body? Can't say - that's for you and your project team to research.

2. Required by physics? I can imagine several possible instances where it would be prudent to have a thrust block on an all-welded underground line. For instance, if I ran several hundred meters of large-bore water line underground, then had a vertical riser and an immediate tie to a piece of equipment with a fast-acting valve, you bet your life I would put a thrust block at the bottom of that riser.

Whether I would prefer to solve this problem with a piping reroute rather than a thrust block probably would depend on the peculiarities of the project. It's likely that putting a rate-limited actuator on the valve would also eliminate the need for the thrust block, but this option may not be feasible for process reasons, or for other sorts of transient loads.

3. Required by your client's standards? You're on your own on this one, too.

General comment - it's unlikely that any transient loads associated with fluid flow variation could damage an all-welded underground line, but my example above would be a case where you could cause a catastrophic failure of the above-ground portion of the line or, worse, an expensive piece of equipment. Catastrophic failures are a good way to get noticed, although perhaps not in the way you would prefer.

General caution - if you're worried about the possibility, there's probably something to be investigated. You need to develop an envelope of possible loads and load combinations and evaluate all of the relevant material and equipment load and stress limits according to the applicable codes and standards. You are the one with the specifics of your project, you'll have to just get to work on it and assemble the things that appear relevant.

You can most likely talk to several people on your project in general terms about fluid momentum transients and other sorts of loadings that might require a thrust block to be installed. Don't neglect the input of your senior piping designers or of people with much field experience. Operators are the guys who are going to have to live with the system you design, so in a very real sense they are your customers.

Also, don't neglect the input of the technical representatives of the equipment you are trying to protect. For example, if you're concerned with a cooling water line to a condenser, by all means ask the condenser's engineer if they have ever had a problem with a failure of the sort you are concerned about. If they have, ask him for general types of acceptable solutions and pick the one most appropriate to your project.

Remember, it's not necessary to limit your sources of information to those who are fully qualified and able to solve the problem. Solving problems is the job of the engineer whose specialty most closely aligns with the particular problem at hand. The number of people working on a project who can provide input to help define a problem is, in general, several times larger than the number of people required to actually solve it.

Sir,

In the above problem, if we can't quantify the anticipated pressure transient, if any, for which we need these thrust block at change of direction, how will we design the thrust blocks - for which pressure of piping ?

regards,

sam

Dears,

I am amplifying the reason why I have raised this query.

In the case of low head high capacity pumps working in parallel, we do not provide axial restraint just at the first elbow in discharge piping of pumps when piping is not going underground for welded piping. Then, why to provide the same for cooling water pumps only? For start-up, shut-down of pumps, rapid non-return valve closures, power trips, there could be similar transients, too, in the other systems.

Also, for two restraints in same rigid piping at pump support and at thrust block, the more load will be going to the stiffer restraint, which may be the pump support!

So, is it not better to attack the source of transient & solve the same by putting vacuum breakers and air valves to prevent water column separation, delaying valve closure etc ?

regards,

sam

Look up Joukousky equation calculte your load add a dlf of 2.0