Just got back from vacation or I’d have chimed in on this one earlier.

I’m in agreement with Cpt. Kenny et al here. Much better to let the vendor know up front what loads you want the equipment to withstand. Recently I was involved late on a project in which the loads had been left to the vendors’ discretion. I encountered two time-consuming and frustrating problems. The first was that I had difficulty getting allowable load information from the vendors. In some cases the vendors demanded payment for the additional calculations involved since it was not part of the original contract. In other cases the loads were received long after the stress analyses were completed. The project is now in construction and some of the allowables have still not been received. The second problem was that vendors provided allowables that were difficult or impossible to meet. In one very lengthy email exchange a vendor repeatedly said that his nozzles were not designed to accept any stresses. When I finally protested that even bolting on an instrument would add some stress to the nozzle the vendor replied, “The vessel nozzles are not designed to accept piping loads. All external piping should be independently supported.” Exasperated, I sent my CAESAR II calcs to our in-house vessel engineer and told him to take care of it.

For many years I’ve asked the vessel group to include criteria in the RFQ essentially identical to Mr. Luf’s above. I picked these up from some long-forgotten source in the 1970’s. (I confess to being unaware of their Markl-Rossheim origins.) Our proposals now include the statement:

Vessel nozzles shall be designed to accept the following loads:

Axial force (lb f) = 3.25(D+3)^3
Lateral force in any direction (lb f) = 1.5(D+3)^3
Bending or torsional moment (ft lb) = (60(D+3)^3)/12

Where D = outside diameter of the nozzle pipe size (in).

I should add that Kenny makes an excellent point concerning the nozzle/shell location of the load. I shall make sure that’s clarified in future proposals.

Finally, I offer a lesson-learned from my personal school-of-hard-knocks inventory: Never, never, never purchase an FRP vessel without an up-front agreement on nozzle allowables. FRP vendors seem always to design for zero loads. I am frequently reminded of a case in which the vendor successfully quadrupled the cost of vessel in order to redesign for very reasonable piping loads that had not been included in the original RFQ.