Not using proper Filters results in severe damage to Oil Pump and Heater for company

I have a  large Oil Company  that provides field lubrication services I work for and have designed and built  numerous pumps and heater set ups for them they use in the field to do Hot oil flushes to clean out newly installed piping and for the recycling ,recovery and cleaning  of dirty oil   for large industrial clients like Natural Gas Pumping Stations and Electric Power Plants. I got a call late one morning  from one of the crews working on their latest job there on a $30 Million Gas Compression facility under construction in West Virginia where they are doing a Hot Oil Flush to clean out pipes after they have been installed and  joints welded .

Typical gas plant piping  that gets flushed after its installed 

Seems they are having trouble with 2 of the elements on the 3 element  480 volt-3 Phase - 90 amp- 800 Lb   Heater I designed.
 When the tech on site tells me whats going on and gives me readings he is getting from his meters  it sounds bad .
So I get to the Oil Company  office/ plant  fire up a  company  1 ton 4x4 pickup  which I will need to get back into this very rural area and fuel it up along with auxiliary tank and  load it with another back up heater and enough tools and fittings to get them back up and running plus survival gear pack god forbid I should get stuck overnight on the road always a possibility when travelling back roads in bad winter weather .
After 4 hours I am on site  its bad there already running a week behind schedule and can not get oil up to 160 degrees it needs to be to properly flush.
After looking over the heater for sure the elements that cost $750.00 a piece are shot.
Not going to be a good day.
We had two options empty all the equipment off  the truck pull trucks beside each other get an onsite crane/forklift  to lift the units on and off trucks or try and rebuild it on the truck. I opted for option 1#
We opened up the heaters top element to find it destroyed and melted.

We also find jammed in the heater  outlet a piece of what looks like window screening and plenty of rocks and debris ,which stopped the flow of oil which allowed elements to overheat .
This would not have happened had they been paying attention to the pump as it was defiantly giving indications there was a problem along with pressure gauge.They had already damaged a pump the week before when a rock got in the impeller and damaged it because they where not paying attention  .
When we opened the filter unit on output of heater we found the filter units which used that screening material had been ripped apart by the rocks  and that's where screen came from it had traveled thru pipes back thru pump and into heater . Thank God it jammed there and not in the piping some where .
To make maters worse elements 2# and 3#  where melted so bad even with a big  hammer they could not be dislodged so we had to unpack truck and move in the new unit as it was getting dark.
Its after we start hooking lines back up I notice there is no filter on the pump heater inlet.
Had there been a course  filter on the inlet side  the rocks pebbles etc would have been captured and allowed oil to still circulate  but since protocol was not followed it created a very big problem and massive cost . Needles to say more training and precautions are going to be put into effect to prevent future problems. Almost every pumping system you will ever find has a filter screen of some type on the input of the pump to prevent these problems that/s why swimming pool pumps have the plastic basket filter in front to catch leaves, The workers on site thought they did not need to do it and will now face the consequences of there actions.